nvJPEG Library

A GPU-accelerated JPEG decoding library.

1. Introduction

1.1. nvJPEG Decoder

The nvJPEG library provides high-performance, GPU accelerated JPEG decoding functionality for image formats commonly used in deep learning and hyperscale multimedia applications. The library offers single and batched JPEG decoding capabilities which efficiently utilize the available GPU resources for optimum performance; and the flexibility for users to manage the memory allocation needed for decoding.

The nvJPEG library enables the following functions: use the JPEG image data stream as input; retrieve the width and height of the image from the data stream, and use this retrieved information to manage the GPU memory allocation and the decoding. A dedicated API is provided for retrieving the image information from the raw JPEG image data stream.

Tip: Throughout this document, the terms “CPU” and “Host” are used synonymously. Similarly, the terms “GPU” and “Device” are synonymous.

The nvJPEG library supports the following:

JPEG options:

  • Baseline and Progressive JPEG decoding

  • 8 bits per pixel

  • Huffman bitstream decoding

  • Upto 4 channel JPEG bitstreams

  • 8- and 16-bit quantization tables

  • The following chroma subsampling for the 3 color channels Y, Cb, Cr (Y, U, V):

    • 4:4:4

    • 4:2:2

    • 4:2:0

    • 4:4:0

    • 4:1:1

    • 4:1:0

Features:

  • Hybrid decoding using both the CPU (i.e., host) and the GPU (i.e., device).

  • Input to the library is in the host memory, and the output is in the GPU memory.

  • Single image and batched image decoding.

  • Single phase and multiple phases decoding.

  • Color space conversion.

  • User-provided memory manager for the device and pinned host memory allocations.

1.2. nvJPEG Encoder

The encoding functions of the nvJPEG library perform GPU-accelerated compression of user's image data to the JPEG bitstream. User can provide input data in a number of formats and colorspaces, and control the encoding process with parameters. Encoding functionality will allocate temporary buffers using user-provided memory allocator.

Before calling the encoding functions the user should perform a few prerequisite steps using the helper functions described in nvJPEG Encoder Helper API Reference.

1.3. Thread Safety

Not all nvJPEG types are thread safe.

When using decoder APIs across multiple threads, the following decoder types should be instantiated separately for each thread: nvjpegJpegStream_t, nvjpegJpegState_t, nvjpegBufferDevice_t, nvjpegBufferPinned_t

When using encoder APIs across multiple threads, nvjpegEncoderState_t should be instantiated separately for each thread.

For user provided allocators (inputs to nvJPEGCreateEx()), user needs to ensure thread safety.

2. JPEG Decoding

2.1. Using JPEG Decoding

​The nvJPEG library provides functions for both the decoding of a single image, and batched decoding of multiple images.

2.1.1. Single Image Decoding

For single-image decoding you provide the data size and a pointer to the file data, and the decoded image is placed in the output buffer.

To use the nvJPEG library, start by calling the helper functions for initialization.

  1. Create nvJPEG library handle with one of the helper functions nvjpegCreateSimple() or nvjpegCreateEx().
  2. Create JPEG state with the helper function nvjpegJpegStateCreate(). See nvJPEG Type Declarations and nvjpegJpegStateCreate().

    Below is the list of helper functions available in the nvJPEG library:

    • nvjpegStatus_t nvjpegGetProperty(libraryPropertyType type, int *value);
    • [DEPRECATED] nvjpegStatus_t nvjpegCreate(nvjpegBackend_t backend, nvjpegHandle_t *handle , nvjpeg_dev_allocator allocator);
    • nvjpegStatus_t nvjpegCreateSimple(nvjpegHandle_t *handle);
    • nvjpegStatus_t nvjpegCreateEx(nvjpegBackend_t backend, nvjpegDevAllocator_t *dev_allocator, nvjpegPinnedAllocator_t *pinned_allocator, unsigned int flags, nvjpegHandle_t *handle);
    • nvjpegStatus_t nvjpegDestroy(nvjpegHandle_t handle);
    • nvjpegStatus_t nvjpegJpegStateCreate(nvjpegHandle_t handle, nvjpegJpegState_t *jpeg_handle);
    • nvjpegStatus_t nvjpegJpegStateDestroy(nvjpegJpegState handle);
    • Other helper functions such as nvjpegSet*() and nvjpegGet*() can be used to configure the library functionality on per-handle basis. Refer to the helper API reference for more details.
  3. Retrieve the width and height information from the JPEG-encoded image by using the nvjpegGetImageInfo() function.

    Below is the signature of nvjpegGetImageInfo() function:

    nvjpegStatus_t nvjpegGetImageInfo(
      nvjpegHandle_t              handle,
      const unsigned char         *data,
      size_t                      length,
      int                         *nComponents,
      nvjpegChromaSubsampling_t   *subsampling,
      int                         *widths,
      int                         *heights); 

    For each image to be decoded, pass the JPEG data pointer and data length to the above function. The nvjpegGetImageInfo() function is thread safe.

  4. One of the outputs of the above nvjpegGetImageInfo() function is nvjpegChromaSubsampling_t. This parameter is an enum type, and its enumerator list is composed of the chroma subsampling property retrieved from the JPEG image. See nvJPEG Chroma Subsampling.

  5. Use the nvjpegDecode() function in the nvJPEG library to decode this single JPEG image. See the signature of this function below:

    nvjpegStatus_t nvjpegDecode(
      nvjpegHandle_t          handle,
      nvjpegJpegState_t       jpeg_handle,
      const unsigned char     *data,
      size_t                  length, 
      nvjpegOutputFormat_t    output_format,
      nvjpegImage_t           *destination,
      cudaStream_t            stream);

    In the above nvjpegDecode() function, the parameters nvjpegOutputFormat_t, nvjpegImage_t, and cudaStream_t can be used to set the output behavior of the nvjpegDecode() function. You provide the cudaStream_t parameter to indicate the stream to which your asynchronous tasks are submitted.

  6. The nvjpegOutputFormat_t parameter:

    The nvjpegOutputFormat_t parameter can be set to one of the output_format settings below:

    output_format Meaning
    NVJPEG_OUTPUT_UNCHANGED Return the decoded image planar format.
    NVJPEG_OUTPUT_RGB Convert to planar RGB.
    NVJPEG_OUTPUT_BGR Convert to planar BGR.
    NVJPEG_OUTPUT_RGBI Convert to interleaved RGB.
    NVJPEG_OUTPUT_BGRI Convert to interleaved BGR.
    NVJPEG_OUTPUT_Y Return the Y component only.
    NVJPEG_OUTPUT_YUV Return in the YUV planar format.

    For example, if the output_format is set to NVJPEG_OUTPUT_Y or NVJPEG_OUTPUT_RGBI, or NVJPEG_OUTPUT_BGRI then the output is written only to channel[0], and the other channels are not touched.

    Alternately, in the case of planar output, the data is written to the corresponding channels of the nvjpegImage_t destination structure.

    Finally, in the case of grayscale JPEG and RGB output, the luminance is used to create the grayscale RGB.

    The below table explains the combinations of the output formats and the number of channels supported by the library.

    No of Channels in bitstream 1 2 3

    4

    Output Format
    NVJPEG_OUTPUT_UNCHANGED Yes Yes Yes Yes
    NVJPEG_OUTPUT_YUV Only the first channel of the output is populated No Yes No
    NVJPEG_OUTPUT_Y Yes No Yes Yes(a)
    NVJPEG_OUTPUT_RGB Yes(b) No Yes Yes(a)
    NVJPEG_OUTPUT_BGR Yes(b) No Yes Yes(a)
    NVJPEG_OUTPUT_RGBI Yes(b) No Yes Yes(a)
    NVJPEG_OUTPUT_BGRI Yes(b) No Yes Yes(a)
    NOTES:
    1. (a) Must be enabled using nvjpegDecodeParamsSetAllowCMYK().
    2. (b) Luminance is used to create the grayscale RGB.
  7. As mentioned above, an important benefit of the nvjpegGetImageInfo()function is the ability to utilize the image information retrieved from the the input JPEG image to allocate proper GPU memory for your decoding operation.

    The nvjpegGetImageInfo() function returns the widths, heights and nComponents parameters.

    nvjpegStatus_t nvjpegGetImageInfo(
      nvjpegHandle_t             handle, 
      const unsigned char        *data, 
      size_t                     length,     
      int                        *nComponents, 
      nvjpegChromaSubsampling_t  *subsampling, 
      int                        *widths, 
      int                        *heights); 

    You can use the retrieved parameters, widths, heights and nComponents, to calculate the required size for the output buffers, either for a single decoded JPEG, or for every decoded JPEG in a batch.

    To optimally set the destination parameter for the nvjpegDecode() function, use the following guidelines:

    For the output_format:

    NVJPEG_OUTPUT_Y

    destination.pitch[0] should be at least: width[0] destination.channel[0] should be at least of size: destination.pitch[0]*height[0]
    For the output_format destination.pitch[c] should be at least: destination.channel[c] should be at least of size:
    NVJPEG_OUTPUT_YUV width[c] for c = 0, 1, 2 destination.pitch[c]*height[c] for c = 0, 1, 2
    NVJPEG_OUTPUT_RGB and NVJPEG_OUTPUT_BGR width[0] for c = 0, 1, 2 destination.pitch[0]*height[0] for c = 0, 1, 2
    NVJPEG_OUTPUT_RGBI and NVJPEG_OUTPUT_BGRI width[0]*3 destination.pitch[0]*height[0]
    NVJPEG_OUTPUT_UNCHANGED width[c] for c = [ 0, nComponents - 1 ] destination.pitch[c]*height[c] for c = [ 0, nComponents - 1]
  8. Ensure that the nvjpegImage_t structure (or structures, in the case of batched decode) is filled with the pointers and pitches of allocated buffers. The nvjpegImage_t structure that holds the output pointers is defined as follows:

    typedef struct
    {
        unsigned char * channel[NVJPEG_MAX_COMPONENT]; 
        unsigned int pitch[NVJPEG_MAX_COMPONENT];
    } nvjpegImage_t;

    NVJPEG_MAX_COMPONENT is the maximum number of color components the nvJPEG library supports in the current release. For generic images, this is the maximum number of encoded channels that the library is able to decompress.

  9. Finally, when you call the nvjpegDecode() function with the parameters as described above, the nvjpegDecode() function fills the output buffers with the decoded data.

2.1.2. Decode by Phases [DEPRECATED]

Decode by phases is deprecated starting CUDA 10.2. Use Decoupled Phases instead

Alternately, you can decode a single image in multiple phases. This gives you flexibility in controlling the flow, and optimizing the decoding process.

To decode an image in multiple phases, follow these steps:

  1. Just as when you are decoding in a single phase, create the JPEG state with the helper function nvjpegJpegStateCreate().
  2. Next, call the functions in the sequence below (see Decode API -- Multiple Phases.)
    • nvjpegDecodePhaseOne()
    • nvjpegDecodePhaseTwo()
    • nvjpegDecodePhaseThree()
  3. At the conclusion of the third phase, the nvjpegDecodePhaseThree() function writes the decoded output at the memory location pointed to by its *destination parameter.

2.1.3. Decode using Decoupled Phases

The nvJPEG library allows further separation of the host and device phases of the decode process. The host phase of the decoding will not need to access to device resources.

A few examples of decoupled APIs can be found under Decode API - Decoupled Multiple Phases.

Below is the sequence of API calls to decode a single image

  1. Initialize all the items that are used in the decoding process:
    1. Create the library handle using one of the library handle initialization routines.
    2. Choose decoder implementation nvjpegBackend_t, and create decoder using nvjpegDecoderCreate().
    3. Create JPEG decoder state using nvjpegDecoderStateCreate().
    4. Create JPEG stream using nvjpegJpegStreamCreate().
    5. Create the pinned and device buffers used by the decoder using the below APIs respectively. These buffers are used to store intermediate decoding results.
      • nvjpegBufferPinnedCreate()
      • nvjpegBufferDeviceCreate()
    6. Link the buffers to the JPEG state using the below APIs respectively:
      • nvjpegStateAttachPinnedBuffer()
      • nvjpegStateAttachDeviceBuffer()
    7. Create decode parameters using the below API. This is used to set the output format, and enable ROI decode:

      nvjpegDecodeParamsCreate()

  2. Perform decoding:
    1. Parse the jpeg bit-stream using nvjpegJpegStreamParse()
      • Encoded bitstream information, like channel dimensions, can be retrieved using the below API. This information is used to allocate the output pointers in nvjpegImage_t.
        • nvjpegJpegStreamGetComponentsNum()

        • nvjpegJpegStreamGetComponentDimensions()

    2. Call the decode API in the below sequence to decode the image:
      • nvjpegDecodeJpegHost()
      • nvjpegDecodeJpegTransferToDevice()
      • nvjpegDecodeJpegDevice()

2.1.4. Batched Image Decoding

For the batched image decoding you provide pointers to multiple file data in the memory, and also provide the buffer sizes for each file data. The nvJPEG library will decode these multiple images, and will place the decoded data in the output buffers that you specified in the parameters.

2.1.4.1. Single Phase

For batched image decoding in single phase, follow these steps:

  1. Call nvjpegDecodeBatchedInitialize() function to initialize the batched decoder. Specify the batch size in the batch_size parameter. See nvjpegDecodeBatchedInitialize().

  2. Next, call nvjpegDecodeBatched() for each new batch. Make sure to pass the parameters that are correct to the specific batch of images. If the size of the batch changes, or if the batch decoding fails, then call the nvjpegDecodeBatchedInitialize() function again.

2.1.4.2. Multiple Phases [DEPRECATED]

Batched Decoding in multiple phases is deprecated starting CUDA 10.2. Use Single Phase Batched Decoding instead

To decode a batch of images in multiple phases, follow these steps:

Note:

This is the only case where the JPEG state could be used by multiple threads at the same time.

  1. Create the JPEG state with the helper function nvjpegJpegStateCreate().
  2. Call the nvjpegDecodeBatchedInitialize() function to initialize the batched decoder. Specify the batch size in the batch_size parameter, and specify the max_cpu_threads parameter to set the maximum number of CPU threads that work on single batch.
  3. Batched processing is done by calling the functions for the specific phases in sequence:
    • In the first phase, call nvjpegDecodePhaseOne() for each image in the batch, according to the index of the image in the batch. Note that this could be done using multiple threads. If multiple threads are used then the thread index in the range [0, max_cpu_threads-1] should be provided to the nvjpegDecodeBatchedPhaseOne() function. Before proceeding to the next phase, ensure that the nvjpegDecodePhaseOne() calls for every image have finished.
    • Next, call nvjpegDecodePhaseTwo()..
    • Finally, call nvjpegDecodePhaseThree()..
  4. If you have another batch of images of the same size to process, then repeat from 3.

2.2. nvJPEG Type Declarations

2.2.1. nvJPEG Backend

typedef enum {
	NVJPEG_BACKEND_DEFAULT = 0, 
	NVJPEG_BACKEND_HYBRID = 1,
	NVJPEG_BACKEND_GPU_HYBRID = 2
} nvjpegBackend_t; 

The nvjpegBackend_t enum is used to select either default back-end by default, or use GPU decoding for baseline JPEG images, or use CPU for Huffman decoding.

Member Description
NVJPEG_BACKEND_DEFAULT Default back-end is selected internally
NVJPEG_BACKEND_HYBRID Uses CPU for Huffman decoding
NVJPEG_BACKEND_GPU_HYBRID The function nvjpegDecodeBatched will use GPU decoding for the baseline JPEG images with interleaved scan when batch size is greater than 100. The batched multi-phase APIs will use CPU for Huffman decode. All single image APIs will use GPU-assisted Huffman decode.

2.2.2. nvJPEG Bitstream Handle

struct nvjpegJpegStream;
typedef struct nvjpegJpegStream* nvjpegJpegStream_t;

This handle stores the bit-stream parameters on the host. This helps retrieve bitstream meta-data using APIs defined in nvJPEG Stream API.

2.2.3. nvJPEG Decode Device Buffer Handle

struct nvjpegBufferDevice;
typedef struct nvjpegBufferDevice* nvjpegBufferDevice_t;

This nvjpegBufferDevice_t is used by decoder states to store the intermediate information in device memory.

2.2.4. nvJPEG Decode Parameter Handle

struct nvjpegDecodeParams;
typedef struct nvjpegDecodeParams* nvjpegDecodeParams_t;

This decoder parameter handle stores the parameters like output format, and the ROI decode parameters that are set using APIs defined in nvJPEG Chroma Subsampling.

2.2.5. nvJPEG Decode Pinned Buffer Handle

struct nvjpegBufferPinned;
typedef struct nvjpegBufferPinned* nvjpegBufferPinned_t;

This nvjpegBufferPinned_t handle is used by decoder states to store the intermediate information on pinned memory.

2.2.6. nvJPEG Decoder Handle

struct nvjpegJpegDecoder;
typedef struct nvjpegJpegDecoder* nvjpegJpegDecoder_t;  	

This decoder handle stores the intermediate decoder data, which is shared across the decoding stages. This decoder handle is initialized for a given nvjpegBackend_t. It is used as input to the Decode API—Decoupled Decoding.

2.2.7. nvJPEG Host Pinned Memory Allocator Interface

typedef int (*tPinnedMalloc)(void**, size_t, unsigned int flags);
typedef int (*tPinnedFree)(void*);
typedef struct 
{
tPinnedMalloc pinned_malloc;
tPinnedFree pinned_free;
} nvjpegPinnedAllocator_t;      

When the nvjpegPinnedAllocator_t *allocator parameter in the nvjpegCreateEx() function is set as a pointer to the above nvjpegPinnedAllocator_t structure, then this structure will be used for allocating and releasing host pinned memory for copying data to/from device. The function prototypes for the memory allocation and memory freeing functions are similar to the cudaHostAlloc() and cudaFreeHost() functions. They will return 0 in case of success, and non-zero otherwise.

However, if the nvjpegPinnedAllocator_t *allocator parameter in the nvjpegCreateEx() function is set to NULL, then the default memory allocation functions cudaHostAlloc() and cudaFreeHost() will be used. When using nvjpegCreate() or nvjpegCreateSimple() function to create library handle, the default host pinned memory allocator will be used.

2.2.8. nvJPEG Image

typedef struct
	{unsigned char * channel[NVJPEG_MAX_COMPONENT]; 
	unsigned int pitch[NVJPEG_MAX_COMPONENT];
	} nvjpegImage_t; 

The nvjpegImage_t structure (or structures, in the case of batched decode) is used to fill with the pointers and pitches of allocated buffers. The nvjpegImage_t structure that holds the output pointers.

Member Description
NVJPEG_MAX_COMPONENT Maximum number of color components the nvJPEG library supports. For generic images, this is the maximum number of encoded channels that the library is able to decompress.

2.2.9. nvJPEG Device Memory Allocator Interface

typedef int (*tDevMalloc)(void**, size_t); 
typedef int (*tDevFree)(void*); 
typedef struct 
  { 
    tDevMalloc dev_malloc; 
    tDevFree dev_free; 
  } nvjpegDevAllocator_t;

Users can tell the library to use their own device memory allocator. The function prototypes for the memory allocation and memory freeing functions are similar to the cudaMalloc() and cudaFree() functions. They should return 0 in case of success, and non-zero otherwise. A pointer to the nvjpegDevAllocator_t structure, with properly filled fields, should be provided to the nvjpegCreate() function. NULL is accepted, in which case the default memory allocation functions cudaMalloc() and cudaFree() is used.

When the nvjpegDevAllocator_t *allocator parameter in the nvjpegCreate() or nvjpegCreateEx() function is set as a pointer to the above nvjpegDevAllocator_t structure, then this structure is used for allocating and releasing the device memory. The function prototypes for the memory allocation and memory freeing functions are similar to the cudaMalloc() and cudaFree() functions. They should return 0 in case of success, and non-zero otherwise.

However, if the nvjpegDevAllocator_t *allocator parameter in the nvjpegCreate() or nvjpegCreateEx() function is set to NULL, then the default memory allocation functions cudaMalloc() and cudaFree() will be used. When using nvjpegCreateSimple() function to create library handle the default device memory allocator will be used.

2.2.10. nvJPEG Opaque JPEG Decoding State Handle

struct nvjpegJpegState;
typedef struct nvjpegJpegState* nvjpegJpegState_t;

The nvjpegJpegState structure stores the temporary JPEG information. It should be initialized before any usage. This JPEG state handle can be reused after being used in another decoding. The same JPEG handle should be used across the decoding phases for the same image or batch. Multiple threads are allowed to share the JPEG state handle only when processing same batch during first phase (nvjpegDecodePhaseOne) .

2.2.11. nvJPEG Opaque Library Handle Struct

struct nvjpegHandle;
typedef struct nvjpegHandle* nvjpegHandle_t;

The library handle is used in any consecutive nvJPEG library calls, and should be initialized first.

The library handle is thread safe, and can be used by multiple threads simultaneously.

2.2.12. nvJPEG Output Pointer Struct

typedef struct
  {
    unsigned char * channel[NVJPEG_MAX_COMPONENT];
    unsigned int pitch[NVJPEG_MAX_COMPONENT];
  } nvjpegImage_t;

The nvjpegImage_t struct holds the pointers to the output buffers, and holds the corresponding strides of those buffers for the image decoding.

See Single Image Decoding on how to set up the nvjpegImage_t struct.

2.3. nvJPEG API Reference

This section describes the nvJPEG decoder API.

2.3.1. nvJPEG Helper API Reference

2.3.1.1. nvjpegGetProperty()

Gets the numeric value for the major or minor version, or the patch level, of the nvJPEG library.

Signature:

nvjpegStatus_t nvjpegGetProperty(
	libraryPropertyType   type, 
	int                   *value);

Parameters:

Parameter Input / Output Memory Description
libraryPropertyType type Input Host One of the supported libraryPropertyType values, that is, MAJOR_VERSION, MINOR_VERSION or PATCH_LEVEL.
int *value Output Host The numeric value corresponding to the specific libraryPropertyType requested.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.2. nvjpegGetCudartProperty()

Gets the numeric value for the major version, minor version, or the patch level of the CUDA toolkit that was used to build nvJPEG library. For the same information on the nvJPEG library itself, see nvjpegGetProperty().

Signature:

nvjpegStatus_t nvjpegGetCudartProperty(
	libraryPropertyType   type, 
	int                   *value);

Parameters:

Parameter Input / Output Memory Description
libraryPropertyType type Input Host One of the supported libraryPropertyType values, that is, MAJOR_VERSION, MINOR_VERSION or PATCH_LEVEL.
int *value Output Host The numeric value corresponding to the specific libraryPropertyType requested.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.3. nvjpegCreate() [DEPRECATED]

Allocates and initializes the library handle.

Note: This function is deprecated. Use either nvjpegCreateSimple() or nvjpegCreateEx() functions to create the library handle.

Signature:

nvjpegStatus_t nvjpegCreate(
	nvjpegBackend_t			backend,
	nvjpegDevAllocator_t 		*allocator,
	nvjpegHandle_t			*handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegBackend_t backend Input Host A backend parameter for the library. This backend will be used for all the functions called with this handle. If this is set to DEFAULT then it automatically chooses one of the underlying algorithms.
nvjpegDevAllocator_t *allocator Input Host Device memory allocator. See nvjpegDevAllocator_t structure description. If NULL is provided, then the default CUDA runtime cudaMalloc() and cudaFree() functions will be used.
nvjpegHandle_t *handle Input/Output Host The library handle.

The nvjpegBackend_t parameter is an enum type, with the below enumerated list values:

typedef enum {
	NVJPEG_BACKEND_DEFAULT = 0, 
	NVJPEG_BACKEND_HYBRID = 1,
} nvjpegBackend_t; 

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.4. nvjpegCreateSimple()

Allocates and initializes the library handle, with default codec implementations selected by library and default memory allocators.

Signature:

nvjpegStatus_t nvjpegCreateSimple(nvjpegHandle_t *handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t *handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.5. nvjpegCreateEx()

Allocates and initializes the library handle using the provided arguments.

Signature:

nvjpegStatus_t nvjpegCreateEx(nvjpegBackend_t backend, 
          nvjpegDevAllocator_t *dev_allocator, 
          nvjpegPinnedAllocator_t *pinned_allocator, 
          unsigned int flags,
          nvjpegHandle_t *handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegBackend_t backend Input Host A backend parameter for the library. This backend will be used for all of the functions called with this handle. If this is set to “DEFAULT" then it will choose one of underlying algorithms automatically.
nvjpegDevAllocator_t *dev_allocator Input Host Device memory allocator. See nvjpegDevAllocator_t structure description. If NULL is provided, then the default CUDA runtime functions cudaMalloc() and cudaFree() will be used.
nvjpegPinnedAllocator_t *pinned_allocator Input Host Pinned host memory allocator. See nvjpegPinnedAllocator_tstructure description. If NULL is provided, then the default CUDA runtime functions cudaHostAlloc() and cudaFreeHost() will be used.
nvjpegHandle_t *handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.6. nvjpegDestroy()

Releases the library handle.

Signature:

nvjpegStatus_t nvjpegDestroy(nvjpegHandle_t handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input/Output Host The library handle to release.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.7. nvjpegSetDeviceMemoryPadding()

Use the provided padding for all device memory allocations with specified library handle. A large number will help to amortize the need for device memory reallocations when needed.

Signature:

nvjpegStatus_t nvjpegSetDeviceMemoryPadding(
	size_t padding,
	nvjpegHandle_t handle);

Parameters:

Parameter Input / Output Memory Description
size_t padding Input Host Device memory padding to use for all further device memory allocations.
nvjpegHandle_t *handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.8. nvjpegGetDeviceMemoryPadding()

Retrieve the device memory padding that is currently used for the specified library handle.

Signature:

nvjpegStatus_t nvjpegGetDeviceMemoryPadding(
	size_t *padding,
	nvjpegHandle_t handle);

Parameters:

Parameter Input / Output Memory Description
size_t *padding Output Host Device memory padding that is currently used for device memory allocations.
nvjpegHandle_t *handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.9. nvjpegSetPinnedMemoryPadding()

Use the provided padding for all pinned host memory allocations with specified library handle. A large number will help to amortize the need for pinned host memory reallocations when needed.

Signature:

nvjpegStatus_t nvjpegSetPinnedMemoryPadding(
	size_t padding,
	nvjpegHandle_t handle);

Parameters:

Parameter Input / Output Memory Description
size_t padding Input Host Pinned host memory padding to use for all further pinned host memory allocations.
nvjpegHandle_t handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.10. nvjpegGetPinnedMemoryPadding()

Retrieve the pinned host memory padding that is currently used for specified library handle.

Signature:

nvjpegStatus_t nvjpegGetPinnedMemoryPadding(
	size_t *padding,
	nvjpegHandle_t handle);

Parameters:

Parameter Input / Output Memory Description
size_t *padding Output Host Pinned host memory padding that is currently used for pinned host memory allocations.
nvjpegHandle_t handle Input/Output Host The library handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.11. nvjpegJpegStateCreate()

Allocates and initializes the internal structure required for the JPEG processing.

Signature:

nvjpegStatus_t nvjpegJpegStateCreate(
	nvjpegHandle_t      handle,
	nvjpegJpegState_t   *jpeg_handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t *jpeg_handle Input/Output Host The image state handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.12. nvjpegJpegStateDestroy()

Releases the image internal structure.

Signature:

nvjpegStatus_t nvjpegJpegStateDestroy(nvjpegJpegState handle);		

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegState handle Input/Output Host The image state handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.13. nvjpegDecoderCreate()

Creates a decoder handle.

Signature:

nvjpegStatus_t nvjpegDecoderCreate(
	nvjpegHandle_t nvjpeg_handle, 
	nvjpegBackend_t implementation, 
	nvjpegJpegDecoder_t* decoder_handle);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t nvjpeg_handle Input Host Library handle.
nvjpegBackend_t backend Input Host Backend parameter for the decoder_handle.The back end applies to the functions defined in section 4.5, when called with this handle.
nvjpegJpegDecoder_t decoder_handle Input/Output Host Decoder state handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.14. nvjpegDecoderDestroy()

Destroys the decoder handle.

Signature:

nvjpegStatus_t nvjpegDecoderDestroy(
	nvjpegJpegDecoder_t decoder_handle); 

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegDecoder_t decoder_handle Input/Output Host Decoder handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.15. nvjpegDecoderJpegSupported()

Determines whether the decoder_handle is able to handle the bit-stream stored in jpeg_stream.

Signature:

nvjpegStatus_t nvjpegDecoderJpegSupported(
	nvjpegJpegDecoder_t decoder_handle, 
	nvjpegJpegStream_t jpeg_stream,
	nvjpegDecodeParams_t decode_params,
	int* is_supported);	

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegDecoder_t decoder_handle Input Host Decoder state handle
nvjpegJpegStream_t jpeg_stream Input Host Bit stream meta-data
nvjpegDecodeParams_t decode_params Input Host Decoder output configuration
int* is_supported Output Host Return value of 1 indicates bitstream can be decoded by the decoder_handle, 0 indicates that the bitstream is not supported

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.16. nvjpegDecoderStateCreate()

Creates the decoder_state internal structure. The decoder_state is associated with the nvjpegBackend_t implementation that was used to create the decoder_handle.

Signature:

nvjpegStatus_t nvjpegDecoderStateCreate(
	nvjpegHandle_t nvjpeg_handle,
	nvjpegJpegDecoder_t decoder_handle,
	nvjpegJpegState_t* decoder_state); 

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t nvjpeg_handle Input Host Library handle.
nvjpegJpegDecoder_t decoder_handle Input Host Decoder handle.
nvjpegJpegState_t* decoder_state Input/Output Host nvJPEG Image State Handle.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.17. nvjpegJpegStreamCreate()

Creates jpeg_stream that is used to parse the JPEG bitstream and store bitstream parameters.

Signature:

nvjpegStatus_t nvjpegJpegStreamCreate(
	nvjpegHandle_t handle, 
	nvjpegJpegStream_t *jpeg_stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host Library handle
nvjpegJpegStream_t *jpeg_stream Input Host Bitstream handle

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.18. nvjpegJpegStreamDestroy()

Destroys the jpeg_stream structure.

Signature:

nvjpegStatus_t nvjpegJpegStreamDestroy(
	nvjpegJpegStream_t *jpeg_stream);

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegStream_t *jpeg_stream Input Host Bitstream handle

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.19. nvjpegBufferPinnedCreate()

Creates a pinned buffer handle.

Signature:

nvjpegStatus_t nvjpegBufferPinnedCreate(
	nvjpegHandle_t handle, 
	nvjpegPinnedAllocator_t* pinned_allocator,
	nvjpegBufferPinned_t* buffer);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host Library handle.
nvjpegPinnedAllocator_t* pinned_allocator Input Host Pinned host memory allocator. See nvjpegPinnedAllocator_t structure description.
nvjpegBufferPinned_t* buffer Input/Output Host nvJPEG pinned buffer object.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.20. nvjpegBufferPinnedDestroy()

Destroys a pinned buffer handle.

Signature:

nvjpegStatus_t nvjpegBufferPinnedDestroy(
	nvjpegBufferPinned_t buffer);

Parameters:

Parameter Input / Output Memory Description
nvjpegBufferPinned_t* buffer Input/Output Host nvJPEG pinned buffer object.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.21. nvjpegStateAttachPinnedBuffer()

Link the nvJPEG pinned buffer handle to decoder_state. The pinned_buffer is used by the decoder to store the intermediate information that is used across the decoding stages. Pinned buffer can be attached to different decoder states, which helps to switch between implementations without allocating extra memory.

Signature:

nvjpegStatus_t nvjpegStateAttachPinnedBuffer(
	nvjpegJpegState_t decoder_state,
	nvjpegBufferPinned_t pinned_buffer);

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegState_t decoder_state Input Host nvJPEG decoder state.
nvjpegBufferPinned_t pinned_buffer Input Host nvJPEG pinned buffer container.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.22. nvjpegBufferPinnedRetrieve()

Retrieves the pinned memory pointer and size from the nvJPEG pinned buffer handle. Allows the application to re-use the memory once the decode is complete.

Signature:

nvjpegStatus_t nvjpegBufferPinnedRetrieve(
	nvjpegBufferPinned_t buffer, 
	size_t* size, void** ptr);

Parameters:

Parameter Input / Output Memory Description
nvjpegBufferPinned_t buffer Input Host nvJPEG pinned buffer container.
size_t* size Input/Output Host Size in bytes of the pinned buffer.
void** ptr Input/Output Host Pointer to the pinned buffer.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.23. nvjpegBufferDeviceCreate()

Creates the device buffer handle.

Signature:

nvjpegStatus_t nvjpegBufferDeviceCreate(
	nvjpegHandle_t handle, 
	nvjpegDevAllocator_t* device_allocator,
	nvjpegBufferDevice_t* buffer);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host Library handle.
nvjpegDevAllocator_t* device_allocator Input Host Device memory allocator. See nvjpegDevAllocator_t structure description.
nvjpegBufferDevice_t* buffer Input/Output Host nvJPEG device buffer container.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.24. nvjpegBufferDeviceDestroy()

Destroys the device buffer handle.

Signature:

nvjpegStatus_t nvjpegBufferDeviceDestroy(
	nvjpegBufferDevice_t buffer);		

Parameters:

Parameter Input / Output Memory Description
nvjpegBufferDevice_t* buffer Input/Output Host/Device nvJPEG device buffer container. Device pointers are stored within the host structures.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.25. nvjpegStateAttachDeviceBuffer()

Link the nvJPEG device buffer handle to the decoder_state. The device_buffer is used by the decoder to store the intermediate information that is used across the decoding stages. Device buffer can be attached to different decoder states, which helps to switch between implementations without allocating extra memory.

Signature:

nvjpegStatus_t nvjpegStateAttachDeviceBuffer(
	nvjpegJpegState_t decoder_state,
	nvjpegBufferDevice_t device_buffer);

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegState_t decoder_state Input Host nvJPEG decoder state.
nvjpegBufferDevice_t device buffer Input Host/Device nvJPEG device buffer container. Device pointers are stored within the host structures.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.26. nvjpegBufferDeviceRetrieve()

Retrieve the device memory pointer and size from the nvJPEG device buffer handle. Allows the application to re-use the memory after the decode is complete.

Signature:

nvjpegStatus_t nvjpegBufferDeviceRetrieve(
	nvjpegBufferDevice_t buffer, 
	size_t* size, 
	void** ptr);

Parameters:

Parameter Input / Output Memory Description
nvjpegBufferDevice_t buffer Input Host nvJPEG device buffer container.
size_t* size Input/Output Host Device buffer size in bytes.
void** ptr Input/Output Host Pointer to the device buffer.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.27. nvjpegDecodeParamsCreate()

Creates a handle for the parameters. The parameters that can be programmed include: output format, ROI decode, CMYK to RGB conversion.

Signature:

nvjpegStatus_t nvjpegDecodeParamsCreate(
	nvjpegHandle_t handle, 
	nvjpegDecodeParams_t *decode_params);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host Library handle.
nvjpegDecodeParams_t *decode_params Input/Output Host Decode output parameters.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.1.28. nvjpegDecodeParamsDestroy()

Destroys the decode_params handle.

Signature:

nvjpegStatus_t nvjpegDecodeParamsDestroy(
	nvjpegDecodeParams_t *decode_params);

Parameters:

Parameter Input / Output Memory Description
nvjpegDecodeParams_t *decode_params Input/Output Host Decode output parameters.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2. Retrieve Encoded Image Information API

The helper functions for retrieving the encoded image information.

2.3.2.1. nvjpegGetImageInfo()

Decodes the JPEG header and retrieves the basic information about the image.

Signature:

nvjpegStatus_t nvjpegGetImageInfo(
	nvjpegHandle_t              handle, 
	const unsigned char         *data, 
	size_t                      length, 
	int                         *nComponents, 
	nvjpegChromaSubsampling_t   *subsampling, 
	int                         *widths, 
	int                         *heights); 

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
const unsigned char *data Input Host Pointer to the encoded data.
size_t length Input Host Size of the encoded data in bytes.
int *nComponents Output Host Chroma subsampling for the 1- or 3- channel encoding.
int *widths Output Host Pointer to the first element of array of size NVJPEG_MAX_COMPONENT, where the width of each channel (up to NVJPEG_MAX_COMPONENT) will be saved. If the channel is not encoded, then the corresponding value would be zero.
int *heights Output Host Pointer to the first element of array of size NVJPEG_MAX_COMPONENT, where the height of each channel (up to NVJPEG_MAX_COMPONENT) will be saved. If the channel is not encoded, then the corresponding value would be zero.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2. nvJPEG Stream API

These functions store the parsed bit-stream data on the host.

2.3.2.2.1. nvjpegJpegStreamParse()

Parses the bitstream and stores the metadata in the jpeg_stream struct.

Signature:

nvjpegStatus_t nvjpegJpegStreamParse(
	nvjpegHandle_t handle,
	const unsigned char *data, 
	size_t length,
	int save_metadata,
	int save_stream,
	nvjpegJpegStream_t jpeg_stream);		

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
const unsigned char *data Input Host Pointer to the bit-stream.
size_t length Input Host Bit-stream size.
int save_metadata Input Host (Not enabled. Marked for future use). If not 0, then the JPEG stream metadata (headers, app markers, etc.) will be saved in the internal JpegStream structure for future usage.

If 0, then the meta data (headers, app markerms etc.) will be discarded.

int save_stream Input Host If not 0, then the whole jpeg stream will be copied to the internal JpegStream structure, and the pointer to the JPEG file data will not be needed after this call.

If 0, then JpegStream will just save the pointers (to JPEG file data), and these pointers will be used later during the image decoding.
nvjpegJpegStream_t jpeg_stream Input/Output Host/Device The nvJPEG bitstream handle that stores the parsed bitstream information.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2.2. nvjpegJpegStreamGetFrameDimensions()

Extracts the JPEG frame dimensions from the bitstream.

Signature:

nvjpegStatus_t nvjpegJpegStreamGetFrameDimensions(
	nvjpegJpegStream_t jpeg_stream,
	unsigned int* width,
	unsigned int* height);		

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegStream_t jpeg_stream Input Host Bitstream handle.
unsigned int* width Output Host Frame height.
unsigned int* height Output Host

Frame width.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2.3. nvjpegJpegStreamGetComponentsNum()

Extracts the JPEG frame dimensions from the bitstream.

Signature:

nvjpegStatus_t nvjpegJpegStreamGetComponentsNum(
	nvjpegJpegStream_t jpeg_stream,
	unsigned int* components_num);		

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegStream_t jpeg_stream Input Host Bitstream handle.
unsigned int* components_num Output Host Number of encoded channels in the input.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2.4. nvjpegJpegStreamGetComponentDimensions()

Extracts the component dimensions from the bitstream.

Signature:

nvjpegStatus_t nvjpegJpegStreamGetComponentDimensions(
	nvjpegJpegStream_t jpeg_stream,
	unsigned int component,
	unsigned int* width,
	unsigned int* height)		

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegStream_t jpeg_stream Input Host Bitstream handle.
unsigned int component Input Host Component index.
unsigned int* width Output Host Component height.
unsigned int* height Output Host

Component width.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2.5. nvjpegJpegStreamGetChromaSubsampling()

Gets the chroma subsampling from the jpeg_stream. For grayscale (single channel) images it returns NVJPEG_CSS_GRAY. For 3-channel images it tries to assign one of the known chroma sub-sampling values based on the sampling information present in the bitstream, else it returns NVJPEG_CSS_UNKNOWN. If the number of channels is 2 or 4, then it returns NVJPEG_CSS_UNKNOWN.

Signature:

nvjpegStatus_t nvjpegJpegStreamGetChromaSubsampling(
	nvjpegJpegStream_t jpeg_stream,
	nvjpegChromaSubsampling_t* chroma_subsampling);		

Parameters:

Parameter Input / Output Memory Description
nvjpegJpegStream_t jpeg_stream Input Host Bitstream handle
nvjpegChromaSubsampling_t* chroma_subsampling Output Host Chroma subsampling for the 1- or 3- channel encoding.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.2.2.6. nvjpegJpegStreamGetJpegEncoding()

This function obtains the JPEG encoding type from the jpeg_stream. For baseline images it returns NVJPEG_ENCODING_BASELINE_DCT. For progressive images it returns NVJPEG_ENCODING_PROGRESSIVE_DCT_HUFFMAN.

Signature:

nvjpegStatus_t nvjpegJpegStreamGetJpegEncoding(
	nvjpegJpegStream_t jpeg_stream,
	nvjpegJpegEncoding_t* jpeg_encoding);		

Parameters:

Parameter Input / Output Memory Description
jpeg_stream In Host Input bitstream handle.
jpeg_encoding Out Host Encoding type obtained—baseline or progressive.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.3. Decode API—Single Phase

Functions for decoding single image or batched images in a single phase.

2.3.3.1. ​nvjpegDecode()

Decodes a single image, and writes the decoded image in the desired format to the output buffers. This function is asynchronous with respect to the host. All GPU tasks for this function will be submitted to the provided stream.

Signature:

nvjpegStatus_t nvjpegDecode(
	nvjpegHandle_t          handle,
	nvjpegJpegState_t       jpeg_handle,
	const unsigned char     *data,
	size_t                  length, 
	nvjpegOutputFormat_t    output_format,
	nvjpegImage_t           *destination,
	cudaStream_t            stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
const unsigned char *data Input Host Pointer to the encoded data.
size_t length Input Host Size of the encoded data in bytes.
nvjpegOutputFormat_t output_format Input Host Format in which the decoded output will be saved.
nvjpegImage_t *destination Input/Output Host/Device Pointer to the structure that describes the output destination. This structure should be on the host (CPU), but the pointers in this structure should be pointing to the device (i.e., GPU) memory. See nvjpegImage_t.
cudaStream_t stream Input Host The CUDA stream where all of the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.3.2. ​nvjpegDecodeBatchedInitialize()

This function initializes the batched decoder state. The initialization parameters include the batch size, the maximum number of CPU threads, and the specific output format in which the decoded image will be saved. This function should be called once, prior to decoding the batches of images. Any currently running batched decoding should be finished before calling this function.

Signature:

nvjpegStatus_t nvjpegDecodeBatchedInitialize(
 	nvjpegHandle_t          handle,
 	nvjpegJpegState_t       jpeg_handle,
 	int                     batch_size,
 	int                     max_cpu_threads,
 	nvjpegOutputFormat_t    output_format);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
int batch_size Input Host Batch size.
int max_cpu_threads Input Host Maximum number of CPU threads that can participate in decoding a batch.
nvjpegOutputFormat_t output_format Input Host Format in which the decoded output will be saved.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.3.3. ​nvjpegDecodeBatched()

Decodes the batch of images, and writes them to the buffers described in the destination parameter in a format provided to nvjpegDecodeBatchedInitialize() function. This function is asynchronous with respect to the host. All GPU tasks for this function will be submitted to the provided stream.

Signature:

nvjpegStatus_t nvjpegDecodeBatched(
 	nvjpegHandle_t             handle,
 	nvjpegJpegState_t          jpeg_handle,
 	const unsigned char *const *data,
 	const size_t               *lengths, 
 	nvjpegImage_t              *destinations,
 	cudaStream_t               stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
const unsigned char *const *data Input Host Pointer to the first element of array of the input data. The size of the array is assumed to be batch_size provided to nvjpegDecodeBatchedInitialize() batch initialization function.
const size_t *lengths Input Host Pointer to the first element of array of input sizes. Size of array is assumed to be batch_size provided to nvjpegDecodeBatchedInitialize(), the batch initialization function.
nvjpegImage_t *destinations Input/Output Host/Device Pointer to the first element of array of output descriptors. The size of array is assumed to be batch_size provided to nvjpegDecodeBatchedInitialize(), the batch initialization function. See also nvjpegImage_t.
cudaStream_t stream Input Host

The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4. Decode API—Multiple Phases [DEPRECATED]

Multiple Phase Decoding APIs are deprecated starting CUDA 10.2. Use Decoupled Decoding APIs instead

The nvJPEG library provides an ability to control the decoding process in phases. In the simple case of a single-image decode you can split the decoding into phases. For decoding multiple images, you can overlap the decoding phases of separate images within a single thread. Finally, for the batched decode you can use multiple threads to split the host tasks. Synchronization between phases should be handled with CUDA events and CUDA stream synchronization mechanisms, by the user.

Note: Note that first phases are synchronous with the respect to the host, while the second and third phases are asynchronous--for both single image and batched decode.

2.3.4.1. ​nvjpegDecodePhaseOne() [DEPRECATED]

The first phase of a single-image decode. You provide all the inputs, and the nvJPEG library performs any required preprocessing on the host. Any previous calls to nvjpegDecodePhaseOne() and nvjpegDecodePhaseTwo() with the same nvjpeg_handle parameter should be finished prior to this call.

Signature:

nvjpegStatus_t nvjpegDecodePhaseOne(
	nvjpegHandle_t          handle,
	nvjpegJpegState_t       jpeg_handle,
	const unsigned char     *data,
	size_t                  length,
	nvjpegOutputFormat_t    output_format,
	cudaStream_t            stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
const unsigned char *data Input Host Pointer to the encoded stream.
size_t length Input Host Size of the encoded stream.
nvjpegOutputFormat_t output_format Input Host Format in which the decoded image will be saved.
cudaStream_t stream Input Host

The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4.2. ​nvjpegDecodePhaseTwo() [DEPRECATED]

In this second phase of the decoding process, the GPU (that is, the device) is involved. The decoding task is transferred to the device memory. Any required preprocessing is performed on the device. Any previous calls to nvjpegDecodePhaseTwo() and nvjpegDecodePhaseThree() with the same jpeg_handle parameter should be finished prior to this call.

Signature:

nvjpegStatus_t nvjpegDecodePhaseTwo(
 	nvjpegHandle_t       handle,
 	nvjpegJpegState_t    jpeg_handle,
 	cudaStream_t         stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
cudaStream_t stream Input Host

The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4.3. ​nvjpegDecodePhaseThree() [DEPRECATED]

In this third phase of the decoding process, the decoded image is written to the output, in the specified decoding format.

Note: If the same jpeg_handle is shared for decoding multiple images simultaneously, then these multiple images should be of the same output_format.

Signature:

nvjpegStatus_t nvjpegDecodePhaseThree(
 	nvjpegHandle_t       handle,
 	nvjpegJpegState_t    jpeg_handle,
 	nvjpegImage_t        *destination,
 	cudaStream_t         stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
nvjpegImage_t *destination Input/Output Host/Device Pointer to the structure that describes the output destination. This structure should be on host, but the pointers in this structure should be pointing to the device memory. See nvjpegImage_t description for details.
cudaStream_t stream Input Host

The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4.4. ​nvjpegDecodeBatchedPhaseOne() [DEPRECATED]

This first phase of the batched decoding should be called separately for each image in the batch. The batch initialization API, with appropriate batch parameters, should be called prior to starting the task with the batch.

If the batch parameters (batch size, number of threads, output format) did not change, then there is no need to initialize the batch again before starting the task.

It is possible to use multiple threads to split this first phase of the task. In which case, each thread should have a unique index. Provide the index of the image in the batch, and use the same JPEG decoding state parameter.

The thread index for the batch should be in the range of [0, max_cpu_threads-1]. The image index should be in the range of [0, batch_size-1]. Any previous calls to nvjpegDecodeBatchedPhaseOne() and nvjpegDecodeBatchedPhaseTwo() on a different batch with the same JPEG state handle parameter should be completed prior to this call.

Signature:

nvjpegStatus_t nvjpegDecodeBatchedPhaseOne(
 	nvjpegHandle_t          handle,
 	nvjpegJpegState_t       jpeg_handle,
 	const unsigned char     *data,
 	size_t                  length,
 	int                     image_idx,
 	int                     thread_idx,
 	cudaStream_t            stream);	

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
const unsigned char *data Input Host Pointer to the encoded stream.
size_t length Input Host

Size of the encoded stream.

int image_idx Input Host Image index in the batch. Should be in the range from 0 to batch_size-1.
int thread_idx Input Host Thread index that calls this phase. Should be in the range from 0 to max_cpu_threads-1.
cudaStream_t stream Input Host The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4.5.  nvjpegDecodeBatchedPhaseTwo() [DEPRECATED]

This phase should be called once per batch. It should be called only after the nvjpegDecodeBatchedPhaseOne() calls for every image in the batch have finished. Any prior calls to nvjpegDecodeBatchedPhaseTwo() and nvjpegDecodeBatchedPhaseThree() for other batches with the same JPEG state handle parameter should be finished prior this call.

Signature:

nvjpegStatus_t nvjpegDecodeBatchedPhaseTwo(
	nvjpegHandle_t          handle, 
	nvjpegJpegState_t       jpeg_handle, 
	cudaStream_t            stream);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
cudaStream_t stream Input Host The CUDA stream where all the GPU work will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.4.6.  nvjpegDecodeBatchedPhaseThree() [DEPRECATED]

This phase should be called once per batch. It should be called only after the nvjpegDecodeBatchedPhaseTwo() call for the same batch has finished.

Between a call to nvjpegDecodeBatchedPhaseTwo() and a call to this function, no calls are allowed to nvjpegDecodeBatchedPhaseTwo() or nvjpegDecodeBatchedPhaseThree() for any other batch with the same JPEG state handle parameter.

Signature:

nvjpegStatus_t nvjpegDecodeBatchedPhaseThree(
	nvjpegHandle_t            handle, 
	nvjpegJpegState_t         jpeg_handle, 
	nvjpegImage_t             *destinations, 
	cudaStream_t              stream);

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegState_t jpeg_handle Input Host The image state handle.
nvjpegImage_t *destinations Input/Output Host/Device

Pointer to the first element of the array of output descriptors. The size of the array is assumed to be the batch_size parameter that was provided to the batch initialization function. See nvjpegImage_t description for details.

cudaStream_t stream Input Host The CUDA stream to which all the GPU tasks will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.5. Decode API—Decoupled Decoding

This set of decoding API works with the bitstream handles, decode parameter handles, pinned and device buffers handles as input, thus decoupling JPEG bitstream parse, buffer management and setting up decoder parameters from the decode process itself.

Currently only multiphase decoding is available. Multiphase decoupled single image decoding consists of three phases:
  • Host,
  • Mixed, and
  • Device,

Each of the above decodings is carried on according to its individual semantics. Phases on different images can be carried out with different decoding state handles simultaneously, while sharing of some helper objects is possible. See the details of semantics in the individual phases descriptions.

Below are a couple of examples of using decoupled API.

The snippet below explains how to use the API to prefetch the host stage of the processing: first do all of the host work on the host, and then submit the rest of decoding work to the device.

#define BATCH_SIZE 2
nvjpegHandle_t nvjpeg_handle;
nvjpegJpegState_t nvjpeg_decoder_state[BATCH_SIZE];
nvjpegBufferPinned_t nvjpeg_pinned_buffer[BATCH_SIZE];
nvjpegBufferDevice_t nvjpeg_device_buffer;
nvjpegJpegStream_t nvjpeg_jpeg_stream[BATCH_SIZE];
nvjpegDecodeParams_t nvjpeg_decode_params;
nvjpegJpegDecoder_t nvjpeg_decoder;
nvjpegBackend_t impl = NVJPEG_BACKEND_DEFAULT;

unsigned char* bitstream[BATCH_SIZE] // pointers jpeg bitstreams
size_t  length[BATCH_SIZE]; // bitstream sizes

nvjpegImage_t output_images[BATCH_SIZE]; 

// all the images in the batch will be decoded as RGBI
nvjpegDecodeParamsSetOutputFormat(nvjpeg_decode_params,NVJPEG_OUTPUT_RGBI );

// call host phase for two bitstreams
for (int i = 0; i < BATCH_SIZE; i++)
{ 
	nvjpegJpegStreamParse(nvjpeg_handle, bitstream[i], length[i], 0, 0, nvjpeg_jpeg_stream[i]);
	nvjpegStateAttachPinnedBuffer(nvjpeg_decoder_state[i], nvjpeg_pinned_buffer[i]);
	nvjpegDecodeJpegHost(nvjpeg_handle, nvjpeg_decoder, nvjpeg_decoder_state[i], nvjpeg_decode_params, nvjpeg_jpeg_stream[i])
}

for (int i = 0; i < BATCH_SIZE; i++)
{
	// same device buffer being used for decoding bitstreams
	nvjpegStateAttachDeviceBuffer(nvjpeg_decoder_state[i], nvjpeg_device_buffer);
   
	// cuda stream set to NULL
	nvjpegDecodeJpegTransferToDevice(nvjpeg_handle, nvjpeg_decoder, nvjpeg_decoder_state[i], nvjpeg_jpeg_stream[i], NULL);
	// cuda stream set to NULL
	nvjpegDecodeJpegDevice(nvjpeg_handle, nvjpeg_decoder, nvjpeg_decoder_state[i], &output_images[i], NULL); 
	cudaDeviceSynchronize();
}

The below snippet explains how pinned and device buffers can be shared across two instances of nvJPEG Decoder Handle.

#define BATCH_SIZE 4
nvjpegHandle_t nvjpeg_handle;
nvjpegJpegDecoder_t nvjpeg_decoder_impl1;
nvjpegJpegDecoder_t nvjpeg_decoder_impl2;
nvjpegJpegState_t nvjpeg_decoder_state_impl1; 
nvjpegJpegState_t nvjpeg_decoder_state_impl2; 
nvjpegBufferPinned_t nvjpeg_pinned_buffer;
nvjpegBufferDevice_t nvjpeg_device_buffer;
nvjpegJpegStream_t nvjpeg_jpeg_stream;
nvjpegDecodeParams_t nvjpeg_decode_params;

unsigned char* bitstream[BATCH_SIZE] // pointers jpeg bitstreams
size_t  length[BATCH_SIZE]; // bitstream sizes

// populate bitstream and length correctly for this code to work
nvjpegImage_t output_images[BATCH_SIZE]; 

// allocate device memory for output images, for this snippet to work
nvjpegStateAttachPinnedBuffer(nvjpeg_decoder_state_impl1, nvjpeg_pinned_buffer);
nvjpegStateAttachPinnedBuffer(nvjpeg_decoder_state_impl2, nvjpeg_pinned_buffer);
nvjpegStateAttachDeviceBuffer(nvjpeg_decoder_state_impl1, nvjpeg_device_buffer);
nvjpegStateAttachDeviceBuffer(nvjpeg_decoder_state_impl2, nvjpeg_device_buffer);

// all the images in the batch will be decoded as RGBI
nvjpegDecodeParamsSetOutputFormat(nvjpeg_decode_params,NVJPEG_OUTPUT_RGBI ); 

for (int i = 0; i < BATCH_SIZE; i++)
{ 
	nvjpegJpegStreamParse(nvjpeg_handle,bitstream[i],length[i],0,0,nvjpeg_jpeg_stream);
	
	// decide which implementation to use, based on image size
	unsigned int frame_width;
	unsigned int frame_height;
	nvjpegJpegStreamGetFrameDimensions(nvjpeg_jpeg_stream,&frame_width, &frame_height));
	nvjpegJpegDecoder_t& decoder = (frame_height*frame_width > 1024 * 768 ) ? nvjpeg_decoder_impl2: nvjpeg_decoder_impl1;
	nvjpegJpegState_t& decoder_state = (frame_height * frame_width > 1024 * 768) ? nvjpeg_decoder_state_impl2:nvjpeg_decoder_state_impl1;

	nvjpegDecodeJpegHost(nvjpeg_handle,decoder,decoder_state,nvjpeg_decode_params,nvjpeg_jpeg_stream);

	// cuda stream set to NULL
	nvjpegDecodeJpegTransferToDevice(nvjpeg_handle,decoder,decoder_state,nvjpeg_jpeg_stream,NULL);

	// cuda stream set to NULL
	nvjpegDecodeJpegDevice(nvjpeg_handle,nvjpeg_decoder,decoder_state,&output_images, NULL); 
	cudaDeviceSynchronize();
}

2.3.5.1. nvjpegDecodeJpegHost()

This is the first stage of the decoupled decoding process. It is done entirely on the host, hence it is synchronous with respect of the host.

If a pinned buffer is attached to the decoder state, then the pinned buffer object will be used to allocate the pinned memory required for the host decoding phase. There wouldn’t be allocation if the pinned buffer object already handles the required amount of pinned memory.

If pinned buffer object is not attached, then the state will use heap host memory to allocate the memory required for the host processing.

In this phase device is not participating. Hence the device selection, device initialization, and device memory initialization can be done later in the decoding process.

This function works on a parsed stream. The parsed stream handle that is available after calling the nvjpegJpegStreamParse() function should be provided to this function.

Signature:

nnvjpegStatus_t nvjpegDecodeJpegHost(
	nvjpegHandle_t handle,
	nvjpegJpegDecoder_t decoder,
	nvjpegJpegState_t decoder_state,
	nvjpegDecodeParams_t decode_params,
	nvjpegJpegStream_t jpeg_stream);		

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegDecoder_t decoder Input Host The nvJPEG decoder handle.
nvjpegJpegState_t decoder_state Input Host The nvJPEG decoder state handle.
nvjpegDecodeParams_t decode_params Input Host Handle to decode the output properties.
nvjpegJpegStream_t jpeg_stream Input Host Handle to the parsed bitstream data.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.5.2. nvjpegDecodeJpegTransferToDevice()

This phase contains both host and device operations. Hence it is a mix of synchronous and asynchronous operations with respect to the host. All the device operations will be submitted to the provided stream.

This phase should be called only after the host phase with the same decoder handle, decoder state handle and parsed jpeg stream handle. Device should be initialized and device buffer should be attached to decoder_state handle using nvjpegStateAttachDeviceBuffer() prior to calling this API. This device buffer object will be resized to the required amount of memory if needed. For the host memory buffer, this phase will use whatever was used in the host phase: either the attached pinned buffer or the state’s host memory buffer.

Signature:

nvjpegStatus_t nvjpegDecodeJpegTransferToDevice(
	nvjpegHandle_t handle,
	nvjpegJpegDecoder_t decoder,
	nvjpegJpegState_t decoder_state,
	nvjpegJpegStream_t jpeg_stream,
	cudaStream_t stream);		

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegDecoder_t decoder Input Host The nvJPEG decoder handle.
nvjpegJpegState_t decoder_state Input Host The nvJPEG decoder state handle.
nvjpegJpegStream_t jpeg_stream Input Host Handle to the parsed bitstream data.
cudaStream_t stream Input Host The CUDA stream to which all the GPU tasks will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.5.3. nvjpegDecodeJpegDevice()

This phase consists of decode operations that take place mainly on the device (no significant host side computation is done). Hence this phase is asynchronous with respect to the host. This phase should be called after nvjpegDecodeJpegTransferToDevice() for a given decoder_state handle and decoder handle.

In this function call the host memory buffers are not used, so if the pinned buffer was attached to the state, then it can be reused somewhere else. Note that at this point the Jpeg stream handle is not needed anymore, since parts that are needed for device decoding will be copied to the device memory in the previous phase.

Signature:

nvjpegStatus_t nvjpegDecodeJpegDevice(
	nvjpegHandle_t handle,
	nvjpegJpegDecoder_t decoder,
	nvjpegJpegState_t decoder_state,
	nvjpegImage_t *destination,
	cudaStream_t stream);		

Parameters:

Parameter Input / Output Memory Description
nvjpegHandle_t handle Input Host The library handle.
nvjpegJpegDecoder_t decoder Input Host The nvJPEG decoder handle.
nvjpegJpegState_t decoder_state Input Host The nvJPEG decoder state handle.
nvjpegImage_t *destination Input/Output Host/Device Pointer to a structure that describes the output destination. This structure should be on host, but the pointers in this structure should be pointing to the device memory. See nvJPEG Image for details.
cudaStream_t stream Input Host The CUDA stream to which all the GPU tasks will be submitted.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.6. nvJPEG Decode Parameters

This category of APIs are used to set the decoding parameters. These APIs should be used with the decode APIs defined in Decode API—Decoupled Decoding.

2.3.6.1. nvjpegDecodeParamsSetOutputFormat()

This function is used to set the decode output format. See nvjpegOutputFormat_t described in step 6 of Single Image Decoding. The output parameter of nvjpegOutputFormat_t defaults to NVJPEG_OUTPUT_UNCHANGED if not set using this API.

Signature:

nvjpegStatus_t nvjpegDecodeParamsSetOutputFormat(
	nvjpegDecodeParams_t decode_params,
	nvjpegOutputFormat_t output_format);	

Parameters:

Parameter Input / Output Memory Description
nvjpegDecodeParams_t decode_params Input Host Decode output parameter handle.
nvjpegOutputFormat_t output_format Input Host See step 6 of Single Image Decoding.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.6.2. nvjpegDecodeParamsSetROI()

This function enables the region of interest-only (ROI-only) decode. To disable the ROI-only, i.e., to decode the whole image, set:

  • offset_x = 0,
  • offset_y = 0,
  • roi_width = -1, and
  • roi_height = -1.
Note: ROI decode is disabled by default.

The ROI window cannot go out of image bounds. That is:

  • offset_x cannot be lower than zero, or
  • offset_x + roi_width cannot be larger than the JPEG image width.

If the output format is NVJPEG_OUTPUT_YUV or NVJPEG_OUTPUT_UNCHANGED, then the offset_x and offset_y values have to be multiples of the maximum subsampling factor, as defined in the JPEG standard.

Signature:

nvjpegStatus_t nvjpegDecodeParamsSetROI(
	nvjpegDecodeParams_t decode_params,
	int offset_x, 
	int offset_y, 
	int roi_width, 
	int roi_height); 		

Parameters:

Parameter Input / Output Memory Description
nvjpegDecodeParams_t decode_params Input Host The decode output parameter handle.
int offset_x Input Host Image offset along the horizontal direction relative to the top left corner.
int offset_y Input Host Image offset along the vertical direction relative to the top left corner.
int roi_width Input Host Image width relative to offset_x.
int roi_height Input Host Image height relative to offset_y.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.6.3. nvjpegDecodeParamsSetAllowCMYK()

If enabled, the nvJPEG library assumes that the JPEG with 4 encoded color components is in CMYK colorspace, and enables the conversion to RGB/YUV colorspace. The CMYK-to-RGB conversion is disabled by default. The conversion is based on the subtractive scheme—this behaviour matches OpenCV’s handling of 4-component JPEGs.

Signature:

nvjpegStatus_t nvjpegDecodeParamsSetAllowCMYK(
	nvjpegDecodeParams_t decode_params,
	int allow_cmyk);		

Parameters:

Parameter Input / Output Memory Description
nvjpegDecodeParams_t decode_params Input Host Decode output parameter handle.
int allow_cmyk Input Host Enable CMYK to RGB conversion.

Returns:

nvjpegStatus_t - An error code as specified in nvJPEG API Return Codes.

2.3.7. nvJPEG API Return Codes

The nvJPEG API adheres to the following return codes and their indicators:

typedef enum
{
 NVJPEG_STATUS_SUCCESS = 0,
 NVJPEG_STATUS_NOT_INITIALIZED = 1,
 NVJPEG_STATUS_INVALID_PARAMETER = 2,
 NVJPEG_STATUS_BAD_JPEG = 3,
 NVJPEG_STATUS_JPEG_NOT_SUPPORTED = 4,
 NVJPEG_STATUS_ALLOCATOR_FAILURE = 5,
 NVJPEG_STATUS_EXECUTION_FAILED = 6,
 NVJPEG_STATUS_ARCH_MISMATCH = 7,
 NVJPEG_STATUS_INTERNAL_ERROR = 8,
 NVJPEG_STATUS_IMPLEMENTATION_NOT_SUPPORTED = 9
} nvjpegStatus_t;	

Description of the returned error codes:

Returned Error (Returned Code) Description
NVJPEG_STATUS_SUCCESS (0) The API call has finished successfully. Note that many of the calls are asynchronous and some of the errors may be seen only after synchronization.
NVJPEG_STATUS_NOT_INITIALIZED (1) The library handle was not initialized. A call to nvjpegCreate() is required to initialize the handle.
NVJPEG_STATUS_INVALID_PARAMETER (2) Wrong parameter was passed. For example, a null pointer as input data, or an image index not in the allowed range.
NVJPEG_STATUS_BAD_JPEG (3) Cannot parse the JPEG stream. Check that the encoded JPEG stream and its size parameters are correct.
NVJPEG_STATUS_JPEG_NOT_SUPPORTED (4) Attempting to decode a JPEG stream that is not supported by the nvJPEG library.
NVJPEG_STATUS_ALLOCATOR_FAILURE (5) The user-provided allocator functions, for either memory allocation or for releasing the memory, returned a non-zero code.
NVJPEG_STATUS_EXECUTION_FAILED (6) Error during the execution of the device tasks.
NVJPEG_STATUS_ARCH_MISMATCH (7) The device capabilities are not enough for the set of input parameters provided (input parameters such as backend, encoded stream parameters, output format).
NVJPEG_STATUS_INTERNAL_ERROR (8) Error during the execution of the device tasks.
NVJPEG_STATUS_IMPLEMENTATION_NOT_SUPPORTED (9) Not supported.

2.3.8. nvJPEG Chroma Subsampling

One of the outputs of the nvjpegGetImageInfo() API is nvjpegChromaSubsampling_t. This parameter is an enum type, and its enumerator list comprises of the chroma subsampling property retrieved from the encoded JPEG image. Below are the chroma subsampling types the nvjpegGetImageInfo() function currently supports:

typedef enum
{
 NVJPEG_CSS_444,
 NVJPEG_CSS_422,
 NVJPEG_CSS_420,
 NVJPEG_CSS_440,
 NVJPEG_CSS_411,
 NVJPEG_CSS_410,
 NVJPEG_CSS_GRAY,
 NVJPEG_CSS_UNKNOWN
} nvjpegChromaSubsampling_t;	

Examples of nvJPEG

This package contains the library header and a set of libraries—static and shared. Shared libraries (the libnvjpeg.so and the respective versioned libraries) have all of the CUDA toolkit dependencies statically linked. However, if you want to link against the static library (libnvjpeg_static.a) you also need to link the other dependencies—for example dl, rt and thread libraries.

Example of linking shared library:

g++ -Icuda-linux64-nvjpeg/include -lnvjpeg -Lcuda-linux64-nvjpeg/lib64 my_example.cpp -o my_example

Example of linking static library:

g++ -Icuda-linux64-nvjpeg/include -lnvjpeg_static -ldl -lrt -pthread -Lcuda-linux64-nvjpeg/lib64 my_example.cpp -o my_example

Example

Below example shows how to use the various nvJPEG APIs.

Compile with the following command from the examples folder, assuming CUDA 9.0 is installed at the path /usr/local/cuda-9.0:

g++ -O3 -m64 nvjpeg_example.cpp -I../include -lnvjpeg -L../lib64 -I/usr/local/cuda-9.0/include -ldl -lrt -pthread -lcudart -L/usr/local/cuda-9.0/lib64 -Wl,-rpath=../lib64 -Wl,-rpath=/usr/local/cuda-9.0/lib64 -o nvjpeg_example

The below examples show how to decode the JPEG files using either single or batched API, and write the decoded files as BMP images.

To decode a single image:

./nvjpeg_example -i /tmp/my_image.jpg -fmt rgb -o /tmp

To decode multiple images in the folder using the batched API in separate phases:

./nvjpeg_example -i /tmp/my_images/ -fmt rgb -b 32 -pipelined -batched -o /tmp

Run the command ./nvjpeg_example -h for the description of the parameters.

3. JPEG Encoding

This section describes the encoding functions of the nvJPEG Library.

3.1. Using the Encoder

The user should perform the below prerequisite steps before calling the nvJPEG encoding functions. See also nvJPEG Encoder Helper API Reference.

3.1.1. Encoding the Parameters

The user should create an encoding parameters structure with nvjpegEncoderParamsCreate() function. The function will be initialized with default parameters. User can use an appropriate nvjpegEncoderParamsSet*() function to set a specific parameter.

The quality parameter can be set, using nvjpegEncoderParamsSetQuality() function, to an integer value between 1 and 100, and this quality parameter will be used as a base for generating the JPEG quantization tables.

The parameters structure should be passed to compression functions.

Note: The encoding parameters structure can be reused to compress multiple images simultaneously, but no changes to the parameters should be made during the ongoing encoding, or encoding result will be undefined.

3.1.2. Encoding the State

The user should create the encoding state structure using nvjpegEncoderStateCreate() function. This function will hold intermediate buffers for the encoding process. This state should be passed to the compression functions.

Note: The encoding state structure can be reused to encode a series of images, but no encoding should be performed on multiple images with the same encoding state at the same time - otherwise result of the encodings will be undefined.

3.1.3. Encoding the Image

The nvJPEG library provides a few interfaces for compressing the image in different formats and colorspaces. See below.

3.1.3.1. nvjpegEncodeYUV

Input for this function is an image in YUV colorspace. See nvjpegEncodeYUV(). The source argument should be filled with the corresponding YUV planar data. The chroma_subsampling argument should have the chroma subsampling of the input data. If the chroma subsampling in the encoding parameters is the same as input chroma subsampling, then the user's input data will be directly used in the JPEG compression. Otherwise chroma will be resampled to match the chroma subsampling of the encoding parameters.

Input data should be provided with respect to the subsampling factors. That is, the chrominance image planes should have sizes aligned to the corresponding subsamplings. For example:

  • Image dimensions: 123x321
  • Input chroma subsampling is: NVJPEG_CSS_410
  • Chroma subsampling factor for this chroma subsampling: is 4x2
  • Given the above, the encoder library expects the user to provide:
    • Y plane with size: 123 x 321
    • Cb and Cr plane with size: 31 x 161

3.1.3.2. nvjpegEncodeImage

See nvjpegEncodeImage(). Input for this function, i.e., how data should be provided in the source argument, is determined by the input_format argument. For the interleaved formats (ending with I) only the first channel is used. For the non-interleaved formats, all the channels in the input format are used.

For example, if the user has interleaved the RGB image of size W x H, stored continuously, and the pointer to it is pImage, then source should be:

  • source.channel[0] = pImage
  • source.pitch[0] = W*3

When the same image is stored in planar format, with image planes pointers stored continuously in the array pImage[3], then source should be:

  • source.channel[0] = pImage[0]
  • source.channel[1] = pImage[1]
  • source.channel[2] = pImage[2]

The pitch values for each channel in the source parameter should be set accordingly to the data layout.

The nvJPEG library will perform the color transformation to the YCbCr, and will compress the result.

3.1.4. Retrieving the Compressed Stream

Often it is not feasible to accurately predict the final compressed data size of the final JPEG stream for any input data and parameters. The nvJPEG library, while encoding, will calculate the size of the final stream, allocate temporary buffer in the encoder state and save the compressed data in the encoding state's buffer. In order to get final compressed JPEG stream, the user should provide the memory buffer large enough to store this compressed data. There are two options for how to do this:

  1. Use the upper bound on compressed JPEG stream size for the given parameters and image dimensions:
    1. Use the nvjpegEncodeRetrieveBitstream() function to retrieve the maximum possible JPEG stream size at any given time.
    2. Allocate the memory buffer at any given time.
    3. Encode the image using one of the encoding functions.
    4. Retrieve the compressed JPEG stream from the encoder state after successful encoding, using the nvjpegEncodeRetrieveBitstream() and the allocated buffer.
  2. Wait for the encoding to complete, and retrieve the exact size of required buffer, as below:
    1. Encode the image using one of the encoding functions.
    2. Use the nvjpegEncodeRetrieveBitstream() function to retrieve the size in bytes of the compressed JPEG stream.
    3. Allocate the memory buffer of at least this size.
    4. Use the nvjpegEncodeRetrieveBitstream() function to populate your buffer with the compressed JPEG stream.
Note: As the same encoding image state can be reused to compress a series of images, the nvjpegEncodeRetrieveBitstream() function will return the result for the last compressed image.

3.1.5. JPEG Encoding Example

See below the example code, and the block diagram shown in Figure 1, for encoding with nvJPEG Encoder.

Figure 1. JPEG Encoding Using nvJPEG Encoder
nvJPEG Encoder Example

nvjpegHandle_t nv_handle;
nvjpegEncoderState_t nv_enc_state;
nvjpegEncoderParams_t nv_enc_params;
cudaStream_t stream;
 
// initialize nvjpeg structures
nvjpegCreateSimple(&nv_handle);
nvjpegEncoderStateCreate(nv_handle, &nv_enc_state, stream);
nvjpegEncoderParamsCreate(nv_handle, &nv_enc_params, stream);
 
nvjpegImage_t nv_image;
// Fill nv_image with image data, let’s say 640x480 image in RGB format
 
// Compress image
nvjpegEncodeImage(nv_handle, nv_enc_state, nv_enc_params,
    &nv_image, NVJPEG_INPUT_RGB, 640, 480, stream);
 
// get compressed stream size
size_t length;
nvjpegEncodeRetrieveBitstream(nv_handle, nv_enc_state, NULL, &length, stream);
// get stream itself
cudaStreamSynchronize(stream);
std::vector<char> jpeg(length);
nvjpegEncodeRetrieveBitstream(nv_handle, nv_enc_state, jpeg.data(), &length, 0);
 
// write stream to file
cudaStreamSynchronize(stream);
std::ofstream output_file(“test.jpg”, std::ios::out | std::ios::binary);
output_file.write(jpeg.data(), length);
output_file.close();

3.2. nvJPEG Encoder Type Declarations

This section describes the nvJPEG Encoder Type Declarations.

nvjpegInputFormat_t

typedef enum
{
    NVJPEG_INPUT_RGB         = 3, 
    NVJPEG_INPUT_BGR         = 4, 
    NVJPEG_INPUT_RGBI        = 5, 
    NVJPEG_INPUT_BGRI        = 6 
} nvjpegInputFormat_t;

The nvjpegInputFormat_t enum is used to select the color model and pixel format of the input image. It is used for conversion to YCbCr during encoding.

Member Description
NVJPEG_INPUT_RGB Input image is in RGB color model. Pixel format is RGB.
NVJPEG_INPUT_BGR Input image is in RGB color model. Pixel format is BGR.
NVJPEG_INPUT_RGBI Input image is in RGB color model. Pixel format is interleaved RGB.
NVJPEG_INPUT_BGRI Input image is in RGB color model. Pixel format is interleaved BGR.

3.2.2. nvjpegEncoderState_t

The nvjpegEncoderState_t is a structure that stores intermediate buffers and variables used for compression.

3.2.3. nvjpegEncoderParams_t

The nvjpegEncoderParams_t is a structure that stores JPEG encode parameters.

3.3. nvJPEG Encoder Helper API Reference

The nvJPEG Encoder helper functions are used for initializing.

3.3.1. nvjpegEncoderStateCreate()

Creates encoder state that stores intermediate buffers used in compression.

Signature:

nvjpegStatus_t nvjpegEncoderStateCreate(
	nvjpegHandle_t handle,
	nvjpegEncoderState_t *encoder_state,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_state Output Host Pointer to the encoder state structure, where the new state will be placed.
stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.3.2. nvjpegEncoderStateDestroy()

Destroys the encoder state.

Signature:

nvjpegStatus_t nvjpegEncoderStateDestroy(
	nvjpegEncoderState_t encoder_state);

Parameters:

Parameter Input / Output Memory Description
encoder_state Input/Output Host Encoder state structure that will be released.

3.3.3. nvjpegEncoderParamsCreate()

Creates the structure that holds the compression parameters.

Signature:

nvjpegStatus_t nvjpegEncoderParamsCreate(
	nvjpegHandle_t handle, 
	nvjpegEncoderParams_t *encoder_params,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_params Output Host

Pointer to the location where the new parameters structure will be placed.

stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.3.4. nvjpegEncoderParamsDestroy()

Destroys the encoder parameters structure.

Signature:

nvjpegEncoderParamsDestroy(
	nvjpegEncoderParams_t encoder_params);

Parameters:

Parameter Input / Output Memory Description
encoder_params Input/Output Host

Encoder params structure that will be released.

3.3.5. nvjpegEncoderParamsSetEncoding()

Sets the parameter quality in the encoder parameters structure.

Signature:

nvjpegStatus_t nvjpegEncoderParamsSetEncoding(
	nvjpegEncoderParams_t encoder_params,
	nvjpegJpegEncoding_t etype,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_params Input/Output Host

Encoder params structure handle.

etype Input Host

Encoding type selection (Baseline/Progressive). Default is Baseline.

stream Input Host

CUDA stream where all the required device operations will be placed.

3.3.6. nvjpegEncoderParamsSetQuality()

Sets the parameter quality in the encoder parameters structure.

Signature:

nvjpegStatus_t nvjpegEncoderParamsSetQuality(
	nvjpegEncoderParams_t encoder_params,
	const int quality,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_params Input/Output Host

Encoder params structure handle.

quality Input Host

Integer value of quality between 1 and 100, where 100 is the highest quality. Default value is 70.

stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.3.7. nvjpegEncoderParamsSetOptimizedHuffman()

Sets whether or not to use optimized Huffman. Using optimized Huffman produces smaller JPEG bitstream sizes with the same quality, but with slower performance.

Signature:

nvjpegStatus_t nvjpegEncoderParamsSetOptimizedHuffman(
	nvjpegEncoderParams_t encoder_params,
	const int optimized,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_params Input/Output Host

Encoder params structure handle.

optimized Input Host If this value is 0 then non-optimized Huffman will be used. Otherwise optimized version will be used. Default value is 0.
stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.3.8. nvjpegEncoderParamsSetSamplingFactors()

Sets which chroma subsampling will be used for JPEG compression.

Signature:

nvjpegStatus_t nvjpegEncoderParamsSetSamplingFactors(
	nvjpegEncoderParams_t encoder_params,
	const nvjpegChromaSubsampling_t chroma_subsampling,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_params Input/Output Host

Encoder params structure handle.

chroma_subsampling Input Host

Chroma subsampling that will be used for JPEG compression. If the input is in YUV color model and chroma_subsampling is different from the subsampling factors of source image, then the NVJPEG library will convert subsampling to the value of chroma_subsampling. Default value is 4:4:4.

stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.4. nvJPEG Encoder API Reference

This section describes the nvJPEG Encoder API.

nvjpegEncodeGetBufferSize()

Returns the maximum possible buffer size that is needed to store the compressed JPEG stream, for the given input parameters.

Signature:

nvjpegStatus_t nvjpegEncodeGetBufferSize(
	nvjpegHandle_t handle,
	const nvjpegEncoderParams_t encoder_params,
	int image_width,
	int image_height,
	size_t *max_stream_length);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_params Input/Output Host

Encoder parameters structure handle.

image_width Input Host

Input image width.

image_height Input Host Input image height.
stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.4.2. nvjpegEncodeYUV()

Compresses the image in YUV colorspace to JPEG stream using the provided parameters, and stores it in the state structure.

Signature:

nvjpegStatus_t nvjpegEncodeYUV(
	nvjpegHandle_t handle,
	nvjpegEncoderState_t encoder_state,
	const nvjpegEncoderParams_t encoder_params,
	const nvjpegImage_t *source,
	nvjpegChromaSubsampling_t chroma_subsampling, 
	int image_width,
	int image_height,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_state Input/Output Host Internal structure that holds the temporary buffers required for the compression and also stores the final compressed JPEG stream.
encoder_params Input Host

Encoder parameters structure handle.

source Input Host Pointer to the nvjpeg structure that holds the device pointers to the Y, U(Cb) and V(Cr) image planes and the respective strides.
chroma_subsampling Input Host Chroma subsampling of the input data.
image_width Input Host

Input image width.

image_height Input Host Input image height.
stream Inputt Host

CUDA stream where all the required device operations will be placed.

3.4.3. nvjpegEncodeImage()

Compresses the image in the provided format to the JPEG stream using the provided parameters, and stores it in the state structure.

Signature:

nvjpegStatus_t nvjpegEncodeImage(
	nvjpegHandle_t handle,
	nvjpegEncoderState_t encoder_state,
	const nvjpegEncoderParams_t encoder_params,
	const nvjpegImage_t *source,
	nvjpegInputFormat_t input_format, 
	int image_width,
	int image_height,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_state Input/Output Host Internal structure that holds the temporary buffers required for the compression and also stores the final compressed JPEG stream.
encoder_params Input Host

Encoder parameters structure handle.

source Input Host Pointer to the nvjpeg structure that holds the device pointers to the Y, U(Cb) and V(Cr) image planes and the respective strides.
input_format Input Host

Value of nvjpegInputFormat_t type that describes the input data.

image_width Input Host

Input image width.

image_height Input Host Input image height.
stream Input Host

CUDA stream where all the required device operations will be placed.

3.4.4. nvjpegEncodeRetrieveBitstream()

Retrieves the compressed stream from the encoder state that was previously used in one of the encoder functions.

  • If data parameter is NULL then the encoder will return compressed stream size in the length parameter.
  • If data is not NULL then the provided length parameter should contain the data buffer size.
  • If the provided length is less than compressed stream size, then an error will be returned. Otherwise the compressed stream will be stored in the data buffer and the actual compressed buffer size will be stored in the length parameter.

Signature:

nvjpegStatus_t nvjpegEncodeRetrieveBitstream(
	nvjpegHandle_t handle,
	nvjpegEncoderState_t encoder_state,
	unsigned char *data,
	size_t *length,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
handle Input Host

Library handle

encoder_state Input/Output Host The encoder_state that was previously used in one of the encoder functions.
data Input/Output Host Pointer to the buffer in the host memory where the compressed stream will be stored. Can be NULL (see description).
length Input/Output Host Pointer to the input buffer size. On return the NVJPEG library will store the actual compressed stream size in this parameter.
stream Inputt Host

CUDA stream where all the required device operations will be placed.

4. JPEG Transcoding

This section describes the transcoding functions of the nvJPEG Library.

4.1. nvJPEG Transcoder Helper API Reference

This section describes the nvJPEG Transcoder helper API.

4.1.1. nvjpegEncoderParamsCopyMetadata()

Copies the metadata (JFIF, APP, EXT, and COM markers) from the parsed stream.

Signature:

nvjpegStatus_t nvjpegEncoderParamsCopyMetadata(
	nvjpegEncoderState_t encoder_state,
	nvjpegEncoderParams_t encode_params,
	nvjpegJpegStream_t jpeg_stream,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_state In/Out Host Internal structure that stores the temporary buffers required for the compression.
encode_params Out Host Encoder parameters that will be used for compression.
jpeg_stream In Host Input parsed stream.
stream In Host CUDA stream where all the required device operations will be placed.

4.1.2. nvjpegEncoderParamsCopyQuantizationTables()

Copies the quantization tables from the parsed stream.

Signature:

nvjpegStatus_t nvjpegEncoderParamsCopyQuantizationTables(
	nvjpegEncoderParams_t encode_params,
	nvjpegJpegStream_t jpeg_stream,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encode_params Out Host Encoder parameters that will be used for compression.
jpeg_stream In Host Input parsed stream.
stream In Host CUDA stream where all the required device operations will be placed.

4.1.3. nvjpegEncoderParamsCopyHuffmanTables()

Copies the Huffman tables from the parsed stream.

Signature:

nvjpegStatus_t nvjpegEncoderParamsCopyHuffmanTables(
	nvjpegEncoderState_t encoder_state,
	nvjpegEncoderParams_t encode_params,
	nvjpegJpegStream_t jpeg_stream,
	cudaStream_t stream);

Parameters:

Parameter Input / Output Memory Description
encoder_state In/Out Host Internal structure that stores the temporary buffers required for the compression.
encode_params Out Host Encoder parameters that will be used for compression.
jpeg_stream In Host Input parsed stream.
stream In Host CUDA stream where all the required device operations will be placed.

4.2. JPEG Transcoding Example

See below the example code.

cudaStream_t stream;
// create library handle
nvjpegHandle_t handle;
nvjpegCreateSimple(&handle);

/////////////////////////////////// nvJPEG decoding ////////////////////////////////////////
// create bitstream object
nvjpegJpegStream_t jpeg_stream;
nvjpegJpegStreamCreate(handle, &jpeg_stream);
  
// parse jpeg stream
nvjpegJpegStreamParse(handle,
    data_ptr,
    data_size,
    1,  // save metadata in the jpegStream structure
    0,
    jpeg_stream);
 
// create decoder and decoder state
nvjpegJpegDecoder_t decoder;
nvjpegJpegState_t decoder_state;
nvjpegDecoderCreate(handle, NVJPEG_BACKEND_DEFAULT, &decoder);
nvjpegDecoderStateCreate(handle, decoder, &decoder_state);
   
// create and set up decoder parameters
nvjpegDecodeParams_t decode_params;
nvjpegDecodeParamsCreate(handle, &decode_params);
nvjpegDecodeParamsSetOutputFormat(decode_params, NVJPEG_OUTPUT_RGBI);
  
// decode image
nvjpegImage_t output_image;
nvjpegDecodeJpeg(handle, decoder, decode_params, jpeg_stream, decoder_state, &output_image, stream);
  
/////////////////////////////////// nvJPEG Transcode and encode API ///////////////////////////////////
nvjpegEncoderState_t encoder_state;
nvjpegEncoderParams_t encode_params;
  
// get encoding from the jpeg stream and copy it to the encode parameters
nvjpegJpegEncoding_t jpeg_encoding;
nvjpegJpegStreamGetJpegEncoding(jpeg_stream, &jpeg_encoding);
nvjpegEncoderParamsSetEncoding(encode_params, jpeg_encoding);
  
// copies according data to the encode parameters
nvjpegEncoderParamsCopyMetadata(encode_params, jpeg_stream, stream);
nvjpegEncoderParamsCopyQuantizationTables(encode_params, jpeg_stream, stream);
nvjpegEncoderParamsCopyHuffmanTables(encode_params, jpeg_stream, stream);
  
// retrieve frame dimensions
unsigned width, height;
nvjpegJpegStreamGetFrameDimensions(jpeg_stream, &width, &height);

// encode using encode parameters
nvjpegEncodeImage(nvjpeg_handle, encoder_state, encode_params, &output_image,
    input_format, width, height, stream); 
 
// get compressed stream size
size_t length;
nvjpegEncodeRetrieveBitstream(nvjpeg_handle, encoder_state, NULL, &length, stream);
// get stream itself
cudaStreamSynchronize(stream);
std::vector<char> jpeg(length);
nvjpegEncodeRetrieveBitstream(nvjpeg_handle, encoder_state, jpeg.data(), &length, 0);

Notices

Notice

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