Operation Reference

The data processing graph within a DALI Pipeline is defined by calling operation functions. They accept and return instances of DataNode, which are symbolic representations of batches of Tensors. The operation functions cannot be used to process data directly.

The constraints for defining the processing pipeline can be found in this section of Pipeline documentation.

The following table lists all operations available in DALI:

Function	Device support	Short description
audio_decoder	CPU	Legacy alias for decoders.audio().
audio_resample	CPU, GPU	Resamples an audio signal.
batch_permutation	CPU	Produces a batch of random integers which can be used as indices for indexing samples in the batch.
bb_flip	CPU, GPU	Flips bounding boxes horizontaly or verticaly (mirror).
bbox_paste	CPU	Transforms bounding boxes so that the boxes remain in the same place in the image after the image is pasted on a larger canvas.
box_encoder	CPU, GPU	Encodes the input bounding boxes and labels using a set of default boxes (anchors) passed as an argument.
brightness	CPU, GPU	Adjusts the brightness of the images.
brightness_contrast	CPU, GPU	Adjusts the brightness and contrast of the images.
caffe2_reader	CPU	Legacy alias for readers.caffe2().
caffe_reader	CPU	Legacy alias for readers.caffe().
cast	CPU, GPU	Cast a tensor to a different type.
cast_like	CPU, GPU	Cast the first tensor to the type of the second tensor.
cat	CPU, GPU	Joins the input tensors along an existing axis.
coco_reader	CPU	Legacy alias for readers.coco().
coin_flip	CPU, GPU	Generates random boolean values following a bernoulli distribution.
color_space_conversion	CPU, GPU	Converts between various image color models.
color_twist	CPU, GPU	Adjusts hue, saturation, brightness and contrast of the image.
constant	CPU, GPU	Produces a batch of constant tensors.
contrast	CPU, GPU	Adjusts the contrast of the images.
coord_flip	CPU, GPU	Transforms vectors or points by flipping (reflecting) their coordinates with respect to a given center.
coord_transform	CPU, GPU	Applies a linear transformation to points or vectors.
copy	CPU, GPU	Creates a copy of the input tensor.
crop	CPU, GPU	Crops the images with the specified window dimensions and window position (upper left corner).
crop_mirror_normalize	CPU, GPU	Performs fused cropping, normalization, format conversion (NHWC to NCHW) if desired, and type casting.
dl_tensor_python_function	CPU, GPU	Executes a Python function that operates on DLPack tensors.
dump_image	CPU, GPU	Save images in batch to disk in PPM format.
element_extract	CPU, GPU	Extracts one or more elements from input sequence.
erase	CPU, GPU	Erases one or more regions from the input tensors.
expand_dims	CPU, GPU	Insert new dimension(s) with extent 1 to the data shape.
external_source	CPU, GPU	Allows externally provided data to be passed as an input to the pipeline.
fast_resize_crop_mirror	CPU	Performs a fused resize, crop, mirror operation.
file_reader	CPU	Legacy alias for readers.file().
flip	CPU, GPU	Flips the images in selected dimensions (horizontal, vertical, and depthwise).
gaussian_blur	CPU, GPU	Applies a Gaussian Blur to the input.
get_property	CPU, GPU	Returns a property of the tensor passed as an input.
grid_mask	CPU, GPU	Performs the gridmask augumentation (https://arxiv.org/abs/2001.04086).
hsv	CPU, GPU	Adjusts hue, saturation and value (brightness) of the images.
hue	CPU, GPU	Changes the hue level of the image.
image_decoder	CPU, Mixed	Legacy alias for decoders.image().
image_decoder_crop	CPU, Mixed	Legacy alias for decoders.image_crop().
image_decoder_random_crop	CPU, Mixed	Legacy alias for decoders.image_random_crop().
image_decoder_slice	CPU, Mixed	Legacy alias for decoders.image_slice().
jitter	GPU	Performs a random Jitter augmentation.
jpeg_compression_distortion	CPU, GPU	Introduces JPEG compression artifacts to RGB images.
laplacian	CPU, GPU	Computes the Laplacian of an input.
lookup_table	CPU, GPU	Maps the input to output by using a lookup table that is specified by keys and values, and a default_value for unspecified keys.
mel_filter_bank	CPU, GPU	Converts a spectrogram to a mel spectrogram by applying a bank of triangular filters.
mfcc	CPU, GPU	Computes Mel Frequency Cepstral Coefficiencs (MFCC) from a mel spectrogram.
multi_paste	CPU, GPU	Performs multiple pastes from image batch to each of outputs
mxnet_reader	CPU	Legacy alias for readers.mxnet().
nemo_asr_reader	CPU	Legacy alias for readers.nemo_asr().
nonsilent_region	CPU, GPU	Performs leading and trailing silence detection in an audio buffer.
normal_distribution	CPU, GPU	Generates random numbers following a normal distribution.
normalize	CPU, GPU	Normalizes the input by removing the mean and dividing by the standard deviation.
numba_function	CPU, GPU	Invokes a njit compiled Numba function.
numpy_reader	CPU, GPU	Legacy alias for readers.numpy().
one_hot	CPU, GPU	Produces a one-hot encoding of the input.
optical_flow	GPU	Calculates the optical flow between images in the input.
pad	CPU, GPU	Pads all samples with the fill_value in the specified axes to match the biggest extent in the batch for those axes or to match the minimum shape specified.
paste	GPU	Pastes the input images on a larger canvas, where the canvas size is equal to input size * ratio.
peek_image_shape	CPU	Obtains the shape of the encoded image.
per_frame	CPU, GPU	Marks the input tensor as a sequence.
permute_batch	CPU, GPU	Returns a batch of tensors constructed by selecting tensors from the input based on indices given in indices argument.
power_spectrum	CPU	Calculates power spectrum of the signal.
preemphasis_filter	CPU, GPU	Applies preemphasis filter to the input data.
python_function	CPU, GPU	Executes a Python function.
random_bbox_crop	CPU	Applies a prospective random crop to an image coordinate space while keeping the bounding boxes, and optionally labels, consistent.
random_resized_crop	CPU, GPU	Performs a crop with a randomly selected area and aspect ratio and resizes it to the specified size.
reinterpret	CPU, GPU	Treats content of the input as if it had a different type, shape, and/or layout.
reshape	CPU, GPU	Treats content of the input as if it had a different shape and/or layout.
resize	CPU, GPU	Resize images.
resize_crop_mirror	CPU	Performs a fused resize, crop, mirror operation. Both fixed and random resizing and cropping are supported.
roi_random_crop	CPU	Produces a fixed shape cropping window, randomly placed so that as much of the provided region of interest (ROI) is contained in it.
rotate	CPU, GPU	Rotates the images by the specified angle.
saturation	CPU, GPU	Changes the saturation level of the image.
sequence_reader	CPU	Legacy alias for readers.sequence().
sequence_rearrange	CPU, GPU	Rearranges frames in a sequence.
shapes	CPU, GPU	Returns the shapes of inputs.
slice	CPU, GPU	Extracts a subtensor, or slice.
spectrogram	CPU, GPU	Produces a spectrogram from a 1D signal (for example, audio).
sphere	CPU, GPU	Performs a sphere augmentation.
squeeze	CPU, GPU	Removes the dimensions given as axes or axis_names.
ssd_random_crop	CPU	Performs a random crop with bounding boxes where Intersection Over Union (IoU) meets a randomly selected threshold between 0-1.
stack	CPU, GPU	Joins the input tensors along a new axis.
tfrecord_reader	CPU	Legacy alias for readers.tfrecord().
to_decibels	CPU, GPU	Converts a magnitude (real, positive) to the decibel scale.
torch_python_function	CPU, GPU	Executes a function that is operating on Torch tensors.
transpose	CPU, GPU	Transposes the tensors by reordering the dimensions based on the perm parameter.
uniform	CPU, GPU	Generates random numbers following a uniform distribution.
video_reader	GPU	Legacy alias for readers.video().
video_reader_resize	GPU	Legacy alias for readers.video_resize().
warp_affine	CPU, GPU	Applies an affine transformation to the images.
water	CPU, GPU	Performs a water augmentation, which makes the image appear to be underwater.
decoders.audio	CPU	Decodes waveforms from encoded audio data.
decoders.image	CPU, Mixed	Decodes images.
decoders.image_crop	CPU, Mixed	Decodes images and extracts regions-of-interest (ROI) that are specified by fixed window dimensions and variable anchors.
decoders.image_random_crop	CPU, Mixed	Decodes images and randomly crops them.
decoders.image_slice	CPU, Mixed	Decodes images and extracts regions of interest.
experimental.audio_resample	CPU, GPU	Legacy alias for audio_resample().
experimental.debayer	GPU	Performs image demosaicing/debayering.
experimental.inflate	GPU	Inflates/decompresses the input using specified decompression algorithm.
experimental.peek_image_shape	CPU	Obtains the shape of the encoded image.
experimental.remap	GPU	The remap operation applies a generic geometrical transformation to an image. In other words, it takes pixels from one place in the input image and puts them in another place in the output image. The transformation is described by mapx and mapy parameters, where:
experimental.decoders.image	CPU, Mixed	Decodes images.
experimental.decoders.image_crop	CPU, Mixed	Decodes images and extracts regions-of-interest (ROI) that are specified by fixed window dimensions and variable anchors.
experimental.decoders.image_random_crop	CPU, Mixed	Decodes images and randomly crops them.
experimental.decoders.image_slice	CPU, Mixed	Decodes images and extracts regions of interest.
experimental.decoders.video	CPU, Mixed	Decodes a video file from a memory buffer (e.g. provided by external source).
experimental.readers.video	CPU, GPU	Loads and decodes video files using FFmpeg.
noise.gaussian	CPU, GPU	Applies gaussian noise to the input.
noise.salt_and_pepper	CPU, GPU	Applies salt-and-pepper noise to the input.
noise.shot	CPU, GPU	Applies shot noise to the input.
random.coin_flip	CPU, GPU	Generates random boolean values following a bernoulli distribution.
random.normal	CPU, GPU	Generates random numbers following a normal distribution.
random.uniform	CPU, GPU	Generates random numbers following a uniform distribution.
readers.caffe	CPU	Reads (Image, label) pairs from a Caffe LMDB.
readers.caffe2	CPU	Reads sample data from a Caffe2 Lightning Memory-Mapped Database (LMDB).
readers.coco	CPU	Reads data from a COCO dataset that is composed of a directory with images and annotation JSON files.
readers.file	CPU	Reads file contents and returns file-label pairs.
readers.mxnet	CPU	Reads the data from an MXNet RecordIO.
readers.nemo_asr	CPU	Reads automatic speech recognition (ASR) data (audio, text) from an NVIDIA NeMo compatible manifest.
readers.numpy	CPU, GPU	Reads Numpy arrays from a directory.
readers.sequence	CPU	Reads [Frame] sequences from a directory representing a collection of streams.
readers.tfrecord	CPU	Reads samples from a TensorFlow TFRecord file.
readers.video	GPU	Loads and decodes video files using FFmpeg and NVDECODE, which is the hardware-accelerated video decoding feature in the NVIDIA(R) GPU.
readers.video_resize	GPU	Loads, decodes and resizes video files with FFmpeg and NVDECODE, which is NVIDIA GPU’s hardware-accelerated video decoding.
readers.webdataset	CPU	A reader for the webdataset format.
reductions.max	CPU, GPU	Gets maximal input element along provided axes.
reductions.mean	CPU, GPU	Gets mean of elements along provided axes.
reductions.mean_square	CPU, GPU	Gets mean square of elements along provided axes.
reductions.min	CPU, GPU	Gets minimal input element along provided axes.
reductions.rms	CPU, GPU	Gets root mean square of elements along provided axes.
reductions.std_dev	CPU, GPU	Gets standard deviation of elements along provided axes.
reductions.sum	CPU, GPU	Gets sum of elements along provided axes.
reductions.variance	CPU, GPU	Gets variance of elements along provided axes.
segmentation.random_mask_pixel	CPU	Selects random pixel coordinates in a mask, sampled from a uniform distribution.
segmentation.random_object_bbox	CPU	Randomly selects an object from a mask and returns its bounding box.
segmentation.select_masks	CPU	Selects a subset of polygons by their mask ids.
transforms.combine	CPU	Combines two or more affine transforms.
transforms.crop	CPU	Produces an affine transform matrix that maps a reference coordinate space to another one.
transforms.rotation	CPU	Produces a rotation affine transform matrix.
transforms.scale	CPU	Produces a scale affine transform matrix.
transforms.shear	CPU	Produces a shear affine transform matrix.
transforms.translation	CPU	Produces a translation affine transform matrix.