Overview

This algorithm is used to reduce both spatial and temporal noise in video sequences. Noise levels can vary significantly depending on lighting conditions, camera sensor sensibility and quality, etc. VPI's temporal noise reduction is more suited to handle thermal and shot noise, which follow gaussian and poisson distributions respectively.

There are currently 3 versions of the algorithm, with varying degrees of speed, configurability and quality. Not all always available in a given backend and platform combination.

Noise reduction factor can be customized by means of two parameters: scene lighting condition and strength (a value between 0 and 1). Setting it to low light scenes results in increased reduction strength, but might result in loss of detail in highly textured regions or even some ghosting effect. Using bright light mode does the opposite: less ghosting and mode details preserved, but reduced noise reduction factor.

The example below shows the temporal noise reduction in action. Hover the mouse pointer over the video and click the maximize button to see more details.

Noisy input	Parameters	De-noised output
	scene: outdoor medium light strength: 1.0 version: 3

Note: Video output requires HTML5-capable browser that supports mp4 video decoding.

Implementation

Depending on the chosen algorithm version, the algorithm employs different techniques such as bilateral filtering for handling spatial noise and/or a temporal IIR filter associated with a motion detector.

Algorithm Version

There are 3 versions of the algorithm, each one with different speed/configurability/quality trade-offs:

VPI_TNR_V1 - Offers basic noise reduction that works well when noise levels aren't too high. Lighting conditions and noise reduction strength are fixed and can't be configured, but in general it provides good speed.
VPI_TNR_V2 - Offers improved noise reduction, and can be configured for a particular lighting condition. Still provides good speed.
VPI_TNR_V3 - Offers best noise reduction quality and configurability, in exchange of some performance decrease.

Availability of each level depends on backend and device, see Limitations and Constraints for more information. To pick the best available version, just use VPI_TNR_DEFAULT when specifying algorithm version.

Scene Lighting Condition

Versions 2 and 3 allow the user to specify of scene's lighting condition, which in turn controls the noise reduction strength for a particular scene. Higher strength will lead to less noise, but sometimes loss of detail in highly textured regions and some ghosting, especially around fast moving objects. If input noise is high, due to poor lighting and/or higher sensor sensibility, this might be a suitable trade-off.

The following scene presets are available:

VPI_TNR_PRESET_OUTDOOR_LOW_LIGHT - outdoor scenes with poor lighting conditions, leading to high noise.
VPI_TNR_PRESET_OUTDOOR_MEDIUM_LIGHT - outdoor scenes with sufficient lighting but still with some noise.
VPI_TNR_PRESET_OUTDOOR_HIGH_LIGHT - outdoor scenes with good lighting conditions and less noise.
VPI_TNR_PRESET_INDOOR_LOW_LIGHT - indoor scenes with poor lighting conditions.
VPI_TNR_PRESET_INDOOR_MEDIUM_LIGHT - indoor scenes with sufficient lighting.
VPI_TNR_PRESET_INDOOR_HIGH_LIGHT - indoor scenes with good lighting.

For each preset, user can define a strength factor, basically a floating point number from 0 (least amount of noise reduction) and 1 (maximum amount). 0.5 is a good default to be picked in most cases.

Usage

Initialization phase
1. Include the header that defines the temporal noise reduction algorithm
  #include <vpi/algo/TemporalNoiseReduction.h>
2. Create the stream in which the algorithm will be executed. In this example we're using CUDA/GPU.
  VPIStream stream;
  
  vpiStreamCreate(VPI_DEVICE_TYPE_CUDA, &stream);
3. Create the image that will store each frame fetched from the video source. Frames are to be fetched directly as NV12. If instead they are in a format not supported by the algorithm, Image Format Converter can be used to implement the required conversions.
  VPIImage input;
  
  vpiImageCreate(width, height, VPI_IMAGE_TYPE_NV12, 0, &input);
4. Create the output and previous output image buffers with same dimensions and type as input.
  VPIImage prevOutput, output;
  
  vpiImageCreate(width, height, VPI_IMAGE_TYPE_NV12, 0, &prevOutput);
  
  vpiImageCreate(width, height, VPI_IMAGE_TYPE_NV12, 0, &output);
5. Create the algorithm payload. It'll process video sequence of a scene with moderate lighting conditions, with maximum strength (strength = 1).
  VPIPayload tnr;
  
  VPI_CHECK_STATUS(vpiCreateTemporalNoiseReduction(stream, width, height, VPI_IMAGE_TYPE_NV12, VPI_TNR_DEFAULT,
  
  VPI_TNR_PRESET_OUTDOOR_MEDIUM_LIGHT, 1, &tnr));
Processing phase
1. Fetch a new frame from input video sequence and write it into input.
  while (FetchFrame(vid, &input))
  
  {
2. Submit it to the stream for processing. If it's the first frame, 2nd parameter, prevFrame must be NULL, or else the output of previous iteration must be passed.
  if (isFirstFrame)
  
  {
  
  vpiSubmitTemporalNoiseReduction(tnr, NULL, input, output);
  
  }
  
  else
  
  {
  
  vpiSubmitTemporalNoiseReduction(tnr, prevOutput, input, output);
  
  }
3. (optional) Sync to the stream and use/display the de-noised frame.
  vpiStreamSync(stream);
4. Swap output and prevOutput. In next iteration, output will be input as prevOutput, and current prevOutput buffer will receive the next de-noised frame.
  VPIImage tmp = output;
  
  output = prevOutput;
  
  prevOutput = tmp;
  
  }
  
  Consult the Temporal Noise Reduction sample application for a complete example.

For more details, consult the API reference.

Limitations and Constraints

Constraints for specific backends supersede the ones specified for all backends.

All Backends

Input and output images must have the same dimensions and type.
The following image types are accepted:
- VPI_IMAGE_TYPE_NV12

CUDA

The following algorithm versions are available:

VPI_TNR_V3

PVA