Temporal Noise Reduction

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 version depends on backend and device, see VPITNRVersion. 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.

For each VPITNRPreset, 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 chosen in most cases.

C API functions

For list of limitations, constraints and backends that implements the algorithm, consult reference documentation of the following functions:

Function	Description
vpiInitTemporalNoiseReductionParams	Initializes vpiSubmitTemporalNoiseReduction with default values.
vpiCreateTemporalNoiseReduction	Creates a payload for Temporal Noise Reduction algorithm.
vpiSubmitTemporalNoiseReduction	Submits a Temporal Noise Reduction operation to the stream.

Usage

Language: C/C++ Python

1. Import VPI module

   import vpi

2. Initialization phase
   1. Create the Temporal Noise Reduction object, configuring it to handle NV12_ER inputs. The CUDA backend will be used to execute the algorithm.

      with vpi.Backend.CUDA:
          tnr = vpi.TemporalNoiseReduction(size, vpi.Format.NV12_ER)

3. Processing phase
   1. Fetch a new frame from input video sequence. Here it's assumed that it's already VPI image with NV12_ER format.

      while inVideo.read(input)[0]:

   2. Feed it into the TNR object. A denoised version of the input is returned.

          denoised = tnr(input, preset=vpi.TNRPreset.INDOOR_MEDIUM_LIGHT, strength=1)

1. Initialization phase
   1. Include the header that defines the temporal noise reduction algorithm

      #include <vpi/algo/TemporalNoiseReduction.h>

   2. 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, Convert Image Format can be used to implement the required conversions.

          VPIImage input;
          vpiImageCreate(width, height, VPI_IMAGE_FORMAT_NV12_ER, 0, &input);

   3. Create the output and previous output image buffers with same dimensions and type as input.

          VPIImage prevOutput, output;
          vpiImageCreate(width, height, VPI_IMAGE_FORMAT_NV12_ER, 0, &prevOutput);
          vpiImageCreate(width, height, VPI_IMAGE_FORMAT_NV12_ER, 0, &output);

   4. Create the algorithm payload. It'll process video sequence of a scene with moderate lighting conditions, with maximum strength (strength = 1).

          VPIPayload tnr;
          vpiCreateTemporalNoiseReduction(VPI_BACKEND_CUDA, width, height, VPI_IMAGE_FORMAT_NV12_ER, VPI_TNR_DEFAULT, &tnr);

   5. Create the stream where the algorithm will be submitted for execution.

          VPIStream stream;
          vpiStreamCreate(0, &stream);

2. 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.

              VPITNRParams params;
              vpiInitTemporalNoiseReductionParams(&params);
       
              params.preset   = VPI_TNR_PRESET_OUTDOOR_MEDIUM_LIGHT;
              params.strength = 1.0f;
       
              if (isFirstFrame)
              {
                  vpiSubmitTemporalNoiseReduction(stream, VPI_BACKEND_CUDA, tnr, NULL, input, output, &params);
              }
              else
              {
                  vpiSubmitTemporalNoiseReduction(stream, VPI_BACKEND_CUDA, tnr, prevOutput, input, output, &params);
              }

   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;
          }

3. Cleanup phase
   1. Free resources held by the stream, the payload, and the input and output images.

          vpiStreamDestroy(stream);
          vpiPayloadDestroy(tnr);
          vpiImageDestroy(input);
          vpiImageDestroy(prevOutput);
          vpiImageDestroy(output);

Consult the Temporal Noise Reduction sample application for a complete example.

For more information, see Temporal Noise Reduction in the "C API Reference" section of VPI - Vision Programming Interface.

Performance

For information on how to use the performance table below, see Algorithm Performance Tables.
Before comparing measurements, consult Comparing Algorithm Elapsed Times.
For further information on how performance was benchmarked, see Performance Benchmark.

clear filters Device: Jetson AGX Orin  -  Streams: 1 2 4 8