Banding in denoised video clips: possible causes and available solutions

Some video clips contain large areas of uniform color with very fine gradients (like areas of the sky, walls, etc.). These areas are often affected by the banding problem, which shows up after the original noise is removed from the clip by a noise filter and then compressed by a lossy video codec.

The example frames below have been taken from different points of a typical processing workflow to illustrate the problem and possible solitions.

1. An example frame from the original clip (unprocessed, noisy):	2. A frame cleaned by Neat Video (denoised, not yet compressed):
The frame shows some obvious noise but there is no visible banding. That is the kind of frame usually received by Neat Video for processing.	As you can see, the denoised frame produced by Neat Video is very clean and smooth. There is no noise. There is no visible banding either. Such a denoised frame is passed by Neat Video back to the host application.
3. After receiving the denoised frame from Neat Video, the host application applies some lossy video compression to produce the output video file. That is usually the point where the banding problem is introduced into the video data: the video codec applying lossy compression introduces a very noticeable banding into the frame. The resulting frame from the output clip looks like this (denoised, compressed):	4. The problem of banding can be avoided using different approaches. One of them is to keep some of the original noise in the output clip. The presence of noise prevents the output codec from introducing the banding. Neat Video includes two filter presets (available in the "Banding in processed video" group of pre-defined presets) that do just that: they decrease the amount of spatial noise reduction applied to the video data to keep some of the noise in the output clip. The resulting frame from the output clip produced using that technique:
You can clearly see some banding in the highlighted rectangular area.	As you can see, there is much less banding (or it is much less noticeable) as compared with the version to the left. There is more noise remaining in the frame though, so using this technique requires finding a balance between noise reduction and banding.

Additional notes about banding

There may be different sources of banding in the output clips. Banding can be produced by (starting with most common causes):

• inaccurate video compression by host application;
• inaccurate decompression by player software (QuickTime on Mac is especially bad at that);
• inaccurate processing by host application itself;
• limited precision of the data representation used;
• other causes.

The general technique described above (preserving some of the original noise in the clip) is one of possible solutions for the banding problem. It is usually efficient irrespective of the source of the banding.

Another available solution is to add a small amount of some artificial noise after all original noise has been removed by Neat Video. That can be done using any generator of video noise available in the host application.

Yet another approach is to use a better video codec, which does not introduce such a strong banding into compressed video clip. However, that may be not always possible because most lossy codecs do have this problem.