FluxSmooth

An Avisynth filter for spatio-temporal smoothing of fluctuations

By Ross Thomas <ross@grinfinity.com>

There is no copyright on this code, and there are no conditions on its distribution or use. Do with it what you will.

Description

One of the fundamental properties of noise is that it's random. One of the fundamental properties of motion is that it's not. This is the premise behind FluxSmooth, which examines each pixel and compares it to the corresponding pixel in the previous and last frame. Smoothing occurs if both the previous frame's value and the next frame's value are greater, or if both are less, than the value in the current frame.

I like to call this a "fluctuating" pixel, then I like to wipe that pixel from existence by averaging it with its neighbours. This is (by default) done in a spatio-temporal manner, in that for each fluctuating pixel its 8 immediate spatial neighbours as well as its 2 temporal neighbours (the abovementioned corresponding pixel from the previous and next frames) are considered for inclusion in the average. If the value of each pixel is within the specified threshold, it is included. If not, it isn't.

This filter seems to remove almost all noise from low-noise sources (such as DVD) and a lot of noise from high-noise sources (such as cable TV captures), while maintaining a good amount of detail.

If your CPU supports integer SSE operations (Intel Pentium III and better, AMD Athlon and better) an optimized version of the algorithm will be used.

Usage

FluxSmooth([clip], int temporal_threshold, int spatial_threshold)

Parameter	Meaning	Default
temporal_threshold	Temporal neighbour pixels within this threshold from the current pixel are included in the average. If set to -1, no temporal smoothing occurs.	7
spatial_threshold	Spatial neighbour pixels within this threshold from the current pixel are included in the average. If set to -1, no spatial smoothing occurs.	7

Parameter

Meaning

Default

temporal_threshold

Temporal neighbour pixels within this threshold from the current pixel are included in the average.

If set to -1, no temporal smoothing occurs.

spatial_threshold

Spatial neighbour pixels within this threshold from the current pixel are included in the average.

If set to -1, no spatial smoothing occurs.

Known Issues

The very edges of the frame are unprocessed.
The very first and very last frame of a clip is unprocessed.
Appears to cause an access violation when used with n-pass encoding in CCE. Since I don't have CCE I can't duplicate it... Any help in this regard would be appreciated.

TODO

Optimize SSE code with regard to pairing, stalls, and so on.

Author

Ross Thomas <ross@grinfinity.com>

History

Version	Description
1.0	First "stable" release. I think it's been tested enough, but wait for a bunch of bugs to emerge and make me a liar... Fixed a bug that, in conjunction with a bug in the built-in resizers, caused an access violation under certain circumstances. Thanks to sh0dan for spotting that one :). Added "SetCacheHints" and upgraded to "AvisynthPluginInit2" in 2.5 version.
0.4	Implemented iSSE-optimized version, which runs roughly double the speed of the C++ version. Some small optimizations to C++ version. Now smooths chroma as well as luma.
0.3	Fixed bad bug that caused incorrect smoothing: no more in-place filtering. Changed defaults back to what they were, now that the algorithm works correctly. Spent some time benchmarking and tweaking various pieces of code, so should now be significantly faster.
0.2	Fixed non-fatal bug that caused a request for one frame beyond the end of the clip. Changed to in-place filtering so could squeeze a few optimizations here and there. Changed too-high defaults. First Avisynth 2.5/YV12 release.
0.1	First release. Alpha code.