TComb

Revision as of 16:11, 24 December 2014

Description

TComb is a temporal comb filter (it reduces cross-luminance (dot crawl) and cross-chrominance (rainbows) artifacts in static areas of the picture). It will ONLY work with NTSC material, and WILL NOT work with telecined material where the rainbowing/dotcrawl was introduced prior to the telecine process! It must be used before IVTC or deinterlace in order to work. In terms of what it does it is similar to GuavaComb/DeDot.

TComb does support seeking... that is, jumping to a random frame will produce the same result as if you had linearly run up to that frame. For dot crawl removal TComb requires at least 3 static fields of the same parity and for rainbow removal TComb requires at least 5 static fields of the same parity.

Requirements

• AviSynth 2.5.8 or later
• Supported color formats: YUY2, YV12

Syntax and Parameters

TComb (clip, int "mode", int "fthreshL", int "fthreshC", int "othreshL", int "othreshC", bool "map", float "scthresh", bool "debug", int "opt")

clip   =

Input clip.

int  mode = 2

Controls whether both luma/chroma are processed or only one or the other.

Possible settings:

• 0 - process luma only (dot crawl removal)
• 1 - process chroma only (rainbow removal)
• 2 - process both

int  fthreshL = 4

int  fthreshC = 5

Filtered pixel correlation thresholds.

One of the things TComb checks for is correlation between filtered values over the length of the filtering window. If all values differ by less than fthreshL (for luma) or fthreshC (for chroma) then the filtered values are considered to be correlated.

Larger values will allow more filtering (will be more effective at removing rainbowing/dot crawl), but will also create more artifacts.

Smaller values will produce less artifacts, but will be less effective in removing rainbowing/dot crawl. A good range of values is between 4 and 7.

int  othreshL = 5

int  othreshC = 6

Original pixel correlation thresholds.

One of the things TComb checks for is correlation between original pixel values from every other field of the same parity. Due to the oscillation period, these values should be equal or very similar in static areas containing dot crawl or rainbowing. If the pixel values differ by less than othreshL (for luma) or othreshC (for chroma) then the pixels are considered to be correlated.

Larger values will allow more filtering (will be more effective at removing rainbowing/dotcrawl), but will also create more artifacts.

Smaller values will produce less artifacts, but will be less effective in removing rainbowing/dotcrawl. A good range of values is between 4 and 8.

bool  map = false

Identifies pixels that are being replaced with filtered values.

Each pixel in the output frame will have one of the following values indicating how it is being filtered:

0 - not being filtered

85 - [1 2 1] average of (n,n+1,n+2)

170 - [1 2 1] average of (n-2,n-1,n)

255 - [1 2 1] average of (n-1,n,n+1)

** n = current frame

float  scthresh = 12.0

Scenechange threshold; sets the scenechange detection threshold as a percentage of maximum change on the luma plane.

Use the debug output to see which frames are detected as scenechanges and the scenechange statistics.

bool  debug = false

Will enable debug output. The only thing it shows are the scenechange stats.

The info is output via OutputDebugString(). You can use the utility "DebugView" from sysinternals to view the output. The frame numbers in the debug output correspond to the input clip after a SeparateFields() call. TComb internally invokes SeparateFields() before itself and weave() after itself.

int  opt = 4

Controls which cpu optimizations are used.

Possible settings:

• 0 - use C routines
• 1 - use MMX routines
• 2 - use ISSE routines
• 3 - use SSE2 routines
• 4 - auto detect

Basic Setup/Usage:

Setting up TComb is pretty simple. The only values that would ever really need adjusting are fthreshL/fthreshC, othreshL/othreshC, and mode.

Set mode to 0 if you want to do dot crawl removal only, set it to 1 if you want to do rainbow removal only, or set it to 2 to do both.

Dot Crawl Removal Tweaking (fthreshL/othreshL):
To find good values for fthreshL/othreshL, start with the following line:

TComb(mode=0, fthreshL=255, othreshL=255)

Now, keep othreshL at 255 but set fthreshL down to 1. Keep increasing fthreshL in steps of 1 to 2 until you find the point at which all dot crawl is removed. Remember that value.
Next, set fthreshL back to 255, and set othreshL to 1. Now, increase othreshL in steps of 1 or 2 until you find the point at which all dot crawl is removed. You've now got values for fthreshL/othreshL.

Rainbowing Removal Tweaking (fthreshC/othreshC):
To find good values for fthreshC/othreshC, start with the following line:

TComb(mode=1, fthreshC=255, othreshC=255)

Now, keep othreshC at 255 but set fthreshC down to 1. Keep increasing fthreshC in steps of 1 to 2 until you find the point at which all (or most) rainbowing is removed. Remember that value.
Next, set fthreshC back to 255, and set othreshC to 1. Now, increase othreshC in steps of 1 or 2 until you find the point at which all (or most) rainbowing is removed. You've now got values for fthreshC/othreshC.

Once you've got values for mode, fthreshL/fthreshC, and othreshL/othreshC, add the necessary TComb() line into your script and run through part of it. If you see any artifacts try lowering your fthresh/othresh values.

Changelog

  05/16/2006  v2.0 Beta 2
      + Stricter checking of othreshL/othreshC when looking for oscillation
      + For dot crawl detection require at least one vertical neighbor (y-1/y+1, x-1/x/x+1)
      - fixed possible crash with yuy2 input (sse2 planar<->packed conversions)

  03/31/2006  v2.0 Beta 1
      - complete rewrite

  06/24/2005  v0.9.0
      - Initial Release

To Do List

     - remove buffering of frames/info that aren't actually used (was there for development/testing purposes).
       Should save a lot of RAM usage.

     - release v2.0 final

External Links

• Scintilla's Guide - Additional usage information mainly for dot crawl.

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