Thresholded changing of luma values. Is it possible?

[GodofaGap]

I have been messing around with ColorYUV trying to remove some MPEG2 compression noise in low contrast areas which comes out very blocky when compressed with x264 or XviD (I will post pics if needed), but basically I can't get it to do what I want as every operation works on all values on luma.

What I want is a function that touches pixels above or beneath a certain threshold, but leaves the rest alone. For example: if luma of a pixel is smaller than 20, change it to 16 (or substract a value of X would be sufficient too), if 20 or higher leave luma alone.

Does anyone knows if a function of that sort exists, or perhaps if one could be made. I'm certainly no AVS script hero.

Right now I am just substracting a value and then expanding the range back again by using gain, which is not that bad in itself but makes the vid a tad more dark.

Thanks for any insights. :)

[GodofaGap]

After some more reading this seems to do what I want:


### clips range below threshold to black for clips in TV scale

function MakeBlackTV (clip c, int luma_range)
{
int = coloryuv(c, off_y=-16-luma_range).coloryuv(off_y=16+luma_range)
mask = subtract(int,c) # creates mask with only the changed pixels
output = subtract(c.coloryuv(off_y=-16),mask).coloryuv(off_y=16)

return output
}

Now lets hope it solves my problem. :)

[krieger2005]

Use lut-tool of Masktools: mt_lut("x 20 <= 16 x ?")