Colour range in Avisynth

[Guado]

Hi, I'm wondering whether there's a filter for avisynth which detects only grayscale colours in an image and removes all the rest of colours in it.

For example, I have some images with black and green colours. I want to detect only the black or gray colours, and remove the green.
I can do that in photoshop, but I have a large amount of images that need to be processed like that.

I've read that Layer Filter can do that, but I can't find it anywhere.

Any help would be appreciated. It doesn't matter if it's not an avisynth filter but another software.

Thanks in advance.

[jagabo]

I find the description of what you want to do confusing. You want to keep the greyscale parts of the image and do what with the colored parts? Make them greyscale? Make them black? Some other color? You only need to process the green? Or all colors?

[Guado]

I find the description of what you want to do confusing. You want to keep the greyscale parts of the image and do what with the colored parts? Make them greyscale? Make them black? Some other color? You only need to process the green? Or all colors?

Hi, jagabo. Thanks for your reply.
I need to "remove" the coloured parts. I mean, make them white.

[jagabo]

There are probably easier ways but here's one that uses only basic tools built into AviSynth:

function AbsChroma(clip src)
{
  # sum of abs(chroma-128)

  posu=UtoY(src).ColorYUV(off_y=-128)
  negu=Invert(src).UtoY().ColorYUV(off_y=-128)

  posv=VtoY(src).ColorYUV(off_y=-128)
  negv=Invert(src).VtoY().ColorYUV(off_y=-128)

  Overlay(Overlay(posu,negu,mode="Add"), Overlay(posv,negv,mode="Add"),mode="Add").BicubicResize(src.width, src.height)
}

src=AviSource("source.avi") # get source file
white=ColorYUV(src, off_y=256, cont_u=-256, cont_v=-256) # make a white video
mask=AbsChroma(src).ColorYUV(off_y=-4).ColorYUV(gain_y=256000) # convert chroma to a mask

Overlay(src,white,0,0,mask)

In the mask=AbsChroma() line off_y is a threshold (how perfectly grey a pixel has to be to be replaced), change gain_y if you want less sharp edges. Also play around with gamma_y instead of or in addition to gain_y.

[AlanHK]

Maybe this:
http://forum.doom9.org/showthread.php?t=151259

But I'm not sure about "Black". Video uses RGB and a few other spaces I have less familiarity with, but I don't think it uses CMYK.

[Guado]

There are probably easier ways but here's one that uses only basic tools built into AviSynth:

function AbsChroma(clip src)
{
  # sum of abs(chroma-128)

  posu=UtoY(src).ColorYUV(off_y=-128)
  negu=Invert(src).UtoY().ColorYUV(off_y=-128)

  posv=VtoY(src).ColorYUV(off_y=-128)
  negv=Invert(src).VtoY().ColorYUV(off_y=-128)

  Overlay(Overlay(posu,negu,mode="Add"), Overlay(posv,negv,mode="Add"),mode="Add").BicubicResize(src.width, src.height)
}


src=AviSource("source.avi") # get source file
white=ColorYUV(src, off_y=256, cont_u=-256, cont_v=-256) # make a white video
mask=AbsChroma(src).ColorYUV(off_y=-4).ColorYUV(gain_y=256000) # convert chroma to a mask

Overlay(src,white,0,0,mask)

In the mask=AbsChroma() line off_y is a threshold (how perfectly grey a pixel has to be to be replaced), change gain_y if you want less sharp edges. Also play around with gamma_y instead of or in addition to gain_y.

That code really works!
Thanks a lot.

However, I can't figure out how to load images instead of videos in "src".
When loading an image, I get the following error:

"ColorYUV: requires YUV input"

[Guado]

Maybe this:
http://forum.doom9.org/showthread.php?t=151259

But I'm not sure about "Black". Video uses RGB and a few other spaces I have less familiarity with, but I don't think it uses CMYK.

Hi, AlanHK.
Thanks for your reply.

I'll take a look at that filter.

[AlanHK]

However, I can't figure out how to load images instead of videos in "src".
When loading an image, I get the following error:

"ColorYUV: requires YUV input"

src=ImageSource("image.png").ConvertToYV24(()

see
http://avisynth.org/mediawiki/ImageSource
http://avisynth.org/mediawiki/Convert

[Cornucopia]

For a less exact shorter version of what jagabo sugggested, you could always just use Greyscale().

Scott

[jagabo]

For a less exact shorter version of what jagabo sugggested, you could always just use Greyscale().

No, the code I posted converts all colored pixels bright white. So, for example, a dark red pixel becomes white, not dark grey.

[Guado]

Thanks, the code is working now.

[Cornucopia]

...I see where that came from now. Guess I never fully understood the nature of the question. Still don't. What would this be used for?

Scott