Can a 1D LUT be used in ffmpeg using lutrgb?

Question

I am using ffmpeg and trying to change the color of certain pixels in a video stream using the lutrgb filter. The aim is to change any pixel with a green value greater than 145 to a white pixel. So far I have tried the following commands:

-vf lutrgb=r='if((g > 145),255,val)':g='if(val > 145, 255, val)':b='if(g > 145, 255, val)'

-vf lutrgb=g='if(val>145,255,val)':r=255:b=255

-vf lutrgb=r='if(gt(val,145),255,val)':g='if(val>145,255,val)':b='if(gt(val,145),255,val)'

However, these are not delivering the desired result. Is it possible to have ffmpeg use a 1D LUT where the input values for r, g and b can be set based on a condition, for example, if r=ANY, g>145 and b=ANY, then r=255, g=255 and b=255? Any insight to whether this is possible is much appreciated.

Answer 1

The LUT filters don't have cross-referencing of channels. Use geq instead

geq=r='if(gt(g(X,Y),145),255,p(X,Y))':g='if(gt(g(X,Y),145),255,p(X,Y))':b='if(gt(g(X,Y),145),255,p(X,Y))'