Any image processing expert?

when we extract the YIQ colors from RGB picture why do we do this

sNtsc = rgb2ntsc(sBmp);
picY = sNtsc(:,:,1)*256-128; % Y luminance component
picI = sNtsc(:,:,2)*256-128; % I chrominance component
picQ = sNtsc(:,:,3)*256-128; % Q chrominance component

each component of YIQ is being multiplied by 256 and subtracted by 128? why is that?

Answer 1

[Image Analyst]

sNTSC will be in the range 0-1. sNTSC is already a YIQ image. Evidently the author wanted to scale the intensities to -128 to +127. I don't know why.

I wouldn't even bother using that color space. Why are you using that in preference to color spaces like HSV and LAB?