I'm seeing some weird results when trying to compare image qualities in a few different color spaces. Have a look at my graph:
I want to compare with another publication, which reported PSNR(YUV) and SSIM(Y). However, I don't understand how I can have SSIM(YUV)=0.9 for the highest quality point on the right, but only have SSIM(Y)=0.7 for the exact same image. How can there be such a big difference? Is this normal? Or am I doing something wrong?
For completeness, here are reference image and the image under test:
And the MATLAB code I use for converting RGB to YUV:
function YUV=rgb2yuv(RGB) R = RGB(:,:,1); G = RGB(:,:,2); B = RGB(:,:,3); Y = 0.299 * R + 0.587 * G + 0.114 * B; U = 0.5 - 0.168736 * R - 0.331264 * G + 0.5 * B; V = 0.5 + 0.5 * R - 0.418688 * G - 0.081312 * B; % ^^^ I tried to use 0.0 as well, but SSIM values are identical YUV=cat(3,Y,U,V); end