HDMI is 8bpc, aka 8 bits per color. with RGB, that's 24 bits total. with 32bit in DVI, you are actually using the first 24 bits of that for the actual colors. So in the end, both are 24bits per pixel, which means the "normal" RGB range of 0-255 in colors. If there's a real difference, it's either because of your monitor (weird hardware problem or settings), or output settings on you computer.
5/24/15 at 11:39am