wrote:
This a curiousity question only. When I convert an on screen image from RGB to CMYK the difference is very apparent However, if I then convert the same CMYK back to RGB, no change. Is it me or..?
Thanks,
Brian
You probably know that many colors exist in RGB that are not possible with CMYK, and vice versa.
When you convert an RGB image to CMYK, photoshop "adjusts" the colors which would be impossible to print, and tries to find the closest match possible in CMYK-space. Often, its not very close, which is obvious to your eyes.
What is important to realize, is the image you end up with contains only colors that are *shared* by the two color spaces. So when you convert back to RGB, no adjustment needs to be made to the colors, and you don’t see any difference.
Technically, the colors are slightly adjusted because the colors are calculated differently and there is a finite number of possible colors, usually 16.8 million, if I remember correctly. You may see a slight change due to rounding errors. These rounding errors are cumulative, so you should avoid switching between color spaces many times. Eventually it will start to cause ugly "banding" and other problems. You can reduce the effects by starting with "16 bits per channel".
-Adam