如何解决：HSI到RGB转换导致RGB颜色超过255

Question

Edit: Thank you everyone who helped but the problem still persist. So, is there any better formula to edit saturation without needing clamping? Non linear formula might work but I don't know exact good formula. Thx

I am trying to develop a photo editing system that allow people to increase and decrease hue/saturation/lightness which is similar to what ipiccy.com does. I am using HSI<->RGB conversion. First, each pixel are convert from RGB to HSI. Secondly, user specify the amount of saturation she wants to add. Thirdly, system add user's specified value to original saturation value converted in first step and then convert these HSI value to RGB. My problem is that when I convert new HSI value back to RGB, some of the RGB values are more than 255. So, colors are not displayed properly.

I have been reading and trying for days but no luck in getting right. Anyone know how to solve it? Any clue or any link to read or solution is welcome. Thanks a lot.

Answer 1

It all depends on how you alter the saturation value. If you do a simple add, then you absolutely must employ clamping, i.e. truncate over-255 values to 255. And the same for sub-zero values. This will lead some colors to overlap. You could also employ different formulas to make overflowing more difficult, but this might lead to behavior the user doesn't understand. fact is, when you change a picture, information loss due to truncation is almost a given. I'd try to warn the user and offering an undo function: e.g. showing oversaturated areas as white or magenta or blinking, as some cameras do. Keeping the user from causing info loss would limit user interaction too much, IMHO.