https://bugs.kde.org/show_bug.cgi?id=359909
--- Comment #8 from DrSlony <b...@londonlight.org> --- I agree that a user-selectable intent would be best, but I am not a Qt programmer and to do this properly involves much more than just adding a combo. To not mislead users, I believe this combo should only show the intents which the source-target profiles actually support (can be done using LCMS2). As I can't code that, the next best thing is to use a default intent which does not distort colors for those people who have a profile which is capable of using the perceptual intent. Longer explanation follows. Most consumer screens are not capable of fully reproducing even the sRGB gamut. For example my high end laptop can only reproduce 75% of the sRGB gamut - it cannot show the extreme reds of sRGB. Despite this, I still want reds which it can show to be correctly red, and blues which it can show to be correctly blue. The colorimetric intents perfectly preserve colors of the source gamut which do fit within the target gamut, and those colors which are too red or too blue to be shown by the screen will be rounded off to the nearest red or blue that can be shown - colors which fall outside the target gamut will be rounded off nearest reproducible color instead. The perceptual intent will shrink the source gamut to fit inside the target gamut, in one of several ways, by changing all colors. How much it changes the hues depends on how much it needs to shrink the gamut. That is what makes perceptual a very bad choice as a default in an image viewer - what most people want in an image viewer is to see photos with accurate colors, and perceptual will change all of them. For example the reds could turn more pink, deep blue will turn purple, etc. This is useful for example if you want to adjust saturation of colors which your screen cannot reproduce - it allows you to "see" them, even though their hues are wrong, but at that moment you don't care about the hue, you just want to not over-saturate. When viewing a normal photo though you want relative colorimetric. All rendering intents are not supported by all profiles. Matrix profiles only support the colorimetric intents. LUT profiles support perceptual intents, but it's up to the program making the LUT profile whether one will be enabled by default, and how it will work. Keep this in mind, as some people could say that perceptual looks fine, because they don't know their profile does not even support it and what they're actually seeing is relative colorimetric. This is the leading cause of why you haven't had more bug reports about this - most people are oblivious about color management and don't have ICC profiles for their monitors, of those who do only some will have LUT profiles, and of those who have LUT profiles only some will have a perceptual mapping table in their profile. When it comes to showing an image on screen, not for the purpose of matching it to a print but jus to enjoy it, which is what Gwenview's main task is, relative colorimetric is the right choice for everyone who just wants to see the photo correctly without shifted hues. For those few of us who have (and need) a profile which supports both perceptual and relative colorimetric, having Gwenview force perceptual shoots us in the foot. -- You are receiving this mail because: You are watching all bug changes.
