I'm getting questions about negative light values and "values larger than 255" and why one would not clip them at every step of a chain of operations even if the initial input image and final output images are both (say) sRGB. (Maybe putting quotes around "gamut" was not quite enough to be clear.) Here are some links that kind of answer the question, right off the top of my head. http://entropymine.com/imageworsener/clamp-int/ http://www.imagemagick.org/discourse-server/viewtopic.php?f=22&t=22287 As soon as you do operations such as unsharp-mask, you produce "blacker than black" (negative, say) and "whiter than white" (larger than the upper bound of your color cube, if your color space is a represented by a cube of values, ignoring transparency and CMYK issues for simplicity). Unless your colorspace is large enough (unbounded, say) to fit those "unnatural" colors, you need to decide what to do with them at every step. Another simplistic example: Suppose you are "rotating" colors (in the sense of performing a rotation of the color values around some anchor color understood as points in 3D space). If you clamp at every step, this operations is not reversible, because the pieces of the cube that stick out after the rotation are lost forever. If you don't clamp, this operation is reversible. My simplistic example suggests that if you want to modify an image using transformed color coordinates, and want to be able to return to "untransformed" color coordinates losing as little information as possible, you don't want to clamp. My point: Clamping at every step demonstrably makes things worse, at least some of the time. Metaphor: imaginary numbers were initially seen as "artificial" means to solving equations in which only "real" numbers appeared: They were not part of the statement of the problem, and they did not appear explicitly in the final answer. People only wanted the "real" solutions to the problem. (Because they're real!) If, however, you go "The problem is real and the solution is real, so everything in between must be real" and start ignoring the imaginary parts of the real numbers at every step, you'll get the wrong answer quite often. Conclusion: It's not because colors are not found in the initial image and cannot be displayed in the output that they should be discarded at every step. ----- I wrote more than I wanted. Hopefully I've made things clearer. _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list List archives: https://mail.gnome.org/archives/gimp-developer-list
