Idea Digital Imaging wrote:
I've made a number of ProPhoto to sRGB device links with collink using a range of different settings.All of them create images with odd dark blobs appearing in saturated blues.
Yes, I've seen this. The problem is that the ProPhoto primaries are so way out there, it runs into all sorts of problems. One is that none of its primaries can be represented in ICC Lab PCS. They all have a* or b* that exceed the -128 to 128 range: Red: 0.797668, 0.288040, 0.000000 [Lab 60.608273, 139.168888, 104.497022] Green: 0.135193, 0.711884, 0.000000 [Lab 87.576439, -186.694184, 150.993860] Blue: 0.031342, 0.000092, 0.824905 [Lab 0.082699, 90.249204, -172.271644] In fact the green and the blue primaries are outside the spectrum locus, meaning that they are imaginary. Notice that the blue has almost no luminance level! Given that key technologies such as CIECAM02 color appearance space were never designed to work on non-real world colors, attempting to transform the whole of the ProPhoto gamut runs into issues, particularly near blue. While I have attempted to mitigate this issue in using CIECAM02 in the next release, the attempt is not entirely successful for ProPhoto. There are two possible approaches that may work. One is not to use CIECAM02, ie. try the "rl" intent for instance. The other (if you haven't been doing so) is to setup the link with an image specific source gamut as well as the ProPhoto source colorspace, so that the transformation is not attempting to map the whole ProPhoto gamut, but just a real world portion of it. You could even try some other RGB colorspace gamut, such as AdobeRGB or sRGB as the "image" source gamut. See if either of those ideas help. Graeme Gill.