robert@xxxxxxxxxxxxxxxxxx wrote: > For example, here is a comparison between a paper profiled with i1Profiler > and one profiled with Argyll: > > i1Profiler Colorimetric: DMax 2.44, Volume: 93,000 > Argyll Colorimetric: DMax 2.5, Volume: 97,000 > > i1Profiler Perceptual: DMax 2.46, Volume: 92,000 > Argyll Perceptual: DMax 2.08, Volume: 90,000 Hi Robert, you don't say how you are computing these numbers. When I look at a profile, I typically measure it's gamut from the absolute colorimetric data since that represents the underlying device limit, so it's not clear how you are measuring a "Perceptual Gamut". Similarly for DMax - profiles don't contain density information, since it uses completely differet CMF's to the CIE observer. L* value of black is a more typical characterization, and, it's not clear how you are measuring a "DMax". > This is from Beta RGB, with Beta RGB specified in colprof (i1Profiler > doesn't require a source profile to be specified). As you can see, the > colorimetric mapping is excellent in Argyll, whereas the perceptual mapping > is not at all good. Beta RGB is a large gamut space. Unless you have an image that completely fills this gamut, you would never use it as a source gamut for a print conversion - you will get excessive compression, and very dull looking output for typical images. If your images are stored in a large gamut space, then you really have to use a source gamut that better represents the gamut of what you are mapping, either a more typical output referred space such as sRGB, or a gamut created from the specific images. > It seems as though your interpretation of Perceptual is very strict, with an > overall squeezing in of the out-of-gamut colors. This results in a lower > gamut volume ... and, more critically, a very much lower DMax. I don't see anything like that for typical RGB source spaces. Typically the RGB space is idealized and has a zero black, so the output it the minimum value possible in the print space, consistent with the black point neutral axis constraints. For instance, lets take Fogra39 with a 300% ink limit: xicclu -fif -ir -l300 Fogra39.icm 0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.934413 0.764857 0.275418 1.000000 [CMYK] xicclu -ff -ir -l300 Fogra39.icm 0.934413 0.764857 0.275418 1.000000 [CMYK] -> Lut -> 9.068751 1.323905 -3.212585 [Lab] collink -v -ir -G -l300 sRGB.icm Fogra39.icm test.icm xicclu test.icm 0.000000 0.000000 0.000000 [RGB] -> Lut -> 0.746010 0.642229 0.507217 1.000000 [CMYK] xicclu -ff -ir -l300 Fogra39.icm 0.746010 0.642229 0.507217 1.000000 [CMYK] -> Lut -> 10.606275 0.116586 -0.063567 [Lab] So L* of 10.6 vs. 9, but the gamut mapped black is much more neutral. > If this is not a bug and not a user error, then, IMO, the perceptual mapping > in Argyll is almost unusable as is. That's not the feedback I get from most people - it's generally regarded as very good, often better than the alternatives. Graeme Gill.