About wide vs. small gamuts, 8 vs. 16-bit &sRGB vs. Adobe'98

Started Apr 3, 2003 | Discussions thread
OP Magne Nilsen Senior Member • Posts: 1,120
Re: Thanks. One more question...

alFR wrote:

In view of what you say about quantization errors
in colourspace conversions, what do you think is the best workflow
out of these?
1. Open D60 image in PS using default sRGB space (based on the EXIF
colourspace tag), edit, print.
2. Open D60 image in PS, assign custom camera profile, convert to
working space, edit, print.

For the D60 clearly #2, since the results of Canons conversion IMO is relatively too far away from sRGB - colorwise. For other cameras it depends on how good job the manufacturer have done in delivering an image conversion close enough to sRGB or Adobe'98 - i.e. the 10D looks much closer to accomplishing just that.

i.e. do the errors introduced by the conversion to the working
space negate the benefits of assigning a custom profile?

No - if the color values are clearly off you are best served with an input device profile. Preferably from a 16-bit linear image since that would give a much smoother conversion. With a already gammacorrected image the conversion must be done in the form of a huge LUT (Look-Up-Table) that essentially undos the manufacturers errors Some of those undos can be a bit on the harsh side, but should not normally incur any visible problems.

The rounding and quantization errors that occurs in these colourspace conversions would not normally accumulate to more than 1 or maximum 2/255 of a R,G or B value change. I have not met any humans that can perceptually catch that small changes yet, but if this occurs in the shadows and you later bring those shadows up a lot with curves, you could probably see some of this as posterization or banding, but I think you had to work hard to make this a problem


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