Re: gamut mapping, was Re: Proof Colors in Photoshop
Re: gamut mapping, was Re: Proof Colors in Photoshop
- Subject: Re: gamut mapping, was Re: Proof Colors in Photoshop
- From: Graeme Gill <email@hidden>
- Date: Sat, 03 Aug 2013 12:17:06 +1000
Steve Upton wrote:
> and through the profile. Sometimes, too many times, in-gamut colors are unavailable *no
> matter what source colors are provided*. I've especially seen this with dark yellows
> (i.e. browns) and many gamut boundary colors.
That's because there is a trade-off between smoothness and gamut. You're stuffing
a 4 dimensional cube into 3 dimensions, and there is no guarantee that the mapping
is topologically smooth - in fact, with difficult devices (typically non dye inksets)
you can and do get inter-penetration of the different ink compositions, causing
sudden discontinuities in ink composition as you move about the gamut, and yellow is
often the culpret. If you could transform and print each pixel completely independently,
this wouldn't be an issue, but in practice the B2A tables are interpolated and ink
diffuses on the paper, and this interpolation and/or ink mixing between discontinuous
points results in a highly inaccurate color.
The only way to avoid such regions is to restrict the gamut (I think Harold Boll calls
this "tapering the gamut"). So you end up with the situation you describe - achievable
device colors that the B2A table won't generate for you.
Graeme Gill.
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