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: Steve Upton <email@hidden>
- Date: Mon, 12 Aug 2013 15:46:54 -0700
On Aug 2, 2013, at 7:17 PM, Graeme Gill <email@hidden> wrote:
> 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.
Sorry for the delayed reply. Was out in the Canadian wilderness for a week or so.
Graeme, I agree with you overall, about the need / tendency for unavailable colors. My concern is for colors that don't seem to fall into this "acceptable" range.
I haven't seen them with Argyll profiles yet, but other profiling engines / mapping algorithms. I'll report more when I get our analysis tools a bit further along
regards,
Steve
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