RE: Multi-color ICC profiles
RE: Multi-color ICC profiles
- Subject: RE: Multi-color ICC profiles
- From: Max Derhak <email@hidden>
- Date: Tue, 22 Dec 2015 20:31:38 +0000
- Thread-topic: Multi-color ICC profiles
I wouldn't say that multi-color profiling is something of a dying art.
I'd classify it as a fairly tricky thing to do with some serious caveats WRT V4 ICC profiles. Some of the challenges include:
1. Dimensional complexity makes characterization challenging. You need lots more patches to get good characterization. What works for 4 colors becomes overwhelming for 7 colors.
2. Ink Load issues (lots more ink possibilities
3. Dimensional complexity makes device to PCS A2Bx tags in profiles really really big or rather inaccurate. The size of the n-dimensiona tables is determined by the number of sampling points raised to the power of the number of device channels. Its an exponential problem often resulting in much sparser sampling of the device address space to keep the profile size reasonable.
4. Ink separation is much more involved to get good smooth transitions while achieving full gamut available with extra inks. In the B2Ax PCS to device tables there is only 1 way to specify how to achieve each Lab value.
5. Large differences in ink values for adjoining grid points in the B2Ax output table separation can result in greater interpolation errors between grid points.
Thus when you use a multi-color icc profile in Photoshop it is very likely the preview will be less than desirable, and most likely not a faithful representation of the actual output.
With up and coming iccMAX based multi-color profiles there are greater possibilities to either directly model mathematically the characterization of the inkset or use selection of lower dimensional sub tables for greater accuracy profiles of smaller size.
Max Derhak (PhD)
Principal Scientist Onyx Graphics
Co-Chair International Color Consortion
-----Original Message-----
From: colorsync-users-bounces+max.derhak=email@hidden [mailto:colorsync-users-bounces+max.derhak=email@hidden] On Behalf Of G Mike Adams
Sent: Tuesday, December 22, 2015 11:10 AM
To: Roger Breton
Cc: 'colorsync-users?lists. apple. com' List
Subject: Re: Multi-color ICC profiles
Roger,
> Next step is the experimentation -- you'd imagine.
>
> So I installed the profile in my Windows 10 PC and turned to
> Photoshop, naturally ;-) There must zillions of "advanced" proprietary packages that offer all kinds of "advanced" tools for those who thrive on multi-color profiles?
Not really. Fact is that multi-color was always a pretty small niche of the industry, and nowadays many multi-color machine manufacturers as well as RIP manufacturers have “contoned” the process, meaning that it’s done internally, and what you generate is simply a CMYK profile, so, sadly, you could call multi-color profiling something of a dying art.
>
> So, I took a grayscale image and converted it to the muti-color profile.
>
> After conversion, I end up with three extra channels, Red, Green and Blue. Fair.
>
> Two things.
>
> First, read the CIE Lab values returned good neutrals (a* and b* = 0).
> Second, the appearance of the image didn't evoke anything neutral but more like "red" cast?
>
> This may be more a question for the Photoshop Forum on Adobe's web site but, in case..., is the user expect to "Edit" the RGB Channels after conversion? To obtain a correct color appearance?
>
> It would seem that way…
No.
Fact is Photoshop has never rendered an accurate screen image of any multi-color profile once you go ahead and make the conversion. You may also have noted that if you install a multi-color profile and go look for it to soft-proof with, it won’t be there.
However, you can get a pretty good idea of how a multi-color profile will look printed by going to convert to profile, selecting the mc profile you want, and clicking “preview.” You’ll probably have to drag the box out of the way, but what’s on the screen then is a pretty good representation. Then of course if you go ahead and click OK, it whacks out.
A couple things though:
First is that any multi-color profile — is made for a very specific printing condition. I can’t image really why you’d ever want to do a conversion in Photoshop to begin with. If you don’t have the entire printing condition at hand — machine/media/resolution/ink/density/RIP — then your converted result is going to be pretty useless to you.
And if you do, well, then use the RIP to do the conversion. That’s what it’s for.
Second is that properly made and properly used, the value of N-colors is to extend gamut beyond CMYK. Differing profiling packages have differing controls, and I guess it’s at least possible for someone making a multi-color profile to extend the N-channels into non-chroma areas. But there’s no reason to. So if you’re doing any tests starting with a greyscale image, once you get the other channels — whatever they are — they should all be empty.
Mike Adams
Correct Color
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