Re: soft proofing of spot colours
Re: soft proofing of spot colours
- Subject: Re: soft proofing of spot colours
- From: Marco Ugolini <email@hidden>
- Date: Tue, 22 Jan 2008 11:03:39 -0800
- Thread-topic: soft proofing of spot colours
In a message dated 1/21/08 2:05 PM, Matthew Larmour wrote:
> Can someone confirm if Adobe apps colour manage spot colours for soft proofing
> purposes, and explain the mechanism?
If I understand your question correctly, you are asking whether or not
applications like Photoshop or InDesign can print spot colors to a
color-managed printer in an accurate manner. Is that correct?
The short answer is "not exactly", because (a) spot colors are properly
defined in L*a*b* -- not RGB or CMYK. Currently I don't believe that there
is an option in Adobe apps to use split print paths, one for the source
colors (RGB or CMYK) *and* one for L*a*b*-defined spot colors; and (b) often
enough several spot colors live outside the gamut of the output device
anyway.
In other words, all that the Adobe apps can do reliably is to use the target
profile and convert all of the source colors to it. But the source colors
can only be in *one* single color space.
So, I may be incorrect about this, but I believe that there is currently no
reliable way in Adobe apps to proof CMYK colors separately from spot colors
defined in L*a*b* values. To do that, one has to use an external RIP that
offers a separate and specific printing path for spot colors. ColorBurst
X-Proof offers that feature, for example. But even that is a limited option,
since the RIP can only match those spot colors that do *not* exceed the
gamut of the output device. If they do exceed it, then the match will be off
by varying degrees.
Another theoretically possible way to proof spot colors would be to convert
all source colors to L*a*b*, but the trick there is to find a way to
maintain the accurate L*a*b* numbers for the spot colors after the
conversion is done. I have not tried to do it this way myself, so please let
me know if you try it out, and how it works for you.
Finally, one last concern would be to verify that the hue angle of the spot
color is kept constant on the output device even when it is not solid. Tints
of it may deviate from the proper hue for a number of reason, so that a
yellow spot color may start appearing greenish at some point, or a blue may
turn purple, and so on.
Marco Ugolini
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