RE: white point variation, was :File Preparation for 4 color...
RE: white point variation, was :File Preparation for 4 color...
- Subject: RE: white point variation, was :File Preparation for 4 color...
- From: Steve Upton <email@hidden>
- Date: Thu, 8 Nov 2007 11:16:30 -0800
At 6:46 AM -0500 11/8/07, Robert Rock wrote:
>Question about profiling:
>I am attempting to create a CMYK profile using the XRite DTP70. The targets
>I generated for the printer to print require 5 targets for the set. This is
>an unusual substrate as it involves printing the CMYK targets on a clear
>acetate (reversed), then printing over with an opaque white, to give the
>illusion of paper behind the color. Now here's the problem....I received
>only 4 of the 5 targets back from the printer (their oversight) so had to
>wait a couple weeks to get the final target. This target has an obvious
>difference in the color of the white "backing", so that it has the
>appearance of being printed on a slightly yellower paper. I don't want to
>start over again on this. Is there a way to somehow equalize this target
>data so that appears to be printed on the same paper? Am I clear?
>Here's an image to show the difference:
Hi Bob,
This is not an easy situation but I think you can probably fix it.
What you need to do is remove the white point from all the measurements before you put them together.
So, first you measure the sheets in groups so all the same white points are together - or separate files for all of them if they each have a different white (which your image implies).
Then you normalize all the colors on each sheet to Y using the technique in the appendix of the ICC spec. This is the same method that is used to prepare color information when profiles are built (usually in the software itself). It effectively makes them all 'relative colorimetric' readings.
Then combine the measurements into one file and build your profile. You will lose the original white point information so if you want to do proofing you may need to edit the resulting profile's white point to reflect the white of one of the sheets..
make sense? It is mostly massaging in Excel but it is not trivial. It really comes down to how tough it is to get the targets reprinted...
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
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