CHROMiX

Iterative Lab to CMYK conversion

I wonder if someone can tell me if ColorThink can do the following, or if not, is there some software that can?

  1. Read, enter, or import Lab values for some color swatches. These could be ink draw-downs or swatches from a customer’s spec sheet or the Pantone book.

  2. Come up with a suggested CMYK build for these swatches using an ICC profile, probably the GRACoL profile.

  3. I would then build a page in Quark with swatches that used these initial builds and print it out on our GRACoL calibrated Epson proofer.

  4. I would read in these swatches from the Epson with an EyeOne and enter these new Lab values.

  5. I would need the software to compare the initial Lab values with the new Lab values, tell me the delta-E, and suggest new CMYK values that would be a closer match.

  6. I would then repeat steps 3-5 several times until the delta-E numbers got low enough.

The hard part is that I need the software to be smart enough to say “I know I recommended some initial values, but I can see that they didn’t quite do it, so judging from the Lab values they actually produced, here is a new recommendation that should be closer”.

Thanks,

Jamie

Hi Jamie,

This is a creative idea, and in a perfect world it would probably work as you envision. In practice though, I think there would be enough variation between Quark, and your proofer, and the EyeOne that you’d probably end up chasing your tail rather then actually reducing your dE. And then if your ultimate goal is to reproduce this on press, then that would be another wrench into the works.

But I think the software you are looking for is ColorPicker. It is part of the ProfileMaker suite of programs, and I think the features you need do not require a dongle. In ColorPicker you can call up a Lab value or choose from Pantone libraries - and it will give you the CMYK build given a profile you choose (like GRACoL). Next, you hit a “Minimize dE” button to run the values through the profile again, and it re-calculates the expected dE error while it tweaks the CMYK values. Don’t forget to hit “Set” to lock in your changes.

In our experience, this works very well. With reasonable, in gamut colors we regularly see dE values improve by 2 - 3 dE with that minimize button, and the resulting output is very close.

Let me know if you need help finding ColorPicker.

1 Like

Several software solutions for hardcopy proofing already do this. From a pure profile standpoint, GMG Colorserver does this (proprietery though)…perhaps something from ORIS as well, but I’m not sure. AFAIK, this is not Colorthink’s gig.

Mike

-----Original Message-----
From: jstotz
To: ColorThinkForum@colorforums.com ColorThinkForum@colorforums.com
Sent: Mon Jun 15 20:08:04 2009
Subject: Iterative Lab to CMYK conversion

I wonder if someone can tell me if ColorThink can do the following, or if not, is there some software that can?

  1. Read, enter, or import Lab values for some color swatches. These could be ink draw-downs or swatches from a customer’s spec sheet or the Pantone book.

  2. Come up with a suggested CMYK build for these swatches using an ICC profile, probably the GRACoL profile.

  3. I would then build a page in Quark with swatches that used these initial builds and print it out on our GRACoL calibrated Epson proofer.

  4. I would read in these swatches from the Epson with an EyeOne and enter these new Lab values.

  5. I would need the software to compare the initial Lab values with the new Lab values, tell me the delta-E, and suggest new CMYK values that would be a closer match.

  6. I would then repeat steps 3-5 several times until the delta-E numbers got low enough.

The hard part is that I need the software to be smart enough to say “I know I recommended some initial values, but I can see that they didn’t quite do it, so judging from the Lab values they actually produced, here is a new recommendation that should be closer”.

Thanks,

Jamie

Oris does this as well as EFI Fiery XF