White Point Editing-Good or Bad?

General Color & Graphics Printer Calibration & Profiling
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The general consensus, from everything that I’ve read at least, says to use AbsCol intent when matching a press or proofer on an inkjet printer, which makes sense.

This way the inkjet will show you the exact colors (as best it can) of the press/proofer. Which of course includes showing you a yellowish (or other color) paper white in some cases. If you do not want the yellow tint to appear on the inkjet prints, but you still want to use AbsCol intent, you can edit the white point of the destination profile to match the wp of the source profile.

So my question is, are there any downsides to editing the wp like this? If you lay the proofer output next to the inkjet output, shouldn’t all of the colors match (as well as ICC worflow allows) except for the paper white?
Is it best to leave the wp alone so you eye isn’t referencing two distinct white points when viewing the output?

Thanks for any clearification.

Chris M

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At 11:52 AM -0800 2/28/05, cmcfarling wrote:

The general consensus, from everything that I’ve read at least, says to use AbsCol intent when matching a press or proofer on an inkjet printer, which makes sense.

yes, although as you are finding, it doesn’t always work first time around…

This way the inkjet will show you the exact colors (as best it can) of the press/proofer. Which of course includes showing you a yellowish (or other color) paper white in some cases.

right

If you do not want the yellow tint to appear on the inkjet prints, but you still want to use AbsCol intent, you can edit the white point of the destination profile to match the wp of the source profile.

yes you could but I would not recommend it. All colors are relative to white. So if you change the white without changing the image / palette colors then the colors will look different relative to white… not typically good

So my question is, are there any downsides to editing the wp like this? If you lay the proofer output next to the inkjet output, shouldn’t all of the colors match (as well as ICC worflow allows) except for the paper white?

no, they shouldn’t. If you don’t want to simulate paper white then do relative colorimetric proofs and leave it at that. If you can find a proofing paper that is the same color as the simulated color then you can do a very effective relative colorimetric proof - in fact I prefer this method.

Is it best to leave the wp alone so you eye isn’t referencing two distinct white points when viewing the output?

two whites is OK but the colors need to be formulated relative to each white (and you shouldn’t view them side by side). If you choose to do absolute colorimetric proofing then you can tweak the white of the reference profile OR the proofer profile. Just remember that if you tweak a reference profile for a particular use then it should never be used for other purposes, like soft proofing. It’s a good idea to name such profiles to avoid future confusion. - like “SWOP TR001for xxx proofer”. Also, like we always say…trim all abs col proofs before viewing

Thanks for any clearification.

no problem… a very good question.

Regards,

Steve

o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX

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Speaking of editing white points…how do the ICC based inkjet Rips like that of EFI handle this, surely they can do better than absolute colorimetric?

I know with GMG you can alter the white point and have the correction calculated throughout the rest of the profile. That way you can use one paper type to simulate any number of paper shades.

mike

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At 3:01 PM -0800 2/28/05, Michael Eddington wrote:

Speaking of editing white points…how do the ICC based inkjet Rips like that of EFI handle this, surely they can do better than absolute colorimetric?

not that I know of… what would be better than abs col? (I mean from a good profile)

I know with GMG you can alter the white point and have the correction calculated throughout the rest of the profile. That way you can use one paper type to simulate any number of paper shades.

Right. I don’t know about their architecture but the impression I get is that they build a device-link style profile in their system. Tweaks on top of that are not really outside the ICC spec. On top of it in some cases but not really outside of it…

When I brought up the problems of ICC color and profile conversions with Lars Borg of Adobe (past chair of ICC) he sort of wondered what I was referring to… then he said that he had yet to see an ICC profile from today’s packages that he liked… which got ME wondering what I was talking about…

Regards,

Steve

o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX

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We’ll for instance I created a RGB output profile on an Epson 4000 recently and printed to it simulating a press condition using abs col. My proof white point was 4.75 delta E away from the target white point. Blah. I can edit the white point and improve it, but I guess I just find it a little cumbersome.

With GMG I can get the delta E of the white points down below 0.5 in many cases, often without tweaking at all. I can then alter the white point by either entering new target data in LAB and let the software calculate a new white, or I can edit the CMYK at the back end of the device-link profile…the actual CMYK that the printer gets, and calculate the correction throughout the profile.

I suppose this isn’t really cutting on abs col specifically, just wondering what tools are available in other proofing solutions and if there as good or better than GMG’s.

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At 11:45 AM -0800 3/1/05, Michael Eddington wrote:

what would be better than abs col? (I mean from a good profile)

We’ll for instance I created a RGB output profile on an Epson 4000 recently and printed to it simulating a press condition using abs col. My proof white point was 4.75 delta E away from the target white point. Blah. I can edit the white point and improve it, but I guess I just find it a little cumbersome.

yes it is…

With GMG I can get the delta E of the white points down below 0.5 in many cases, often without tweaking at all. I can then alter the white point by either entering new target data in LAB and let the software calculate a new white, or I can edit the CMYK at the back end of the device-link profile…the actual CMYK that the printer gets, and calculate the correction throughout the profile.

understood

I suppose this isn’t really cutting on abs col specifically, just wondering what tools are available in other proofing solutions and if there as good or better than GMG’s.

I think GMG’s strength is in the automated tweaking of the transform…

In your specific case, can you determine if the 4000’s profile will render the desired Lab color correctly? (isolating it from the other profile and its possibly questionable white point)… I am working on this type of trouble-shooting and am curious about isolating the problem…

In fact the more stuff you can send me directly (profiles, measurements, etc) for this problem the quicker I can get to the bottom of it. First I want to see if I can anticipate the error using the profiles themselves, and then…

Regards,

Steve

o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX

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We’ll, I tried defining a color patch using the Lab values of the target white point and proofing it. It was closer, but not really acceptable with a delta E of 3.9. But maybe I should give a little more info…the target profile was measured from paper not containing any optical whitening agents with a SpectroScan. The Epson 4000 paper does have whitening agents and was measured with an ICColor with a uv filter. The white point of the Epson profile is given as X=.87, Y=.917, Z=.77 (in Lab 96, -2.7, -1.2) but when measured without a uv filter its more like L*=96, a*=-.3, b*=-4.17. Target white is 92, .77, .96. Practically all the the delta E is calculated from the difference in the b*.

Using GM ColorPicker, I loaded my Epson profile and added the target white point as a new color, defining it in Lab. I created a color patch using those RGB values that should have resulted in zero delta E (or 1.1 at the most) and output that (using rel col w/ bpc, no press simulation), but got pretty much the same results.