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Author Topic: i1Profiler - i1Pro-uvcut vs. i1Pro-normal does make a difference  (Read 5161 times)
rasworth
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« Reply #20 on: September 07, 2011, 01:33:20 PM »
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Forget print matching, all I'm saying is the softproofs from two profiles will have a slightly different hue, one derived from a i1Pro-normal and one from an i1Pro-uvcut, using the same printer target and both profiles generated from i1Profiler.

My understanding is the B to A path is via perceptual intent (or relative or sautration), and the A to B "return trip" is via absolute intent, if Display Paper White is checked.  Since we have two differing sets of absolute neutral rendering curves, the softproof has to be different.

Richard Southworth
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digitaldog
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« Reply #21 on: September 07, 2011, 01:38:51 PM »
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Forget print matching

I have from the beginning because if I understand you, you report they both match.

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all I'm saying is the softproofs from two profiles will have a slightly different hue, one derived from a i1Pro-normal and one from an i1Pro-uvcut, using the same printer target and both profiles generated from i1Profiler.

Exactly. So where’s the disconnect? In the proofing tables. They should match the output. One apparently doesn’t. You feel, and you may be spot on, that the differences is due to how the data was collected. But I’m asking why there is this disconnect in only the one table.

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My understanding is the B to A path is via perceptual intent (or relative or sautration), and the A to B "return trip" is via absolute intent, if Display Paper White is checked.  Since we have two differing sets of absolute neutral rendering curves, the softproof has to be different.

You need the Absolute rendering for the display yes, but that doesn’t change the aim which is a match. Would you agree that the soft proof with the paper simulation should match the print? You seem to be saying they don’t. The question is why.

We use the simulate check box to see a more correct soft proof. With it off, I would not expect a good print to screen match. But with it on, there’s a mismatch but only from one profile and the only differences is the filter. I’d think both tables would be affected assuming the software is building both tables correctly.
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Andrew Rodney
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rasworth
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« Reply #22 on: September 07, 2011, 02:12:15 PM »
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Ok, I believe I understand your point, and I believe I "know" the answer.

Test prints made with both profiles resulted in essentially identical prints, as viewed under my fairly bright somewhere around 4000K environment.  So my conclusion is the actual rgb values fed to the printer in perceptual intent (I didn't try much with relative or sautration) at least in the high mid-tones were also close to identical.  The only way to do a truly "honest" print comparison would be to have a strong uv presence for the print done via the i1Pro-normal and a weak uv source (my actual viewing environment) on the print done via the i1Pro-uvcut.  Assuming the illumination was otherwise identical I would have different print appearances, and I might well have good softproof results with both profiles.

But that's truly the issue, we don't generally view prints with illuminants containing strong uv.  Almost every profile I've examined from paper manufacturers (at least for those papers with OBAs) was obviously created with a uvcut instrument, i.e. the white point was much less "blue" than anything I could detect using an i1Pro-normal.  So given that we don't had the capability to do some sort of sophisticated mix of targets measured with and without uv detection, a uvcut instrument may usually provide the "best" solution, at least in terms of matching the softproof of papers with OBAs.

If I'm correct then this is as much a problem with PMP as i1Profiler, more an issue with the whiteners used in resin coated papers.  And I never found much improvement using the OBA correction in PMP, the few times I tried it both ways I couldn't tell any difference.  To be really honest, I've had past issues with softproofing in terms of the yellowish tendency, and it's only now using an uvcut instrument that I seem to have better results.  Of course, that could be due to several factors, including my eyeballs.

Richard Southworth
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digitaldog
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« Reply #23 on: September 07, 2011, 02:23:24 PM »
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So my conclusion is the actual rgb values fed to the printer in perceptual intent (I didn't try much with relative or sautration) at least in the high mid-tones were also close to identical. 

Easy to test in Photoshop (better if you have ColorThink Pro). In Photoshop, convert an image both ways (two documents). Go to Image > Apply Image.
Set whichever image isn't listed as the target as the source. Set the Channel as RGB. Set the Blending to Subtract, with an Opacity of 100, a Scale of 1, and an Offset of 128.
If the images were truly 100% identical, every pixel in the image would be a solid level 128 gray. Pixels that aren't level 128 gray are different by the amount they depart from 128 gray. You can use Levels to exaggerate the difference, which makes patterns easier to see. Just move the sliders on either side to the center as far as you can.

In ColorThink you can do this on a low rez image (or better, a target), load and build two Color Lists. Save out Lab. Load both, run a dE report. You’ll see exactly what colors are the same or different.
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Andrew Rodney
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rasworth
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« Reply #24 on: September 07, 2011, 03:42:07 PM »
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Very interesting experiment.

First I performed for perceptual and relative intents, little difference, very narrow histogram, had to bring the level sliders way in to visually observe much difference, barely discernable near-gray tones at 100 left and 155 right.

I then converted the image (PDI-Target) thru both profiles using absolute intent, significant difference particularly in the higher mid-tones, bringing in the level sliders to 100 and 155 created a very visible difference image.

So I believe my conclusion was correct, i.e. profiles created using both instruments show very little difference in the forward direction (lab to rgb) for perceptual and relative intents, and a very distinct difference for absolute.  This is consistent with my visual evaluation of prints made with both profiles, obviously very similar since the 3880 received nearly identical rgb values for every pixel.  And it is consistent with the difference I saw in softproofs.

Richard Southworth

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digitaldog
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« Reply #25 on: September 07, 2011, 04:22:54 PM »
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So I believe my conclusion was correct, i.e. profiles created using both instruments show very little difference in the forward direction (lab to rgb) for perceptual and relative intents, and a very distinct difference for absolute.  This is consistent with my visual evaluation of prints made with both profiles, obviously very similar since the 3880 received nearly identical rgb values for every pixel.  And it is consistent with the difference I saw in softproofs.

I would expect two different instruments to have slight differences. Even the same instrument measuring the same target twice will (if you compare the lab values in ColorThinnk). The differences should be pretty small (an average of less than 1 but worst could be 1).

But that they are different still doesn’t explain the mismatch in the tables.
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Andrew Rodney
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rasworth
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« Reply #26 on: September 07, 2011, 04:44:57 PM »
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What mismatch?  Given the relative/perceptual tables are close, then the absolute has to be significantly different because the white points are significantly different.  And if I were able to irradiate the uvnormal print with sufficient uv I might also be able to achieve a reasonable softproof match for the uvnormal version as well as the uvcut, and the two prints would look different even though the B to A tables were similar.

I don't see an inconsistency.

Richard Southworth
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digitaldog
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« Reply #27 on: September 07, 2011, 04:46:02 PM »
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Why doesn’t the soft proof match?
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Andrew Rodney
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rasworth
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« Reply #28 on: September 07, 2011, 05:05:56 PM »
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Because of the white point "error".  The profile made from the uvnormal instrument contains a white point that is bluer than the actual white point of the paper under any illuminant that doesn't contain significant uv.  I believe one requirement for successful softproofing is a match between the profile white point and the actual paper white point.

I understand that the paper white point is a parameter that is normally independent of any viewing illuminant, but it becomes warped in the presence of uv.

Richard Southworth
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tony22
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« Reply #29 on: September 07, 2011, 07:41:53 PM »
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Its relevant in explaining to Tony why its necessary to have dual measurements. The point is, you need both and you need to build the profile both ways and pick the winner. You yourself found this to be true:

And I do appreciate the explanation from both you and Marc. So to veer a bit off course from where this conversation is heading, where does that leave people like me who have a non UV-cut and are thinking about the i1Profiler upgrade under the current rebate period? Would we wind up with a solution that is not ideal? (assume I use papers with OBAs, which I do.)
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digitaldog
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« Reply #30 on: September 07, 2011, 07:46:14 PM »
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So to veer a bit off course from where this conversation is heading, where does that leave people like me who have a non UV-cut and are thinking about the i1Profiler upgrade under the current rebate period? Would we wind up with a solution that is not ideal? (assume I use papers with OBAs, which I do.)

Compared to what? The “use or don’t use UV Cut” debate is old and on-going. Some say software compensation is useful. Some may say its not. You have hardware that is what it is. I don’t think its all that pertinent in terms of should you upgrade or not. If the new features, the new color engine or the ability to run in say Lion are useful to you, you’ll probably want to upgrade.

There are disadvantages to papers with OBA’s no matter what Spectrophotometer or software you use.
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
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