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Author Topic: Starting a search for a smaller, but more optimal, profile patch set  (Read 4678 times)

Doug Gray

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #20 on: November 19, 2017, 03:04:19 PM »

Presumably you're driving it with in RGB, so such weirdness could just be a limitation of the profiling used to create its RGB->CMYKLCLMLLK lookup table.

Yes, device space RGB.  However, further investigation shows that only about half the abrupt  b* shift is from the RGB->CMYKLCLMLLK lookup table. The other half is due to differences in inking and how the Isis does M2.  Turns out there is significant fluorescence from the LED's spectral components around 400nm to 430nm which is showing up as a significant bump at 480nm. It's particularly exacerbated because the LED luminance at 480nm is at a significant minimum which greatly magnifies the impact of fluorescence. This  bump does not occur with a standard uV cut tungsten spectro and it is sensitive to the mix of Y, LM and LC relative to the LLK proportions.

Here's ABW compared to printing in color mode RGB w/o color management. Also the spectrum of Costco's glossy showing the bump around 480nm. This isn't there with a regular I1Pro uV Cut.

For the tri color plot, Blue=L*  Orange=a*   Yellow=b*
« Last Edit: November 19, 2017, 07:29:38 PM by Doug Gray »
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GWGill

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #21 on: November 19, 2017, 07:17:34 PM »

The issue with printer targets is that there are occasional large outliers in addition to the bulk of variation which is more consistent with a normal distribution.
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I'm not sure whether just excluding them at some nominal threshold or doing a Gaussian smoothing would be better. Interesting idea though.
A few people use a workflow that excludes such outliers using ArgyllCMS's profcheck -P functionality.
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Doug Gray

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #22 on: November 19, 2017, 11:33:19 PM »

A few people use a workflow that excludes such outliers using ArgyllCMS's profcheck -P functionality.

Graeme,

You have quite a nice set of tools. I've made some similar ones in Matlab but only with options I've needed. Far less extensive that what you have done. I've found Matlab's interactive approach is really handy for exploring the numerical data in different ways. One of the more useful recent tools is creating time stamped, labeled I1Isis compatible tiff files from Cgats at a selectable DPI. Also, I have some specialized (weird) tif files for testing I1Isis alignment tracking. The I1Isis has proved a surprisingly good instrument.

One of the things I'm looking at is trying to identify outliers w/o printing duplicate patch sets. It appears that when an outlier occurs, the variation is higher for successive scans than patches that aren't outliers. This works quite well already for I1Pro scans where outliers aren't as "sticky" but the tracking consistency is so good with the I1Isis that the main variation is from the time slice sampling which creates about .5mm uncertainty on the patch locations. That's pretty small but enough to bounce the outliers around a bit.
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Ethan Hansen

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #23 on: December 05, 2017, 08:32:07 PM »

Here are a few general thoughts on profiling patch sets.

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This will create a patch set with "holes" but holes that don't provide much useful info. Question is: can the profiling software handle these?

This depends on the assumptions made by the profiling software. ArgyllCMS happily handles these situations and the default space-filling patch set does exactly this. In the case of X-Rite, my experience is that the software behavior reflects the code origins. The i1P profiling engine appears to draw heavily on MonacoProfiler which required equally spaced source data points for RGB profiles. i1P inherits some flexibility from ProfileMaker, but it quickly gets brittle with oddball patch sets.

Are you absolutely sure that the variations you see are caused by the printer and not the iSis? One step of the target analysis we perform is to both check a small set of duplicate patch values and validate whether differences between "neighboring color" patches makes sense. Several times a week we flag a measurement that is dubious because of variation.

Patch sizes below 6.6 mm or so on the iSis are more susceptible to spurious readings. Mismeasurements due to angled papers are easier to detect than errors from the timing resolution you mentioned above.

That said, some printers do have variations on how they lay down color. When we start evaluating a particular printer family this is something we check. Depending on the printer we'll either add duplicate patches or use some flavor of radial basis function to derive a correction matrix.

I'm an empirical guy, so I prefer to confirm measurements on hardware less prone to orientation variability than the iSis. If you want, shoot me a PM or email and we can measure one of your targets on a Spectroscan.

Lumpy bumpy RGB output behavior has been an Epson trademark for nearly two decades. Each model improves upon the last, but I wonder whether Epson never resolved the issue completely because doing so would be tacit admission there was a problem in the first place. ABW mode gave a clean slate to the software team.

The spurious peak at 480 nm in iSis M2 measurements moves around somewhat depending on the paper stock and brightener levels for Epson x900 printers. There are two approaches you can use here. First, measure in M1 mode with the caveat that your prints are only going to match when viewed in an ISO 3664:2009 compliant viewing booth. The other is to again measure in M1 but use profiling software with useful software-based optical brightener compensation. Yes, I know i1P has the manual OBC module but its utility is limited at best in the real world.
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Doug Gray

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #24 on: December 09, 2017, 12:03:24 AM »

Here are a few general thoughts on profiling patch sets.

This depends on the assumptions made by the profiling software. ArgyllCMS happily handles these situations and the default space-filling patch set does exactly this. In the case of X-Rite, my experience is that the software behavior reflects the code origins. The i1P profiling engine appears to draw heavily on MonacoProfiler which required equally spaced source data points for RGB profiles. i1P inherits some flexibility from ProfileMaker, but it quickly gets brittle with oddball patch sets.

Are you absolutely sure that the variations you see are caused by the printer and not the iSis? One step of the target analysis we perform is to both check a small set of duplicate patch values and validate whether differences between "neighboring color" patches makes sense. Several times a week we flag a measurement that is dubious because of variation.

Patch sizes below 6.6 mm or so on the iSis are more susceptible to spurious readings. Mismeasurements due to angled papers are easier to detect than errors from the timing resolution you mentioned above.

That said, some printers do have variations on how they lay down color. When we start evaluating a particular printer family this is something we check. Depending on the printer we'll either add duplicate patches or use some flavor of radial basis function to derive a correction matrix.

I'm an empirical guy, so I prefer to confirm measurements on hardware less prone to orientation variability than the iSis. If you want, shoot me a PM or email and we can measure one of your targets on a Spectroscan.

Lumpy bumpy RGB output behavior has been an Epson trademark for nearly two decades. Each model improves upon the last, but I wonder whether Epson never resolved the issue completely because doing so would be tacit admission there was a problem in the first place. ABW mode gave a clean slate to the software team.

The spurious peak at 480 nm in iSis M2 measurements moves around somewhat depending on the paper stock and brightener levels for Epson x900 printers. There are two approaches you can use here. First, measure in M1 mode with the caveat that your prints are only going to match when viewed in an ISO 3664:2009 compliant viewing booth. The other is to again measure in M1 but use profiling software with useful software-based optical brightener compensation. Yes, I know i1P has the manual OBC module but its utility is limited at best in the real world.

Ethan,
Isis and I1Pro 2 both purport to measure M0, M1, and M2 but they operate differently with slightly different results. The I1Pro 2 measures M1 by default, Isis M2 (uV cut) by default. Then they illuminate with a uV LED and measure the fluorescence. The I1Pro 2 calculates M2 by subtracting some portion of the uV response from the M1 default and adding in some to determine M1.  Isis adds in uV response to come up with M0 and M1 from its default, M2.

I've been able to deal with the Isis wheel track issue by using 10.5mm patches and aligning the paper so the wheel tracks run near/on the patch transitions. I find the improvements mostly affect some Baryta luster paper that with a surface that tends to crush a bit on the tracks. As for intrinsic variation in a paper without significant track marks, I find printing duplicate patches then sorting the outliers is more effective. I'm pretty well automated for either as needed.
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Doug Gray

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #25 on: December 25, 2017, 11:27:32 PM »

After a bit of experimenting I decided to create a patch set with a much larger set of neutral and near neutral patches. I combined this with a standard grid of 9x9x9 (729 patches). The near neutrals comprised of 1546 patches.

I duplicated the near neutral patches and added the standard grid patches and randomized the set. This made 4 pages of letter size Isis targets.

I made profiles for both Canson Rag Photo Matte and Costco Glossy and printed several targets that comprised of the Colorchecker colors and a neutral ram from L*=2.5 to 100 in steps of 2.5. Each had 2 additional duplicates that were also randomized. Since each set had 64 patches there were a total of 192 patches. These targets were in  16 bit Adobe RGB tif files Isis readable and were printed using Absolute Colorimetric Intent. Only in gamut colors were analyzed.

The results finally eliminated the Costco paper perturbations I was seeing in *b and the neutrals at last had lower dE00s than the more saturated colorchecker patches. Average dE00 for neutrals was .42 on each of the neutral colors and about .72 for ColorChecker's colored patches.

The Canson Rag Photo was even better, coming in at about dE00=.34 for the Colorchecker colors and dE00=.32 for the neutral ramp. So for the Matte paper this particular target patch set does a good job on both color patches and neutrals.

One note of interest is that the dE00 variation for neutrals exceeded the dE76 while the reverse is true for colored patches. This is one of the more curious aspects of color perceptual sensitivity. It's easier to see differences in color when the colors are neutral to near neutral and much more difficult as the colors become more saturated.


These are the results from the Costco Glossy paper which has more variation than good smooth matte papers:

2 Printouts, Epson 9800, Gostco Glossy
ColorCheckerColors dE00: 0.76, dE76: 1.35,   Neutrals (Steps of 2.5 L*) dE00: 0.52, dE76: 0.43
ColorCheckerColors dE00: 0.64, dE76: 1.09,   Neutrals (Steps of 2.5 L*) dE00: 0.40, dE76: 0.35
ColorCheckerColors dE00: 0.58, dE76: 0.91,   Neutrals (Steps of 2.5 L*) dE00: 0.40, dE76: 0.37

ColorCheckerColors dE00: 0.83, dE76: 1.54,   Neutrals (Steps of 2.5 L*) dE00: 0.51, dE76: 0.44
ColorCheckerColors dE00: 0.65, dE76: 1.18,   Neutrals (Steps of 2.5 L*) dE00: 0.36, dE76: 0.31
ColorCheckerColors dE00: 0.55, dE76: 0.87,   Neutrals (Steps of 2.5 L*) dE00: 0.36, dE76: 0.34


And these are the results from the Canson Rag Photo Matte:
3 Printouts, Epson 9800, Epson Enhanced Matte
ColorCheckerColors dE00: 0.33, dE76: 0.50,   Neutrals (Steps of 2.5 L*) dE00: 0.29, dE76: 0.26
ColorCheckerColors dE00: 0.35, dE76: 0.51,   Neutrals (Steps of 2.5 L*) dE00: 0.30, dE76: 0.27
ColorCheckerColors dE00: 0.34, dE76: 0.51,   Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.28

ColorCheckerColors dE00: 0.32, dE76: 0.49,   Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.29
ColorCheckerColors dE00: 0.34, dE76: 0.49,   Neutrals (Steps of 2.5 L*) dE00: 0.31, dE76: 0.28
ColorCheckerColors dE00: 0.35, dE76: 0.52,   Neutrals (Steps of 2.5 L*) dE00: 0.33, dE76: 0.31

ColorCheckerColors dE00: 0.35, dE76: 0.51,   Neutrals (Steps of 2.5 L*) dE00: 0.34, dE76: 0.32
ColorCheckerColors dE00: 0.36, dE76: 0.56,   Neutrals (Steps of 2.5 L*) dE00: 0.32, dE76: 0.29
ColorCheckerColors dE00: 0.35, dE76: 0.54,   Neutrals (Steps of 2.5 L*) dE00: 0.33, dE76: 0.30


Each of the printouts (Two Costco, Three Canson) had 64 total colors duplicated 3 times, hence each of the groups of 3 lines. While the groups were randomized, the same tif file was used for each of the 5 printouts.

I have attached the Isis ready test 192 patch Adobe RGB tif file as well as the CGATS file of the 4 page Isis target from which the profile targets were made.


« Last Edit: December 26, 2017, 01:37:08 AM by Doug Gray »
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Brad Paulson

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #26 on: January 25, 2018, 10:44:30 PM »

Doug, thanks as always for sharing your thoughts.  Just printed out the patches successfully on my Z and waiting to scan. 

Interesting thinking on all the near neutrals - quite a different approach from other patch sets Iíve been using.  I imagine images with this would best be printed in RelCol if possible (rather than P) and that you might have taken this approach even with another spectro for the reasons you develop here.

Addendum later today:  Thinking about it all and watching my patch set dry, actually maybe perceptual would benefit too.  Certainly B/W would be assisted over a more ďstandardĒ patch set with the same number of patches.   The neutrals and white/black transitions seem across the luminosity range to be pretty well nailed down by this approach.... hmm.   The proof of the pudding will be in the printing.   
« Last Edit: January 26, 2018, 12:40:32 AM by Brad Paulson »
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Doug Gray

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #27 on: January 26, 2018, 03:05:38 PM »

Doug, thanks as always for sharing your thoughts.  Just printed out the patches successfully on my Z and waiting to scan. 

Interesting thinking on all the near neutrals - quite a different approach from other patch sets Iíve been using.  I imagine images with this would best be printed in RelCol if possible (rather than P) and that you might have taken this approach even with another spectro for the reasons you develop here.

Addendum later today:  Thinking about it all and watching my patch set dry, actually maybe perceptual would benefit too.  Certainly B/W would be assisted over a more ďstandardĒ patch set with the same number of patches.   The neutrals and white/black transitions seem across the luminosity range to be pretty well nailed down by this approach.... hmm.   The proof of the pudding will be in the printing.

Yes, to the degree Rel Col benefits, Perc. will too. Not that it will be better per se, but Perc. tables are built from the same info and reflect, with I1Profiler, relatively small changes. The tone curve has a very slight "S" curve and the chromaticity is rounded near the gamut edges. As for the neutral renderings. There are sliders in I1Profiler that lets you adjust the way the neutrals are rendered. Generally, the default  the white point is gradually brought in from the paper white to D50 neutral around L*=50. This differs from Rel. Col. which maintains the same paper white point chromaticity coordinates as much as possible down to the DMax. Chromaticity is set by the xy coordinates in the familiar CIEXY horseshoe gamut. You will likely see little effect as the HP spectro is an M2 spectro and most of the Perceptual neutral shift shows up with high OBA media.

Keep in mind that this patch set was what finally made my 9800 printer print neutrals very smoothly without the large b* changes due to ink shifts around L*=80+ I suspect the HP or most other printers don't suffer from this. However, the inclusion ofsuch a large number of neutrals does benefit things because the Delta E 2000 metric is far more sensitive to slight hue/saturation shifts on or near the neutrals.  In most colors Delta E 2000 is much smaller than dE76 but not near neutrals. Especially as saturation goes beyond about 30 (sqrt(a^2+b^2) where dE00 typically gets much smaller than dE76. There can be a difference between dE00 and dE76 of over 4 to 1.  So it's arguably desirable to have a heavier patch concentration of near neutrals than further out.

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Brad Paulson

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Re: Starting a search for a smaller, but more optimal, profile patch set
« Reply #28 on: January 27, 2018, 03:12:57 PM »

Doug - just a quick note to say Iím somewhat blown away by the absolutely visible positive difference your patch set is making to an image Iím have been pretty intensively working on, and that difference over a more equally weighted somewhat larger i1P generated 4357 patch set.  Soft proofing only in P so far, the colors look more realistic and like a dose of clarity had been provided both in relcol and perceptual proofs. Working now on a device link print.  So anyway, itís not just the Epson.
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