New Approach for Generating Optimal Profile Patch Sets

[Doug Gray]

Where is Version 2 posted?

I replaced the original zip file in reply #105.

[JRSmit]

Trying to grasp the essence of this interesting thread, i downloaded Doug's cgats files, and tried to open them in Colorthink Pro.  Does not work. So i used i1Profiler to create a measurement data set, and also saved the tif of the measurement chart. This i could open in the 3D grapher, funny enough it shows the colors transformed into a sRGB color space.

If i load the cgats file in a worksheet, and then do graph it shows the colors, but also transformed into a sRGB space.

This cannot be correct.

What is it i do wrong?

[samueljohnchia]

What is it i do wrong?

When graphing the RGB patch values in CTP, you need to assign printer space to it (the printer profile) rather than srgb. Then they will be graphed as you expect.

[samueljohnchia]

What the program does is create a series of evenly spaced steps in L* from the black point to 100 (in Re. Col.) with a* and b* set to 0. It's then runs these through the supplied profile to generate RGB values that correspond to this. Then the RGB values are adjusted slightly with each channel in turn increased a small amount while the other two are decreased a smaller amount. This produces staggered near neutrals much like what the I1Profiler's patch generator does with near neutrals except that these more closely track the actual neutrals.Yes, you are quite correct. I was trying to say dE00 typically magnifies Lab differences and "exaggerates" implies it increases dE00 inappropriately. I'll fix that post.

Thanks Doug for the insight into how it works and also confirming that we're thinking the same about dE00!

[JRSmit]

When graphing the RGB patch values in CTP, you need to assign printer space to it (the printer profile) rather than srgb. Then they will be graphed as you expect.

Hi samuel, the data set has no profile assigned whatsoever. Apparently it then defaults to sRGB. I want to see the matrix as Dough created it. This without any colorspace.

[samueljohnchia]

Hi samuel, the data set has no profile assigned whatsoever. Apparently it then defaults to sRGB. I want to see the matrix as Dough created it. This without any colorspace.

Hi Jan, what you are asking for makes no sense. Without defining the colour space, RGB values (numbers alone) cannot be graphed in CTP. It is no different from say telling me how big a sheet of paper is in numbers but with no units.

What I think you want is to view the sampling positions of Doug's patch set in relation to printer space. So you need to load the RGB patch data in the Worksheet window, and then assign the preliminary printer profile to the list and graph it.

[JRSmit]

Hi Jan, what you are asking for makes no sense. Without defining the colour space, RGB values (numbers alone) cannot be graphed in CTP. It is no different from say telling me how big a sheet of paper is in numbers but with no units.

What I think you want is to view the sampling positions of Doug's patch set in relation to printer space. So you need to load the RGB patch data in the Worksheet window, and then assign the preliminary printer profile to the list and graph it.

Indeed, when in worksheet, i was able to plot in Lab. showed the matrix very nice.

[Doug Gray]

I'm currently working on finding out what settings are best for generating the small, tracking profile. Currently, it looks like the best settings combines a smallish color grid (m=5) with a stagger value of 10 and -n of 50 to 100 along with a repeat count (-r) of 2. I'm also considering an option to not apply the repeat count to the color grid. There is significant patch to patch variation on the neutrals and, for creating a tracking profile, the color grid errors are much less significant. This would allow increasing the rep count to 4 producing a lopsided near neutral patch set which would give better results around the neutral axis by decreasing their patch error by a factor of two. I'll check it out on my 3 printers to find an optimum.

It's also looking like setting the stagger value to 0 may be optimum for the final profile patch set.

[JRSmit]

Dough, what do you mean with a tracking profile?

[Doug Gray]

Dough, what do you mean with a tracking profile?

It's my term for a profile made with near neutrals patches that have been more closely aligned with the printer's neutral axis. A more precise description would be a profile made with neutrals that are tracked to the printer/paper. Profiles are at their most accurate when printing colors that are closest to the colors of the patches the profile was created with. Creating a profile that includes patches previously determined to be closer to the printer's actual colors (neutral colors in this case) improves accuracy. Because human vision is most sensitive for colors that are near the neutral axis, there is a benefit to focusing specifically on the neutral axis.

It can also produce the best results for B&W printing when using a standard RGB, profiled, workflow.

[rasworth]

I decided to use Doug's new program to create a high quality black and white profile for my Pro-100 using Canon Semi-Gloss paper:

1. Ran the program with the outer grid set to 2 and number of neutrals at 256, no profile selected, creating a cgats file for i1Profiler target generation.  The result fits on one letter size sheet, patches sized for an i1Pro.  The first attachment is the target image.

2. Scanned the target into i1Profiler, generated the first pass profile.  My i1Pro is a uv cut model, so the profile is categorized as M2.

3. Ran Doug's program, again with outer grid set to 2 and number of neutrals at 256, this time with the first pass profile selected, creating the second pass cgats file for a second i1Profiler target.  Same dimensions, one letter size sheet, this time with the tracking neutrals.  The second attachment contains two plots, the left hand size are the neutrals before tracking and the right hand side after tracking, both in the printer profile space.

4. Printed the second pass target, scanned into i1Profiler to create the second and final profile.  Interestingly the six color patches were enough to create a "viable" full color profile, no test prints made but the soft proof in Photoshop looked reasonable, although the gamut was significantly reduced.

5. To test created 101 Lab neutrals, L = 0 to 100, a = b = 0, did an absolute rendering intent conversion thru the second pass profile, and printed in i1Profiler target form.  After drying, scanned into i1Profiler, converted from spectrum data to a Lab list via the i1Profiler measurement output capability.

6.  Finally compared the 101 scanned neutrals to the original list, third attachment shows the dE2000 results.  The paper has a minimum L of about 5 and a maximum of 94, so I discarded the first six and last six measurements.  The remaining 89 dE's average to .48, with 4 exceeding 1.00.

My conclusion is the combination of Doug's program, ColorThink Pro, and i1Profiler provides a quick means to generate a high quality B&W (R=G=B image, not grayscale) profile.  My data is probably somewhat "incestuous" since I used the same instrument for both generating the profiles and testing, but I'm pleased with the results.

Richard Southworth

Added by edit - I believe my last statement is misleading, Doug's program and i1Profiler are all that is required to generate the profiles, ColorThink Pro comes into play for testing.

[rasworth]

Doug,

"-p PageSize  Set the max page patch count size, use with negative -n" has me stumped, please explain.

Richard Southworth

[Doug Gray]

Doug,

"-p PageSize  Set the max page patch count size, use with negative -n" has me stumped, please explain.

Richard Southworth

It's an option to specify the max number of patches on a target page. The default is 957 since that's the max letter size count for an i1iSis. It's an option so that it can be changed to accord with what instrument/paper size one has.

Combining it with  -n -1, to generate whatever number of neutrals is needed to fill out the page(s).  However, it's a bit buggy and I will be shortly revising my program. Most of the changes are to allow scrambling and repeating the neutrals w/o repeating the color patches. There are also some minor other bugs I'm fixing in the tracking neutral generation.

After testing printers and different settings I should have a more optimized program later today. Nothing like printing independent colors/neutrals to improve things.

Nice graphs, BTW.

[rasworth]

Got it.  At default patch size 405 is the max for an i1Pro on letter.  Tried a couple of combinations, unfortunately no perfect fit without a ton of neutrals.

Richard Southworth

[Doug Gray]

I messed up my in gamut verification prints and assigned the wrong profile when printing so I'm a bit delayed. Also changing the command line default to randomize patches. For some reason the Pro1000 has a small history (near patches) effect that the 9800 doesn't. It's pretty tiny compared to the 9500II where it was more apparent. Randomizing helps a bit but mostly when duplicating patches. There is an override to disable patch scrambling.

Hopefully later Friday.

[dehnhaide]

5. To test created 101 Lab neutrals, L = 0 to 100, a = b = 0, did an absolute rendering intent conversion thru the second pass profile, and printed in i1Profiler target form.  After drying, scanned into i1Profiler, converted from spectrum data to a Lab list via the i1Profiler measurement output capability.

Hi Richard,

Thanks for sharing the workflow. I don't seem to understand how you did the "absolute rendering intent conversion thru the second pass profile". Can you clue me how this done, please! I suspect it's done in CTPbut not sure how!

Thanks

[rasworth]

dehnaide,

You're right, used CTP.  I first generated 101 neutrals in Excel, dumped it out as a txt file and pasted a simple CGATS wrapper around it.  Brought it into a CTP worksheet and did an absolute conversion thru the final BW printer profile (see first attachment).

I dumped out the RGB cgats file, extracted the numeric values back into Excel and rounded them to whole integer values, and pasted back into the original file, now labeled rounded.  It's probably not necessary, but I'm not sure what i1Profiler does with decimal valued RGBs.  I then brought the txt file into i1Profiler as a target patch file and printed it with the i1Profiler command with no color management (second attachment).

The process is quicker to do than describe, and allows one to use an instrument in scan mode, in my case an i1Pro, to read 101 test patches in a minute or so.

Richard Southworth

[dehnhaide]

dehnaide,

You're right, used CTP.  I first generated 101 neutrals in Excel, dumped it out as a txt file and pasted a simple CGATS wrapper around it.  Brought it into a CTP worksheet and did an absolute conversion thru the final BW printer profile (see first attachment).

I dumped out the RGB cgats file, extracted the numeric values back into Excel and rounded them to whole integer values, and pasted back into the original file, now labeled rounded.  It's probably not necessary, but I'm not sure what i1Profiler does with decimal valued RGBs.  I then brought the txt file into i1Profiler as a target patch file and printed it with the i1Profiler command with no color management (second attachment).

The process is quicker to do than describe, and allows one to use an instrument in scan mode, in my case an i1Pro, to read 101 test patches in a minute or so.

Richard Southworth

Thanks Richard for the explanations. Much appreciated!

[Doug Gray]

Richard et al,

You might find this of some value. It's a CGATs file in ProPhoto RGB of Lab values from 0 to 100 and can be loaded into I1Profiler. Then a target chart can be saved as a tif file and assigned the ProPhotoRGB profile. It can then be printed from Photoshop using standard color management in Abs. Col. I've included rounded as well as fractional CGATs. Do not use the fractional with I1Profiler since it can only make 8 bit tifs. The fractional file can be used with PatchTool which does create 16 bit tif files.

I've also included lab.txt and labr.txt for reference. The Labr.txt file contains the fractional Lab values that the rounded, 8 bit rgb file generates. These can differ by just under .4 dE though the average dE between the rounded and unrounded is .1. The printed output from I1Profiler should be compared to the Labr.rxt values.

[dehnhaide]

Richard et al,

You might find this of some value. It's a CGATs file in ProPhoto RGB of Lab values from 0 to 100 and can be loaded into I1Profiler. Then a target chart can be saved as a tif file and assigned the ProPhotoRGB profile. It can then be printed from Photoshop using standard color management in Abs. Col. I've included rounded as well as fractional CGATs. Do not use the fractional with I1Profiler since it can only make 8 bit tifs. The fractional file can be used with PatchTool which does create 16 bit tif files.

I've also included lab.txt and labr.txt for reference. The Labr.txt file contains the fractional Lab values that the rounded, 8 bit rgb file generates. These can differ by just under .4 dE though the average dE between the rounded and unrounded is .1. The printed output from I1Profiler should be compared to the Labr.rxt values.

Thanks for sharing this Doug. Is there another way to print in 16bits TIFF aside from PatchTool? This is yet another paid tool and i1Profiler and CTP are enough of an investment for me.


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