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Author Topic: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests  (Read 4916 times)

Doug Gray

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One of the cool things about the work I've done on my own printers is a good design to quantify just how much better profiles get as patch counts increase. This is done by aggregating the RGB patches for all the different profiles being tested, removing the duplicates, then randomizing them so they are spread over all the printer target pages.

The printed targets are then scanned and a program takes the spectral data, descrambles it, and pulls out each of the individual patch sets from which I1Profiler (or Argyll) constructs all the profiles. The profiles can then be individually compared with the largest patch count profile in the set, or even a profile constructed from the total aggregate of patches. Since the profiles are scrambled and randomly distributed across all the printer pages, things like warmup affect all the profiles equally, in a statistical sense. I gather statistics by roundtripping a million or so, in gamut colors and compare the dE00 stats for each of the created profiles. All pretty automatic.

So one can compare profiles without the variation that occurs printing a profile set, making a profile, printing another set and making another profile. When done this way, the changes in virtually anything like temperature, humidity, or even subtle paper differences can easily counter small differences in large patch count profiles and produce confusing and potentially misleading info.


So what's with the crowdsourcing?
I've been kicking around the idea of possibly collecting information on printers and how many patches are needed for a decent profile. This technique only requires printing a set of target pages but will identify exactly how much improvement occurs as patch count increases including various, additional near neutral counts. Thus, if folks are interested in contributing their printed target pages (I will supply the Tiff images of US letter size targets, readable on my i1iSis). All you guys need to do is print them out, dry them for a few days, and mail me them. In return you will get statistics and a collection of (Argyll) profiles since I'm not licensed for making other people's profiles with I1Profiler. Since I get consistent relative differences with Argyll and I1Profiler, this should provide a great deal of info on exactly what one can expect using different patches and especially just where increasing patch count provides little improvement. Should help a lot for people that are using I1Pro's or even CMs for scanning.

I'm initially thinking of image sets of increasing page counts of from 3 to 10 or more with each page having 957 printed patches. The larger set sizes are needed to provide data for really large patch counts but this really isn't needed except perhaps for high end printers and possibly not even then. As an example, my 9800 needs about 2k patches to have the same quality profile as the Pro1000 even though the Pro1000 has a larger gamut.

However, I'm not in the business of making profiles and don't intend to be. This is pure just something I would find fun to do and the information could be more broadly useful. Might also influence what printer I next buy if and when. So I need to collect data on different printers/paper. If the printer/paper is new, I will send you my mailing address and a link to the images which can be printed using ACPU or similar utility that can print w/o color management. Then dried and mailed. I'll do the rest.

What do you folks think?
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samueljohnchia

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #1 on: June 22, 2019, 08:03:39 am »

Hi Doug, fantastic idea and thank you for offering your immense expertise and time to do this. I happen to have an iSis XL (Rev E) and I wonder if it would save you some trouble if I make the measurements myself and email you the data? I am happy to make as many prints as needed to collect all the data needed. I generally prefer to use larger patch sizes than you typically use to minimise measurement errors, even though it takes a bit more ink and paper. My printer is a Canon iPF8400. Original inks of course. I can run both a very high quality matte and glossy paper.
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samueljohnchia

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #2 on: June 22, 2019, 08:09:56 am »

I have noticed in my earlier, less elaborate testing, that my iPF8400 does not benefit much from larger patch counts with the neutrals improving marginally and that's it. I am interested to discover if it has "warm up" issues like your Pro 1000 does and if printing certain adjacent colours has a kind if memory effect or influential effect on each other that might be attributed to the thermal head design. Uniformity across the sheet. That kind of thing. Great that the iSis is so repeatable and precise that it can be trusted to pick up subtle issues like this.
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Daverich

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #3 on: June 23, 2019, 08:35:36 am »

I would be happy to participate. I have an Epson P5000.
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #4 on: June 23, 2019, 11:20:31 am »

Hi guys,

I expect to post US letter size, 8.5" x 11" tiff targets in the next week. There will be separate sets of charts for those using Adobe's ACPU with Windows to recover most of the 3% "shrinkage" ACPU with Windows produces.

This is a bit tricky since my I1iSis charts are symmetrical with registration bars at the bottom as well as the top. This allows the chart to be read in reverse which is handy for detecting certain errors. It also provides slightly better color reading accuracy. It's important that the prints will have no less than 27mm of margin from paper edge to the registration bars on the top and bottom.

I will post a tweaked test chart, including one for Windows ACPU, so you won't waste paper if, for some reason the charts won't print with enough margin for the top and bottom registration bars.

While not the principal purpose, these charts also include a small set (25) of multiple, repeated patches. These are also randomized, to quantify paper/printer color consistency.
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Mick Sang

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #5 on: June 24, 2019, 10:53:55 pm »

Quote
Thus, if folks are interested in contributing their printed target pages (I will supply the Tiff images of US letter size targets, readable on my i1iSis). All you guys need to do is print them out, dry them for a few days, and mail me them.

Quote
I expect to post US letter size, 8.5" x 11" tiff targets in the next week.

Great Idea. I'm in. I look forward to seeing the targets.

Mick
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Alan Goldhammer

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #6 on: June 25, 2019, 09:14:18 pm »

Hi guys,

I expect to post US letter size, 8.5" x 11" tiff targets in the next week. There will be separate sets of charts for those using Adobe's ACPU with Windows to recover most of the 3% "shrinkage" ACPU with Windows produces.

This is a bit tricky since my I1iSis charts are symmetrical with registration bars at the bottom as well as the top. This allows the chart to be read in reverse which is handy for detecting certain errors. It also provides slightly better color reading accuracy. It's important that the prints will have no less than 27mm of margin from paper edge to the registration bars on the top and bottom.

I will post a tweaked test chart, including one for Windows ACPU, so you won't waste paper if, for some reason the charts won't print with enough margin for the top and bottom registration bars.

While not the principal purpose, these charts also include a small set (25) of multiple, repeated patches. These are also randomized, to quantify paper/printer color consistency.
I am in Banff on vacation ship it's  a bit difficult to respond on my android tablet.   Dry Creek Photo developed a windows app for printing out targets that does NOT reduce the size of the patches the way ACPU does.   I have been using t this successfully.   You might check with Ethan Hansen or look for it on their website.

I'm also happy to participate with my Canon Pro-1000 and would be interested to compare results with my Argyll workflow,

Alan
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digitaldog

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #7 on: June 25, 2019, 09:19:37 pm »

Scaling with ACPU on Windows isn't a problem measuring with an iSis XL if the targets are made ideally (to avoid the bug). And of course the end user properly sets up his/her printer driver for paper/size.
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #8 on: June 25, 2019, 11:27:17 pm »

Scaling with ACPU on Windows isn't a problem measuring with an iSis XL if the targets are made ideally (to avoid the bug). And of course the end user properly sets up his/her printer driver for paper/size.

Actually, when I print targets 6mm x 6mm, with ACPU they scan fine, but they are shrunk to just over 5.8mm.  But I don't like operating on the edge and if I resize them just another .5% smaller, so they print about 5.75mm wide, the iSis XL kicks them out.

The issue I'm trying to solve is to make sure the 6mm wide registration bars have enough margin at the top as well as the bottom of the print since I add a registration bar at the bottom so the target can be read in reverse. The iSis design is 30mm margin. Testing shows that it works fine down to 28mm and at 27mm it gets marginal. The 957 patch set of 33 rows and 29 columns just fits on a 8.5 x 11 paper with about 2 mm or so to spare providing the paper is printed so that the top margin is close to the bottom margin. Normally, I print in Photoshop and futz with the top offset so the print is centered. My Canon printers do a good job of centering automatically in Photoshop but the 9800 doesn't. Seems it's idea of centering is the printable area and not the physical page. This seems to be because the 9800 has a larger unprintable margin on the bottom than the top.

Luckily, ACPU centers on the physical page, and just clips unprintable portions. But that is not an issue as the targets don't have ink there.

The issue with ACPU is the shrinkage in Windows. However, testing indicates that a simple resize (nearest neighbor) expanding the page 2% or so works great. It provides that extra bit of margin to keep the iSis happy by slightly reducing the shrinkage and, luckily, provides decent margins on both the top and bottom registration bars.

The remaining problem is, when printed on an Apple which doesn't shrink the print, the registration bars get nearer the top/bottom of the paper. And I need to make sure there is at least 28mm on both.

I may have to provide two sets of targets. One for ACPU with Windows and one for utilities that print properly like Photoshop (with the null print trick to work around their stupid removal of the ability to print directly w/o color management).
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digitaldog

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #9 on: June 26, 2019, 09:42:18 am »

Actually, when I print targets 6mm x 6mm, with ACPU they scan fine, but they are shrunk to just over 5.8mm. 
It's like the man who goes to the doctor and says "When I do this, it hurts" and the doctor replies, "well don't do that".  ;D
We really have IMHO, two bugs. One is ACPU on Windows but the other is X-rite's and what happens when you build a patch size they believe is Kosher. Anyway, I've been scanning targets through ACPU, Mac and Windows for a very long time without issue because I made adjustments for one of the bugs. That doesn't mean user error can't rear it's ugly head so what I did was place a line on the target indicating the size it should print so the user can place a ruler and see if it's within +/- a value I know will scan. No problems.
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #10 on: June 26, 2019, 11:43:11 am »

It's like the man who goes to the doctor and says "When I do this, it hurts" and the doctor replies, "well don't do that".  ;D
We really have IMHO, two bugs. One is ACPU on Windows but the other is X-rite's and what happens when you build a patch size they believe is Kosher. Anyway, I've been scanning targets through ACPU, Mac and Windows for a very long time without issue because I made adjustments for one of the bugs. That doesn't mean user error can't rear it's ugly head so what I did was place a line on the target indicating the size it should print so the user can place a ruler and see if it's within +/- a value I know will scan. No problems.

Yep, adjusting the patch size to overcome ACPU/Windows shrinkage works just fine for printing standard targets. And a single image works great with ACPU on Windows and Macs. And I was perfectly happy with this. Until recently that is.

Here's my problem in some depth:

I noticed a relatively rare anomaly. On occasion, I saw a large difference ( > 3 dE and in a couple cases 10 dE) in some duplicate patches and investigated. Turns out under some conditions a tiny difference in the spectral data can cause pretty large Lab changes. These occur with a highly saturated C, Y, or M inking which produces a very small reflectance over the portion of the spectrum. In these situations, a small change ( < .5% ) can produce quite large variations in dE. This can occur because of a nearly invisible dust particle adhering to the print, surface variations on the paper itself, or even actual variations in the printer inking.

This can be partially detected by doing repeat scans. But only partially. This led me to create charts that had a registration bar at the bottom and allows me to scan the chart in reverse (bottom to top, right to left). When doing precision work, I scan charts in both directions and save the full CGATs files appending a "r" on the reverse scans. When reading in the CGATs, my program inverts the order of reverse scans and averages the two but also tests the dE for each patch to detect these anomalies. When one exists the program examines the spectral data. Invariably, the difference is a slightly raised spectral reflectance in the region with very low reflectance.

So by printing the targets with top and bottom registrations, this problem, while rare, can be detected and reduces the number of rabbit holes I've gone down.

But this constrains the target print. If I increase the patch sizes to accommodate ACPU/windows shrinkage, there isn't room for the necessary top and bottom margins when printed using other programs w/o shrinkage. I can, of course, increase the patch width but then I can't fit 33 rows on an 8.5 x 11 page.  Normally, this isn't an issue as I don't use ACPU for printing other than as a crosscheck.  Annoying.
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digitaldog

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #11 on: June 26, 2019, 12:22:00 pm »

When doing precision work, I scan charts in both directions and save the full CGATs files appending a "r" on the reverse scans.
Be interesting and perhaps produce better overall data if the target were printed twice but the patches themselves be in reverse order. Yes, I know that's two instead of one page.

When I was creating digital press output profiles, the variation across the page is so large, I built targets just like this and in fact, I had a total of (ugh) multiple 13x19 pages: there was a three page target with large patches and a two page target with smaller patches. The patches themselves otherwise had the same colors and as you're doing, the targets had the same patches for some special colors repeated on the sheet. One of each group was rotated 180 degrees. Yes, lots to measure (considering we ran this group of targets multiple times over the days and measured all). With large and small patches, we sample more area over the press sheet and differently with respect to the patches being measured. Same when one rotates each target. Then all that was averaged into one CGATs. Now run this test a few dozen times over the span of a few days, examine each group of averages, see if outliners should remain, average all the averages, run em through ColorAnt.... A lot of work but good pay  ;D

But this is very likely overkill for inkjet work where the dE differences  over the sheet are nothing like we see with digital presses. Maybe two targets with 180 degree rotation would be more than enough. But yeah, it's one more page to print (and scan).
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #12 on: June 26, 2019, 01:33:20 pm »

Be interesting and perhaps produce better overall data if the target were printed twice but the patches themselves be in reverse order. Yes, I know that's two instead of one page.

When I was creating digital press output profiles, the variation across the page is so large, I built targets just like this and in fact, I had a total of (ugh) multiple 13x19 pages: there was a three page target with large patches and a two page target with smaller patches. The patches themselves otherwise had the same colors and as you're doing, the targets had the same patches for some special colors repeated on the sheet. One of each group was rotated 180 degrees. Yes, lots to measure (considering we ran this group of targets multiple times over the days and measured all). With large and small patches, we sample more area over the press sheet and differently with respect to the patches being measured. Same when one rotates each target. Then all that was averaged into one CGATs. Now run this test a few dozen times over the span of a few days, examine each group of averages, see if outliners should remain, average all the averages, run em through ColorAnt.... A lot of work but good pay  ;D

Cool job.
Quote

But this is very likely overkill for inkjet work where the dE differences  over the sheet are nothing like we see with digital presses. Maybe two targets with 180 degree rotation would be more than enough. But yeah, it's one more page to print (and scan).

Your point about changes in color when patches are printed at different locations was something I noticed too. And it's still a significant factor with ink jets though not anywhere near what you were seeing in pre-press. I wound up making a small, 64 count, set of RGB colors, repeating each 16x, then randomizing them. Can just squeeze them onto one iSis page w/o a bottom registration bar. Then adjusted the various settings in the 9800 to minimize the overall variance. The two settings that affected things the most were the vacuum level and platen gap. Got about a 40% reduction in variance.

And the variation in patch location color still overwhelms the much smaller differences of re-reading the same print or even reading the printers in reverse.

One of the things I'm doing in constructing my patch set is to incorporate a small set of repeating patch colors so I can get  similar metrics on submitted samples. It has a particularly large impact on neutral and near neutrals so the set is heavy on these. I'm curious about how well the different prints do at this.

I'm retired with time and money, a dangerous combination. :)
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Mick Sang

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #13 on: June 28, 2019, 10:06:10 pm »

Quote
I'm retired with time and money, a dangerous combination. :)

Life is short. So why not live dangerously and have some fun!
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Alan Goldhammer

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #14 on: July 01, 2019, 09:13:08 am »

Back from Banff and able to better post links.  Here is the Dry Creek Photo Print Utility for accurate scaling of patch sets under Windows.  As I noted in my earlier email, this utility does not shrink patch sets as the ACPU does.  I've been using it without any issues.
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #15 on: July 01, 2019, 11:44:01 pm »

EDITED:

Please use the "Medium" patch set posted later, not the "small" target set attached here.
This provides much more printer info and, better, lets me actually determine the accuracy of the printer without a round-trip to print Lab values.

The trick is to use a special, reverse lookup by doing an exhaustive search for the Lab values that produce the RGB values from the profile under test.


Sorry for the delay. I've reconfigured the test charts to focus more on neutrals and near neutrals since that is a much bigger problem than how many color patches there are. In fact, it takes some work to get the neutrals printing as well as color patches with color patch counts over about 400!

Attached is a zip file with two sets of charts. One for ACPU/Windows and one for utilities that print profile charts without re-sizing.

See the readme.txt file for more info. From the readme:

---
These charts contains the following:

Regular grid spacing of 4x4x4, 5x5x5, 6x6x6, 7x7x7, 8x8x8, and 9x9x9. Also, for 8x8x8 and smaller grids inset grids are also included which somewhat optimizes (AKA packed grids). Additionally, a partial 17x17x17 grid is included. This grid is all the values from 64, 80, ... 192. It is used to get a measure of the improvment in color patches by testing distributed colors within that RGB region against both it and the 9x9x9, which has exactly twice the spacing. My printers exhibit rapid assymptotic approach to an optimal that occurs around 3,000 patches. This high res subset is designed to compare the benefit witihout having to print the full 4913 patches required for just 17x17x17 grid.

But wait, there's more.

Turns out neutrals and near neutrals are much bigger problems with patch color accuracy deviations much larger. However, this can be improved markedly by a fine RGB grid along the neutrals.

So there are a number of near neutral data sets included. In particular a full, 3 level grid along the neutrals with deviations of 7 and 14 are included as in this pattern:

   0     0     0
     0     0     7
     0     0    14
     0     7     0
     0     7     7
     0     7    14
     0    14     0
     0    14     7
     0    14    14
     7     0     0
     7     0     7
     7     0    14
     7     7     0
     7     7     7
     7     7    14
     7    14     0
     7    14     7
     7    14    14
    14     0     0
    14     0     7
    14     0    14
    14     7     0
    14     7     7
    14     7    14
    14    14     0
    14    14     7
    14    14    14
    14    14    21
    14    14    28
    14    21    14
    14    21    21
... to 252


Since these include smaller spacing 7 and 14, the following patterns to make profiles with are "free"

     0     0     0
     0     0     7
     0     7     0
     0     7     7
     7     0     0
     7     0     7
     7     7     0
     7     7     7
     7     7    14
     7    14     7
....

And
     0     0     0
     0     0    14
     0    14     0
     0    14    14
    14     0     0
    14     0    14
    14    14     0
    14    14    14
    14    14    28
    14    28    14
....


All of this data is used to generate metrics such as the deviations between successive points on a line and deviations of centers from points equi-distant. These metrics correlate highly with actual profile errors printing a large, 100 to multiple hundreds, of independent, gamut distributed color patches. The neutral sets provide similar results for estimating neutral color accuracy. They also highly correlate.

Right now I am running checks on the new, inserted high rez grid and, most importantly, various near neutral RGB sets. Turns out this is a much more critical area than the more general color accuracy in even slightly saturated colors. This reflects the greater sensitivity that Delta E 200 has in this area.

I will be posting metrics and their correlation to actual printed Lab colors distributed evenly in the printable gamuts of my three printers. Focus is on glossy. I use Costco glossy as it's cheap and all my tests v Canon Plat Pro, show the performances on my two Canon's are virtually identical outside of a small gamut shift due to the Plat's warmer white point.

« Last Edit: August 08, 2019, 01:42:23 am by Doug Gray »
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Alan Goldhammer

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #16 on: July 02, 2019, 10:27:15 am »

Let us know when you are ready for prime time and if you have any preference for brand and type of paper for testing.  I print on matte and gloss papers and pretty much use Moab (Entrada, Juniper, & Somerset), Hahnemuhle (Bamboo & Photorag Ultra Smooth) and Museo (Silver Rag).

Alan
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #17 on: July 08, 2019, 02:10:29 pm »

One of the benefits of a chart that combines different patch sets is one can then get actual accuracy improvements for different printers/paper combination.

Here's the results from Costco Glossy on 3 the Pro1000, 9500 II, and 9800 and Canson Rag Photo on the Pro1000. Results are quite consistent between paper types on each printer but vary considerably for each printer.



These results are made using random, in gamut colors in sufficient quantity to see the increasingly small improvements as profile patch count is increased. This required from 150 to 500 patches for each profile/printer being tested. This results in high relative accuracy. The relative patch count differences between different runs with different randomized colors is repeatable to a standard deviation of less than .02 dE00 for the higher patch counts ( >= 512( and .04 dE00 for the small counts of 125,216.

A notable result is that the Pro1000 requires only 343 patches to achieve the same quality (Ave dE about .7) as the 9800 and 9500 II using 729 patches.

Also, Once one gets to 512 or 729 patches, the improvements are quite small. Particularly on the Pro1000. Going to 2500 patches produces only between .03 and .10 dE00 improvements.

These results are all from Argyll profiles with default except for  -qh and -r .3 options.

Not shown was that I also compared Argyll with I1Profiler profiles. They are quite similar with less than .1 dE differences. Interestingly, the Argyll outperformed the I1Profiler on the 9800 by .10 dE while the Argyll profiles were slightly better at .03 or so with the Pro1000.


An aside. These were done w/o additional, near neutral patches. They are quite important but the near neutral response differs quite a bit between the two printers. The patch set includes various near neutrals but even though the printers differ significantly from each other in near neutral response, the various near neutrals tested (from about 200 to 600 patches) produced little difference from each other but a large improvement in near neutral accuracy. I'm going to create a similar chart focusing on near neutrals.

Also, testing the "packed" profiles produced improvements but only in proportion to their increase in patch count so I see little reason to continue that line of work. I had seen somewhat larger relative improvements in them but after changing the verification phase to randomly select in gamut Lab values rather than evenly spaced, in gamut values, the differences reduced to fairly low levels.
« Last Edit: July 08, 2019, 03:36:18 pm by Doug Gray »
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RobWignell

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #18 on: July 15, 2019, 08:26:36 am »

Hi Doug

This is really useful information to me.  With far fewer tools for analysis I have played with increasing numbers of patches starting at around 500 per page and increasing the number of pages.  I use a DTP70 for reading patches and it seems to read more consistently with patches >= 9.0mm square.  Through general reading I had concluded that for the best RGB profiles, patch sets >= 2000 are recommended.  My experience is that I generate what seem like competent icc profiles with patch sets around 1000 and that while using larger patch sets might produce small improvements in DE numbers the effect on a printed image is imperceptible.

I notice that you are using a -r setting of 0.3 in Argyll's colprof instead of the default 0.5.  For me, this usually increases the Gamut Volume slightly but can introduce kinks in the gamut model surface, especially in the darker areas.  Have you had this experience?

I would be interested to see what settings you use for targen to generate your patch sets.  In particular, do you use targen to emphasise neutrals.

For experimenting, I use Kodak Ultra Premium High Gloss paper on my Epson 3880 and Epson 7880 (COSTCO stopped selling Kirkland Glossy in Australia a couple of years ago).  I bought the Epson 7880 back from the dead about 18 months ago using cheap 3rd party ink and, once I got it going properly I loaded a set of Cone inks. 

I would be pleased to send you a set of prints on the Kodak paper.
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Doug Gray

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Re: Possible Crowdsourcing Printer Profile Optimal Patch Count Tests
« Reply #19 on: July 15, 2019, 04:26:07 pm »

Hi Doug

This is really useful information to me.  With far fewer tools for analysis I have played with increasing numbers of patches starting at around 500 per page and increasing the number of pages.  I use a DTP70 for reading patches and it seems to read more consistently with patches >= 9.0mm square.  Through general reading I had concluded that for the best RGB profiles, patch sets >= 2000 are recommended.  My experience is that I generate what seem like competent icc profiles with patch sets around 1000 and that while using larger patch sets might produce small improvements in DE numbers the effect on a printed image is imperceptible.
This is consistent with what I'm seeing too. My newest printer, Pro1000, needs fewer patches by almost half to achieve the same quality as my older printers, a 9800 and especially the 9500II. The latter benefits a lot from 2-3k v 1k patches while the Pro1000 gets little better beyond 1k patches.
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I notice that you are using a -r setting of 0.3 in Argyll's colprof instead of the default 0.5.  For me, this usually increases the Gamut Volume slightly but can introduce kinks in the gamut model surface, especially in the darker areas.  Have you had this experience?
No, I haven't seen any difference. OTOH, I scan targets forward and reverse/upside down, and average the readings while looking for large outliers. This reduces scan noise to some degree though not variation related to patch location, a somewhat larger factor.

However, your observations suggest another issue. One quite real but experimentally difficult to measure. Much more important than absolute color accuracy is smoothness. A printer/profile that isn't smooth will produce much more problematic prints on images with lots of gradual gradients. It's extremely hard to see a 1.5 dE error if otherwise the print is smoothly rendered. It's something not normally measured. One of my goals in buying a scanner was to use it to measure printer smoothness but that's when I discovered how large the effect of large area crosstalk was and went down that rabbit how to determine the cause and ultimately developed a program to remove the crosstalk.

I had an idea that may work for getting a smoothness metric, not just metrics on color accuracy. It's something I'm currently working on as it may be a more useful metric than color accuracy.
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I would be interested to see what settings you use for targen to generate your patch sets.  In particular, do you use targen to emphasise neutrals.

I use Matlab for chart creation as well as verification charts. Verification charts typically use Lab values that are randomly picked over the printer/paper gamut using a custom program. The Lab values are converted to rgb device space using the profile(s) under test. After printing/scanning, the dE00 variations between the initial Lab values and the printed/scanned ones are gathered and stats reported. By converting the same Lab values into device space using multiple profiles one can compare the stats for the different profiles w/o the complication of small printer variations that occur like warmup drift.
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For experimenting, I use Kodak Ultra Premium High Gloss paper on my Epson 3880 and Epson 7880 (COSTCO stopped selling Kirkland Glossy in Australia a couple of years ago).  I bought the Epson 7880 back from the dead about 18 months ago using cheap 3rd party ink and, once I got it going properly I loaded a set of Cone inks. 

I would be pleased to send you a set of prints on the Kodak paper.

I'll PM you.
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