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Author Topic: I1Isis 2 XL, the good, bad, and ugly  (Read 1684 times)

Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #20 on: August 30, 2017, 01:49:39 AM »

You will find color variations from different sources. Photo inkjets will, as you've seen, exhibit variation depending on how the printer/paper combination works. Your hypothesis that the paper hold-down is playing a part sounds reasonable. We see this frequently on wide format Epsons, where there are distinct areas of the page that print slightly differently than others. Laser-exposed silver halide printers (Fuji Frontier, Noritsu QSS, etc.) can show a difference usually from one side of the page to another.
Yes, I see large, repeatable variations, mostly horizontal, on my 9800. These are not present on my 9500 II desktop. OTOH, the 9500 exhibits a sort of "warm up" phenomina where the dE changes almost 3 dE when printing a fairly high saturation red. This occurred after the 9500 had been unused for 24 hours. Checking it against after a 2 hour pause showed about a 1 dE "warm up" period. Nothing odd is showing in the image and nozzle checks have always been clean unless it sits more than a few weeks. The 9800's horizontal patterning is quite consistent, and changes only slightly when altering the vacuum or single/dual direction modes. It did improve about 20% or so using the narrow platen selection. The 9500's ink flow warmup issue is visible in the Patchtool image I attached. As you can see, the first rows have pretty significant dE variation.
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Our targets have a number of repeated patches to detect this variability. We also track the behavior of similar colors across the page (e.g. target values with consistent, small offsets) to see if they are consistent. We preprocess each file before feeding to the profiler. The key is to determine whether variations are (a) significant and if so (b) is the printer setup within normal parameters.
My initial test was with a 512 patch set that included 64 distributed RGB patches randomly placed and repeated 8 times. The fact there was significant variation in patches of the same color compared to reading the same sheet and comparing readings of the same patches kicked me off down this rabbit hole.

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Looking at variation, it is worth first checking the level of variability from the iSis itself. A straightforward test is to measure a blank page. Simply print the positioning bar and side markers and measure. Using an OEM paper (Canon or Epson) with a lustre surface will give uniformity well within what the iSis can resolve. We also printed the iSis fiducial marks on pvc sheets of various colors to see how the iSis behaves on colors other than white. Gather short-term repeatability data as well as measurements a day or two apart. You'll derive a baseline for instrument performance.
Funny you should mention that. I did just that earlier today out of curiosity as to whether there was some sort of trend from the start of reading patches as the sheet scan progresses. The I1 Pro shows a significant drift (.2 to .3 L*) and drift from the illuminant has the largest impact at high luminance. Turned out to be less than .1 from start to end. Frankly, I was rather pleasantly surprised.
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Start customizing the canned targets and preprocessing. We toyed with the idea of creating targets with identical patches per page but different layouts. You'll need to average the data first (stay in the spectral domain!) before feeding the summarized data file to i1Profiler. We ended up not going this route for a couple of reasons. First, we typically did not read variations sufficiently far from the iSis noise floor to be worth the doubled measurement times. Also, we have the luxury for most of the profiles we build of having hundreds of the same model of printer to build a reference form. At that point, a significant portion of the profile generation hinges on eigenvectors rather than only the raw data.
Averaging the data is pretty straightforward. I use Matlab as I find it's easier but I understand I1Profiler will average files if you select both and drag and drop. Haven't tried it though.

Curious as to how you use eigenvectors in profile generation. I've kicked around doing some principal factor analysis to see if the spectral functions could be reduced (mostly - SVD here we go) to a linear group in 3 space. and then one should be able to find a matrix to convert linearized scanner RGB to XYZ. I doubt it would work with the 9500 since that has a green and red ink as well as the CYMs. OTOH, the 9800 just uses CYM and lightened version of C and M so it might have a better shot
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #21 on: August 30, 2017, 11:30:47 AM »

Looking at variation, it is worth first checking the level of variability from the iSis itself. A straightforward test is to measure a blank page. Simply print the positioning bar and side markers and measure. Using an OEM paper (Canon or Epson) with a lustre surface will give uniformity well within what the iSis can resolve.

I wanted to test both the consistency of the Isis and get some idea of the production consistency of the (cheap) Costco glossy media I'm using to refine processes before expanding into OEM or specialty media. So I pulled two sheets from the new Costco package and rotated 1 relative to the other 180 degrees which flips top/bottom and right/left. These were then printed with the registration marks and form a 841 patch set 29 by 29 with the default 6 mm patch sizes.

Two Isis read scans were done with each paper. The variation, small as it is between the two papers, is far smaller comparing two scans with the same paper.  Yes!

This says volumes about the excellent Isis repeatability and good positioning to the registration marks. Very low noise baseline.

About .11 ave dE between the two papers and .02 dE on the same paper. See attachments.

The 4 scans were done back to back with the fast, 1 pass (M2) mode over a 10 minute interval.
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #22 on: August 30, 2017, 01:16:43 PM »

>> I see large, repeatable variations, mostly horizontal, on my 9800. These are not present on my 9500 II desktop. OTOH, the 9500 exhibits a sort of "warm up" phenomina where the dE changes almost 3 dE when printing a fairly high saturation red. This occurred after the 9500 had been unused for 24 hours.

Test protocol: For each printer, the Canon 9500 II and the Epson 9800, a page of 512 patches containing 8, randomly located, groups of 64 max spaced RGB triplets was printed. The pages were scanned and each set of 8 patch samples of the same colors were read for both printers. The RGB triplet with the maximum average deltaE on the 9500 and another on the 9800 was used to create a 841 patch set in a square, 29x29, of 6 mm identical patches. These were printed and scanned with the Isis. In both cases the major contributor to Delta E was b* variation so that was the variable studied.

The scans, a matrix of 29 rows by 29 columns was averaged horizontally to determine vertical variation and averaged vertically to determine horizontal variation. Each of these produced a length 29 vector. Attached charts labeled "Horizontal Variation" is a plot of the 29 points, (left to right paper in profile) from averaging each column. "Vertical Variation" charts were row averaged producing a vertical column vector. The 29 points is the average  b* values from top to bottom.

A note about the error bars. These are the standard deviation of the set of 29 samples from which that point on the chart was determined.  Thus, they represent the error bars of samples orthogonal to the plot line. When the horizontal variation is greater than the vertical variation the error bars shown on the vertical plot will also be higher and vice versa. Please note that these error bars are per sample that makes up the point. The error bars of the averaged point itself would be a bit over 80% narrower.


Note the strong shift in *b in the top portion of the Canon 9500 chart representing the average  change vertically. It's useful to compare that to the Patchtool 9500 chart dE chart posted earlier.

Also, the Epson 9800, in a reverse of the Canon 9500, shows more variation horizontally than vertically. This is consistent with what Ethan noted about wide format Epson printers.
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #23 on: August 30, 2017, 05:35:00 PM »

More good stuff from the I1 Isis 2.

In order to rule out whether the Isis was reading some portion of adjacent patches I made a special target file with 841 (29x29) 6 mm black patches. Then I added white stripes .25 mm inset from all patch edges. This changes the actual black patch sizes to 5.5 mm square with white filling the gaps between patches. This maximizes light leakage and makes it easy to detect since the reflectance of the black patches is very low. At DMax of L*=4 (my 9800's BP) leakage of .01% would produce an increase of .9 L*. Running this chart, even with a slight angle tilt, showed no signs of adjacent patch light leakage.

I've included a tif image of the target which anyone can use with an Isis. Just scan it into a target of 841 patches using the defaults and a standard letter size profile page. Save the results as a CGATS files and read it with a text editor or graph the L* values in Excel.

I am way more comfortable now that any variations I see are actually on the media and not leakage from adjacent patches.
« Last Edit: August 30, 2017, 05:58:33 PM by Doug Gray »
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #24 on: September 02, 2017, 05:14:01 PM »

Building on some of the observations and comments, I created two, 9800 glossy profiles using the Isis default target of 957 patches with the following differences:

Target 1: The patches were duplicated then randomized producing a two page target but with the patches randomly scattered.

Target 2: The patches from one default target were duplicated then the columns were relocated. Each column was placed at the max and min horizontal deviation (sorted col extremes). As these columns were filled the two extremes were removed and the process repeated. This also yields 2 target pages where each of the default patches are duplicated though at positions where the horizontal inking variation tends to cancel.

Targets were printed, scanned, and profiles made. Then my 389 patch set of in-gamut LAB colors was printed using the two profiles. This differs from things such as the dE report from ColorThink which reports on the reverse lookup of RGB values and compared them to the target's scanned LAB values. This uses the AtoB1 tables in ICC profiles. Printing photos (colorimetric) does not use AtoB1 tables and only uses the BtoA1 tables.

Here are the statistics on the two, 9800 profiles which use exactly the same patches and page size but with the patches re-ordered to cancel the effect of the predictable portion of horizontal positioning inking sensitivity. Results in Delta E 2000.

CG BASE: dE's-> ave:0.46  median:0.42  <90%:0.75    chart max: 1.36
CG OPT:   dE's-> ave:0.39  median:0.35  <90%:0.67    chart max: 1.16

I consider both of these results to be well within what I would expect for a high quality profile given the relatively small number of unique (957) patches.

The BASE profile benefits from averaging targets with randomly scattered patches while the OPT benefits from strategically placing the patches such that most of the observed horizontal inking variation in the wide format 9800 cancels.


Side Notes:
The inking variation occurs most frequently on channels with a lot of added yellow. Magenta and cyan dominant colors show less pattering. Speculation is that there is only one "Y" ink whereas there are light versions of cyan and magenta.

Also, this technique of compensating for horizontal variation only improves the profile accuracy to the extent the profile is generated from affected patches . Variation in the printed image itself will exhibit this variation but no longer has the risk of compounding variation in creating the profile and variation in printing using the profile.
« Last Edit: September 02, 2017, 05:27:04 PM by Doug Gray »
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