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Author Topic: I1Isis 2 XL, the good, bad, and ugly  (Read 3662 times)

Doug Gray

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I1Isis 2 XL, the good, bad, and ugly
« on: August 19, 2017, 08:13:17 PM »

Well, after getting tired trying to get more out of an I1Pro 2 than it perhaps can offer, I bought the XL. and am putting it though its paces to understand its capabilities as well as limits. Initial tests show a few things:

1. The instrument produces highly repeatable chart readings. The Isis default patch set, 957 patches, fits on letter size sheet. Successive reads produced average dEs of 0.04, and a max dE of .45 on glossy paper. This compares to about .20  with a max of 1.9 with the I1Pro 2 on a 918 patch set with two sheets. Much of this is likely due to the precision feeding and automatic registration of the Isis. So it is reading almost exactly the same locations on the patches. Reading patches printed on different sheets shifting the image slightly produces variations similar to the I1Pro.

2. I hand measured a set of 64 RGB patches evenly spread through the RGB gamut with a distance of 85 (see patchtool) on an Isis target and compared them to the Isis measurements. The average dE was .45 and max was .9.  This was better than I expected as my I1Pro 2 is over 5 years old and has never been factory calibrated. Remarkable, really.

Now for the bad news.

The Isis moves paper using bottom wheels spaced about 2 cm apart and top wheels that are spaced 4.2 cm apart and the top ones can leave "tracks." [added: The 4.2 cm "top wheels" are fixed and seem to be for the purpose of keeping the paper flat]  For glossy prints that have dried for 24 hours, the tracks are nearly invisible and there is no significant impact on the Isis readings. But for thick Luster papers the wheels appear to flatten the paper and create a region, about 1mm wide, where the colors appear, and measure, a more saturated color. For instance a light yellow patch (RGB 255,255,170) produced a b* of 32.40 but on a patch with a tread running through it the b* was 35.54.  Wow!

However, that paper, a Baryta paper, is 300gsm and 16mils thick (.41 mm) which is just under the max thickness of .45 mm the XL can handle. It is likely a smaller effect with thinner paper and is not a significant effect with glossy.

The good news is that the treads are spaced such that it only affects one of every 7 columns so one possible solution is to create a specific patch set that fills the columns were the tread wheels track with blank patches. This would decrease the max number of useable patches by 1/7th but would be pretty solid. This is pretty easy to do with a program script to manipulate CGAT files.

A second approach would be to shift the paper to either the left or right such that the wheel marks were centered on the transition where one patch goes to the next. This should work quite well if the paper alignment is sufficiently repeatable. It has to pretty much ignore readings within 1.3mm or so of that transition to work.  I'm currently testing that.

Here's a cell snap  showing the wheel marks on Finestra BaryTa Fine Art 16mil paper. This was taken in sunlight arranged so that the reflectance showed the wheel marks. There are extra tracks a cm or so apart in the image as I read the paper offset about 1 cm to see the effect of additional tracks.

As an aside, the effect is most noticeable on more saturated colors and not the neutral grays. The dE 2000 differences are much smaller. < 50%. So I doubt this would be visible in photo prints. Overall, it's still better, on average, than manual scanning with an I1 Pro2 and far better with glossy.
« Last Edit: August 22, 2017, 09:13:10 AM by Doug Gray »
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danstart17

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #1 on: August 20, 2017, 04:50:38 AM »

Wow, that's pretty bad.

I'm just getting started with colour management and got the i1pro2, are you using i1profiler to read the charts or a 3rd party?
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #2 on: August 20, 2017, 11:37:16 AM »

Wow, that's pretty bad.

Not really that bad. The light was set up to show the tracks. It's actually not that obvious on the prints.

I'm just getting started with colour management and got the i1pro2, are you using i1profiler to read the charts or a 3rd party?

The Isis 2 XL comes with I1Profiler which can be used to create and print charts.

It does not include a license for I1Profiler profile making s/w, but if you have an I1 Pro and I1Profiler already it will use that license. It can also read targets and save scans in CGAT format for use with other profiling software such as Argyll.
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #3 on: August 20, 2017, 04:40:07 PM »

I made a target of 58, all light yellow RGB (255,255,170), patches. Printed it and scanned with the Isis 2. This makes it easy to both see the wheel tracks and plot the "yellowness" change from the track impressions. There are two rows of 29 patches, all the same light yellow.

Attached is a snapshot showing specular surface reflection as well as a Matlab plot of the b* component of the measured Lab values of each row of patches. The graph has been stretched so that the excursions of b* align with the image. The wheel mark excursions are from about .5 to about 1.5 dE over the average baseline. When carefully measured in tiny steps with an I1 Pro, the peaks go up to over b*=35. Clearly the Isis is averaging over some portion of the 6mm patch size and not just reading it at the peak so expanding the patch width should provide improvement. But how much remains to be seen.

Also, the secondary wheels are every 12 mm and leave visible tracks too but aren't showing up on the measurements.


Additional Info:
I ran the test with a patch width of 6.0 and 7.0mm on glossy media and let dry only 30 minutes. There is a very slight evidence of change from the wheels with the glossy. And, it turns out the 7.0 width just happens to align fairly closely with the patch transition edges.

Much better results.

First and second scan comparisons:

6.0 mm:  Average=.04 dE, Worst case=.37dE
7.0 mm:  Average=.03 dE, Worst case=.07dE

Please note these are dE1976 values. The dE2000 values are only 1/3rd as much which is effectively negligible. These errors are now miniscule in comparison to comparing the two print charts which vary an average of .25 dE1976 or .10 dE2000.

Looking at the error locations spatially, the 6.0 mm set aligned with the wheel marks. The 7.0 mm patch set max errors were randomly distributed. However, they were quite small and quite possibly just due to intrinsic variation in Isis readings.

Wheel mark issues aside, I'm very impressed with the repeatability of the instrument and I now have a process for making excellent profiles on the thicker semigloss/luster media as well.
« Last Edit: August 20, 2017, 06:22:50 PM by Doug Gray »
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #4 on: August 21, 2017, 08:04:15 PM »

I made some tests to determine the region in the patches that are actually measured. The patches are not measured evenly throughout the length and width but are center weighted with low sensitivity to colors that are near the edges. This is, of course, desirable.

To determine what portion and location of the patches were measured I made a series of horizontal and vertical thin white lines spaced such that, when read, each patch would pick up that potion of luminance contributed by the white line. The lines were evenly spaced from the left edge to the right edge over 30 horizontal black patches. Thus each line is .2 mm further right on each successive column for the 6 mm wide patches and .236 mm for the 7 mm wide patches. The ideal position was calculated and the lines were placed at the nearest pixel column on a 600 DPI grid, the native DPI for the Canon 9500 II.

The prints for the default 6 mm wide and an increased 7 mm wide patches were scanned twice with the ISIS 2. The "Y" value (linear luminance) was read and integrated and plotted to show the accumulated luminance contributed as a function of distance from the patch center.

Each chart shows the cumulative luminance vertically as well as horizontally. The solid and dashed blue lines represent the vertical, 6 mm cumulative luminance response v position. The green line is the horizontal for the 6 mm wide patches and the yellow line is the 7 mm wide patch responses.

Summary:
95% of the 6 mm patch color is read within about a 2.8 mm width reasonably centered on the patches. 95% of the 7 mm patch color is read within about a 3.2 mm width.

Interestingly, the vertical response is elongated. I suspect this is due to the horizontal scan microstepping, which appears to be around (.5 mm) but it may also be due to differences in the optics. Curiously, the vertical measurement distance comes somewhat closer to adjacent patch edges and they vary in centering somewhat more than the horizontal exhibits. This suggests there may be some reason to increase the vertical spacing beyond the minimums.

I hope this isn't too geeky but I wanted to get a better sense of how to determine whether and when the wheel tracks can be ignored.

Here's how to use the graphs to determine the effect of the wheel imprints on thick, lustre type media.

look at the graph, either 7mm or 6mm (default) where the tracks occur. They are about 1 mm wide. Use the ratio, relative to 1, of the start and end of the wheel imprints. If they are 1mm offset from the center than only about 25% of the light is used there so a dE of 3 would be reduced to a dE of about .8 .  If the offset from the center was 1.5 mm then the impact would be much less, about 10%. So the dE error would be closer to .3.  OTOH, if the wheel tracks were dead center, the impact would be about 60% so the dE error would come in around 1.8.
« Last Edit: August 21, 2017, 09:54:56 PM by Doug Gray »
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Ethan Hansen

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #5 on: August 25, 2017, 04:07:17 PM »

Doug - Your observations about patch size vs. dE variations are in line withwhat we found. In the earlier post I neglected to mention our experience with thicker papers. Delicate surfaces definitely create problems with the iSis and thick, stiff paper makes matters worse. We still use Spectroscans for such stocks.

Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #6 on: August 25, 2017, 08:44:28 PM »

Doug - Your observations about patch size vs. dE variations are in line withwhat we found. In the earlier post I neglected to mention our experience with thicker papers. Delicate surfaces definitely create problems with the iSis and thick, stiff paper makes matters worse. We still use Spectroscans for such stocks.

Ethan,

I appreciate your sharing the test results you've run. So far I've not had any registration or recognition problems with the ISIS 2 XL but I'm only a week and a half into it. OTOH, I do not use ACPU as the identity transform technique works well and I do need precision in the patch spacing to avoid the track problem. Since XRite's I1Profiler refuses to print from the app I have no choice but to save the tiff file. It's become my preferred approach anyway since I can text label relevant info into the target image in an unused region.

So far it's the leading "spacers" that shift the color readings. If they happen to leave tracks near the center there can be a large impact. It's a negligible effect with glossy's and so far with even thick matte, but the thicker lustre/semigloss Baryta I have it's a real problem. There are also "wheels" further back that grab the paper and these microstep. While they can leave a slightly visible specular difference I haven't seen any significant color reading shift from them on any media I've tested so far.  I really like the Baryta for it's great dynamic range, low OBs, and excellent brightness (L=98). I've found a simple approach that eliminates the problem. Since the spacing is 42mm, setting the patch width at either 6mm or 7mm (both divide evenly into 42mm) then simply printing with a carefully selected horizontal offset causes all the lines to be very near the transition region. Even if the paper alignment isn't perfect and the tracks are up to 1mm offset from the patch transition region the effect is reduced to well under .1 dE.  Verifying my empirical observations was the purpose of the sliding, .5mm white window test described earlier.

As an aside, my gold standard profile test is to print Lab patches then measure them and run statistics on the measured v requested values. This checks the BtoA1 tables whereas just checking the reported Lab values from a profile generating patch scan reports the results of the AtoB1 tables. For various reasons, and especially near gamut boundaries, the AtoB1 tables are more accurate than the BtoA1 tables and actually printing a photo uses the BtoA1 tables. Hence the need to print known colors, measure them, and run statistics on them.

Doing this "gold standard" profile test was easy with patchtool and the I1Pro2 but not with the ISIS which imposes various alignment items in it's target image. So I've worked on a way around that.

I've made a Matlab script that reads the Isis tif file and replaces the patch RGB values with a set from a CGATs file. I convert the reference Lab values to device space using the profile under test in Abs. Col. then call the script to "fix" a generic tif Isis file with those device RGB values. It also treats the patches as collections of 4 grouped pixels and interpolates fractional values. For instance a R value of 150.3 will put 150 in three pixels and 151 in the fourth. This effects a 10 bit printer resolution. Then the image is printed w/o color management (it's already done and in device space) and Isis scans the patches and records the Lab values. Then the measured ones are compared with the requested Lab values. So now that process is not only doable like the I1Pro 2, but much faster and more consistent than the I1Pro 2 process.


« Last Edit: August 26, 2017, 11:06:05 AM by Doug Gray »
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Wayne Fox

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #7 on: August 27, 2017, 06:40:23 PM »

Is this being caused by a mechanical change in the iSis 2 vs. the original model?  Iíve never seen issues with this effect in my iSis, but then again Iíve really never looked at things this closely.

Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #8 on: August 27, 2017, 10:40:48 PM »

Is this being caused by a mechanical change in the iSis 2 vs. the original model?  Iíve never seen issues with this effect in my iSis, but then again Iíve really never looked at things this closely.

It's a fairly small effect. Overall the Isis 2 is extremely consistent. Successive passes normally produce average dEs of .05 or less. That high repeatability, which is much better than their specification (.10), is what made this problem evident. Even then it really only affected fairly thick, Baryta pearl type surface media where the 4.2 cm spacers rubbed against the surface.

I see a variation of up to 2.0 dE with an average of .4 just from running patches randomized to different locations on the same paper and that is unrelated to the track issue. The Isis reads a fairly small area and most of the color data is from a 2mm wide portion in the patch center. This can likely be explained by small differences in the head to paper spacing and possibly tiny differences in the particular nozzles in use over that small region.

As an aside, the larger dE excursions from this, when measured with Delta E 2000, instead of Delta E 1976 are 1/2 to 1/3 the amplitude so, perceptually it's pretty much a non-issue. For instance, one of the color patches that shows the greatest tendency is a highly saturated yellow with a b* close to 100 and this is where the dE 2000 is much less sensitive than the dE 1976.

But, because of the high repeatability of the Isis, and a desire to refine some specialized charts to measure things like imager flatness and registration to the image plane I'm pursuing it just to understand and eliminate or mitigate the effect of some of the variables.
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Ethan Hansen

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #9 on: August 28, 2017, 01:11:04 PM »

Is this being caused by a mechanical change in the iSis 2 vs. the original model?  Iíve never seen issues with this effect in my iSis, but then again Iíve really never looked at things this closely.

It certainly is worse with the iSis 2. The original iSis sometimes leaves crush marks on thick, delicate papers, with matte being affected most. The single iSis v2 we have feeds more consistently but this comes at the cost of more mechanical squishing on the paper surface.

unesco

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #10 on: August 28, 2017, 04:13:44 PM »

I see a variation of up to 2.0 dE with an average of .4 just from running patches randomized to different locations on the same paper and that is unrelated to the track issue. The Isis reads a fairly small area and most of the color data is from a 2mm wide portion in the patch center. This can likely be explained by small differences in the head to paper spacing and possibly tiny differences in the particular nozzles in use over that small region.
I would say that this is rather inconsistency of printer having slightly different results in different location of the page than the measurement variation. Have you tried to measure full page of the identical patches?
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #11 on: August 28, 2017, 05:21:21 PM »

I would say that this is rather inconsistency of printer having slightly different results in different location of the page than the measurement variation. Have you tried to measure full page of the identical patches?

I agree. So far my tests indicate very little variation in measurements made in identical places. It's quite remarkable how consistent the readings are. But the tests also show that only a fairly tiny part of each patch is measured, in effect a portion between 2mm and 3mm square. So that would exacerbate any location or paper variation.

Good idea on the full page test. I've just made one with all the patches using the RGB value that shows the largest variation. Interesting to see if there is some location pattern.
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #12 on: August 28, 2017, 06:32:20 PM »

Here's the results. The statistics are consistent with my randomized set of 64 patches repeated and re-randomized 8 times.

I changed the ink on my 9800 to PK so I could do decent comparison tests with glossy on the 9500. The 9800 exhibits about 30% less variation than the 9500.

The color that exhibited the most variation on the 9800, is a salmon color, device space RGB (255,170,170), Average dE .5, max 1.8.

I used patchtool to compare two scans. One was fed in 2 cm offset from the other to identify effects from the ISIS v effects from the inked paper itself. There are no observable effects from feeding the paper in with an offset.

Indeed, there is an interesting vertical patterning which is likely something the printer is doing, possibly from the way vacuum is applied creating slight variation in head to paper spacing.

The two scans also differed by an average dE of .10 with a maximum of the 841 patches of .31.

Assuming more or less a normal distribution the measurement variance was 1/25th of the variance due to media/ink variation. I suspect most of that is due to slight, sub mm,  shifts in where the readings are taken on each patch.

So the Isis is proving to be extremely consistent. However, because of the relatively small portion of each patch that the sample is taken from it seems that the very best profiles are best made from the use of multiple, randomizing patch sets. I1Profiler offers two variations. unrandomized and randomized but it's fixed. Averaging scans from the two would be much better than just re-reading a single set.
« Last Edit: August 28, 2017, 06:50:52 PM by Doug Gray »
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GWGill

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #13 on: August 28, 2017, 08:46:29 PM »

It's a fairly small effect. Overall the Isis 2 is extremely consistent. Successive passes normally produce average dEs of .05 or less.
I'd attribute higher stability to the nature of the light source more than (or as well as) mechanical repeatability. With ideal mechanical repeatability (i.e. leaving the instrument in the same spot), I found that the ColorMunki is far better than the i1Pro due to the better stability of the (temperature compensated) LED light source over the incandescent lamp.
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #14 on: August 28, 2017, 09:06:28 PM »

I'd attribute higher stability to the nature of the light source more than (or as well as) mechanical repeatability. With ideal mechanical repeatability (i.e. leaving the instrument in the same spot), I found that the ColorMunki is far better than the i1Pro due to the better stability of the (temperature compensated) LED light source over the incandescent lamp.

Absolutely agree. I too have seen the I1Pro shift it's white point depending on how often one takes samples or has held down the strip reading button.

OTOH, I'm very pleased with how well it correlates with the Isis. I wouldn't have been surprised if the average difference in Lab readings was over dE 2. Especially given that I haven't had the I1Pro 2 calibrated since I bought it and the earlier I1s I have, a uv Cut and regular M0, are significantly different than the I1 Pro 2 with an ave dE on a Colorchecker of > 1.7 on the uV cut and 2.2 on the older M0 model. dE2000 on the ones furthest off is much closer, fortunately.

Also, the Isis does use a true, uV cut and, optionally, simulates M1 and M0 with a second pass using, presumably, a uV LED. The readings with high OB paper and M2 and M1 mode for both are remarkably consistent. I do need to test for that anomaly I saw with the I1Pro2 where there would be unexplained if infrequent, overly large responses to the uV LED messing up both the M1 and M2 values.
« Last Edit: August 28, 2017, 09:10:01 PM by Doug Gray »
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Doug Gray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #15 on: August 28, 2017, 09:40:23 PM »

I would say that this is rather inconsistency of printer having slightly different results in different location of the page than the measurement variation. Have you tried to measure full page of the identical patches?

unesco,

I would like to thank you once again. It turns out your suggestion is a highly productive one. For one thing it's voided one hypothesis I had, which was that Isis's small area of patch reading contributed significantly to the dE variation I saw. It doesn't. Very good news but now I have to re-align my thinking towards almost all the observed error being due to the printer's paper handling and not variation in the printer head or the Isis instrument.

I'm now looking at the Canon 9500 II and will be summarizing the relevant data soon. In particular it suggests a mechanism that could work much better than just averaging, redundant, randomly positioned patches.
« Last Edit: August 29, 2017, 12:40:25 AM by Doug Gray »
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Stephen Ray

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #16 on: August 29, 2017, 01:53:15 AM »

Doug,

Can you imagine how consistently the ISIS would handle canvas media?
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unesco

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #17 on: August 29, 2017, 01:27:44 PM »

unesco,

I would like to thank you once again. It turns out your suggestion is a highly productive one. For one thing it's voided one hypothesis I had, which was that Isis's small area of patch reading contributed significantly to the dE variation I saw. It doesn't. Very good news but now I have to re-align my thinking towards almost all the observed error being due to the printer's paper handling and not variation in the printer head or the Isis instrument.

I'm now looking at the Canon 9500 II and will be summarizing the relevant data soon. In particular it suggests a mechanism that could work much better than just averaging, redundant, randomly positioned patches.

Doug, thank you, I am really happy I could help - as an ex-researcher I quite often concentrate on details which looks tiny, but can have significant impact... in this case my tries with Epson 3880 and QTR curve design with my Munki made me think that repeatibility of patch print is the major cause for my curves not being smooth. Even 3 prints of 51 grayscale patches with different distribution on page and then averaging gave results close to spline smoothing of one print. And I talk about visual examination of bull-eye gradient smoothness, not just measurement. Anyway, let's keep researching this complicated printing world ;-)
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Ethan Hansen

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #18 on: August 29, 2017, 02:44:23 PM »

Can you imagine how consistently the ISIS would handle canvas media?

That depends on the media. Thin, fairly stiff canvas with minimal texture and a low-sheen finish works well. Flexible canvas gets mangled in the feed mechanism. Rough textured or glossy surfaces do not read accurately. You need a spherical geometry rather than 45/0 for best results on fabric. Failing that, a polarizing filter helps, Neither is possible with the iSis.

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Re: I1Isis 2 XL, the good, bad, and ugly
« Reply #19 on: August 29, 2017, 08:12:56 PM »

I'm now looking at the Canon 9500 II and will be summarizing the relevant data soon. In particular it suggests a mechanism that could work much better than just averaging, redundant, randomly positioned patches.

Doug - Welcome to the color measurement rabbit hole!

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.

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.

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.

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.
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