Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: l_d_allan on March 14, 2013, 11:33:06 am
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continuation of topic http://www.luminous-landscape.com/forum/index.php?topic=75707.0 that veered OT
I'm wondering how a person could do an inexpensive at-home calibration check of an iSis to get some confidence that its scan readings were reasonable. (X-Rite charges $400 plus shipping, IIRC).
- I'd like to get the equivalent of a "Test Strip" like some strip readers come with. I think I've seen them on eBay.
- I suppose you could try using a QpCard 201, 202, or 203 carefully taped to a sheet of paper.
- that had the outline of the iSis alignment marks printed on it.
- Hopefully it wouldn't jam in the iSis.
- You could perhaps have a bottom sheet, and then a top sheet with cutout for the QpCard.
- http://www.qpcard.com/en_b2c/color-reference-cards.html
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- I don't have any QpCards, but my understanding is that they are on relatively sturdy paper with fade resistent ink (pigment?)
- I believe that QpCards are primarily for camera profiles.
- As a print, they wouldn't be able to have extreme gamut values like RGB([255,0,0],[0,255,0],[0,0,255]), but no print can.
- Is anyone aware of something like a CCSG that is specifically for an iSis, with all the alignment markings, maybe BarCode, and patch values in a Pmp5.txt, i1Profiler.txf, i1Profile.pwxf, and/or ColorPort.xml file?
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- Really, seems like the rather pricey iSis should come with such a "test strip".
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If X-Rite don't offer any sort of calibration test strip, trying to build your own is probably too difficult for you to attempt.
Your most realistic approach would be to find another iSis owner and ask them if they'd scan a target you've already measured and sent to them, then get them to email the measurement data back to you and compare it with your own read of the target. then you'll get an idea of if there are any major faults.
As I'd guess most iSis are owned by CM professionals, you might need to offer payment for this service.
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If you did not buy the spectrometer new and created some reference data with DIY stable color patches you are facing expensive choices anyway. I did the first and not with the expectation that I could avoid a manufacturer's recalibration at some point in time but more to find out when my spectrometer is going bad and has to be recalibrated. A string of opaque acrylic 3mm thick sheet samples measured at day one and the data + samples archived in a black envelope stored cool.
Your white calibration sample that comes with the spectrometer can be aged and you could in theory get another one or create another one if you had a precise spectral measurement of a new one. And no that sample does not have to have the ideal neutral high reflectivity of say a Barite or PTFE tablet, the spectrometer manufacturer may have another opinion on what the better patch white is, per spectrometer model. I have done some cross measurements on two manufacturer's choices and they were different. For saturated colors you can buy (very) expensive ceramic tablets with (very) precise (radio)spectrometer calibration data and it is certain your spectrometer will measure other values. How much and in what direction for several hues and then to know whether that is just the off value that is tolerated between the same instruments or worse and then find a method to compensate that harmonically outside the meter as you will not have access to what a manufacturer does in recalibration (I guess switch parts, lightsources, white patch etc right away and then calibrate as new on very expensive ceramic tiles). Both alternative and manufacturer's methods are not cheap.
There is something you could do and that is checking whether any paper lint, dust etc is in the optical system of the spectrometer. As far as it can be easily taken apart, do not go beyond that stage. I do it sometimes with my Eye1 Pro.
If there is someone with an Isis with a fresh white calibration patch do a cross check with both meters. Check the spectral distribution and the Lab values. I guess it should not be more off than one or two DeltaE.
--
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012, 500+ inkjet media white spectral plots.
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It's not particularly inexpensive, but it's got what you're asking for:
https://www2.chromix.com/colorgear/shop/productdetail.cxsa?toolid=50134
This is a very stable reference card with diamonds for running through your iSis. It comes with original reference values you can use to compare to your iSis measurements.
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Pherold,
Thanks for the link.
Ouch ... $300 USD.
Actually, I wonder if it would really work, even though it appears to have the alignment bar and diamonds for the iSis. My experience is that the minimal width of a test-chart is about 5". I wasn't able to use i1Profiler 1.4.2 (demo) to define a test-chart target to use a 4x6" sheet of inkjet paper. 5x7" was ok. My license/dongle doesn't work for Measure-Tool's Generate-Test-Chart.
Maybe that limitation is just for creating the test-chart in the first place, and you could still scan-measure a really small target such as this one from Chromix. Seems like you might have to tape it to a larger piece of paper to get the iSis to handle it ok. Or not?
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I've gotten the QPcard-201 and QPcard-203 and will give those a try. My understanding is that they have "known values" that will provide more or less objective values for what the iSis measures. I'm unclear on what are reasonable expectations on variances from "actual measurements" vs "factory calibration values".
I was hoping to have had access to a X-Rite Pro-2 from a local photography club that allows rentals, but that hasn't happened yet.
I continue to get semi-random profiles when using PM5 to generate profiles from measurement scans from PM5, MT-5, i1Profiler 1.4.2 (demo), and ColorPort 2.0.5. ArgyllCms 1.5.1 seems much better behaved at least at the eyeball level, but I don't have measurements yet on profiles to compare.
I am getting what seem to be very good profiles ... occasionally ... from PM5, and from ArgyllCms, so that suggests the iSis is working ok. I'm probably doing something wrong with PM5. "Some village is missing its idiot?"
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If X-Rite don't offer any sort of calibration test strip ...
It turns out that X-Rite does sell a "Replacement i1 Scanner Testchart" that might be suitable for my intended purpose:
http://www.xrite.com/product_overview.aspx?ID=1244 (no pictures or specs)
http://www.bhphotovideo.com/c/product/465187-REG/X_Rite_421625_Scanner_Testchart_for_i1.html (picture but no specs)
The Testchart isn't unreasonably priced for my budget, but I couldn't find dimensional specs, or reference values for its 288 patches. I've started another thread to inquire about the specs:
http://www.luminous-landscape.com/forum/index.php?topic=77468.msg620112#msg620112