I'm having a discussion with somebody over on Graeme's list for ArgyllCMS. Chad's posted a GCATS file including spectral measurements he made of a ColorChecker SG using a ColorMunki. The alternating white patches around the perimeter all show significant signs of fluorescent brighteners present. They're flat at 86% reflective from 380nm - 420nm, after which reflectively rises very steeply to a peak of about 93% at around 460nm - 470nm, and then a gradual falloff to the red but with another smaller peak at 91% at 660nm. The spectrum isn't particularly smooth. The GCATS file has a calculated XYZ value of 89.467 91.727 91.969 and a Lab value of 96.709 1.8667 -13.059, decidedly very bluish...and I couldn't even find any common RGB spaces that can encode that without clipping the blue channel. I keep thinking that Chad must somehow have gotten saddled with a counterfeit product, as I simply can't imagine something like this coming out of X-Rite. But I've also never seen a ColorChecker SG in person...which is why I'm asking here. Is the ColorChecker SG really this heavily laced with FWA? If so, why on Earth...? If not, I'll tell Chad to get in touch with somebody at X-Rite on the assumption that something's worng with his chart (or ColorMunki or _something_). b&
Dear Ben, Either the target is from a bad batch (what's the date imprint on it?), or the measurements are bad. On Aug 27, 2015, at 7:23 PM, Ben Goren wrote:
I'm having a discussion with somebody over on Graeme's list for ArgyllCMS. Chad's posted a GCATS file including spectral measurements he made of a ColorChecker SG using a ColorMunki.
The alternating white patches around the perimeter all show significant signs of fluorescent brighteners present. They're flat at 86% reflective from 380nm - 420nm, after which reflectively rises very steeply to a peak of about 93% at around 460nm - 470nm, and then a gradual falloff to the red but with another smaller peak at 91% at 660nm. The spectrum isn't particularly smooth.
The GCATS file has a calculated XYZ value of 89.467 91.727 91.969 and a Lab value of 96.709 1.8667 -13.059, decidedly very bluish...and I couldn't even find any common RGB spaces that can encode that without clipping the blue channel.
I keep thinking that Chad must somehow have gotten saddled with a counterfeit product, as I simply can't imagine something like this coming out of X-Rite. But I've also never seen a ColorChecker SG in person...which is why I'm asking here.
Is the ColorChecker SG really this heavily laced with FWA? If so, why on Earth...?
If not, I'll tell Chad to get in touch with somebody at X-Rite on the assumption that something's worng with his chart (or ColorMunki or _something_).
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On Aug 27, 2015, at 4:23 PM, Ben Goren <ben@trumpetpower.com> wrote:
The GCATS file
Cancel red alert, as they say. Turns out the XYZ and Lab values were calculated using a spectral measurement of a low-CRI fluorescent lamp as the reference instead of D50, and the measurements below 420 nm apparently have no bearing on reality. Re-calculating the absolute values with D50 gives a very reasonable Lab 96.69498 -0.854171 0.157998, and ignoring values from 430nm and bluer has reflectivity varying only from 90.4% - 92.7%. In other words, it was a number of completely unrelated coinciding unusual things conspiring to mimic the appearance of FWA in the chart, despite there being not even the slightest drop of FWA present. ``We apologize for the inconvenience.'' b&
The ColorMunki only measures from 430 to 730 Nm in reflective mode and copies the 430 measurement down to 380 Nm, I guess with the X-rite drivers. The sensor goes to 400 Nm for emitted light so one would expect the LED to be UV-cut. Any UV absorption + OBA effect shown in results must be extrapolated from 430-730 Nm downwards. Old information from that ArgyllCMS list: http://www.freelists.org/post/argyllcms/ColorMunki-or-i1pro-for-CM,8 Met vriendelijke groet, Ernst Dinkla Grafische Techniek Quad, piëzografie, giclée www.pigment-print.com On Fri, Aug 28, 2015 at 5:08 AM, Ben Goren <ben@trumpetpower.com> wrote:
On Aug 27, 2015, at 4:23 PM, Ben Goren <ben@trumpetpower.com> wrote:
The GCATS file
Cancel red alert, as they say.
Turns out the XYZ and Lab values were calculated using a spectral measurement of a low-CRI fluorescent lamp as the reference instead of D50, and the measurements below 420 nm apparently have no bearing on reality. Re-calculating the absolute values with D50 gives a very reasonable Lab 96.69498 -0.854171 0.157998, and ignoring values from 430nm and bluer has reflectivity varying only from 90.4% - 92.7%.
In other words, it was a number of completely unrelated coinciding unusual things conspiring to mimic the appearance of FWA in the chart, despite there being not even the slightest drop of FWA present.
``We apologize for the inconvenience.''
b&
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participants (3)
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Ben Goren
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Ernst Dinkla
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Iliah Borg