[argyllcms] Re: Any use for scanner's bulb's spectral data?
- From: Ernst Dinkla <E.Dinkla@xxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 12 Aug 2013 10:31:02 +0200
On 08/12/2013 09:48 AM, Michael Darling wrote:
Out of curiosity, I measured my scanner's bulb's light spectrum
(spotread -a -H), at night, all other sources of light turned off. It
was quite interesting. (Closest standard illuminant would be F10, but
there's significant differences.)
Is there anything useful that I can do with this spectral data to
improving the color accuracy of my scans?
I looked at the colprof, spotread, and .SP file documentation, mostly
having to do with the -i switch. I'm thinking this only has to do with
illumination on the output side, not the input side... But want to make
sure I'm not missing something!
I'm thinking the profiling process effectively makes the bulb's spectral
data irrelevant... By comparing the values given by the scanner to the
spectral data of the target, it basically takes the bulb's spectrum out
of the equation, right? (Obviously without removing the limitations of
the bulb's spectrum like there's an extremely small amount of 520nm
light, so there's going to be trouble there.)
Set that spectral plot of the scanner light against a plot of the
scanner sensor filters.
And a plot of the CMY dyes of several emulsions. Many scanners, even
desktop models still aim at (or are limited to) reproducing photo
originals. Within the Epson desktop range the V700-V750 target photo
originals (including film) more than the Epson 3200 did. My experience.
You have to know the sensor filter dyes too to get a picture of the
scanner's limitations. I doubt that knowledge could contribute to a
better CM solution, the limitations in total filtering remain.
Conventional printing CMYK pigments and Officeprinter CMYK dyes or
pigments are close enough to chromogenic CMY dyes. It is harder to get
it correct for more pigments beyond CMYK. Few that can scan all the
basic pigments of a watercolor paint box correctly, not to mention real
life colors. The continuous spectrum of a Xenon light source should
improve on that but few scanners have that these days.
In the HP G4010 and G4050 two lamps are available with different
spectral distributions. In some driver modes two scans are made, each
with a different lamp. The two are combined where one delivers the
detail + color and the second one only compensates the color of the
first scan by some smart algorithms. My guess is that it even can create
more color fidelity than if it made one scan with both lamps on. Based
on the different metameric effects created per lamp.
http://nl.hardware.info/reviews/1044/2/hp-scanjet-g4050-review-6-kleuren-technologie
There could be an English version.
http://www.image-engineering.de/library-m/test-reports
Third PDF on that page.
--
Met vriendelijke groet, Ernst Dinkla
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2012: 500+ inkjet media paper white spectral plots.
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