Hello everybody!
I have been using ArgyllCMS to produce an RGB profile for an Epson
Stylus Pro XL. I am using the printer in Linux with the gimp-print
driver. I am using the "scanner as a poor man's colorimeter" technique
with an IT8.7 target from Wolf Faust.
Profiles I generated from scanners have consistently produced a strong
green/cyan cast on the prints.
I then used a video camera + tungsten light source and, to my surprise,
got a better result, but still with a color cast. (Well, not much of a
surprise, tungsten wasn't filtered to daylight, I used the white balance
on the camera.)
I then used a digital camera (Kodak DX6440) under direct sunlight and
got an *excellent* result, with almost no color cast. This camera
doesn't have a "raw" mode (only sRGB JPEG), and there is some clipping
on the primary colors, as one would expect in the sRGB space. No doubt I
will do this again with a camera that gives more control and more
range... I have only tested the profile with "photographic" images, I
haven't tested it against very saturated color patches that may reveal
errors due to the clipping.
My interpretation for those results is :
a. the light source could be a more important factor in color rendition
of these devices than the spectral response of the RGB filters. The
scanners I used offer the worst light source i.e. cold cathode tube,
that looked very "spikey" in a handheld spectroscope.
b. the scanner seems to clip highlights when using a paper with
fluorescent whitening agents. The clipping is different with a camera.
Here are my questions:
1. Please comment on this.
2. What would be the difference between using a colorimeter (eg. Color
mouse CM2C) and a digital camera with a good quality light source (xenon
strobes)?
3. Can I use the peak error and average error reported by the "profile"
command as an indicator of the accuracy of the color measuring device?
Yours, Stephan.
