Re: Profiling Digital Cameras
Re: Profiling Digital Cameras
- Subject: Re: Profiling Digital Cameras
- From: Lars Borg <email@hidden>
- Date: Mon, 15 Sep 2008 14:44:02 -0700
Gerry,
Yes, a core challenge is that the color chart's spectral reflectances
don't match the oil paint pigments used.
Many color charts are printed with a very small set of pigments.
Going from 10 to 1000 patches makes very little difference if they're
all produced using the same 4-5 pigments. The 24-patch Color Checker
supposedly is a nice exception.
And the camera's spectral sensitivities usually don't match the CIE
color matching functions for the standard 2 degree observer (that is,
not meeting the Luther condition).
Given this, a camera calibrated against a chart can reproduce the
chart accurately under the calibration illuminant, but not an
arbitrary scene under an arbitrary illuminant. It seems the long
thread has ignored this point.
The better approach is to calibrate the camera against the actual
reflectances, here oil paint pigments, being used. Several studies
have been done on this topic. To read more, see CIC proceedings.
This is similar to how the issue sometimes is tackled for scanners,
where a unique profile is used for each film stock or other media
with a set of known, unique pigments.
Take care,
Lars
At 6:05 AM -0700 9/15/08, Gerry Yaeger wrote:
I have been following the long running discussion on profiling raw
camera images. Over the 18 years I have sold digital imaging
equipment and worked as a color management consultant to many
companies, 3 different attempts to profile digital cameras come to
mind. These 3 companies had need of faithful reproduction of color.
...
Case #3 was a company that wanted to reproduce oil paintings. I
equipped them with a 3-shot medium format camera, we also tested
scanning backs, the best strobes available and the latest at the
time version of Profilemaker. After much refining of light angles,
polarization etc. we could produce awesome files of the Color
Checker. However, no amount of effort could faithfully reproduce the
colors of the pigments in the oil paintings coming from around the
world. They finally had to edit the files by hand to get the best
result. Again the proprietary capture software used the raw data
from the chip and applied the ICC profile.
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