ColorChecker DC Problem?
ColorChecker DC Problem?
- Subject: ColorChecker DC Problem?
- From: Robin Myers <email@hidden>
- Date: Fri, 27 Jul 2001 12:36:13 -0700
- Organization: Robin Myers Imaging
Dear Group,
Recently we have discovered a problem with some ColorChecker DCs when
used in polarized light situations. Specifically, some of the gray
patches in the I8, J8, K8, and L8 set exhibit a severe change in
lightness when exposed to polarized light. This problem does not occur
with non-polarized lighting.
On one chart, patch J8 (4.61% reflective dark gray) becomes darker than
patch L8 (3.1% reflective black). On another chart, patches J8 and K8
(3.82% reflective) became darker than patch L8.
Since polarized and cross-polarized lighting is a commonly used
technique in fine art reproduction, this is a very serious problem.
What I would like to find out is whether others have experienced this
problem? How widespread is the problem? Are all the ColorChecker DCs
effected? Are other patches effected?
One method to detect this problem is to put a sheet of polarization
material in front of a directional light source (with the plane of
polarization oriented horizontally with respect to the ColorChecker DC)
at a 45 degree angle to the chart surface. Then look at the target from
the opposite side, also at a 45 degree angle. It may require rotating
the chart 90 degrees horizontally to see the effect. It is quite
stunning to see a patch like J8 suddenly turn blacker than its
surrounding patches and also darker than the L8 black patch.
If your ColorChecker DC has this polarization problem, please let me know.
Thank you,
Robin Myers