Re: Nonlinear camera sensors
Re: Nonlinear camera sensors
- Subject: Re: Nonlinear camera sensors
- From: <email@hidden>
- Date: Wed, 02 Feb 2005 20:20:29 -0500
David,
I had the chance over the last few months to receive
ColorChecker spectral data from many people around the
world. You can see the average results in the following
Excel spreadsheet:
http://www.babelcolor.com/download/ColorChecker_RGB_and_spectra.xls
The results in the file are for 9 spectras but they are
very similar for the 14 I received so far (I will update
it when I have a chance, and more spectras...).
You will notice that the average neutral patch is not
PERFECTLY neutral (very close however), with a slight
offset of the same order as what you measure.
This could explain, in part, what you see.
Danny Pascale
dpascale AT babelcolor DOT com
On Wed, 02 Feb 2005 20:00:33 -0500
David Iannarelli <email@hidden> wrote:
I have been evaluating a calibration system for digital
cameras and I found a
possible problem:
There is a shift in white balance vs. illumination
level. In other words, there is a color shift depending
of the grayness of the gray card.
This ought to affect the profiling of cameras. For the
details see:
http://www.vinland.com/Contrast.html
Is this problem isolated to my camera or is it generic
to all or only some brands of cameras?
Hi Bertho,
I have noticed this with my Fuji S2 Pro and Olympus
E-20. The S2 manual says to use a white card when making
a custom white balance in camera. I went back to a white
card for the S2 because of my test with different gray
cards but, I have not tested different white cards to see
if the camera gave me similar results to the gray card
test.
I shoot in the RAW format only and I now shoot a
GretagMacbeth ColorChecker as my primary white balance
practice and use a RAW processing software to gray
balance the image using the third patch from the left
before applying a camera profile. I measured all the
gray patches on my chart and found that this patch was
the most neutral. I stress most neutral. None of the
patches were completely neutral. We are talking a L*a*b*
value of 1 or 2 points here though.
I think using the same card to set your white balance
and then build your profile with that is more important
than which card you use. As long as you get a neutral
gray from your white balance and the final print is the
colors you wanted the subject to be, what else can you
expect? I believe the non proprietary ICC profiling
technology has only been in use since the early 90's.
There is definitely room for improvement. Gelatin film
technology started over 100 years ago. It will take some
time for digital to catch up.
David Iannarelli
email@hidden
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