Re: Custom Reference file for Gretag Color CHecker Chart?
Re: Custom Reference file for Gretag Color CHecker Chart?
- Subject: Re: Custom Reference file for Gretag Color CHecker Chart?
- From: Robin Myers <email@hidden>
- Date: Tue, 14 May 2002 15:56:00 -0700
- Organization: Robin Myers Imaging
>
on 5/11/02 2:05 PM, Steven Kornreich wrote:
>
>
> Would this make any sence.
>
> Here is my situation.
>
> When I shoot the ColorChecker Chart in my studio for making a DCAM profile,
>
> I have all my light polarized so wouldn't it make sence to build a custom
>
> reference file of the chart using the polarize filter on a Spectrolino when
>
> making a reference file of my chart??
>
>
With the exception of possibly the glossy patches (wait, you're talking
>
about the older 24 patch target, not the DCChecker chart, right?), I don't
>
think it would make much difference. The main point of the "P" polarizer
>
filter was for taking "dry" press ink readings of wet ink.
The newer ColorChecker DC has a severe problem with polarized light and
I do not recommend using it in polarized light situations. Many of the
patches on the chart are polarizing, thus making their lightness and
color changeable, depending on the orientation of the polarized illumination.
The older 24 patch ColorChecker does not have this polarization problem.
I would not make a custom polarized reference file since the polarizer
used in the Spectrolino is not the same at those used on the lights,
thus giving a slightly different color reading. My recommendation is to
make a custom reference file for your ColorChecker with unpolarized
light and use it for the polarized shoot.
By the way, the reason for the custom reference file for your
ColorChecker is that the formulation for the patches has been changed at
least three times over the years. I have measured ColorCheckers of three
ages and the spectra for some patches are radically different, though
the color is perceived to be the same. However, digital cameras can see
these spectral differences, thus making a custom target reference file
absolutely necessary.
Robin Myers
-----------
Robin Myers Imaging
www.rmimaging.com
email@hidden
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