RE: X-Rite ColorChecker Passport
RE: X-Rite ColorChecker Passport
- Subject: RE: X-Rite ColorChecker Passport
- From: Roger Breton <email@hidden>
- Date: Sat, 19 Jun 2010 12:48:42 -0400
Robin,
Please excuse my ignorance but I'm both shocked and dismayed by your reply.
In the past, when I measured my venerable full-size ColorChecker chart, with
any of my instruments, I would always set the spectral conversions to D50
because I thought we lived in an ICC world.
Then, when I attempted to recreate digital versions of my custom-measured
ColorChecker charts, using InDesign or Photoshop, I would always diligently
type in the D50 Lab values obtained by my careful measurements.
With my students, in class, I would always report the measurements under D50
illuminant as well.
When using digital versions of the ColorChecker chart in a prepress or
photography color-managed workflow, for the purpose of gaining confidence in
screen calibration and profiling or for comparing to hardcopy proofing,
using AbsCol, how can there be other choices but D50-based calculations?
Since every applications in ICC-compliant color-managed chain is based on
D50 colorimetry?
So, if I may ask, what purpose does it serve you to compute the Lab values
using D65, instead of D50, in your carefully controlled color-managed
workflows : doesn't good ole Photoshop chromatically adapt sRGB and AdobeRGB
behind the scene to D50 anyway?
I'm well aware that ColorCheckers are based on Munsell notations who
themselves are based on Illuminant C.
Best / Roger
>
> Hello Mr. Breton,
>
> Both sRGB and Adobe 1998 RGB use a D65 white point. To make the L*a*b*
> values correspond correctly requires using the D65 white point for the
CIELAB
> calculations.
>
> Regards,
>
> Robin Myers
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