Re: Real-world RGB numbers for the ColorChecker SG
Re: Real-world RGB numbers for the ColorChecker SG
- Subject: Re: Real-world RGB numbers for the ColorChecker SG
- From: Robin Myers <email@hidden>
- Date: Tue, 21 Jun 2005 14:42:24 -0700
On 21 Jun, 2005, at 09:50, Steve Upton wrote:
At 10:05 AM -0500 6/21/05, Jamison Miller wrote:
Greetings ColorSyncers,
Does anyone know of published RGB numbers (or LAB or XYZ for that
matter) for the new Macbeth ColorChecker SG? I've used published
numbers
with the 24-patch ColorChecker to gauge my digital camera exposures
and
white balance up until now, and hope to get better results with the
SG...
The reference file is available as part of the ProfileMaker Pro
package if you have it.
In that particular case it is in spectral for so you may need to
convert it to Lab for your use.
If you want, let me know offline and I can forward it to you
directly...
now when it comes to RGB I have to ask which RGB? I could never
understand why RGB values were included with targets and yet which
flavor of RGB they were was never explained.
I believe Mr. Miller is referring to RGB values for the gray patches on
the ColorChecker SG. When used on some high-end cameras that allow for
tuning of the tonal reproduction curve (TRC), these values can be used
to calibrate the exposure conditions for fine art reproduction.
In this instance, the exact chromaticities of the RGB primaries can be
ignored because the assumption is made that the camera is adjusted to
produce equal RGB values for a neutral reference. The more important
point is the gamma value to use for the camera's RGB values. Using the
green channel RGB value only, adjusting the exposure to achieve a
particular value for the chart's white patch, then tuning the rest of
the gray patch values to achieve the reference value, a very consistent
shooting situation is created that produces a more accurate profile and
allows the profile to be used in subsequent similar shooting
conditions.
For more information on this procedure, check the www.betterlight.com
website in the Downloads/Macintosh area for the Repro Curve package.
The tables do not yet have values for the ColorChecker SG (they are
being edited right now), but you can get an idea of the procedure.
Robin Myers
email@hidden
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