Re: Building custom TDF
Re: Building custom TDF
- Subject: Re: Building custom TDF
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Mon, 18 Feb 2002 09:49:14 -0600
Richard Millott wrote:
>
I have search through the archives but cannot locate the posts
>
relating to the building of a custom Text Data File of the
>
Macbeth DC target. (I would like to build it with out reference
>
to the gloss patches)
Neil Snape suggested my web site, but I do not have anything there about the
DC chart, only the original ColorChecker chart. But if you wish to make a
TDF without the glossy patches, can't you just make a copy of a complete TDF
and then remove the lines for patches S4 through S11 with a text editor?
Michael Shaffer wrote:
>
I have been looking for the same thing ... patch values as Photoshop's
>
Lab, rather than Macbeth's CIE 1931 xyY. Bruce's spreadsheet comes close,
>
but the patch values are relative to his own spectrometer readings, and they
>
do vary from source to source, target to target ... a point in itself, when
>
it's relative to one's values and your color checker.
Any ColorChecker data will be relative to some spectrophotometer, some
physical chart (or charts), etc. The ColorChecker calculator I have will
give you Lab, D50 values. These are spectrally calculated WRT D50 and are
NOT adapted (i.e. approximated) from the Illuminant C reference of the
printed xyY values. I do not know of any other sources for this information,
although I'm sure there are some. GretagMacbeth does not have any "official"
spectral curves for these colors as far as I know (surprising as that may
seem).
Edmund Ronald wrote:
>
I searched high and wide for a ColorChecker file with data in Lab space or
>
some tagged, known space other than the xyY which PS cannot handle.
>
Finally, out of sheer despair I made an image with PS in Apple RGB space,
>
by typing in the RGB values on the chit with the ColorChecker.
The RGB values that come with the ColorChecker chart are useless, IMO
because they have no colorimetric reference. Edmund assumed they are in
Apple RGB space, but there is no basis for that assumption. If you're
looking for colorimetric RGB values for the ColorChecker, you will find a
fairly large assortment here:
<
http://www.brucelindbloom.com/index.html?ColorCheckerRGB.html>
One more thing about "ideal" ColorChecker values. Everyone assumes that the
six neutral patches along the bottom are perfectly neutral. They are not
since the spectra fall off sharply in blue. This is especially noticeable in
the "White" patch, causing that patch to be yellow by two or three delta E.
I notice that the large central white patch of the DC chart has that same
characteristic (b* > 0 for J6, J7, K6, K7).
--
Bruce J. Lindbloom
www.brucelindbloom.com
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