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Re: Building custom TDF
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Re: Building custom TDF


  • Subject: Re: Building custom TDF
  • From: Richard Millott <email@hidden>
  • Date: Tue, 19 Feb 2002 09:32:06 +1100

At 09:49 18/02/2002 -0600, Bruce wrote:
>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).

Thank you all for your responses to my question, but Bruce, special thanks
for
the clues about the text editing. I am most grateful.
Kind regards
Richard
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References: 
 >Re: Building custom TDF (From: "Bruce J. Lindbloom" <email@hidden>)

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