Re: Building custom TDF
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
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.