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1999.07.19 12:53 "White point in CIELab TIFF files", by Martin Bailey
1999.07.19 14:12 "Re: White point in CIELab TIFF files", by Martí María
1999.07.19 16:03 "Re: White point in CIELab TIFF files", by Martin Bailey

1999.07.19 16:03 "Re: White point in CIELab TIFF files", by Martin Bailey

At 16:12 19/07/99 +0200, Martí María wrote:
>
>> 
>> The TIFF 6 spec is more than a little vague about what white point should
>> be used for L*a*b* images, and there's no specified tag to put that data
>> into the file.
>> 
>
>There is a tag to store White point, the tag is:
>
>	Tag  = 318 (13Eh)
>	Type = RATIONAL
>	N     = 2
>
>The chromacity of the white point of the image. This is the chromacity
when each of the primaries has its ReferenceWhite value.
>The value is described using the 1931 CIE xy chromacity diagram and only
the chromacity is specified.
>
>TIFF 6.0 specification has a "Section23: CIE L*a*b* images" where it says
that "White point : does not apply" but
>I have seen several TIFF whith photometric = CIELAB and white point
specified as D50 in this tag.
>
>Hope this helps

Hmmm. I knew about the tag, but the Lab files I have don't use it and I'd
seen the comment about not applying.

Ho hum. I can feel some experimentation coming on. I need to do that to
figure out how 256 levels relates to a range of -127 to +127 anyway :-)



Regards

Martin Bailey

----------------------------------------------------------
 Digital Print & Publishing                 Harlequin Ltd
 martinb@harlequin.com           http://www.harlequin.com
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 I try to ensure that my views expressed here accord with
 my employers, but I am not a spokesman for Harlequin and
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