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From: Bill Radcliffe <BillR@corbis.com>
To: 'Martí María' <martim@abaforum.es>,
        Joris Van Damme <as.van.damme.joris@planetinternet.be>,
        TIFF Mailing List
	 <tiff@olympiakos.com>
Subject: RE: reading LAB files
Date: Fri, 20 Oct 2000 15:25:48 -0700
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For those that may not know...  The little CMS has been integrated into
ImageMagick. This should mean that you can try this out without doing any
coding, since IM uses the TIFF library for all its TIFF handling already.
Please let the group know if you do this since I am not aware of anyone that
is using this functionality yet.

> -----Original Message-----
> From:	Martí María [SMTP:martim@abaforum.es]
> Sent:	Friday, October 20, 2000 12:03 PM
> To:	Joris Van Damme; TIFF Mailing List
> Subject:	RE: reading LAB files
> 
> 
> > Martí María wrote:
> > >
> >
> > I'm sorry but this is not correct for my testfiles. I substract 256 from
> > the a,b parts IF there bit 8 is set, otherwise I leave them alone. I
> > have tested that. Also, the example Michael is giving here seems to
> > support my findings.
> 
> Yes, sorry. I forgot to mention "if greater that 127".
> 
> > The only fast way I've found to convert Lab to RGB and the other way
> > around is using a LUT of about 2 megs big. And that reduces accuracy to
> > about 6 bits per channel, which is fine for fast results, but I do want
> > 16 bits per channel accuracy in the 'perfect' conversion routines. If
> > you know a better way to do either the fast or the perfect conversion,
> > I'd LOVE (!!!) to hear more about it.
> 
> I use trilinear interpolation and ICC profiles. This is relatively fast,
> it gives 16 bits of precission, (dE < 5 on worst case) and
> needs about 300K for 3D LUT. If you want some code
> http://www.lcms.coloraid.de
> In the demo is also a profile that does convert directly from/to encoded
> Lab TIFF.
> 
> Regards,
> Marti Maria
> The little cms project
> http://www.abaforum.es/martim/lcms.htm
> mailto:martim@abaforum.es
> 
> 
