Received: from [192.48.153.1] by phillip.thumbsplus.com (NTMail 3.03.0013/7.aaxh) with ESMTP id pcrews for <pcrews@cerious.com>; Wed, 11 Feb 1998 12:20:42 -0400
Received: from cthulhu.engr.sgi.com (cthulhu.engr.sgi.com [192.26.80.2]) by sgi.sgi.com (950413.SGI.8.6.12/970507) via ESMTP id JAA06494; Wed, 11 Feb 1998 09:10:17 -0800
	env-from (owner-tiff@sgi.engr.sgi.com)
Received: (from majordomo-owner@localhost) by cthulhu.engr.sgi.com (950413.SGI.8.6.12/960327.SGI.AUTOCF) id GAA27584 for tiff-list; Wed, 11 Feb 1998 06:58:24 -0800
Received: from sgi.sgi.com (sgi.engr.sgi.com [192.26.80.37]) by cthulhu.engr.sgi.com (950413.SGI.8.6.12/960327.SGI.AUTOCF) via ESMTP id GAA27577 for <tiff-relay@cthulhu.engr.sgi.com>; Wed, 11 Feb 1998 06:58:22 -0800
Received: from sss.sss.pgh.pa.us (sss.pgh.pa.us [206.210.65.6]) by sgi.sgi.com (950413.SGI.8.6.12/970507) via ESMTP id GAA13313
	for <tiff@sgi.com>; Wed, 11 Feb 1998 06:58:20 -0800
	env-from (tgl@sss.pgh.pa.us)
Received: from sss.sss.pgh.pa.us (localhost [127.0.0.1])
	by sss.sss.pgh.pa.us (8.8.5/8.8.5) with ESMTP id JAA11656;
	Wed, 11 Feb 1998 09:58:08 -0500 (EST)
To: "Than.Olaf" <Than.Olaf@GrunerDruck.de>
cc: "'tiff@sgi.com'" <tiff@sgi.com>
Subject: Re: AW: Tiff JPEG compression for CMYK images 
In-reply-to: Your message of Wed, 11 Feb 1998 13:41:09 +0100 
             <613464343515D1118EBB006097B4CDCA82B1@SPK> 
Date: Wed, 11 Feb 1998 09:58:08 -0500
Message-ID: <11654.887209088@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Sender: owner-tiff@fddi-sgi.sgi.com
Precedence: bulk

"Than.Olaf" <Than.Olaf@GrunerDruck.de> writes:
> I think CMYK has 4 channels.

So it does, but that's irrelevant.  The problem discussed in the message
you quoted had to do with asking the JPEG codec to do RGB->YCbCr
conversion when the input data didn't have three channels.  (If I recall
correctly, the upshot was that Bill was trying to apply JPEG compression
to indexed-color data, which is not going to work in any case.)  For CMYK
data, the code is not going to do any colorspace conversion, and it will
support any number of channels.

> Can i write a class "JPEG" image using libtiff and IJG jpeg-6a with
> PhotometricInterpretation = 5 (CMYK)

Yes.

> Commpression               = 6 (JPEG)
> JPEGProc                     = 1
> JPEGquality                  = xx

No.  libtiff/libjpeg support the newer Compression=7 JPEG scheme defined
by TIFF Tech Note #2.  Please read the Tech Note to find out why
Compression=6 is no good.

			regards, tom lane
			organizer, Independent JPEG Group
