Return-Path: owner-tiff@olympiakos.com
Return-Path: <owner-tiff@olympiakos.com>
Received: from localhost (localhost [127.0.0.1])
	by at1895.spb.edu (8.9.3/8.9.3) with ESMTP id RAA01295
	for <dron@localhost>; Thu, 22 Feb 2001 17:09:16 +0300
Received: from eudoramail.com [209.185.123.45]
	by localhost with POP3 (fetchmail-5.6.0)
	for dron@localhost (single-drop); Thu, 22 Feb 2001 17:09:16 +0300 (MSK)
Received: from gate7.olympiakos.com ([207.176.88.85]) by shared1-mail.whowhere.com; Wed Feb 21 12:08:20 2001
Received: from localhost (daemon@localhost)
	by gate7.olympiakos.com (8.9.3/8.9.3) with SMTP id OAA03901;
	Wed, 21 Feb 2001 14:53:50 -0500
Received: by gate7.olympiakos.com (bulk_mailer v1.9); Wed, 21 Feb 2001 14:53:39 -0500
Received: (from majordom@localhost)
	by gate7.olympiakos.com (8.9.3/8.9.3) id OAA03857
	for tiff-outgoing; Wed, 21 Feb 2001 14:53:38 -0500
X-Authentication-Warning: gate7.olympiakos.com: majordom set sender to owner-tiff@olympiakos.com using -f
Received: from avalanche.arcticus.com ([204.144.221.201])
	by gate7.olympiakos.com (8.9.3/8.9.3) with ESMTP id OAA03847
	for <tiff@olympiakos.com>; Wed, 21 Feb 2001 14:53:32 -0500
Received: from 3dnature.com (glacier [192.168.2.11])
	by avalanche.arcticus.com (8.9.3/8.8.7) with ESMTP id NAA30526
	for <tiff@olympiakos.com>; Wed, 21 Feb 2001 13:01:45 -0500
Message-ID: <3A941DA4.4060901@3dnature.com>
Date: Wed, 21 Feb 2001 12:57:24 -0700
From: "Chris 'Xenon' Hanson" <xenon@3dnature.com>
Reply-To: xenon@3dnature.com
Organization: Arcticus
User-Agent: Mozilla/5.0 (Windows; U; WinNT4.0; en-US; m18) Gecko/20001108 Netscape6/6.0
X-Accept-Language: en
MIME-Version: 1.0
To: tiff@olympiakos.com
Subject: Re: PhotoShop alpha channels and LibTiff
References: <FCDAB278C6F74643A0C1243407D6773B069A52@RDUMAIL.mobiusg.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-tiff@olympiakos.com
Status: RO
Content-Length: 1248
Lines: 30

Chris Losinger wrote:

> 	i have a TIFF created in PhotoShop (vers??). it is saved with an
> alpha channel.
> 	when i go to read this image using TIFFReadRGBAImage, the alpha
> channel is not read. LibTiff treats it as an RGB image, not an RGBA.
> 	tracing the code, i found that the alpha channel is marked:
> EXTRASAMPLE_UNSPECIFIED. when i forced that flag to EXTRASAMPLE_ASSOCALPHA,
> LibTiff returns the proper alpha channel.
> 	what to do about this?
> 	is it a photoshop bug or a libtiff bug?

   I've seen this too, if I created the Alpha channel in Photoshop.

   If I create a 32-bit (24-bit + 8 bit alpha) TGA image in another
program, and load it into Photoshop, Photoshop shows it as RGBA.
If I then save it to TIFF, Photoshop properly flags it as an Alpha
channel, and TIFFReadRGBAImage reads it fine. I'm not sure what
Photoshop does differently when you create an Alpha channel by hand
versus loading it with the image.

   I have no advice, but I'd be interested in the answer myself.

> 	-c

Chris - Xenon
-- 
  Chris Hanson | Xenon@3DNature.com | I've got friends in low latitudes!
         New WCS 5 Demo Version!     http://www.3DNature.com/demo/
  "There is no Truth. There is only Perception. To Perceive is to Exist." - Xen

