Return-Path: <tiff-bounces@lists.maptools.org>
Received: from inas015.isp.belgacom.be (localhost [127.0.0.1])
        by inav005.isp.belgacom.be (8.12.11.20060308/8.12.11/Skynet-IN-AV-3.00) with ESMTP id kB64qOAW007156
        for <joris.at.lebbeke@skynet.be>; Wed, 6 Dec 2006 05:52:24 +0100
        (envelope-from <tiff-bounces@lists.maptools.org>)
Received: from inmx014.isp.belgacom.be (inmx014.isp.belgacom.be [195.238.4.217])
        by inas015.isp.belgacom.be (8.12.11.20060308/8.12.11/Skynet-IN-AS-2.03) with ESMTP id kB64qDw3009033
        for <joris.at.lebbeke@skynet.be>; Wed, 6 Dec 2006 05:52:15 +0100
        (envelope-from <tiff-bounces@lists.maptools.org>)
Received: from duke.maptools.org (r153.dmsolutions.ca [209.217.116.153] (may be forged))
        by inmx014.isp.belgacom.be (8.12.11.20060308/8.12.11/Skynet-IN-2.32) with ESMTP id kB64qB5h017300
        for <joris.at.lebbeke@skynet.be>; Wed, 6 Dec 2006 05:52:12 +0100
        (envelope-from <tiff-bounces@lists.maptools.org>)
Received: from duke.maptools.org (duke.maptools.org [127.0.0.1])
	by duke.maptools.org (8.12.11/8.12.10) with ESMTP id kB64jwqP029202;
	Tue, 5 Dec 2006 23:46:32 -0500
Received: from mail.sidefx.com (mail.sidefx.com [149.99.58.193])
	by duke.maptools.org (8.12.11/8.12.10) with ESMTP id kB64juUu029199
	for <tiff@lists.maptools.org>; Tue, 5 Dec 2006 23:45:56 -0500
Received: from www.sidefx.com (mail.sidefx.com [149.99.58.193])
	by mail.sidefx.com (Postfix) with ESMTP id 076B8510002
	for <tiff@lists.maptools.org>; Tue,  5 Dec 2006 23:45:53 -0500 (EST)
Received: from 70.50.61.182 (SquirrelMail authenticated user edward)
	by www.sidefx.com with HTTP; Tue, 5 Dec 2006 23:45:53 -0500 (EST)
Message-ID: <1355.70.50.61.182.1165380353.squirrel@www.sidefx.com>
In-Reply-To: <457623C5.90603@argyllcms.com>
References: <200612051704.kB5H4sEL015586@duke.maptools.org>
	<4575F91A.9090504@swiftview.com> <457623C5.90603@argyllcms.com>
Date: Tue, 5 Dec 2006 23:45:53 -0500 (EST)
Subject: Re: [Tiff] Re: Tiff Digest, Vol 31, Issue 3
From: "Edward Lam" <edward@sidefx.com>
To: tiff@lists.maptools.org
User-Agent: SquirrelMail/1.4.4
MIME-Version: 1.0
Content-Type: text/plain;charset=iso-8859-1
Content-Transfer-Encoding: 8bit
X-Priority: 3 (Normal)
Importance: Normal
X-BeenThere: tiff@lists.maptools.org
X-Mailman-Version: 2.1.4
Precedence: list
List-Id: TIFF and libtiff discussion <tiff.lists.maptools.org>
List-Unsubscribe: <http://lists.maptools.org/mailman/listinfo/tiff>,
	<mailto:tiff-request@lists.maptools.org?subject=unsubscribe>
List-Archive: <http://lists.maptools.org/mailman/private/tiff>
List-Post: <mailto:tiff@lists.maptools.org>
List-Help: <mailto:tiff-request@lists.maptools.org?subject=help>
List-Subscribe: <http://lists.maptools.org/mailman/listinfo/tiff>,
	<mailto:tiff-request@lists.maptools.org?subject=subscribe>
Sender: tiff-bounces@lists.maptools.org
Errors-To: tiff-bounces@lists.maptools.org
X-UIDL: 000000000023ceae.00001e20
X-MSP-STORE: Wed, 06 Dec 2006 05:52:32 +0100
Status:   

>> The standard conversion from RGB to gray, documented in the textbooks,
>> is grey
>> level =  .33R+.5G+.17B.  So a unitary conversion back to RGB is fine.
>
> And of course this equation is acknowledged to be wrong - you can't
> combine gamma encoded values like this to give a correct greyscale.

Charles Poynton has a nice note explaining this:

http://poynton.com/papers/YUV_and_luminance_harmful.html

Found from the the wikipedia article,
http://en.wikipedia.org/wiki/Luma_%28video%29

-Edward


_______________________________________________
Tiff mailing list: Tiff@lists.maptools.org
http://lists.maptools.org/mailman/listinfo/tiff
http://www.remotesensing.org/libtiff/
