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Message-ID: <45773CDD.1070206@argyllcms.com>
Date: Thu, 07 Dec 2006 08:57:49 +1100
From: Graeme Gill <graeme2@argyllcms.com>
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To: tiff@lists.maptools.org
Subject: Re: [Tiff] Grayscale, or is it?
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Status:   

Joris wrote:

 > I'm forever having trouble with grayscale in TIFF, except that now I
 > really need to resolve it and make a final descision.

 > I see three possibilities.

[I sent this yesterday, but it seems to have gone via the
  bit bucket...]

You've left out possibility 4) - in the printing world, greyscale
is the K (black) channel. It's response is whatever the printing
system I'm using it on is. Note that it has the opposite sense to
an additive display's response (0.0 = white, 1.0 = black).

The reality is that people abuse the image transportation
mechanism (ie. TIFF, PostScript etc.) to transport their
device dependent data, and don't really care whether they've
labelled it accurately or not. Officially in PostScript, the device
grey is meant to be an additive, "gamma = 2.2" type space,
but in practice people with a printing bent simply invert
their K data, and call it "grey".

The modern approach is to transport the device dependent colorspace
data, and label it with an ICC profile.

Graeme Gill.

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