Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!samsung!munnari.oz.au!labtam!graeme
From: graeme@labtam.oz (Graeme Gill)
Newsgroups: comp.graphics
Subject: GIF images lack gamma info too: (was pixel aspect ratio in GIF images)
Summary: GIF files really should include gamma compensation information.
Message-ID: <5031@labtam.oz>
Date: 23 Jul 90 05:05:16 GMT
References: <9866@pt.cs.cmu.edu> <9894@pt.cs.cmu.edu> <RENNIE.90Jul16173632@karp.albany.edu>
Organization: Labtam Limited., Melbourne, Australia
Lines: 22


	While extensions to GIF are being discussed, this may be a good
opportunity to also discuss the inclusion of a field to indicate the gamma of
the display the image has been adjusted for, so that properly written GIF
viewers can compensate for the actual display being used automatically. One
image format which does this already (in a semi-standard way) is the UTAH RLE
format.
	Because most GIF image viewing programs do not compensate the images
for the gamma characteristic of the monitor being used, distributed images
seem to include a variety of gamma compensation levels. I find this variation
second only to aspect ratio in its annoyance factor.
Those images with no compensation (ie. linear images, display gamma = 1.0)
are the ones that appear particularly dark when viewed on most systems.
Systems that compensate for the display gamma will display these dark
images correctly, but the majority of images will appear too light. 
	With an agreed extension, a suitably modified viewer and a utility to
add aspect ratio and gamma information to existing images, then the GIF format
would be much more useful as a system independent format.

				Graeme Gill

				graeme@labtam.oz.au