Re: Image types and related issues [was: Re: filetype extensions]
Larry Masinter <masinter@parc.xerox.com>
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Date: Fri, 13 May 1994 03:13:37 +0200
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From: Larry Masinter <masinter@parc.xerox.com>
To: Multiple recipients of list <www-talk@www0.cern.ch>
Subject: Re: Image types and related issues [was: Re: filetype extensions]
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You're better off assuming that every conversion loses a little, i.e.,
only the original most contentful is served with "loss 1.0".
> [ Note for those who care; Iris RGB and Utah RLE (assumed linear
> encoding) and TIFF (assumed generic RGB coding) are all 24 bit
> lossless formats. Within the assumptions specified, these 3 can be
> freely and repeatedly interconverted without information loss, which
> is why I picked them as examples.]
Well, often authors include other information in TIFF tags that will
be lost when you convert to Iris RGB. For most purposes, you don't
care about those tags, but in a few cases you will.
Furthermore, there are different *kinds* of loss when you convert
things from one format to another, and different uses will care more
about one kind of loss than another.
For example, if you are going to print out a document or view it on a
screen, a high-resolution bitmap rendering of it might be
satisfactory; however, if you're going to merge some of the text into
another document, a SGML rendering of it might be less `lossy' for
your purposes. (even though all of the font information is lost).
Suddenly you might find that `loss' is a vector and not a single
number. (presentation fidelity, structure retention, invertible
conversion, etc.)