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NNTP-Posting-Date: Mon, 24 May 2010 15:51:30 -0500
From: Stephen Sangwine <sjs@essex.ac.uk>
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Date: Mon, 24 May 2010 21:51:30 +0100
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Subject: Re: A generic image decoder - specification design
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Date: 2010-05-24T21:51:30+01:00
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On 2010-05-01 18:03:18 +0100, Gautier write-only 
<gautier_niouzes@hotmail.com> said:

> Hello,
> I've just started a generic image decoder package project.
> You can read the specification here:
> http://gen-img-dec.svn.sourceforge.net/viewvc/gen-img-dec/gid.ads?revision=1&view=markup
Before 
> 
> going on with the implementation, I would be glad to get any
> comment on it.
> From typos, naming, to possible performance considerations related to
> generics, or image formats, or what else ?...
> TIA
> ______________________________________________________________
> Gautier's Ada programming -- http://gautiersblog.blogspot.com/
> NB: For a direct answer, e-mail address on the following web site:
> http://www.fechtenafz.ethz.ch/wm_email.htm

Interesting idea. What you are proposing looks to me like a sort
of binding to various image libraries, in that you provide basic
image reading/writing to a variety of formats. Of course, you
can't handle all the special features of each image format, but
for an application that just needs to read or write the pixels
and a few other basics like palettes, alpha etc, the approach
would be useful. I can speak from experience of developing PNG_IO
to say that handling any non-trivial format is not a small task.
BMP is pretty easy - TIFF is probably the hardest to handle. In
both PNG and TIFF the pixel data is stored in disparate pieces
within the file - not as a single block of pixel data. In the
case of PNG the compression runs across these blocks, not within
each block. What this means is that code for handling the pixel
data can't easily be common to different types of image file.

You have available an Ada package for PNG already in PNG_IO.
I've thought about GIF as a student project now that the
compression is no longer subject to patent protection, but no
work has been done on it yet.

Steve Sangwine