Re: Interlaced vs. Non-interlaced GIFs

Bill O'Donnell x3378 (
Mon, 21 Nov 1994 22:54:18 +0100

Date: Mon, 21 Nov 1994 17:38:19 GMT
From: (Chris Lilley, Computer Graphics Unit)
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Bill O'Donnell said:

> David Koblas said:

>> when I rasterize line drawings is the following process:
>> Frame -> postscript @ 150 dpi -> scale 50% -> GIF
>> This results in an nice anti-aliased image.

Yes. I wish more people would do this.

> ("Inline"
> (:gif :inline nil nil 75)
> :output "<IMG $=SRC $=ALT $?ISMAP>")

which seems to preclude this anti-aliasing. Could I suggest


where SAMPLES-PER-PIXEL is 1, 4, or 9 (maybe that sould be 1,2,3 on
the understanding it is always squared) to allow for antialiasing or
not as a user pref. Bear in mind though that antialiasing and
transparent gifs interact - the rough background colour has to be
antialiased to.

I must confess some ignorance to implementation issues with respect to
anti-aliasing. But it would be easy to add more parameters to the
graphics processing syntax. The rastering engine I am using already
does some anti-aliasing automatically. I'll look into more general
anti-aliasing in a future release, since a lot of people seem to think
it's a good idea.

BTW the syntax quoted does not seem to allow you to specify what
colour is transparent, do you assume white? or is the parameter an RGB
value if it is not NIL. (So, in the GUI, users click on the image to
say what colour they want transparent).

Currently, white is the correct background color 99% of the time,
since the GIFs that Cyberleaf generates are usually from vector
drawings, which are imposed on white "paper." Once again, it would be
easy to extend the processing parameters to specify a color (RGB or
whatever) as the background.

Thanks for the suggestions. I wish I'd tuned into this alias six
months ago.