GIF Format Issues

[Banister Trevor]

The move toward PNG and/or JPEG would be welcome. The 256 color palette can
be restricting. JPEG offers a Q factor which allows site developers to trade
off file size (which equals transmit time) for file quality. It would be a
big benefit to allow the Q factor to be changed in the map URL giving high
bandwidth web visitors a beautiful, high Q factor image, and low bandwidth
users a faster, lower Q factor image.

My concern is that maps tend to have a lot of high frequency components (red
road cutting through a white background). These components don't look so
great with lossy compression schemes like JPEG.  PNG's lossless compression
fixes this, but old browsers (< version 4) can't see PNG. PNG also has
support for 48 bit images which gives you 3 16 bit RGB channels or 4 12 bit
RGBA channels. 

Support for both would be great. Given the choice I'd vote for PNG
  

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Trevor Banister, Sr. Application Designer
Space Imaging
12076 Grant Street
Thornton, CO 80241
Phone: (303) 254-2175 Fax: (303) 254-2211
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Good
Fast
Cheap
Pick any 2



-----Original Message-----
From: Stephen Lime [mailto:steve.lime at dnr.state.mn.us]
Sent: Tuesday, August 31, 1999 10:46 AM
To: mapserver-users at lists.gis.umn.edu
Subject: GIF Format Issues


Greetings: At sometime in the near future a switch from LZW GIF to something
else, PNG, JPEG or non-LZW GIF will be necessary. Unisys, the LZW patent
holder, requires that software using it's compression technology be
licensed. GD,
the free GIF graphics library used within the MapServer uses LZW. GD was
written well before all of these legal happenings and it's unclear what
Unisys' stance
on older software is. New versions of GD support PNG only so it's clear how
those
authors feel.

To make MapServer useful as OpenSource the reliance on LZW to end. GD 2.0 
looks very promising with support for PNG (up to 24bit), JPG and hopefully a
non-LZW
GIF format, but I've seen no timetable for a 2.0 release.

Anyone got any comments or ideas?

Steve
 

Stephen Lime
Internet Applications Analyst
MIS Bureau - MN DNR

(651) 297-2937
steve.lime at dnr.state.mn.us