[mapserver-users] Optimising Image quality

[Ed McNierney]

Tim -

Your thoughts about JPG are correct.  JPG is a better choice for maps
with photographic basemaps; PNG is better for other maps.  I would like
to suggest that you reconsider your feelings against PNG.

I just took a quick look at the last 50,000 user visits to TopoZone, and
98.7% of them were with browsers that support the kinds of PNG images
MapServer generates.  No, that's not universal, but you're never going
to reach 100.00% (0.17% of the visits were with Netscape 2.x browsers!).
The TopoZone site doesn't use PNG images (they're GIF) so there isn't a
self-selection going on here - non-PNG browsers can use TopoZone just
fine.

The TopoZone site opened two years ago, and even then we encountered
only one serious problem in PNG support.  Our maps were all originally
PNG tiles, and Microsoft Internet Explorer 4.x has a bug that prevents
8-bit palettized PNG images from printing correctly in some
circumstances.  We switched to GIF to avoid this problem, but it's a
two-year-old issue.  As of today (the same 50,000 visit sample) 95% of
all TopoZone visitors using Internet Explorer are running 5.x or 6.x.

Many browsers that "don't support PNG" tend to fail in PNG's support for
transparency.  That's not relevant to MapServer.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242



-----Original Message-----
From: Tim Sutton [mailto:sutton_t at giug.net]
Sent: Wednesday, October 24, 2001 4:23 AM
To: MapServer Mailing List
Subject: [mapserver-users] Optimising Image quality


Hi

I have the cvs mapserver running. I am trying to improve the quality
of the map output. If I use jpeg, the images (comprised mainly of
lines and labels) have quite a lot of 'noise'. I suspect the jpeg
output would be more suitable for maps containing raster backdrops
(large colour palettes with few areas of contiguous colour). I can't
use PNG as it is not universally supported by browsers yet.

Can anyone tell me where to get hold of the GD1.2 so that I can create
GIF's on the fly? The GD project site no longer lists it (for
obvious reasons I suppose).

Alternatively, is there any way to improve the quality of jpeg images
produced? I have tried the IMAGEQUALITY [int] paramter. Although the
documentation does not explicitly state it, I presume [int] is a
percentage 0-100 value. I tried the extremes in this range with no
visible improvement in image output quality.

Any suggestions will be greatly appreciated.

Thanks

Tim