I think I can explain this, but probably can't fix it.....
I suspect your image is grainy.... PNG-8 in mapserver is (normally)
achieved by reducing the 24bit color palette to a very simple default
256 color palette. This means that you don't get a logical choice of
what 256 color's you want in your palette. This also means that the true
color of a pixel and the "best match" color in the default palette are
;ikely to differ significantly... hence a grainy appearance. When you
switch to png24 you avoid this progress... but watch the size of your
images.... my png24 256x256 tiles are ~65KB (and unusable)!
Ideally what you want to occur in the compression to 8bit is to analyze
the 24bit images and generate a color palette that will give you best
results.. this is known as "Color Quantization".........
see: http://en.wikipedia.org/wiki/Color_quantization
I'm sorry to say, I don't think mapserver offers this... so I can't
offer you an easy solution... but hopefully an understanding of the
problem if you want to chase it up further. Try the mapserver guys :)
--AH
re: png being smaller.... I've tried every trick in the book (because I
really wanted to use png) and other than say a single flat color, or the
most basic of image I can never get png smaller than jpeg. Map's, and in
particular "useful" maps typically contain content, and hence multiple
colors... consequently png is always bigger for me anyway. I wouldn't
always recommend jpeg over png, I'd just look at whats most important to
you, quality or size. Hope this was of some value....
Bradley Mclain wrote:
Sorry for the triple reply but I managed to solve it by editing the
Mapserver/Untiled.js file to have default image type as png24.
On 7/11/07, *Bradley Mclain * <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Little update which might help shed some light on the matter. I
saved that particular layer and it is a PNG format
not PNG24 or jpeg, so somehow OpenLayers request to Mapserver is
ignoring the new formats.
I did WMS URL requests to Mapserver and it returns the correct
formats.
On 7/11/07, *Bradley Mclain* < [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
For some reason this is not working for me, I changed the
settings in the Mapfile and defined the OUTPUTFORMAT and then
added the format:'image/png', to my Openlayers folder. I even
tried changing my mapfile to export as jpeg so as to match
Openayers but no luck.
Could it have something to do with that I am using the
MapServer.Untiled layer function instead of a WMS.Untiled layer?
On 7/10/07, *Andrew Hughes* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Bart's correct... but just be warned.... jpeg is A LOT
smaller is size than png-24. There's a reason why jpeg is
the default in OpenLayers.
--AH
Bart van den Eijnden (OSGIS) wrote:
OpenLayers uses jpeg by default for WMS layers, so change it in the
constructor of your WMS.Untiled layer:
'format':'image/png', i.e.:
baselayer0 = new OpenLayers.Layer.WMS.Untiled
( "Standaard",
"http://test.intranet.rijkswaterstaat.nl/services/geoservices/startkaart?";
<http://test.intranet.rijkswaterstaat.nl/services/geoservices/startkaart?>,
{layers: 'startkaart', 'format':'image/png', 'transparent':'TRUE'},
{'numZoomLevels': 12, 'ratio':1, isBaseLayer: true} );
Also check you have image/png mapped as a mimetype for PNG24 in your
Mapserver MAP file (OUTPUTFORMAT section).
Best regards,
Bart
--
Bart van den Eijnden
OSGIS, Open Source GIS
http://www.osgis.nl
--------- Oorspronkelijk bericht --------
Van: Bradley Mclain <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]>
Naar: OpenLayers ML <[email protected]> <mailto:[email protected]>
Onderwerp: [OpenLayers-Dev] Poor Image Quality
Datum: 10/07/07 05:07
I am importing an image as an untiled Mapserver layer into
OpenLayers and
it is of extremely good quality but when it shows up in OpenLayers
it's
quality is terrible.The image when viewed through Mapserver is not
as good
as the original but it still much better than what it is showing up
as in
OpenLayers. I have my Mapserver image format as PNG24.
Any ideas on what might be causing this and how to fix it?CheersBrad
_______________________________________________
Dev mailing list
[email protected] <mailto:[email protected]>
http://openlayers.org/mailman/listinfo/dev
_______________________________________________
Dev mailing list
[email protected] <mailto:[email protected]>
http://openlayers.org/mailman/listinfo/dev
_______________________________________________
Dev mailing list
[email protected]
http://openlayers.org/mailman/listinfo/dev
