Interpolate image

[Pål Kristensen]

Hi!

I have recently installed ms4w 2.2.6 beta which include MS 5.0 RC2. The
reason for this was to test the new AGG rendering engine when using
Mapserver as a WMS server, with only high resolution (RGB) rasters as the
data source. Most WMS servers around (both free and commercial) uses nearest
neighbor interpolation on the resulting image that is transfered to the
client. In situations where the source data is only hires rasters or imagery
(as in my case), the quality of the output would be much better if you could
apply an bilinear interpolation to the produced image (see the attached
images for an example). Because in most cases the pixels in the source data
and the pixels on the screen do not match up, even if I have produces
pyramids on the source data (using gdal gdaladdo with the average option
sett). The only WMS servers that has the ability to interpolate the
resulting image with bilinear interpolation (that I have discovered) is the
ESRI ArcIMS ArcMap image service and the ESRI ArcGIS Server.

I kind of hoped that the new AGG rendering back-end would give an option to
set the interpolation method used in the output, but I see no difference
when using AGG instead of GD. (IMAGEMODE is 24bit (RGB) PNG in both cases).
Am I missing something here, or do not AGG increase the image quality if the
resulting image if the data source is only rasters? Does anyone have any
experience concerning this issue, and maybe could give me some advice?

ArcGIS Server
http://www.nabble.com/file/p12754990/ArcGIS_Server.png 


Mapserver 5.0 rc2 with AGG rendering
http://www.nabble.com/file/p12754990/MapServer_5rc2_AGG.png 

Regards,
Pål Kristensen
Norwegian Mapping and Cadastre Authority
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