[mapserver-users] JPEG and OVERSAMPLE_RATIO

[Cédric MOULLET]

Hi,
The following issue has been observed with MapServer 6.0.3:

1. Very good quality for a PNG with RESAMPLE=BILINEAR and
OVERSAMPLE_RATIO=16:
[image:
http://wms-bgdi.bgdi.admin.ch/?lang=xx&LAYERS=ch.swisstopo.pixelkarte-grau-pk100_bazl&FORMAT=image%2Fpng&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&SRS=EPSG%3A21781&BBOX=513184,143152,519840,149808&WIDTH=256&HEIGHT=256]

2. Less good quality for a PNG or JPEG with default resampling settings:
[image:
http://wms-bgdi.bgdi.admin.ch/?lang=xx&LAYERS=ch.swisstopo.pixelkarte-grau-pk100_original&FORMAT=image%2Fpng&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&SRS=EPSG%3A21781&BBOX=513184,143152,519840,149808&WIDTH=256&HEIGHT=256]

3. Awful quality for JPEG with RESAMPLE=BILINEAR and OVERSAMPLE_RATIO=16:
[image:
http://wms-bgdi.bgdi.admin.ch/?lang=xx&LAYERS=ch.swisstopo.pixelkarte-grau-pk100_bazl&FORMAT=image%2Fjpeg&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&SRS=EPSG%3A21781&BBOX=513184,143152,519840,149808&WIDTH=256&HEIGHT=256]

Any idea why the OVERSAMPLE_RATIO affects heavily the quality of JPEG
images ?

Thanks in advance for your help,
Cédric
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