AGG renderer in conjunction with WMS TRANSPARENT=true parameter

[Pål Kristensen]

Hi!

Edit: Reposting because the first post was not accepted by the mailing-list
for some reason. 

I'm trying to use the AGG renderer and reduce the resulting 24bits image to
8bits by using the quantize method. This works quite well when the WMS
parameter TRANSPARENT=false, but when set to true the BGCOLOR parameter
seems to be ignored and the quality of the rendered vectors clearly
degrades.

When requesting 24bit images the TRANSPARENT parameter works correctly. See
the examples below:

24bit png, transparent true -> OK:
http://159.162.103.7/cgi-bin/NorgeTopo?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap&SRS=EPSG:32633&BBOX=62423.20,6794915.15,66383.94,6797147.88&LAYERS=Hoydekurver&STYLES=&WIDTH=926&HEIGHT=522&FORMAT=image/png;%20mode=24bit&BGCOLOR=0xffffff&TRANSPARENT=true

24bit png, transparent false -> OK:
http://159.162.103.7/cgi-bin/NorgeTopo?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap&SRS=EPSG:32633&BBOX=62423.20,6794915.15,66383.94,6797147.88&LAYERS=Hoydekurver&STYLES=&WIDTH=926&HEIGHT=522&FORMAT=image/png;%20mode=24bit&BGCOLOR=0xffffff&TRANSPARENT=false

8bit png, transparent false -> OK:
http://159.162.103.7/cgi-bin/NorgeTopo?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap&SRS=EPSG:32633&BBOX=62423.20,6794915.15,66383.94,6797147.88&LAYERS=Hoydekurver&STYLES=&WIDTH=926&HEIGHT=522&FORMAT=image/png&BGCOLOR=0xffffff&TRANSPARENT=false

8bit png, transparent true -> NOT OK:
http://159.162.103.7/cgi-bin/NorgeTopo?VERSION=1.1.1&SERVICE=WMS&REQUEST=GetMap&SRS=EPSG:32633&BBOX=62423.20,6794915.15,66383.94,6797147.88&LAYERS=Hoydekurver&STYLES=&WIDTH=926&HEIGHT=522&FORMAT=image/png&BGCOLOR=0xffffff&TRANSPARENT=true

This is the output formats from the mapfile:
...
   OUTPUTFORMAT
      NAME "png8bit"
      DRIVER "AGG/PNG"
      MIMETYPE "image/png"
      EXTENSION "png"
      FORMATOPTION "QUANTIZE_FORCE=ON"
      FORMATOPTION "QUANTIZE_COLORS=256"
      FORMATOPTION INTERLACE=OFF
   END

   OUTPUTFORMAT
      NAME "png24bit"
      DRIVER "AGG/PNG"
      MIMETYPE "image/png; mode=24bit"
      EXTENSION "png"
      IMAGEMODE "RGB"
      FORMATOPTION INTERLACE=OFF
   END

   OUTPUTFORMAT
      NAME "jpeg24"
      DRIVER "AGG/JPEG"
      MIMETYPE "image/jpeg"
      EXTENSION "jpg"
      FORMATOPTION "QUALITY=60"
   END
...

Regards,
Pål Kristensen
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