[mapserver-dev] Paletted PNG and Quantization

[Stephen Woodbridge]

Christy,

You might try this:

     OUTPUTFORMAT
         NAME "agg_qn"
         DRIVER "AGG/PNG"
         EXTENSION "png"
         MIMETYPE "image/png"
         IMAGEMODE RGB
         FORMATOPTION "INTERLACE=false"
         FORMATOPTION "QUANTIZE_NEW=ON"
         FORMATOPTION "QUANTIZE_FORCE=ON"
         FORMATOPTION "QUANTIZE_DITHER=OFF"
         FORMATOPTION "QUANTIZE_COLORS=256"
         #TRANSPARENT ON
         #FORMATOPTION "TRANSPARENT=ON"
     END

You can replace FORMATOPTION "QUANTIZE_NEW=ON" with your two lines below 
I think.

-Steve W

On 4/13/2012 11:22 AM, Christy Nieman wrote:
> Hi all,
>
> Just wanted to make sure that I'm doing this right before filing a bug:
>
> With MapServer 6.0.2 and master, I wanted to have an 8-bit PNG with the
> colours defined by a palette. In previous versions of MapServer, all I
> had to do was put
>
> FORMATOPTION "PALETTE_FORCE=TRUE"
> FORMATOPTION
> "PALETTE=/mnt/data1/mapsherpa_v3_demo_data/map/map_overlay/templates/palette_rgba.txt"
>
> in the OUTPUTFORMAT. When I did this in MapServer >= 6, I got a very
> ugly output (looked like there was hardly any anti-aliasing happening).
> Looking in mapimageio.c around line 422, I discovered that I needed to
> also have FORMATOPTION "QUANTIZE_COLORS=<a number greater than 0>" in
> the OUTPUTFORMAT or no quantization would happen to add the required
> colours for anti-aliasing.
>
> The documentation for the AGG/PNG driver explicitely says that
> “PALETTE_FORCE=on” is used to reduce image depth with a predefined
> palette. This option is incompatible with the previous quantization
> options. But this would seem to no longer be true.
>
> Is this a documentation error, or a problem in the mapimageio.c code?
>
> Thanks,
> Christy
> --
> Christy Nieman
> GIS Technician
> DM Solutions Group, Inc.
> Email: cnieman at dmsolutions.ca <mailto:cnieman at dmsolutions.ca>
> Web: http://dmsolutions.ca
>
>
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