[mapserver-dev] Paletted PNG and Quantization

[Christy Nieman]

Thanks for the reply, SteveW.

How does this perform with for creating tiled maps?  The reason I use a 
palette is to make sure colours of features are the same between tiles.

Christy

On 04/13/2012 12:45 PM, Stephen Woodbridge wrote:
> 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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