[mapserver-dev] Paletted PNG and Quantization

[Stephen Woodbridge]

I have used it with tile generation and it performs quite well at 
avoiding the color shifts between tiles, but setting a palette does a 
better job. I have not tried an explicit palette in a while but I do not 
maintain a tile cache here.

Given it a try. Also try my output block and swap you explicit palette 
and see if the quality issues are resovled. You did post your whole 
output block so I'm not sure if there were other thing affecting the 
quality, like using driver GD/PNG vs AGG/PNG.

-Steve W

On 4/13/2012 1:06 PM, Christy Nieman wrote:
> 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
>>>
>>>
>>> _______________________________________________
>>> mapserver-dev mailing list
>>> mapserver-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/mapserver-dev
>>
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