[mapserver-dev] OUTPUTFORMAT with AGG and IMAGEMODE PC256?

Daniel Morissette dmorissette at mapgears.com
Tue Aug 12 13:40:36 EDT 2008

Thanks Steve and Thomas. The information that you sent helps a lot.


thomas bonfort wrote:
> you have to use IMAGEMODE RGB, although the formatoptions you can
> apply will create the equivalent of a pc256 image.
> instead of the palette options you gave, there's also
> which will have the "best" 256 colors retained to create the pc256
> image (note that original (ie mapfile) colors aren't kept, so you
> can't do tiling with this as adjacent tiles aren't guaranteed to have
> the same color for a given feature).
> an intermediate method is to use a palette, in which you only specify
> the colors you want to keep (with some scripting magic involving a
> `grep -i color mapfile.map`). the 256 - n remaining colors will be
> automatically computed, insuring seamless tiles *and* best-fit colors.
> thomas
> On Tue, Aug 12, 2008 at 4:39 PM, Daniel Morissette
> <dmorissette at mapgears.com> wrote:
>> Dev's,
>> Is there a way that we could allow the use of IMAGETYPE PC256 with the
>> AGG/PNG driver, in the interest of reducing the size of the output images?
>> i.e. an OUTPUTFORMAT like this:
>>    NAME                  "png"
>>    DRIVER                "AGG/PNG"
>>    MIMETYPE              "image/png"
>>    IMAGEMODE             "PC256"
>>    EXTENSION             "png"
>>    FORMATOPTION          "PALETTE=/path/to/palette.txt"
>> END
>> I realize that AGG requires RGB buffers internally to do its antialiasing,
>> but could we not post-process the image to convert it from the internal RGB
>> representation to PC256 before generating the output? With a very simple
>> test that I made, producing the same (very simple) map in PC256 mode instead
>> of RGB makes it pass from 38kb to 5kb... that is quite a gain, well worth
>> the extra CPU time.
>> Or is this possible already and if yes what is the OUTPUTFORMAT definition
>> to use?
>> Thanks
>> Daniel
>> --
>> Daniel Morissette
>> http://www.mapgears.com/
>> _______________________________________________
>> mapserver-dev mailing list
>> mapserver-dev at lists.osgeo.org
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Daniel Morissette

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