[mapserver-users] 8 bit versus 24 bit output in MapServer 6.x

[Richard Greenwood]

For what it's worth:

https://github.com/mapserver/mapserver/issues/4512

Rich

On Tue, Oct 23, 2012 at 7:30 PM, Stephen Woodbridge
<woodbri at swoodbridge.com> wrote:
> On 10/23/2012 4:31 PM, Richard Greenwood wrote:
>>
>> All -
>>
>> I've have always used 8 bit GIFs because they are generally the
>> smallest. I serve a rural area with flaky internet and I do a good bit
>> with mobile, so size is more important to me than pixel-perfect.
>> Since MapServer 6.0 I have found 8 bit output (GIF or PNG) to be much
>> more buggy than 24 bit output. Bugs that I have been able to isolate
>> and report have been fixed very quickly by the devs, but I'm
>> struggling with a couple now that are sporadic and that I can not
>> shrink down to a reproducible bug report. I see the same issues in
>> Windows and Linux. I'm running 6.0.3 on both. So:
>> 1. What image format are people generally using? Am I stuck in the
>> past with 8 bit images? Should I just go with 24 bit and not worry
>> that my images are several times larger?
>> 2. My general sense is that the root of the issues I'm seeing are in
>> the shift from GD to AGG. Are PC256 PNGs generated by GD or AGG?
>> 3. Any general advise for 8 bit output? For GIF is use the default (I
>> don't define an OUTPUTFORMAT block) for PNG I do define an
>> OUTPUTFORMAT block and use IMAGEMODE PC256.
>>
>> The two issues that I'm struggling with right now are that my label
>> colors change as I pan and zoom, and that the HATCH fill pattern
>> extends outside of its polygons. In both cases switching from an 8 bit
>> output to a 24 bit output resolves the issue.
>>
>> Thanks,
>> Rich
>>
>
> Rich,
>
> I use 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
>
> It gives me 8-bit png and I have no problem with it. Here is an example
> using mapserver and mapcache
>
> http://imaptools.com:8080/demo/tiger-tiles.html
>
> And here is an example using just mapserver and draw on demand:
>
> http://imaptools.com:8080/demo/tiger2011.html
>
> I think both of these are using:
>
> MapServer version 6.0.2 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG SUPPORTS=PROJ
> SUPPORTS=AGG SUPPORTS=FREETYPE SUPPORTS=ICONV SUPPORTS=FRIBIDI
> SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER SUPPORTS=GEOS
> INPUT=POSTGIS INPUT=OGR INPUT=GDAL INPUT=SHAPEFILE
>
> Hope this helps,
>   -Steve W
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-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com