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

[Stephen Woodbridge]

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