[mapguide-users] patch for Ticket #743 / png8 transparency

Zac Spitzer zac.spitzer at gmail.com
Wed Sep 26 19:47:22 PDT 2012

One of the issues is that with subpixel rendering using AGG, a map using
60 base colours will actually use more than 60 colours for fine edges
(so I believe)

The reason why we use a predefined palette for tiles is that for
Explore Australia,
we were having heaps of problems with the colour of ocean changing
between tiles,
obviously this is less of a problem with a single image dynamic map.

Perhaps the ultimate solution would be to feed to predefined palette into the
the quantization routines as a hint, with any used predefined colours being
discarded. Perhaps this could be triggered when a certain threshold is reached,
i.e. a full palette. An obvious example would be a map using a raster background


On Thu, Sep 27, 2012 at 2:33 AM, Jackie Ng <jumpinjackie at gmail.com> wrote:
> Unless I got this PNG8 quantization business all wrong, if the resulting
> image would use < 256 colors then there shouldn't be a need for the
> quantizer to compute a palette is there? Just take this list of colors that
> we've extracted out of all the Layer/Symbol Definitions and let the PNG8
> quantizer "fill in the blanks" up to the 256 colors.
> If we have defined these colors in our Layer/Symbol definitions, I think
> they should be respected if the total number of colors used < 256.
> - Jackie
> --
> View this message in context: http://osgeo-org.1560.n6.nabble.com/patch-for-Ticket-743-png8-transparency-tp5003596p5004724.html
> Sent from the MapGuide Users mailing list archive at Nabble.com.
> _______________________________________________
> mapguide-users mailing list
> mapguide-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapguide-users

Zac Spitzer
Solution Architect / Director
Ennoble Consultancy Australia
+61 405 847 168

More information about the mapguide-users mailing list