mapnik-org/mapnik — Issue #686: png256 rasters becoming black and white
Author: artemp
Created: 2011-10-11 08:08:14+00:00
State: open
Labels: Agg_Renderer

Here's how I produce the issue :
Step 1 :
Generate a large png tile in png256 mode.
Step 2 :
Use the previously generated large tile as a raster source (Gdal plugin, default symbolizer) for a new image rendered as png256 too.
=> the resulting image is in a poor gray scale.

Doing this in standard png doesn't have any trouble.

With suggestion of Marcin Rudowski, I tried to set the image type as "png256:m=h" with no visible changes in the resulting images.

Here is a compressed file with 2 rasters and a tile extracted out of each raster. One couple raster/tile is standard png, the other is png256 (not "png256:m=h").
http://www.mediafire.com/?w2883d8wn2g72 (30.38 Mo)
(raster's projection is EPGS:900913 Google spherical mercator)