Mapnik Output Formats

Mapnik supports rendering with both AGG and Cairo (see MapnikRenderers for more detail), and can create maps or map tiles in a variety of formats.

Tradeoffs

Mapnik Format Renderer Type Visual Quality Rendering Speed* Size* Relevant Code
png AGG 32-bit png 0.12 s 16 KB source:trunk/include/mapnik/png_io.hpp
png256 AGG 8-bit png256 0.12 s 8 KB source:trunk/include/mapnik/png_io.hpp
jpeg AGG ? jpeg 0.12 s 8 KB source:trunk/include/mapnik/jpeg_io.hpp
ARGB32 (png) CAIRO 32 bit png24 0.24 s 20 KB source:trunk/include/mapnik/cairo_renderer.hpp
RGB24 (png) CAIRO 24 bit alpha png32 0.24 s 20 KB source:trunk/include/mapnik/cairo_renderer.hpp
svg CAIRO N/A svg 0.28 s 980 KB source:trunk/include/mapnik/cairo_renderer.hpp
pdf CAIRO N/A pdf 0.40 s 232 KB source:trunk/include/mapnik/cairo_renderer.hpp
ps CAIRO N/A postscript 0.36 s 1.4 MB source:trunk/include/mapnik/cairo_renderer.hpp

* Rendering speeds and output sizes based on sample 256 X 256 tiles created using the GettingStarted sample data, run using Mapnik SVN Head (r 747), cairo 1.8.0, and pycairo 1.4.12.

More tests with complex styles, labeling are needed

PNG Quantization

In the 0.7.1 release, Mapnik gained some enhanced (beta) flexibility around reducing colors. See details at [mapnik-devel email http://lists.berlios.de/pipermail/mapnik-devel/2010-March/001081.html] and ticket #477: http://trac.mapnik.org/ticket/477#comment:10 

- c=256 - limit number of colors (default 256), works with octree and
hextree

- t=2 - select transparency mode: 0-no alfa, 1-binary alfa(0 or 255),
2-full alfa range, default is 2, works with octree and hextree

- m=o - choose quantization method, available options: o-existing
octree, h-new hextree with optimizations, default is octree

- g=2.0 - kind of gamma correction for pixel arithmetic in hextree
method, default value 2.0 worked best with most of my test images, value
1.0 means no gamma correction.

So to use new format i.e. in python:
  view.save("test.png",'png256:m=h')
or other example in c++:
  save_to_file(vw, "test.png", "png256:t=1:c=128");

Tradeoffs

TODO: discussion of tradeoffs and situations to use which format

References