[Matplotlib-users] Transparent png - the sequel

[Robert L. <ro...@le...>]

Having just had a call from a client saying 'love the new graph, but why is the 
background sky blue' and thinking 'I've never done anything with sky blue in my 
life! - what have I broken', I then proceeded to learn more about Microsoft's 
lack of standards support than I really wanted or could spare the time to do.

The upshot is that transparent png's work perfectly in all tested browsers, as 
well as sundry image viewers/editors but not in IE, sigh!

I wondered why I hadn't struck this problem before so I looked at a few of my 
older, gnuplot generated, transparent png's, which worked perfectly in IE. A 
quick look with gimp shows that gnuplot uses a different technique for 
transparency than does Matplotlib. The transparent colour info for the gnuplot 
image is R:0, G:0, B:0, Alpha:0, Index:254 while for Matplotlib it is R:255, 
G:255, B:255, Alpha:0, with no Index.

Now I don't know enough (er, anything) about the low level detail of the png 
format, but I wonder if it is possible to achieve the same result in Matplotlib 
or do I need to post-process (using ImageMagick or similar) to generate the same 
style of png or possibly gif's?

Robert