[Matplotlib-users] overlay of images

[Teemu R. <Tee...@he...>]

Hi,

I recently got matplotlib working on OSX (only agg so far) and am now 
trying to create a picture with two overlayed images so that only a certain 
range of values of the top-most figure are blended with the bottom one.

The first image would be plotted with the gray palette:
im_bottom=figimage(bottom_data,xo=0, yo=0,cmap=cm.gray)

The second image would be in colors:
im_top=figimage(top_data,xo=0, yo=0,cmap=cm.hot)

I would like to 'threshold' the top figure so that only values, say, 
greater than 30 are plotted with 'hot' colors and elsewhere the gray 
im_bottom is shown (without blending it with the colors of im_top).

I was hoping that I could do something easy like this:
im_top=figimage(where(less(data_top,30),do_not_plot_this_value,data_top),xo=0,yo=0,cmap=cm.hot,alpha=0.5)

How to do this?
Do I have to combine the RGB values of the two images 'manually'?


Cheers,


--
Teemu Rinne