[svg-developers] Way to get average Pixelvalue of a picture segment defined by geometric object/path?

[[e-mail] [svg-developers]]

Is there a (simple) way to get the average value for pixels 'behind' geometric objects? I whant to do some mosaiic-style path and determine colors for each tile based on a raster/pixel image.

clarification image:
Loading Image... http://kai.dj/tmp/obj.png

I'd like to have some getAvgValue(Path1) functionality
 or SVG-mosaiic-filter or anything with that functionality