Resolution of raster images in SVG

Currently, when writing a SVG, all raster images produced by imshow are
scaled to a fixed, low resolution. (72dpi?)

The least I would expect is the 'dpi=' option of savefig to be used for
writing PNGs in the SVG renderer.

Even better would be to switch off rescaling completely for any vector
output (EPS and SVG). This would allow optimal quality in post-processing.

I even believe that rescaling to a uniform resolution should be an
option, not the default.

Has anybody else spent thought on this?