I sent this message to the list this time yesterday and it doesn't seem to have either arrived or bounced - so I'm trying again.
I've written a patch (attached) to allow the PS backend to respect the
dpi that's given to the FigureCanvasPS on initialisation when saving
images. The solution I came with to do this isn't the nicest, but I
couldn't see any significantly different way to do it without changing
the rendering process for images.
What I've done is add a get_image_magnification method to the default
backend with a default return value of 1.0. This magnification factor
is then taken by the draw method of the figure, axes or image and passed
as a keyword argument to the make_image method of the image where it
used to scale the widthDisplay and heightDisplay returned from the
bounding box. (I also changed the self.make_image(False) call in
Image.write_png to self.make_image() as I'm pretty sure that's what was
meant to be - and if I hadn't the introduction of my new keyword
argument would have resulted in a zero size image.)
By returning a magnification of dpi/72.0, the PS backend is able to
instruct the image instances to create larger images which it then
scales by an appropriate value on output to give the requested dpi.
This patch, or something like it, is vital for me at the moment because
the low 72 dpi output used by matplotlib at the moment gives rise to
some fairly significant distortion to my results. I imagine others will
come across the same problem.
I hope this patch is useful,
mpl.patch (6.01 KB)