problems when zooming in to the pixel level

Dear All,

i'm displaying an image (cmap = gray, interpolation = nearest: i want to
see the pixels) and i plot point (markers) on top of the image. These
markers are calculated at the subpixel level so i want to zoom in to see
whether they are placed correctly.

When zooming in i notice two things:

1. at certain zoomlevels the image disappears (i do see the markers). At
other zoomlevels i see a tremendous change in brightness of the image.
Especcially at high zoomlevels i see this behaviour

2. when i zoom in a lot (selecting rectangle all over), the display gets
slower and slower... In the end, when viewing about 5x5 pixels or so it
becomes too slow...

Any ideas? I would love to use matplotlib (i really like it) but it
seems to have performance problems when displaying images is your main

Rein van den Boomgaard

(if needed i could send a zip file with programs and data)