Non-linear axis

[Irene Dumkow <irene.dumkow(at)uni-essen.de>]

I am trying to add axis to an image. This part works (using a contour
plot
for the axis and matching the image size and plot window). My problem
is that I would like to have one of the y-axis with a non-linear
scaling, 
in this particular case it is basically y1*y1. I tried something with
reading in the tickvalues, calculating the new values and than using
YTICKNAMES, but IDL still does the y-scale linearly. Any hints,
pointers, etc would be more
than welcome.

Irene Dumkow