linear-space image converted to log-space

Hi,

I have a need to reproduce an image like this:

http://diamondhead.org/linear_logspace.png

beginning with data like this:

http://diamondhead.org/linear_linearspace.png

Using logarithmic scaling, the first image (produced by a custom
graphics package) expands lower frequency components while contracting
the higher frequency components.  To do this in object graphics, I
believe I will have to reconstruct the image data so that the lower
frequency [the bottom] information is replicated according to a log
scaling scheme.

I can think of some [tortured] ways to do this but keep thinking there
must be some sophisticated way to handle this in IDL.  Any thoughts
would be appreciated.

Thanks,
-Kevin