Fast 2d brown/pink noise generation?

[Mathias]

Dear NG,

I'm looking for a fast way to produce 2d-noise images with 1/f or 1/f^2 
spectrum. I currently generate the noise via inverse FFT, but since I 
need lots of data (~10^7 for a monte carlo simulation) it needs to be 
really fast. Does someone know a faster way than my approach?

- Dimensionality is between 20x20 and 100x100
- The spectrum doesn't need to be exactly pink/brown, an approximation
    is fine.
- Implementation in either matlab or scientific python (LAPACK anyway)


Thanks a lot for hints, literature, algorithms!
    Mathias