[GRASSLIST:9145] Equalizing contrast between air-photos

[Craig Aumann]

I have a bunch of air-photos (geotiffs) which overlap slightly.  Is
there an easy way to equalize the contrasts between all the air-photos?

For example, how would one do this for two air-photos? What if its a
block of 4??

Each individual air-photo is quite large, so computational burden is a
concern. 

I'm also quite willing to consider non-GRASS options. I'm not that up on
image processing issues.  

Thanks!
Craig

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