[Gimp-user] threshold function parameters that vary by position? (going to B&W from a book page photo)

[Nick LaForge <nicklaforge gmail com>]

Hello,

I would like to obtain a black and white image of a photograph of a book page.

My attempt to do this is by running the threshold function over the
entire image.  This appears to give the desired result, but only
locally.  It appears that the optimum parameters of the threshold
function vary by position (i.e., according to some scalar field), with
one extreme in the center of the glare and then radiating outward.  So
just running the threshold function over the entire image with
constant parameters always gives sub-optimum contrast for 75% of the
image.  Will I have to find a way to run the threshold function with
non-constant parameters, or is there some other tool to do the job?

Thanks for reading,
Nick