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

On 04/01/2012 02:32 AM, Nick LaForge wrote:

You can see from the trend that there does exist a set of parameters
for the threshold function that gives acceptable contrast for every
given point, and that this one parameter (the upper level) increases
monotonically as it moves along the "vector field".

Something to try:

1) Run the Colors > Auto > Equalize filter against your image.

2) Then use the Colors > Curves tool, setting the "left" value at 0
and the "right" value at 255, to create a very steep, nearly
vertical "curve."  Move this back and forth until you come close to
the finished appearance you want.

3) Finally, run the threshold tool.

This method first increases contrast in low contrast areas while
reducing it in high contrast areas ("Equalize"), then allows you to
do a more-than-one-color threshold effect that adds or removes
values near the threshold for a two color conversion ("Curves") and
finally the Threshold tools gives you a two color map.

YMMV, there are so many ways, etc. etc.



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