Python: Normalize image exposure

Question

I\'m working on a project to measure and visualize image similarity. The images in my dataset come from photographs of images in books, some of which have very high or low expos

Answer 1

Histogram equalisation works surprisingly well for this kind of thing. It's usually better for photographic images, but it's helpful even on line art, as long as there are some non-black/white pixels.

It works well for colour images too: split the bands up, equalize each one separately, and recombine.

I tried on your sample image:

Using libvips:

$ vips hist_equal sample.jpg x.jpg

Or from Python with pyvips:

x = pyvips.Image.new_from_file("sample.jpg")
x = x.hist_equal()
x.write_to_file("x.jpg")