2.2.2 Adaptive Thresholding
When the lighting is not uniform in an image, a global threshold (or pair of
thresholds) does not work very well. The part of the wanted image that is too dark
is changed to background (see previous example). To solve this a threshold (or pair
of thresholds) is need which uses only local information. There are two main
approaches to this:
- Breaking the image into many smaller overlapping sub images, each of which has
a histogram which can be used to choose the threshold(s) for the sub-image
- A less cpu intensive approach using local values - e.g. mean, median,
(max+min)/2, etc.
