Adaptive Threshold

When discussing the thresholding operation, we assumed that the gray levels of the background and the objects to inspect were reasonably uniform across the image. In real-life scenarios, this is rarely the case. In particular, the lighting conditions can vary significantly from one side of the image to the other, especially when the camera’s field of view is more than a few tens of centimeters.

The intensity gradient problem

Let’s consider the following checkerboard image, affected by a strong intensity gradient due to non-uniform lighting: