Only one maximum or minimum - Avoid error due to local extrema

2) Large amplitude difference in focus measure

The focus measure should vary greatly between the point of the true focus plane and the various defocused plane.

3) Wide range

The focus measure should vary continuously within a large range of errors. This ensures that the algorithm will work even at situations when the image is highly defocused.

4) Minimum computational complexity

Speed and easy implementation

5) General Applicability

Algorithm should not be limited to only special type(s) of images.
In this project, I have used 3 different types of images to reinforce this criterium.