Calculating image acutance

Is there a simple algorithm for calculating an acutance value (or sharpness) for a graysc开发者_运维知识库ale image?

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As I understand it, the Accutance is the mean value of the Gradient Filter.

Example in Mathematica:

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Relationship between brightness and the blurriness of an image

The question's title is confusing, but the answer answers this.