Quantify how blurred is an image

[Christ0phe]

Hello:
I would like to implement an IMAQ-algorithm so that I am able to quantify the - blurriness - of an image. The aim in my application is to accept only the non-blurred images. I saw some references in the literature speaking about edge detections and Sobel filters but cannot find a way to make it complete. Any help would be appreciated.
Chris

[Mike H2]

Typically many of our customers use edge detection with variable slope values to see the steepness of the edge's slope. You may want to also look at our auto-focus example that is on the web.

Auto-Focus Example

[Steverino]

IMHO, I think a measure of blurriness is a relative measurement. In other words, you can use measure of stdev of gray values, or the stdev of the gray values after processing (e.g., edge detection), but the value would need to be referenced to some other value. If the sceen doesn't change, then perhaps you can determine what this value is on a well-focused image. After that, you can set some kind of threshold value of your measurement.