Method of measuring the focus of close-up images of eyes

A method of determining whether an image of an eye is in focus wherein the image contains an iris portion having a radius r.sub.i and a pupil portion having a radius r.sub.p and there is an pupil/iris boundary between the iris portion and the pupil portion, the image is formed of pixels and there are at least 5 pixels of the iris portion of the image and at least 5 pixels of the pupil portion of the image on a single line comprised of:

• a. selecting a set of pixels along a line passing through the pupil/iris boundary the set containing at least 5 iris portion pixels and at least 5 pupil portion pixels:
• b. computing a statistical value M.sub.i of all iris pixels in the selected set;
• c. computing a statistical value M.sub.p of all pupil pixels in the selected set;
• d. computing a step size H such that H=M.sub.i -M.sub.p ;
• e. determining a gradient of pixel values along the line for the selected set of pixels;
• f. forming a second set of pixels by excluding from the selected set of pixels that pixel having a largest absolute gradient value;
• g. determining an average S of the absolute gradient values of the pixels in the second set of pixels;
• h. computing 1/w=S/H;
• and
• i. if 1/w is greater than 0.5 using the image for identifying a subject whose eye is in the image using iris identification techniques and if 1/w is less than or equal to 0.5 selecting a new image and repeating steps a through h.