Autofocus technique has been widely used in optical tracking and measure system, but it has problem that when the
autofocus device should to work. So, no-reference image sharpness assessment has become an important issue. A new
Sharpness Function that can estimate current frame image be in focus or not is proposed in this paper. According to
current image whether in focus or not and choose the time of auto focus automatism. The algorithm measures object
typical edge and edge direction, and then get image local kurtosis information to determine the degree of image
sharpness. It firstly select several grads points cross the edge line, secondly calculates edge sharpness value and get the
cure of the kurtosis, according the measure precision of optical-equipment, a threshold value will be set beforehand. If
edge kurtosis value is more than threshold, it can conclude current frame image is in focus. Otherwise, it is out of focus.
If image is out of focus, optics system then takes autofocus program. This algorithm test several thousands of digital
images captured from optical tracking and measure system. The results show high correlation with subjective sharpness
assessment for s images of sky object.