A method comprises detecting edges in at least a region of a captured focus image, using adjacent pixels of the region to obtain first edge detection results and filtering the first edge detection results. The first filtering comprises comparing differences in pixel contrast in the first edge detection results with a first threshold value and removing the differences in pixel contrast that are less than the first threshold value from the first edge detection results. The method further comprises detecting edges in at least the region, using non-adjacent pixels of the region to obtain second edge detection results and filtering the second edge detection results. The second filtering comprising comparing differences in pixel contrast in the second edge detection results with a second threshold value and removing the differences in pixel contrast that are less than the second threshold value from the second edge detection results.