A new algorithm in which the defined hit-miss transform is reformulated by a grayscale erosion of the image with a grayscale structural element of three levels is developed. A necessary condition is defined to choose the correct intermediate grayscale level in the structural element. Then a single-channel incoherent optical correlator with only an image and a structural element is developed to execute the hit-miss transform in parallel by one step thresholding. Experimental results for the face recognition are demonstrated.