Patent ID: 7583311

Claim:
An automatic focusing device comprising: an image pick-up element for picking up an image of an object, and obtaining an image signal; an A/D converting circuit for converting the image signal obtained by the image pick-up element into a digital image signal; a contrast acquiring portion for producing a luminance signal through a scanning which contains at least a part where the scanning is performed in a zigzag manner, from the digital image signals obtained by the A/D converting circuit, and for acquiring a contrast value from the produced luminance signal, a cumulative adding portion for adding the contrast value obtained by the contrast acquiring section in accumulation to compute a contrast evaluating value; and a focus lens drive portion for driving a focus lens to a position where the contrast evaluating value computed by the cumulative adding portion becomes maximum, wherein the contrast acquiring portion includes: a luminance signal producing section for producing a luminance signal from the digital image signal obtained by the A/D converting circuit; at least one delay section for delaying the luminance signal produced by the luminance signal producing section; a luminance signal reordering section for reordering a luminance signal delayed by the delay section and a luminance signal produced in the luminance signal producing section so that a reordered luminance signal contains at least a part where the scanning is performed in a zigzag manner; and a contrast extracting section for scanning the luminance signal reordered in the luminance signal reordering portion so that the reordered luminance signal contains at least a part where the scanning is performed in a zigzag manner to extract a contrast value.