Patent ID: 8102464

Claim:
An automatic focusing method in a high-noise environment, applicable to a digital imaging device for adjusting focus distances for at least one object to be photographed, the automatic focusing method comprising: taking a first farthest object distance image under a first exposure condition and a second farthest object distance image under a second exposure condition at a farthest object distance of the digital imaging device; taking a first nearest object distance image under the first exposure condition and a second nearest object distance image under the second exposure condition at a nearest object distance of the digital imaging device; capturing at least one corresponding digital image under the first exposure condition at different object distances between the farthest object distance and the nearest object distance respectively; selecting at least two digital images taken at adjacent object distances sequentially from the digital images to create a composite image, repeating the step until all the digital images captured under the first exposure condition have been superposed sequentially to create the composite images; calculating an object distance corresponding to each of the composite images; calculating high-frequency signals of some pixels in the composite images; calculating the high-frequency signals of at least some pixels in the second farthest object distance image; calculating the high-frequency signals of at least some pixels in the second nearest object distance image; and determining an object distance corresponding to the maximum high-frequency signal as an optimum focusing object distance depending on the relational curve for the farthest object distance, the object distances corresponding to the composite images, and the nearest object distance and corresponding high-frequency signals corresponding thereto, and photographing the object to be photographed.