Patent ID: 7268817

Claim:
A method of automatically focusing a camera, comprising the steps of: measuring a high frequency amount in an image signal according to a position of a focus lens at three or more positions; identifying at least three positions, x 1 , x 2 , and x 3 along with their corresponding high frequency amounts y 1 , y 2 , and y 3 ; respectively; determining an absolute value of a difference between y 2 and y 1 ; determining an absolute value of a difference between y 1 and y 3 ; and if the absolute value of the difference between y 2 and y 1 is not less than a first threshold value, and if the absolute value of the difference between y 1 and y 3 is not less than a second threshold value, then proceeding with the steps of determining a quadratic function f(x) where f(x) is a high frequency amount in the image signal and x is a position of the focus lens, and determining a position where a derivative ⅆ f ⁡ ( x ) ⅆ x of the quadratic function f(x) is equal to zero corresponding to largest amount of high frequency.