Image definition calculation method, automatic focusing method and system

The invention discloses an image definition calculation method, an automatic focusing method and an automatic focusing system. The automatic focusing method comprises the steps of: 1, carrying out thepreliminary focusing of a lens, and enabling the lens to move to a focusing limit value range; 2, shooting a target image, and calculating the definition of each frame of the image; and 3, based on adefinition value of each frame of the image, driving a zoom motor to move, and carrying out peak value search until the zoom motor moves to a focusing position corresponding to the maximum definitionvalue, thereby finishing automatic focusing. According to the automatic focusing method, preliminary focusing is carried out firstly, definition calculation is carried out after preliminary focusing,finally peak value searching is carried out, the zooming motor is driven to move to the focusing position corresponding to the maximum definition value, focusing is completed, and compared with an existing focusing method, the