1. A metering method of automatic exposure for determining an exposure value of a picture having a subject, comprising: a subject detecting step comprising using focus values of the picture to detect the subject and passing subject region information to an automatic exposure metering function; and an exposure value calculating step comprising having the auto exposure metering function use the subject region information to calculate an exposure value of the picture, wherein the exposure value calculating step comprises: calculating an average luminance of a left region, a center region, and a right region; sorting the luminance of the left, center, and right regions and calculating a Contrast_Ratio; finding interesting regions; and calculating the exposure value according to the equation: 
 Exposure value=(1−Contrast_Ratio)×subject+Contrast_Ratio×interesting regions.