1. An auto-detect method for detecting a single-frame image format, comprising: dividing a single-frame image into a plurality of macro-blocks; dividing each of the macro-blocks into a plurality of sub-blocks; generating a meta-block in each of the sub-blocks; calculating a pixel luminance sum characteristic value for each of the meta-blocks; calculating a first confidence of a left half and a right half of the single-frame image according to the pixel luminance sum characteristic values; calculating a second confidence of an upper half and a lower half of the single-frame image according to the pixel luminance sum characteristic values; and determining a format of the single-frame image according to the pixel luminance sum characteristic values, and the first confidence and the second confidence of the single-frame image.