1. A method for image zoom out processing, comprising: determining whether a predetermined zoom out ratio is smaller than a first predetermined threshold, wherein the predetermined zoom out ratio is a ratio of an original resolution of an image to a target resolution, and the original resolution is greater than the target resolution; when the predetermined zoom out ratio is smaller than the first predetermined threshold, performing a zoom out process on the image according to the first predetermined threshold by a bilinear interpolation algorithm to obtain a zoomed out image; determining whether a product of a resolution of the zoomed out image and the first predetermined threshold is greater than or equal to the target resolution; when the product is greater than or equal to the target resolution, continuing the step of performing the zoom out process on the image according to the first predetermined threshold by the bilinear interpolation algorithm to obtain the zoomed out image; and when the product is smaller than the target resolution, performing the zoom out process on the image according to a second predetermined threshold, so that the resolution of the zoomed out image reaches the target resolution, wherein the second predetermined threshold is calculated according to an equation: N ┌log N X┐−1 *M=X, where N is the first predetermined threshold, M is the second predetermined threshold, X is the predetermined zoom out ratio, and ┌ ┐ is a rounding up operation.