1. An image processing method for scaling an image from an original resolution to a target resolution, wherein a pixel value P T of a target pixel point N T in the target resolution is theoretically composed of original pixel values P 1 -P K of original pixel points N 1 -N K in the original resolution, and K is a positive integer larger than 1, the method comprising: a computer performing the steps of: finding theoretical combination ratios R 1 -R K corresponding to the original pixel points N 1 -N K ; converting the theoretical combination ratios R 1 -R K to corresponding weights W 1 -W K , wherein each of the corresponding weights W 1 -W K is an integer between 1 and 2 n , n is an integer, and the sum of the corresponding weights W 1 -W K is 2 n ; and calculating the original pixel values P 1 -P K with the corresponding weights W 1 -W K using a scaler, to generate the pixel value P T of the target pixel point N T and complete the image processing, wherein converting the theoretical combination ratios R 1 -R K to corresponding weights W 1 -W K further comprise checking a look-up table to obtain the corresponding weights W 1 -W K , wherein the look-up table has a plurality of table fields, each having a field order, and provides a conversion rule from a value to an integer not larger than 2 n , and n is an integer, and wherein checking the look-up table to obtain the corresponding weights W 1 -W K further comprise: providing a theoretical combination ratio R K ; determining whether the theoretical combination ration R K being look up is less than a limit value; and setting the corresponding weight W K to zero if the theoretical combination ratio R K being looked up is less than the limit value.