A circuit and a method for image processing are provided. The image processing circuit has an adaptor and a sharpening circuit. The adaptor has a processing unit and a weight generator. The processing unit receives an input video signal, and the input video signal has information of a plurality of pixels. The processing unit processes the input video signal to calculate a color difference value of a target pixel of the pixels. The weight generator generates a weighting signal according to the color difference value. The sharpening circuit performs a sharpening operation on the input video signal according to the weighting signal to generate a sharpened video signal.