The present invention provides an image processing circuit and associated image processing method. In the image processing circuit, a characteristic value calculation circuit is designed to calculate the plurality of characteristic values of consecutive-three-pixels with increasing/decreasing brightness, the plurality of left-side characteristic values of consecutive-three-pixels with increasing/decreasing brightness and the plurality of right-side characteristic values of consecutive-three-pixels with increasing/decreasing brightness, for the brightness adjustments. The adjusted brightness values of the present invention have sharper edges to improve the image quality.