An image processing device and a method thereof are provided. In the image processing method, an adjusting value is computed according to a pixel of a current image and a plurality of reference pixels nearby. In addition, a weighted coefficient is computed according to a gray-scale difference between the pixel of the current image and a pixel of a previous image. Further, a weighted adjusting value is computed according to the adjusting value and the weighted coefficient. Besides, the pixel of the current image is adjusted according to the weighted adjusting value to generate a pixel of an output image. Thereby, the current image is adjusted adaptively to increase the quality of the output image.