An image processing method for increasing the stereoscopic effect of an image is provided. Difference mask data including an object area and a background area is created from image data, and the center coordinate of the object area is calculated. Then, a gradation pattern is selected in accordance with the average brightness value of the object area and applied to the background area, whereby a gradation mask data is created. After that, the image data of the background area is converted into image data based on the gradation mask data, so that the stereoscopic effect of the image is increased.