An image processing method includes the following steps. Firstly, foreground image data and background image data are received, wherein the foreground and the background image data corresponds to the same pixel in a display panel. Then, a foreground ratio and a background ratio are determined in response to an operational event. Next, a first value is obtained by multiplying the foreground image data by the foreground ratio, and a second value is obtained by multiplying the background image data by the background ratio. Then, an output image data is obtained by adding the first value and the second value. After that, the output image data is displayed at the pixel in the display panel.