A controller for generating an output image to be rendered on a transparent display panel is provided. The controller is configured to: receive an input image; calculate an opacity of each pixel in the input image according to a predetermined equation associated with the transparent display panel; determine a display mode of one or more portions of the input image according to transparency indication information associated with the one or more portions of the input image, wherein the display mode corresponds to transparency of the one or more portions in the input image; and obtain the output image to be displayed on the transparent display panel according to the determined display mode of the one or more portion of the input image.