A computer implemented method for controlling the display of a tile image on a display of a computer device, the method comprising: supplying image texture data to a shader program executed on the computer device, the image texture data comprising a plurality of sets of predefined masks, each set of predefined masks for forming a respective tile image comprising multiple portions, wherein each mask (502, 506, 510) of the set determines how a respective portion of the tile image is to be rendered, wherein the image texture data for predefined masks (502, 506, 510) for rendering a portion of the tile image is stored in a respective channel of an image file, wherein each channel stores a plurality of predefined masks (502, 506, 510) for creating that portion of the image, and wherein the set of predefined masks for rendering the tile image comprises a mask from each channel and wherein each of the predefined masks (502, 506, 510) for forming a tile image has a predefined colour value for the respective portion of the tile image; selecting at random tile images for display from a plurality of tile images to form an image to be used in a computer game; determining a location where each mask (502, 506, 510) in the set of predefined masks for forming the respective portion of a selected tile image is stored, in the image texture data; supplying an indication of said location to the shader program executed on the computer device to control the shader program to use the set of predefined masks to form the selected tile image on said display, the predefined masks being digested by the shader program to compose the selected tile image; querying computer memory of the computer device to determine tint colours to be applied to each of the predefined masks (502, 506, 510) of the selected tile image, and supplying an indication of the determined tint colours to the shader program to adjust the predefined colour value of each of the predefined masks (502, 506, 510) of the selected tile image using the determined tint colours; and selecting a shade adjustment parameter at random, and using the shade adjustment parameter to adjust at least one of the determined tint colours prior to supply to the shader program, or supplying the shade adjustment parameter to the shader program to adjust at least one of the determined tint colours. supplying image texture data to a shader program executed on the computer device, the image texture data comprising a plurality of sets of predefined masks, each set of predefined masks for forming a respective tile image comprising multiple portions, wherein each mask (502, 506, 510) of the set determines how a respective portion of the tile image is to be rendered, wherein the image texture data for predefined masks (502, 506, 510) for rendering a portion of the tile image is stored in a respective channel of an image file, wherein each channel stores a plurality of predefined masks (502, 506, 510) for creating that portion of the image, and wherein the set of predefined masks for rendering the tile image comprises a mask from each channel and wherein each of the predefined masks (502, 506, 510) for forming a tile image has a predefined colour value for the respective portion of the tile image; selecting at random tile images for display from a plurality of tile images to form an image to be used in a computer game; determining a location where each mask (502, 506, 510) in the set of predefined masks for forming the respective portion of a selected tile image is stored, in the image texture data; supplying an indication of said location to the shader program executed on the computer device to control the shader program to use the set of predefined masks to form the selected tile image on said display, the predefined masks being digested by the shader program to compose the selected tile image; querying computer memory of the computer device to determine tint colours to be applied to each of the predefined masks (502, 506, 510) of the selected tile image, and supplying an indication of the determined tint colours to the shader program to adjust the predefined colour value of each of the predefined masks (502, 506, 510) of the selected tile image using the determined tint colours; and selecting a shade adjustment parameter at random, and using the shade adjustment parameter to adjust at least one of the determined tint colours prior to supply to the shader program, or supplying the shade adjustment parameter to the shader program to adjust at least one of the determined tint colours.