A method includes displaying a bitmap of unique groups of colored tiles on the display screen and reading a color value of a first pixel in a first tile in the bitmap. Color values of tiles within the first tile's group are determined. The position of the first pixel within the first tile is determined. The position of the first tile's group within the bitmap and the position of the first tile within the bitmap are also determined. The position of the first pixel in the bitmap and the position of the bitmap on the display screen are calculated. A performance metric is calculated based at least in part on the position of the bitmap on the display screen.