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We can layer textures one on top of another by using a technique similar to the one that allows television viewers to see a forecaster standing in front of a weather map when in actuality the forecaster is standing in front of a blue wall in a studio. The colors of the background weather map is substituted for the blue color. (Have you noticed that they never wear blue?) We can do the same thing. We want to place the word "hello" on top of a map of the world. The black background of the "hello" image will be treated as transparent. To create a pixel in the final image, we find the colors in the corresponding pixel locations in the two input images and combine the two.