342 CHAPTER 9 ADVANCED DRAWING Where the (Affordable web hosting)
342 CHAPTER 9 ADVANCED DRAWING Where the swirl is red, you re seeing just that red. The layer mode is Normal, so GIMP takes each pixel in the top layer (the red swirl), determines that it s not transparent, and shows you only that. Outside of the swirl, the top layer is transparent, so GIMP shows you the next layer down. Simple! But what happens if you set the layer mode to Subtract (Figure 9-10)? Figure 9-10. The red swirl with Subtract mode Why did the red swirl turn that color? In Subtract mode, the color you see is the result of subtracting the front layer (the swirl) from the back layer (the background). Each color channel is subtracted separately. Remember that white is the combination of the three primary colors: red, green, and blue. Each color has a range from 0 to 255 (8 bits, in computer terminology). A white pixel is (255, 255, 255) to the GIMP. A red pixel is (255, 0, 0): all the red, with no green or blue. So: white red = (255 255, 255 0, 255 0) or (0, 255, 255). The result has no red at all, but full green and blue: it s cyan. That s why the red swirl on top of a white background becomes cyan in Subtract mode.
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