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Composting, part 2: practice

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1 Author(s)
J. F. Blinn ; California Inst. of Technol., Pasadena, CA, USA

For pt. 1 see ibid., 1994. The author discusses the practice of image composting and in particular the Porter-Duff "over" operator. In part 1 we derived the operator for compositing a foreground pixel F "over" a background pixel B as: B(1-F/spl alpha/)+F, where each pixel is a vector with four components: red, green, blue, and alpha (the coverage or opacity amount), and standard vector algebra applies. I've found it most useful to provide "over" as an inplace operator; you have an image stored in a frame buffer and want to lay another image on top of it. In other words, the result of "F over B" replaces B. Pixel representation, conversions, pixel arithmetic, 16-bit over 8-bit, 8-bit over 8-bit, and other 8-bit possibilities are discussed.<>

Published in:

IEEE Computer Graphics and Applications  (Volume:14 ,  Issue: 6 )