Interlacing (bitmaps)

Article summary

interlacing over a 16×16 image In computing, interlacing (also known as interleaving) is a method of encoding a bitmap image such that a person who has partially received it sees a degraded copy of the entire image. When communicating over a slow communications link, this is often preferable to seeing a perfectly clear copy of one part of the image, as it helps the viewer decide more quickly whether to abort or continue the transmission. Interlacing is supported by the following formats, where it is optional: * GIF interlacing stores the lines in the order 0,8,16,\dots,(8n),\ 4, 12, \dots, (8n+4),\ 2,6,10,14,\dots,(4n+2),\ 1,3,5,7,9,\dots,(2n+1). * PNG uses the Adam7 algorithm, which interlaces in both the vertical and horizontal direction. * TGA uses two optional interlacing algorithms: **Two-way: 0,2,4,\dots,(2n),\ 1,3,\dots,(2n+1), **And four-way: 0,4,8,\dots,(4n),\ 1,5,\dots,(4n+1),\ 2,6,\dots,\ (4n+2),3,7,\dots,(4n+3). * JPEG, JPEG 2000, and JPEG XR (actually using a frequency decomposition hierarchy rather than interlacing of pixel values) * PGF (also using a frequency decomposition) Interlacing is a form of incremental decoding, because the image can be loaded incrementally. Another form of incremental decoding is progressive scan.…

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