Adam7 algorithm

Adam7 is an interlacing algorithm for raster images, best known as the interlacing scheme optionally used in PNG images. An Adam7 interlaced image is broken into seven subimages, which are defined by replicating this 8 8 pattern across the full image: The subimages are then stored in the image file in numerical order. Adam7 uses seven passes and operates in both dimensions, compared to only four passes in the vertical dimension used by GIF. This means that an approximation of the entire image can be perceived much more quickly in the early passes, particularly if interpolation algorithms such as bicubic interpolation are used.

Adam7 is an interlacing algorithm for raster images, best known as the interlacing scheme optionally used in PNG images. An Adam7 interlaced image is broken into seven subimages, which are defined by replicating this 8 8 pattern across the full image: The subimages are then stored in the image file in numerical order. Adam7 uses seven passes and operates in both dimensions, compared to only four passes in the vertical dimension used by GIF. This means that an approximation of the entire image can be perceived much more quickly in the early passes, particularly if interpolation algorithms such as bicubic interpolation are used. File:Adam7_pass_1.png|Pass 1, 1/64 = 1.5625% File:Adam7_pass_2.png|Pass 2, 1/32 = 3.125% File:Adam7_pass_3.png|Pass 3, 1/16 = 6.25% File:Adam7_pass_4.png|Pass 4, 1/8 = 12.5% File:Adam7_pass_5.png|Pass 5, 1/4 = 25% File:Adam7_pass_6.png|Pass 6, 1/2 = 50% File:Adam7_pass_7.png|Pass 7, 1/1 = 100% When rendering, the image will generally be interpolated at earlier stages, rather than just these pixels being rendered. Using this 3-pass pattern means the first pass is (1/2) 2  = 1/4 (25%) of the image. Iterating this pattern once yields a 5-pass scheme; after 3 passes this yields which is then filled in to: In the 5-pass pattern, the first pass (1/4) 2  = 1/16 (6.25%) of the image. Iterating again yields the 7-pass Adam7 scheme, where the first pass (1/8) 2  = 1/64 (1.5625%) of the image. In principle this can be iterated, yielding a 9-pass scheme, an 11-pass scheme, and so forth, or alternatively an adaptive number of passes can be used, as many as the image size will allow (so the first pass consists of a single pixel), as is usual in scale-free multiscale modeling. In the context that PNG was developed (i.e., for the image sizes and connection speeds in question), a 7-pass scheme was seen as sufficient, and preferable to a simple 5-pass scheme. ==External links== Animated comparison of Adam7 and GIF interlacing

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