Adam7 algorithm

[1] Adam7 is named after Adam M. Costello, who suggested the method on February 2, 1995, and after the seven steps involved.

It is a rearrangement[2] of this five-pass scheme[3] that had earlier been proposed by Lee Daniel Crocker: Alternative speculative proposals at the time included square spiral interlacing and using Peano curves, but these were rejected as being overcomplicated.

It thus offers worse frequency behavior, showing artifacts (pixelation) at the early stages, in return for simpler implementation.

Similarly, GIF interlacing 1324 can be seen as iteration of the 12 pattern, but only in the vertical direction (12 expands to 1.2. which is filled in as 1324).

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,[why?]