The Free On-line Dictionary of Computing (30 December 2018):

Adam7

    One of the progressive coding methods
   used in PNG images.  Adam7, named after its author, Adam
   M. Costello, consists of seven distinct passes over the image.
   Each pass transmits a subset of the pixels in the image.
   The pass in which each pixel is transmitted is defined by
   replicating the following 8-by-8 pattern over the entire
   image, starting at the top left:

    1 6 4 6 2 6 4 6
    7 7 7 7 7 7 7 7
    5 6 5 6 5 6 5 6
    7 7 7 7 7 7 7 7
    3 6 4 6 3 6 4 6
    7 7 7 7 7 7 7 7
    5 6 5 6 5 6 5 6
    7 7 7 7 7 7 7 7

   (2000-09-12)