progressive coding

progressive coding
interlace
interlaced image
non-interlaced

   <graphics, file format, algorithm> (Or "interlacing") An
   aspect of a {graphics} storage format or transmission
   {algorithm} that treats {bitmap} {image} data non-sequentially
   in such a way that later data adds progressively greater
   {resolution} to an already full-size image.  This contrasts
   with {sequential coding}.

   Progressive coding is useful when an image is being sent
   across a slow communications channel, such as the {Internet},
   as the low-resolution image may be sufficient to allow the
   user to decide not to wait for the rest of the file to be
   received.

   In an interlaced {GIF89} image, the {pixels} in a row are
   stored sequentially but the rows are stored in interlaced
   order, e.g. 0, 8, 4, 12, 2, 6, 8, 10, 14, 1, 3, 5, 7, 9, 11,
   13, 15.  Each vertical scan adds rows in the middle of the
   gaps left by the previous one.

   {PNG} interlaces both horizontally and vertically using the
   "{Adam7}" method, a seven pass process named after Adam
   M. Costello.

   Interlacing is also supported by other formats.  {JPEG}
   supports a functionally similar concept known as {Progressive
   JPEG}.  [How does the algorithm differ?]

   {JBIG} uses {progressive coding}.

   See also {progressive/sequential coding}.

   ["Progressive Bi-level Image Compression, Revision 4.1",
   ISO/IEC JTC1/SC2/WG9, CD 11544, 1991-09-16].

   (2000-09-12)