code: def adam7_generate(width, height):
      
  
      for xstart, ystart, xstep, ystep in adam7:
          if xstart >= width:
              continue
          yield ((xstart, y, xstep) for y in range(ystart, height, ystep))
docs: Generate the coordinates for the reduced scanlines
      of an Adam7 interlaced image
      of size `width` by `height` pixels.
  
      Yields a generator for each pass,
      and each pass generator yields a series of (x, y, xstep) triples,
      each one identifying a reduced scanline consisting of
      pixels starting at (x, y) and taking every xstep pixel to the right.