File format:

Each *.pix file is a stream of characters, 0-9,A-F, which stand for
gray values 0-15 (0-F hex).  0 is black, 15 (F) is white, and the
16 levels are equally spaced in brightness (or at least they are
linear in how they control the intensity that the electron guns
apply to the CRT - what our eyes do with that is beyond me).

As for dimensions,

frontb.pix is 144 (0-143) pixels across by 333 (0-332) pixels down, written
row-wise, i.e. characters 0-143 are row 0, chars 144-287 are row 1, etc. to
row 332.

backb.pix is 128 (0-127) pixels across by 337 (0-336) pixels down, stored
the same way [chars 0-127 are row 0, 128-255 are row 1, etc.]