I just made a few minor modifications to the origininal source (available
at ftp.uu.net:/graphics/png/code/pnmtopng.zip) to get a clean compile, and
fixed the usage information.
-Ingo

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                47188   97708  48.3% -lh5- d54a Jul 15  1995 bin/pngtopnm
[generic]                27474   53436  51.4% -lh5- 2e1a Jul 15  1995 bin/pnmtopng
[generic]                  917    2213  41.4% -lh5- 97e1 Jul 15  1995 manual/pngtopnm.man
[generic]                  893    1914  46.7% -lh5- 7637 Jul 15  1995 manual/pnmtopng.man
[generic]                  249     339  73.5% -lh5- ee3a Jul 16  1995 readme.amiga
[generic]                 1063    2062  51.6% -lh5- ade3 Jul 15  1995 src/pngtopnm.1
[generic]                 2775    9953  27.9% -lh5- 2b2c Jul 15  1995 src/pngtopnm.c
[generic]                 1026    1921  53.4% -lh5- b256 Jul 15  1995 src/pnmtopng.1
[generic]                 2696    8843  30.5% -lh5- 62d1 Jul 15  1995 src/pnmtopng.c
[generic]                  405     775  52.3% -lh5- baf3 Jun  6  1995 src/readme
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total        10 files   84686  179164  47.3%            Jul 16  1995