Pngcrush is an optimizer for PNG (Portable Network Graphics) files. It can be run from a commandline in an MSDOS window, or from a UNIX, LINUX or Amiga commandline. 

Its main purpose is to reduce the size of the PNG IDAT datastream by trying various compression levels and PNG filter methods. It also can be used to remove unwanted ancillary chunks, or to add certain chunks including gAMA, tRNS, iCCP, and textual chunks.

PERMISSION  UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP     NAME
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[unknown]                    0       0 ****** -lh0- 0000 Apr 20 15:01 pngcrush-wos/
[unknown]                13804   38146  36.2% -lh5- 6139 Apr 14 23:20 pngcrush-wos/ChangeLog
[unknown]                 1516    3081  49.2% -lh5- 7a3d Jan 23  2012 pngcrush-wos/pngcrush.txt
[unknown]               141395  325676  43.4% -lh5- 5738 Apr 20 00:00 pngcrush-wos/pngcrush_wos
---------- ----------- ------- ------- ------ ---------- ------------ ----------
 Total         4 files  156715  366903  42.7%            Apr 20 21:52