$ optipng -preserve -strip all -o7 <em>file</em>.png
** Processing: file.png
400x400 pixels, 4x16 bits/pixel, RGB+alpha
Reducing image to 3x16 bits/pixel, RGB
Stripping metadata...
Input IDAT size = 42804 bytes
Input file size = 43049 bytes
Trying:
zc = 9 zm = 9 zs = 0 f = 0 IDAT size = 27513
Selecting parameters:
zc = 9 zm = 9 zs = 0 f = 0 IDAT size = 27513
Output IDAT size = 27513 bytes (15291 bytes decrease)
Output file size = 27570 bytes (15479 bytes = <u>35.96%</u> decrease)
$