Screenshot tools for Linux and macOS generally produce image files in the .png
file format. PNG is a lossless compression format, meaning that it can be compressed without losing quality, which is unlike another commonly used image format, JPG. There are 3 command-line tools which can be used to compress PNG files, pngout, optipng, and advpng.
➜ pngout terminator-terminal-window.png
In: 11405 bytes terminator-terminal-window.png /c6 /f5
Out: 8790 bytes terminator-terminal-window.png /c2 /f5
Chg: -2615 bytes ( 77% of original)
➜ optipng -o7 terminator-terminal-window.png
** Processing: terminator-terminal-window.png
800x266 pixels, 3x8 bits/pixel, RGB+transparency
Input IDAT size = 8715 bytes
Input file size = 8790 bytes
Trying:
zc = 9 zm = 9 zs = 0 f = 0 IDAT size = 8140
zc = 9 zm = 8 zs = 0 f = 0 IDAT size = 8140
Selecting parameters:
zc = 9 zm = 8 zs = 0 f = 0 IDAT size = 8140
Output IDAT size = 8140 bytes (575 bytes decrease)
Output file size = 8215 bytes (575 bytes = 6.54% decrease)
➜ advpng -z4 terminator-terminal-window.png
8215 7232 88% terminator-terminal-window.png
8215 7232 88%