1. Read data from /dev/fb0
[15bit] raw15toraw24 < /dev/fb0 > raw24.tmp
[16bit] raw16toraw24 < /dev/fb0 > raw24.tmp
[24bit] cat /dev/fb0 > raw24.tmp
[32bit] raw32toraw24 < /dev/fb0 > raw24.tmp
2. Raw Data to ppm
rawtoppm 800 600 raw24.tmp > ppm24.tmp
3. ppm to png
pnmtopng <ppm24.tmp >screenshot.png
