Oneliner to speed up screenshot taking process.
adb shell screencap -p | perl -pe 's/\x0D\x0A/\x0A/g' > screenshot.png
Combined with the adb shell start
command that launches intents and activities the process of taking screenshots can be completely automated.
Unlock the screen:
adb shell input keyevent 82
Power buttona
adb shell input keyevent 26