I have a Honor 6, android 4.4.2, TWRP 18.104.22.168 recovery
Screen should be 1920x1080 (FullHD)
To activate ADB on TWRP, I had to go to "Mount" menu, and then click "USB Storage", elseway no devices shown in adb.
But I can't find a clear pic of my screen.
I have attached a zip file with framebuffer.raw
Edit : This said, in TWRP there is a screen capture function, just press voulme down + power, the screen flash, screenshot done.
You'll find them in /sdcard/picture/screenshot (if rooted)
if not maybe you'll have to access them via TWRP file manager or USB connexion.
Here is what I get :