Screenshot only active monitor (gnome-screenshot)

To only shoot the current screen is not the default behaviour, nor is it an option in gnome-screenshot, nor any other screenshot application as far as I know.

Like practically anything however, it can be scripted.

An example

The script further below will:

• take a screenshot
• automatically create a (numbered) image in an arbitrary directory

• automatically crop the image to the section of the screen you are currently on (retrieved from the mouse position), and create a cropped image named:

  cropped_<image>.png
  

To prevent overwriting earlier screenshots, these cropped images are numbered like their oroginals.

screenshot

if I am on the left screen:

if I am on the right screen:

The script

#!/usr/bin/env python3
import os
from PIL import Image
import subprocess

# ---set the name of your (automatically numbered) screenshots (no extension)
imagename = "screenshot"
# ---set the path to where you (want to) save your screenshots
savepath = "/home/jacob/Bureaublad"

def get(cmd):
    return subprocess.check_output(cmd).decode("utf-8")

n = 1 
while True:
    name = imagename+"_"+str(n)+".png"
    path = os.path.join(savepath, name)
    if os.path.exists(path):
        n += 1
    else:
        break

# make the shot
subprocess.call(["gnome-screenshot", "-f", path])
# get the width of the left screen
screenborder = [int(n) for n in [s for s in get("xrandr").split()\
                if "+0+0" in s][0].split("+")[0].split("x")]
# read the screenshot
im = Image.open(path)
width, height = im.size
# get the mouse position
mousepos = int(get(["xdotool", "getmouselocation"]).split()[0].split(":")[1])
top = 0
bottom = height

if mousepos <= screenborder[0]:
    left = 0
    right = screenborder[0]
else:
    left = screenborder[0]
    right = width
# create the image
im.crop((left, top, right, bottom)).save(os.path.join(savepath, "cropped_"+name))

How to use

1. The script needs xdotool, to get the mouse position:

   sudo apt-get install xdotool
   

   Furthermore, not sure if python3-pil is installed by default:

   sudo apt-get install python3-pil
   

2. Copy the script above into an empty file, save it as crop_screenshot.py

3. In the head section of the script, set the desired name of the screenshot and the directory you use for your screenshots:

   # ---set the name of your (automatically numbered) screenshots (no extension)
   imagename = "screenshot"
   # ---set the path to where you (want to) save your screenshots
   savepath = "/home/jacob/Bureaublad"
   

4. Test- run the script from a terminal:

   python3 /path/to/crop_screenshot.py
   

   The result:

   

5. If all works fine, add it to a shortcut. Choose: System Settings > "Keyboard" > "Shortcuts" > "Custom Shortcuts". Click the "+" and add the command:

   python3 /path/to/crop_screenshot.py
   

Note

The script, as it is, simply splits the image on the width of your left screen. This is sufficient, because your screens are of the same y-resolution and aligned.

The script can however very well be edited to work with any screen arrangement, with any number of screens, as long as the screens are arranged in a non-overlapping arrangement. The math is a bit more complicated in that case however.

If anyone is interested, I will add it later.

Not withstanding the elegant script above, on ubuntu 16.04 I found that alt-print-screen, as desribed in: Print Screen captures two Spaces not one works. Actually this just prints the current window. If the aim is to capture a background I don't think it will work.

One option is to press Shift + PrtSc and then drag the cross from one corner of the monitor to the other corner. Release and it takes a screenshot of that area.