How do I click snapshot of a particular part of the screen?

Hi,

I want to click snapshot of the screen. Earlier I had to click snapshot of the whole screen hence it was easy. But now the situation has changed

Resolution of my game is 720x1440. But I want to click snapshot of only top part (720x1280). Issue is that I don't know how to do it(in snapshot command,if in height section,if I write 1280,then it is not working properly. Looks like it is dependent on screen size)

Please help me regarding this

Thanks in advance