editing of pic in small portion only

[phraensys]

there is this picture (taken by my note3) that i want to edit, i.e. use spen to annotate, etc..
but i'm just wondering why does it only occupy a portion of the screen (area A with green diagonal lines) and not occupy the entire screen (area B with blue diagonal lines)
how do i stretch the work area usage and utilize the entire area of the screen (area B with blue diagonal lines)?
please refer to the attached image

 

[fantom305]

I have the one on the picture and it does the same to me with and without the spen however I also use one called photo editor from google play....link: https://forums.androidcentral.com/e...om.iudesk.android.photo.editor&token=OfghwjMk, and this one gives you the capability of zooming to 200 % which covers the entire screen. You might want to give a try.