If you really get into the very cool Acorn Image Editing app you might wish to set it up in the Photos app Share Menu. Then you can just select a photo you wish to edit externally and use the Share Menu to pop it into Acorn for sophisticated editing.
Acorn As The External Editor
It is not difficult to set up Acorn or most other image editing applications as an external editor in the Photos app. First, you have to set up Acorn as an external editor. Open Photos and click on the Share Menu in the upper right corner of the window (next to the Search box) and select “More…”,
You will be taken to the Extensions Window in System Preferences:
Check the box for Acorn and then close the window. Now, this is supposed to work right out of the box, but I could not get it to stick in El Capitan OS until I restarted my Mac.
Once you have completed this set up, select a photo in the Photos app, click on the Share Menu and choose Acorn:
Photos Exports a copy of the photo and Acorn will open with the particular image. Edit your image. When you are finished editing, select File/Share/Add to Photos. A copy of the original image will be placed back in the Photos app:
Yes, this is a little convoluted. Once Acorn is set up as an external editor, it really is not a big deal to edit an image outside of the Photos app.
As you know, I have been using Extensions inside the Photos app to do heavy editing. However, now that I have the Acorn app setup as an external editor, I may be using it more to do some sophisticated editing to my images.