What is the difference between merge layers and flatten image?

What is the difference between merge layers and flatten image?

Merging layers is just that: combining layers into a single one.
Flattening is merging plus transforming the resulting layer into a background. A background has different properties, many edits, like transform or perspective cannot be applied to a background.

I often wondered the same thing and never paid attention when doing either that one stays a layer and the other becomes a background. D, thanks for asking and Michel, thanks for the answer.

I always merge and never flatten.

I always merge and never flatten.

I am pretty sure it's because you always keep your background unaltered, which is the best thing to do. Suppose you have used the image/transform or distort menu: the background is transformed into a 'normal' layer. If you want to save at that point, PSE will only save as PSD. You'll have to flatten to get the jpeg option.

One important difference is that merging layers will preserve transparency, flattening will not.

Juergen

One other alternative is merge visible - Shift+Ctrl+Alt+E
I use this all the time especially when stepping thru a tutorial that tells me to do some things to two or more different layers and then merge down to combine two or more layers.

The problem with merging the layers is that you have lost all ability to go back and make changes to a specific layer other than using Undo. And, the problem with Undo is you lose all subsequent actions after the undo point.

I flatten a lot of images and save only as a Jpeg but I never do so until I have completed all edits and am satisfied that I have no intention of revisiting that image. Anything that I consider one of my "maybe 5% good picture" remains in PSD format.

Just my 2¢

Rusty

The problem with merging the layers is that you have lost all ability to go back and make changes to a specific layer other than using Undo. And, the problem with Undo is you lose all subsequent actions after the undo point.

Rusty

Imagine you are merging layers and want to keep the layers to be merged: you can do this by merging the layers to a new layer (Ctrl Shift Alt E), name it clearly, and leave the original layers toggled off. This gives you the possibility to keep the history and start again, even if you have other layers above.
The above shortcut combination is one I use very often.