Expert: Scott Valentine - 3/1/2009

Question
I am starting a course on adobe photoshop cs4 and would like you to explain to me what a flattened image is.  I know this is probably a silly question for you but this is all very new to me.  Thank you

Answer
Hi Sandy,

It's not a silly question at all! Photoshop uses a model of image editing that allows you to 'stack' pieces of images together in layers. These layers can contain any image information that Photoshop supports, including pictures, paint, text, etc. Layers can be transparent or opaque, or some measure of each.

When you work with layers, you can turn each one on or off to see how things change. However, most file types do not support preserving these layers for later editing. So you have to 'flatten' the file for them to be able to read the image.

Now, there is a distinction to be made, here... every file that you export from Photoshop (except one special type of TIFF file) is already flattened, in that there is no layer information. When talking about flattening in Photoshop, however, this means you have decided you are done editing the layers and wish to have one single layer. There is a command from the top menu (Layers > Flatten Image) that creates a single, flat layer from all the currently visible layers.

In 10 years or so, I've not seen a good reason to do this except to save file size or to send the Photoshop file to someone else that should not be allowed to edit the individual layers. In the first case, hard drive space is cheap, so I'd say not to bother (though files with many layers can slow down some computers). In the second case, I'd recommend sending a copy that has been flattened, and preserve the layered original.

I never really advocate 'destructive' editing, or editing that is irreversible. Flattening your PSD file is 100% irreversible once you save it. You can't go back and change anything, just that one layer. Instead, there is a short cut to 'merge visible to a new layer'. This lets you create a flattened copy of the current image, which you can copy and paste into a new document. That way, you have the layered original, but can work on a flattened copy (for example, if your computer can't handle a large, layered file open at once).

To do this, create a new, blank layer and select it. Then hold down Ctrl + Alt + Shift + E (or Cmd + Opt + Shift + E on a Mac). That makes a copy onto the new layer of whatever is visible. Copy and paste that into a new document and you have the best of both worlds!

I know it's a bit long-winded, but I hope this clears things up for you!

-Scott