In a complex design, it's not hard to accumulate dozens of layers, which can bloat file size and make it hard to find what you're looking for. Whenever possible, you should look for opportunities to merge and flatten layers to keep the design clean and well ordered. Merging layers refers to combining some of the layers in a design while keeping other layers separate. Flattening the image involves compressing all the layers into one flat background layer.
Open the File
Choose File, Open and select the file you want to modify.
Launch the Layers Palette
Choose Window, Layers to open the Layers palette and show all existing layers.
Merge Multiple Layers into One
To merge two layers into one, drag them one above the other in the Layers palette and select the layer at the top of the two. Choose Layer, Merge Down to combine the selected layer with the layer below it in the list. The name of the lower layer is used when you combine layers with the Merge Down command.
Merge the Linked Layers
To merge more than one layer at a time, first link the layers as described in Task 2 in this part. Then choose Layer, Merge Linked to combine all the linked layers.
Merge All Visible Layers
An alternative to merging linked layers is to first turn off the visibility of all layers that you do not want to merge. Choose Layer, Merge Visible to combine all visible layers. Then go back to the Layers palette and turn the hidden layers back on. The current, or active, layer name is used when you combine layers using the Merge Visible command.
Flatten the Image
To reduce all the layers in a document to one, choose Layer, Flatten Image. If any layers are hidden as you do this, a dialog box appears, asking whether you want to discard the layer or cancel the operation. Click Discard to flatten the image and delete the hidden layers.
Watching the Layer Order When Merging
If linked layers are not adjacent to each other, the image could be altered when you merge the layers. This is especially true when opacity or blending modes have been used.