Since Stamp Visible’s ears are burning, I’d better introduce you to it. Picture this: You have an image composed of multiple layers, and you want to apply an effect or filter to all the layers at once. You could merge all the layers to do what you need, but you know that you might need to change something later, so flattening the image really isn’t an option.
What if you could leave all the layers intact and create a flattened version on top of the layer stack? This is Stamp Visible. Click on the top layer in the Layers panel to make it active, and then press Command-Option-Shift-E (PC: Ctrl-Alt-Shift-E). This will make a flattened layer on top composed of all the visible layers. (If nothing happens, make sure that the top layer you selected isn’t an invisible layer.) While you should be using smart objects instead, there are plenty of times that Stamp Visible is the fastest option, such as creating a sharpening layer on top.
This tip previously published in Colin Smith’s Photoshop Tips column, in the May, 2020 issue of Photoshop User magazine.