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I get asked this next question quite a bit. When should you merge layers? And the answer is really as little as possible, because when you start merging layers, so let's take an example of what I'm talking about here. I've got these four individual layers here. Because these four layers are individual and separate if I want to change their position on the screen or work on them individually, I don't have to make selections first. I just target that particular layer and do whatever I want to do to it. If I want to move it, I get the Move tool. I move it and so forth. If I start merging these layers together, well then it just makes it more complicated to isolate a particular section of that layer and move it.
I have to make a selection first. Now in this particular example, it's not that big deal because none of these four thumbnails are overlapping or touching each other. Right, so they are clearly isolated on a transparent background. If you start merging layers that are overlapping each other into a single layer, well now, it's actually a destructive action. For instance, if I have the Dahlia layer, then I get my Move tool, press V for Move, and I just start overlapping these layers like this, well, because they are individual layers it's not a big deal. I can always go and move that layer back. Okay, but if I had these four layers like this again and I merged this into a single layer, well I'm going to be losing the pixels of the Lily that are behind the Dahlia image there.
I think that probably makes sense to most of you. So, you have to decide when do you merge and basically the answer is when you're guaranteed absolutely certain that you never need to change your mind. If you know that to be true, then merge away. How do you merge layers? Select any two layers that you want to merge. So, I'm going to select the Lily and Mixed layers here and a couple of different ways to go about it. You can go to the flyout menu of the Layers panel. So, every panel has what we call a flyout menu. In the upper right-hand corner, there is a little dropdown. If you click on that, that brings up a pop-up menu for options for that particular layer and one of them here is Merge Layers.
So, there is a keyboard shortcut for it. That's what I typically use, Command+E, but for you menu folks, there is where the menu command is, Merge Layers. You'll see those two layers became one layer. They were blended or merged into one particular layer. Now the layer name that got retained was the top layer. So, I just undid that by the way. Command+Z, Ctrl+Z. Lily is merging down into Mixed, and the top layer name is the layer name that got retained. So, just select any two layers. We'll go ahead and Shift+Click on these two again and Command+E or Ctrl+E. And that will merge those two selected layers into a single layer.
Okay, I'm going to go ahead and undo that. Now there is Merge, but there is also Rasterize. This actually is something that you might do a little bit more often than merging. If you take a look at this set of layers here, these are Smart Objects, just to review what a Smart Object is. These thumbnails are actually much larger than their size currently indicates. Before we scale these thumbnails down, I converted them into a Smart Object, which encapsulates or includes, embeds, the full version of this file inside this main Photoshop document. So, if I want to change the scale of it any time, I can go back to the original source.
Just to kind of prove the concept, if I double-click on one of these thumbnails that has the Smart Object badge, go ahead and double-click, I get this message saying blah, blah, blah. You're going to do this. It's going to open up a different file. Okay, save changes. Okay, go ahead and click OK. It opens up that full-sized version. You can see the view percentage here is only 50%, so it's pretty big file. And what's happening though is it's embedding this full-size file inside that master Photoshop document that we just opened this from. So, I'm going to go ahead and close this. Now the result of having these four Smart Objects embedded inside this document is that the file size of this particular file is much larger than it would be if I know I don't intend to scale these images down again.
So, rather than merging, I want to keep individual layers here, but I want to throw away the extra information that I don't think I need anymore. So, that's the difference between Merge and Rasterize. Merge actually combines layers into one. Rasterize just throws out the extra information and just leaves you the visual result of that particular file there. So, I'm going to go ahead and right-click on the name of a layer. You'll see that one of the menu commands here is Rasterize Layer. I'm going to go ahead and choose that, and you'll see the Smart Object badge is now removed from that layer. It's just a regular layer at this point. So, if I were to scale it all the way down and scale it back up, that would have been destructive.
So, I have lost that Smart Object information. If I wanted to right-click on the Mixed layer and choose Rasterize Layer, I can do each one individually or you could choose to rasterize the whole group by right-clicking on Thumbnails and saying Merge Group. That would turn it all into one layer and remove all the Smart Object information at the same time. So, the difference between Merge and Rasterize just depends on what you're starting out with. Are you starting with a Smart Object layer? A layer that you've placed in from Illustrator as vector artwork, again, as a Smart Object, or do you have a group selected? If I choose Merge Group, that's going to both rasterize and merge all four of those layers into one layer.
And it will retain the group name as its final layer name. Again, just be careful with these commands. They are very destructive. You can't get that information back if you were to save this file and reopen it. It's gone. I'm going to go ahead and just revert because I haven't saved it. So, I'm going to go to File > Revert to get back to where we were and we have all that information back restored. Great powerful commands, useful when you need them, to reduce file size or reduce complexity of a document, maybe you don't need to keep 300 layers in a document. And so some people will merge them down or rasterize them down just to keep the file size of their overall master document down.
But again, these are two commands that you should use sparingly.
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