Written By Steve Patterson

In this Photoshop tutorial, we're going to look at a great way to help keep things running smoothly as we edit our images by keeping our Photoshop file sizes as small as possible using adjustment layers!

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In a previous tutorial, we looked at one of the major benefits of adding Photoshop's adjustment layers to our photo editing workflow, which is that they allow us to work flexibly and non-destructively on our images. We can make as many edits and re-edits as we want to a photo and never have to worry about making a single permanent change to the original image. Be sure to check out our Non-Destructive Photo Editing with Adjustment Layers tutorial for more information.

Being able to work non-destructively on our images is certainly a great reason to stop using Photoshop's standard image adjustments and start using adjustment layers, but there's other equally good reasons to make the switch. One of the biggest complaints with Photoshop is that no matter how much memory (RAM) you have in your computer, it never seems to be enough. And with the number of megapixels in the latest digital cameras always increasing, the problem just keeps getting worse. Larger photos mean larger file sizes, and the larger the file size, the more of your computer's memory Photoshop needs to work with it. And that's just to get the original photo open your screen. Typically, as you edit the photo, you add more and more layers, and each one of those layers takes up more and more of your computer's memory. On top of that, Photoshop needs even more memory to complete all of the fancy, complex math that goes on behind the scenes as you're working on the image.

If your computer runs out of memory as you're working, Photoshop has to use the scratch disk, which is simply an area of your computer's hard drive that Photoshop uses as memory. The problem is, your hard drive is much, much slower than actual system memory, which means that any time Photoshop is forced to use the scratch disk, it will run that much slower.

Is there any way that we can reduce the amount of memory that Photoshop needs? There sure is, and that's by keeping our file sizes as small as possible. One way to do that would be to throw out our expensive digital cameras and start taking all of our photos with the little 2 or 3 MP camera inside our cell phones, although the bride and groom may not be too impressed when you show up to take their wedding photos with your iPhone. A better solution would be to come up with a more efficient way of working on our images, one that keeps our file sizes in Photoshop as small as possible without sacrificing any of our editing capabilities. A great way to do that is by using adjustment layers. Let's look at an example.

Here we have a photo I snapped one Spring evening while walking through a park:

The image is underexposed and needs to be brightened. Back in our Screen Your Way To Better Exposure tutorial, we looked at a quick and easy way to fix underexposed images using Photoshop's Screen blend mode. I'm going to quickly run through the same steps here. Before I do anything though, let's find out how large my Photoshop document currently is. We can do that by looking along the bottom of the document window:

You'll see two file sizes listed beside each other. The one on the left tells us how large the Photoshop file would be if we were to flatten the document down to a single layer, while the one on the right tells us how large our file actually is (the unflattened version) with all of its separate layers still intact. My document window is currently showing the exact same file size (22.8 MB) for both the flattened and unflattened version, and that's because I just opened the image and haven't done anything to it yet. If we look in the Layers palette, we can see that the photo is sitting all by itself on the Background layer, and since there's only one layer in the document, both the flattened and unflattened version are exactly the same size:

Let's see what happens when I start brightening the image using what we might call the "traditional" way of working in Photoshop. First, I'll duplicate the Background layer using the keyboard shortcut Ctrl+J (Win) / Command+J (Mac). Photoshop adds a copy of the Background layer directly above the original and names the copy "Layer 1". Then, to brighten my image, I'm going to go up to the Blend Mode option at the top of the Layers palette and change the blend mode from "Normal" to Screen:

Simply by changing the blend mode of the duplicate layer to Screen, the photo now appears brighter:

That was certainly easy enough, but let's see what's happened to the size of our Photoshop file. Again, we can see the current file size by looking along the bottom of the document window. In my case, if we look at the size of the unflattened version (the number on the right), we can see that just by duplicating my Background layer, I've managed to double the size of the file. Instead of needing 22.8 MB of memory to display my image, Photoshop now needs 45.6 MB of memory:

I think my photo could still use a little more brightening, so I'm going to duplicate "Layer 1" by again pressing the keyboard shortcut Ctrl+J (Win) / Command+J (Mac). This adds a second copy of my image directly above "Layer 1". I'm going to leave the blend mode of this new layer set to Screen since I'm using it to brighten my image even more, but I actually find that the image is now a little too bright, so I'm going to fine-tune the brightness by lowering the Opacity of the new layer down to 50%:

I've now successfully brightened the photo using nothing more than a couple of copies of the image, the Screen blend mode and the Opacity setting:

Let's check on our file size at the bottom of the document window, where we can see that our original 22.8 MB file has now tripled in size to 68.3 MB, all because we duplicated the original image twice:

Brightening the image with the Screen blend mode has resulted in the colors looking a little dull, so I'm going to finish things off by boosting the color saturation. This time, rather than simply duplicating the top layer, I'm going to merge all three existing layers onto a new layer above them using the keyboard shortcut Shift+Ctrl+Alt+E (Win) / Shift+Command+Option+E (Mac). We can see in the Layers palette that all three layers have now been merged onto a fourth layer at the top:

To boost the colors, I'll go up to the Image menu at the top of the screen, then I'll choose Adjustments, and then I'll select the Hue/Saturation command. Rather than affecting every color in the image, I just want to boost the color of the flower itself, not the leaves behind it. So when the Hue/Saturation dialog box appears, I'll select Reds from the Edit option at the top of the dialog box. This allows me to target only the red colors in the photo, which means the green leaves in the background won't be affected. Then I'll click on the Saturation slider in the middle of the dialog box and drag it towards the right to a value of around +45:

I'll click OK to exit out of the dialog box, and we can see that the photo now appears more colorful:

With about two minutes worth of work, I've managed to turn a dark, underexposed image into a bright and colorful one. Unfortunately, I've also managed to increase the file size of my Photoshop document from the 22.8 MB it was originally all the way up to 91.1 MB, which mean Photoshop now needs four times the amount of memory to display my image on the screen, not to mention all the additional memory it now needs to perform all the math behind the scenes:

Keep in mind that this was just a simple example of how quickly the file size of our Photoshop documents can increase as we edit our images. Your computer may not have a problem working with a document that's only 91.1 MB in size, but with serious photo editing work, or if you're creating complex photo effects, you could easily find yourself working with hundreds of layers, each one taking up more and more of your computer's memory. And as I mentioned earlier, the problem only gets worse as the number of megapixels in today's digital cameras continually increases.

How can we keep the file size of our Photoshop documents from getting out of control? One simple and effective way is by using adjustment layers whenever possible. Let's go through the exact same steps that we just looked at, but this time, rather than creating copy after copy of our image, we'll use adjustment layers!

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