Join Tim Grey for an in-depth discussion in this video Selections, alpha channels, and layer masks, oh my!, part of Photoshop: Selections and Layer Masking (2013).
Layer masking is easily my favorite subject in Photoshop and that's in large part because I'm admittedly a control freak. And I love being able to exercise maximum control over my photographic images. Layer masking makes it possible to create very cool and interesting composite images and also to apply targeted adjustments. In other words, adjustments that only affect a specific area of a photo, and yet layer masking is often perceived as a very challenging subject, one that is very complex.
There's certain amount of truth to that, but I would suggest that the complexity is not as complex as it seems when it comes to layer masking in Photoshop. Let me show you a really good example of that. In the context of layer masking, we have a variety of different topics that seem like disparate topics. We have selections, which allow you to select a particular area of the image. We have layer masks which allow you to identify which areas of an image will be visible or which areas will be affected by a particular adjustment. And then we have channels.
You're familiar, I'm sure, with the RGB channels. The red, green, and blue channels that identify the color values for an image. But there are also alpha channels. And alpha channels are usually described as a channel that reflects the visibility of pixels within an image. That's only one example of how an alpha channel gets used. But, suffice it to say there are selections, layer masks, alpha channels. Lots and lots of things to understand when we simply want to create a composite image, or apply a targeted adjustment. But actually, things are not as complicated as they seem. To begin with, selections, alpha channels, layer masks, these are all essentially the exact same thing.
Sure, they're implemented in different ways, and you use them for different purposes, but they're really quite simple when it all comes down to it. In fact, so simple that they're really just a black and white image. Let's take a look. In this image I have a saved selection. Well, the saved selection is really just an alpha channel. So I'll go to my Channels panel, you could choose Window > Channels from the menu, if your Channels panel is not visible. And you'll see that I have a sky channel. There's the usual RGB composite channel. We have a red channel, a green channel, and a blue channel. Those identify the color in the image.
But we also have the sky channel, and if I click on it, you'll see that the name seems to fit. This channel reflects the sky. The sky is white and the foreground of the image, the rest of the image, everything except the sky is black. Well this reflects a selection. The sky is selected, and the foreground is not selected. Or this could reflect a layer mask. The sky is visible or being affected by an adjustment. And the foreground is not. So, we have an alpha channel that could simply reflect a selection, which could reflect a layer mask.
They're all the same thing. They're all just a black and white image, where white represents something that is enabled or visible. Black represents something that is disabled or not visible and shades of grey represent values that are partially visible or partially enabled. In fact, I can create a selection based on this channel. I'll just click on the Load Channel as Selection button. I'll click on the RGB tile to get back to the color image here. And you can see now I have a selection of the sky. And I can use that selection to apply a targeted adjustment.
In fact I can add an adjustment layer and utilize that selection as the basis of a layer mask so that my adjustment only affects the sky. But you can see they're all essentially the same thing. A selection is just a representation of the actual layer mask or of the alpha channel or whatever it may be, but Photoshop is thinking of this selection not as a dashed outline that is animated like marching ants, but rather as a black and white image, where white represents selected and black represents not selected.
Or as a layer mask where white represents the area being affected by the adjustment and black represents areas not being affected by an adjustment. As would be the case with a layer mask used in conjunction with an adjustment layer, but also a saved selection is an alpha channel. You'll notice my sky selection, and because my layer mask, associated with my levels adjustment layer is currently active, I'm also seeing a temporary mask. Showing me, once again, that Photoshop is thinking about all of these things, selections, alpha channels, layer masks, all of them are reflected as black and white images. So when you understand that basic concept, a couple of things happen. To begin with, suddenly the subject is not quite so complex. We have essentially one construct, a layer mask or an alpha channel or a selection, call it what you will but it's just a black and white image being used in a variety of different ways.
But also you get a sense of the underlying issue in terms of layer masking or applying targeted adjustments, creating composite images. And that is an object essentially that is defining attributes of an image based on another black and white image that can reflect the shape of that image or portions of that image. In the context of layer masking, creating composite images or applying targeted adjustments really understanding that a black and white image is what's being used in the background by Photoshop to identify specific regions of the image. Well, that knowledge will prove very, very helpful for you. So as you can see, things aren't as complex as they might initially appear. And actually it's relatively straight forward, all things considered. And with that knowledge you'll be able to perform incredible tricks with your images.
- Basic concepts
- Selection tools
- Advanced selection techniques
- Creating composite images
- Applying targeted adjustments
- Creating a vignette effect with masking