Join Deke McClelland for an in-depth discussion in this video Choking a mask with Gaussian Blur and Levels, part of Photoshop CS4 One-on-One: Mastery.
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Now you'll see that we still have these icky edges that are surrounding the hadrosaur which is why I've gone ahead and saved my progress so far as icky edges.psd. What we need to do is go ahead and choke our mask inward, so that we're getting rid of these bad edge artifacts. Now there is a couple of different ways to choke edges in a layer mask inside of Photoshop. I want to show you both of the ways. So there is an old-school method that we'll see in this exercise and there is a new-school method that we'll see in the next exercise. For our purposes the new-school method is going to work out better. That's not always the case. Sometimes old school is going to work better. So it's good to have both of these techniques in your arsenal.
So let's start by making sure that the layer mask thumbnail is active here in the Duckbill layer and it is. Go ahead and click on it to make it active. Then what you want to do is you want to give yourself a little bit of blur to work with around the edges and the idea there is we are softening up the edges to turn the edges gray, so that we can then turn around and scoot the edges inward by making them darker or scoot the edges outward by making them lighter. So I'm going to go up here to the Filter menu and I'm going to choose Blur and I'm going to choose Gaussian Blur. Then inside the Gaussian Blur dialog box I'm going to enter a radius value of 2 pixels. That's just going to give me a little bit of wiggle room right there.
Notice that it creates a heck of an edge artifact but it also gets rid of those clunky jagged edges that we had before. So we get a halo instead. That's fine. The reason we're going get halo is because we're not only blurring inward but we're also blurring outward. So by virtue of the fact that we're blurring the white edges of this mask outward, we're incorporating more of the edge pixels and thereby producing a glow. That is to be expected. Now if you want fewer edge pixels to work with then you want a lower radius values, something like 1 pixels might work out well, but notice that if I work with a radius of 1, I still has some pretty jagged edges. I'll go ahead and scroll over here so that we can see what I'm talking about. You can see that we have some chunky edges going on and I can get rid of those by raising that radius value to 2. When you start raising the radius value, you do get smoother edges as you are about to see but you also end up rounding off corners. So that's something to bear in mind as well.
All right click OK. Now then what we have, I'll go ahead and Alt-click or Option-click on this mask thumbnail, so we can see the mask by itself. This before, nice and sharp, a little bit jagged though. And this is after, nice and smooth but awfully blurry. Well we can use the Levels command in order to make the dark luminance levels right here darker and the light one lighter, thereby increasing the contrast of those edges. By emphasizing white, we can move the edges outward; by emphasizing black, we can move the edges inward. You'll see what I'm talking about in just a moment.
Alt-click or Option-click again on this mask thumbnail so that we see the image and not the mask. The mask though is still active. Press Ctrl+L or Command+L on the Mac to bring up the Static Levels command. Notice if I decrease the white point value, I'm moving the edges outward because I'm emphasizing the white details, which are the dinosaur of course inside of this mask. That's not what I want to do. That would be by the way what's known as a spread. If you want to spread the selection, you decrease the white point value. So let's go ahead and take that value back up. What I want to do is choke it so I'm going to increase the black point value. I'm going to take it up pretty significantly up to 170. I'm saying anything with the brightness value of 170 or darker becomes black.
Then I'm going to turn around in order to increase the contrast of the edges a little to smooth things out. I'm going to turn around and reduce the white point value to 195. Now we have some nice, sharp edges, which is a good thing. Then I'll click OK in order to accept that modification. That allowed us to scoot those edges around. It's a combination once again of Gaussian Blur followed by the Levels command. Now it's not necessarily working out perfectly, at this point actually some of the details are fantastic. Look at the smoothness of that nasal cavity. Let's go ahead and zoom in on that so you can see what I'm talking about. Let's bring up the History palette right there. I if went ahead and switch back a couple of states here. This is how the nasal cavity used to look. We had a halo going on, we have this color fringing, as well as some jagged transitions, and this is what the transitions look like now. So much better. As a result of these two very simple commands working with each other.
But we do have a little bit of an issue over here. This pesky area right here is still pesky. So here's what I do. I just want to scoot the edges over to the left, like 1 pixel is going to do me. But if I scoot this over then I'm going to scoot everybody over like the whole thing is going to move, and I don't want to see that happen. So instead what you do is you just grab the area that you want to scoot and you do it using the Rectangular Marquee tool. I'll go ahead and select that tool. Then make sure that you select and area like this that has a nice horizontal edge associated with it because we're going to be moving the pixels over to the left. I don't want to create a new weird transition at this end point here, at the division between the move pixels and the stationery pixels, so I'm choosing an area that's horizontally flat.
Then I'll go ahead and Shift+Drag around here like so, Shift+Drag here a little bit and all the way down to about here is what we want. Again I'm going to pick an area that's nice and flat, nice horizontal transition. But you know what, the fact that I'm keeping this area selected can prove to be a problem. So I'll go ahead and Alt+Drag or Option+Drag around this area to deselect it. That should give me better results. We still have a little bit of an issue here. Let's go ahead and leave this selected as it is. So there is my selection outline. Press Ctrl+Alt+Left-arrow or Command+Option+Left-arrow in the Mac in order to duplicate and move these pixels one, pixel over. Notice that's what you get. So this before and this is after. We have nice transitions up here, because we were very deliberate about the area that we selected.
Now the only area where we got a problem and this is pretty subtle but it's still obvious when you zoom in. I went ahead and moved this mask over on the left-hand side of this left edge. We just wanted to move it left where the right edge was concerned, not left where the left edge is concerned. So let's undo that modification by pressing Ctrl+Z Command+Z on a Mac and I'm going to Alt+Drag or Option+Drag on a Mac to deselect this region like so. Just have a little bit of a hole there and then press Ctrl+Alt+Left-arrow or Command+Option+Left-arrow on the Mac. Isn't that awesome? Works out beautifully.
And that is the highly desirable masked version of the dinosaur. But I was telling you that's the old school way to approach it. We can do a lightly better job that involves better feedback for one thing. A single command instead of both Gaussian Blur and Levels and doesn't require us to get in there with Marquee tool. Using this button right here, Mask Edge, inside of the New Mask palette inside Photoshop CS4, and I'm going to show you how that works in the next exercise.
Recommended prerequisites: Photoshop CS4 One-on-One: Fundamentals and Photoshop CS4 One-on-One: Advanced, both part of the lynda.com Online Training Library®.
Download Deke's customized keyboard layouts and color settings for Photoshop from the Exercise Files tab.
- Defining the essentials of masking
- Resizing images with content-aware scaling
- Adjusting perspective with Vanishing Point
- Applying Smart Filters to create complex effects
- Using the Auto-Align tool to build composite images