Use Blend If to Replace Sky
We have this photo here. And... Sometimes you take pictures and they look okay, but they would look much better if we had a more dramatic sky and there's a lot of ways that you can do sky replacements. Some of them just simply take a long time. I like to save a lot of time when I'm working 'cause I'm sure some of you are so busy that you try to do as much work as you can with quality and speed. So if I wanted to remove this sky, I can take advantage of a feature that not a lot of people ever use for this purpose, which is the "Blend If" feature. So if I... And by the way, this is the sky that I want to use. So if I double-click to the side of the layer, I bring up the Layer Style window. Right below that knock out section, this section here, we have the "Blend If." This allows us to blend layers together based on their luminance values. Somewhat like blending modes, but we can control exactly what we're blending. Gray, this layer, or the layers below; "This Layer" means the layer we ha...
ve selected, "Underlying Layers" mean the underlying layers from the selected layer. We can work with gray or, this is what most people don't do, is work with the red, green, or blue channels. For those of you that don't know, all RGV images are made up of red, red light, even though it looks black and white there, green light, and blue light. So we can use these as ways to blend images together to make things disappear or become transparent. When you're working with layer mask, black hides, white reveals. You can think of this as a layer mask. I'm gonna click on "RGB" to bring all my channels back. I can double-click to the side of the layer. Now looking at my image, if I want to remove the sky, which channel do you think I would more likely use to remove the sky? We have red, green, and blue. Nobody, really?
Blue, yeah, thank you. Blue. So...(laughs) So we select "blue." This layer is the... The layer I have selected is the farm photo, so I'm gonna work with this layer. So watch what happens when I click and drag the blue. See, this is the blue here on the right side, look at the sky, see that? And when you get to a certain point, you're gonna start seeing a lot of pixelation, a lot of rough edges. All you need to do is hold "Alt," "Option" on the Mac, and... click on this icon there to split it in half and it creates a smoother transition. So basically, what this is saying is anything that's this shade of gray-- this is really gray, it's not really blue. It's using the blue channel, so whatever this shade of blue, or the gray that you saw in the RGBs, and darker will disappear. From this shade to this shade it'll be a gradual transition, and from this shade to this shade it'll be 100% visible. So once I press "OK," you can see that Photoshop did a great job in all the small details so I didn't really have to worry about masking and making those changes to the sky replacement because the sky was completely blue. Now, when I show this technique, people sometimes ask, "Well, what if I have a blue car or a person wearing a blue shirt?" Their shirt would also disappear, but what you would do at that point is one of two things. You can create a new layer, much like we did with the... The photo of the museum, the Louvre Museum, where I used the original sky on top of the composited sky, I could do the same thing if I, for example, if these horses were blue and they disappeared, I could just make a selection out of the horses that are not blue, and then create a layer mask and that will be on top of the pixels that are disappearing. So that would be a workaround in case you do have something that's blue in the foreground and it's not just the sky. But in this example, the only blue thing that we had was the sky and it did a really good job. The great thing about this technique is that we can... move it around, we could transform it... When you press "CTRL+T," "Command+T" to transform and you can't see the handles, "CTRL+0," "Command+0" to zoom out and see the handles. So now I can adjust the sky anyway that I want, and I'm not really worried about masking.