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Now it's time to deal with the background mountains. We need to extract the mountains, for two reasons. First, we're going to handle them in a different manner than the other elements in the matte painting. Second, we're going to add moving clouds later on in After Affects, so the clouds need to be separated from the mountains. Let's start by looking to our alpha channels and see which channel has the most contrast between the mountains and the sky. The red channel has the most contrast, but this is going to have to be a two-step process.
On the left side the mountains are nicely silhouetted against the white sky, but on the right side, you can see that the mountains are light against a darker sky. So we need to make two copies of this channel to apply different curves to isolate different sections of the mountains. I'm going to select the first copy of the red channel, then press Command+M on the Mac and Ctrl+M on Windows to open up the Curves dialog. Now I'll click into the white part of the sky with the Eyedropper tool and that shows where on the curve the white point needs to be moved, to make the sky completely white.
I'll use the eyedropper again against the mountains and take note of where the circle shows up on the curve. That's where the black point needs to be moved in to make the mountains completely black. I'll work back and forth on this curve a bit to see which gives me the best results. I want the mountains as completely isolated as possible from the sky. You're not going to get it perfect; you'll have to do some cleanup on this plate. Now select the second copy of the alpha channel, and we're going to do the opposite.
We're going to try and make the mountain white and sky completely black. Again, use the Eyedropper tool on the plate to identify where that gray is and then pull the black point in to make that gray completely black. Then pull the white point in to the left to get the mountains as white as possible. Again, this isn't going to be perfect, and you'll want to do a little bit of adjusting to get the best possible result. That looks about as good as it's going to get. Now we need the opposite of this, so select all and then Command+I or Ctrl+I to invert the channel.
Now we've got the black mountains against the white sky, which we can use as a mask to paint into on the other alpha channel. We'll need to do some cleanup on this channel before we start using it, so zoom in so you can really see what you're doing and lasso all the way around this to try and get the mountain completely black. Luckily, the edge is pretty well defined by the high-contrast mask. With black loaded into the background color picker, I'm going to hit Delete, and I'm going to turn on the visibility of the RGB channel so I can see where the edge of the mountain is.
And there's also some cleanup that needs to be done in the white part of the sky. I need to hit X to make sure white is loaded into my background color picker and hit Delete. Make sure you've got all of these little white specks on the edge cleaned up. Now I want to load this selection I created in by Command+Clicking into the layer icon Preview on the Mac and Ctrl+Clicking on Windows. Then return to that first copy of the alpha channel and we're going to use this selection to paint in to.
Now I'm going to use a brush with the Opacity set to 100% to paint white into the selection. I can be fairly sloppy here, since the selection has this area nicely defined. Once I've painted over the edge, I need to invert the selection. So go up to the top menu and choose Select > Inverse and then load black into the foreground color picker and paint along the top of the mountain. Right about now you're probably saying to yourself, man, this masking stuff is a lot of work. Why don't you just hand marquee it? The answer is that hand marqueeing will never give you an edge as nice as what you can get by pulling a mask from the source material.
And as you become more adapt to creating masks, it will be much faster than hand marqueeing around the complex surface. There are some areas you won't be able to get with this high-contrast-mask technique and you'll end up doing some hand marqueeing. So that you can clearly see the edge of the mountain, you may want to turn off the visibility on the alpha channel and turn on the visibility of the RGB channel. With a selection made, I'm going to select and turn back on my alpha channel, hit Delete, and then invert the channel and paint into it with black.
I've got to do a little bit of touch-up on this left side of the mountain. I could paint this, but the lasso will probably be quicker. I still need to clean up this entire bottom area, so I'm going to marquee select it and with black loaded into the background color picker, hit Delete. I still need to clean up the top and I'll do that with the Lasso tool, again.
I'll press X to load white into the background color picker and then hit Delete. On this right side, neither of the masks got the edge of the mountain, and I'm going to have to hand marquee that. Using the Lasso tool, carefully trace around the edge of the mountain. You can turn off the visibility of the alpha channel so that you can more clearly see the scene as you're tracing. When you're done, turn alpha channel back on, press X to load white into the background color picker, and hit Delete.
Then invert the selection and with black loaded into the brush, touch up that edge of the mountain. I almost have the mountain isolated, but I still want to subtract these foothills from the selection. Now I'll load in that first mask that was used to isolate the foothills by Command+Clicking or Ctrl+Clicking into the layer icon preview and then hit Delete. Now all I've got to do is lasso trace around the roof of the mountain chalet.
With the Lasso tool selected, I'm going to hold down on the Option+Alt key to temporarily turn this into the Polygonal Lasso tool and then draw around the straight hard surfaces of the roof. Then lasso around the entire bottom area of the composition. Hit Delete. Now we have the mountains nicely separated out. This is actually the opposite of what is needed, so select All, which is Command+A on the Mac and Ctrl+A on Windows, and then select the Inverse, which is Command+I on the Mac and Ctrl+I on Windows.
Now, Command+Click or Ctrl+Click into the layer icon preview to load the selection that we've just created. We're going to copy the mountains out, but we need to make sure the RGB channel is selected and not one of the alpha channels. Then return at the Layers panel and select any of the RGB layers. Now we need to do a Copy Merge to copy the mountains out. Press Command+Ctrl+Shift+C on the Mac and Ctrl+Shift+C on Windows. If you do a regular copy, it only copies the pixels on the current layer, not all of the pixels under the current selection.
Then Command+Shift+V on the Mac and Ctrl+Shift+V on Windows to paste the information back into the exact same place you copied it out of. And then rename the layer Mountains. If you press on the eyeball to the left of the layer while holding down the Option key on the Mac or the Alt key on Windows, it will solo that layer. And that can be useful for confirming that you've got the mountains nicely isolated on the layer. With our mountains separated, we're ready to do some color correction on them and make them look like they're completely covered with snow.
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