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In this movie I'll show you how to use one layer to cast a shadow onto another. Now this is pure 2D fakery, which means the effect only works under certain conditions. First of all, the object casting a shadow and its background have to be on independent layers. Also, you want a fair amount of space between the object and the background for the effect to work out right. And you want your background to have as little perspective associated with it as possible. In our case, we have this nice flat horizon line, and that is the best-case scenario where this effect is concerned.
All right, I'm going to grab my existing shadow layer here inside the Layers panel and press the Backspace key, or the Delete key on the Mac, in order to get rid of it. Now, I need to access that shark. It happens to be located inside the shark group right there, so I'll twirl open the folder. And then you can see my shark layer toward the bottom of the list here. Notice I have a layer mask. If your layer includes a layer mask then you want to convert the layer mask to a selection outline by pressing the Ctrl key, or the Command key on a Mac, and clicking on that layer mask thumbnail. If you don't have a layer mask then you would go ahead and Ctrl+Click or Command+Click on the layer thumbnail itself. All right.
Now I'm going to switch to the background layer, just make sure I don't have any special layers selected, and then I'll go up to the Select menu and choose Transform Selection, which allows me to modify the selection outline independently of the image itself. Now at this point you want to go ahead and drag this top handle all the way down and beyond the bottom handle, so you end up flipping the selection outline like so, and that'll give you a negative H value. Now I have a very specific value in mind. I'm going to click on this bottom point in the reference point matrix here on the far-left side of the options bar, and then I'm going to change the H value to -35%.
The link icon should be turned off because we don't want to modify the Width value. And then press the Enter key in order except that modification. And while I'm still working inside the Free Transform mode here, I'm going to press Shift+Down Arrow one, two, three, four, five, six, seven, eight, nine, ten times in a row, so that I scoot that shadow down far enough that the top fin is just barely outside the canvas. And now I'll press the Enter key, or the Return key on the Mac, in order to accept that modification. All right, let's create a new layer by pressing the Alt key, or the Option key on the Mac, and clicking that black-white icon at the bottom of the Layers panel.
Then I'll choose Solid Color, and now I'll go ahead and call this new layer shadow, and I'll click OK. Photoshop will then bring up the Color Picker dialog box. By default, the colors should be set to black--that is, the H, S and B values are all set to zero. If so, go ahead and click OK. And we now have a nice black shadow. Now, there's two ways to work, depending on how realistic you want things to be. You can go ahead and click on the layer mask thumbnail for that shadow layer in order to select it, and then you would go to the Window menu and choose the Masks command to bring up the Masks panel.
And you could increase the Feather value to let's say about 30 pixels, in order to create a nice soft cash shadow. And the great thing about the Feather value is it's a dynamic modification, so you can change your mind anytime you like. The problem is, I'd like the shadow to work better with the grass on the background, so I'd like to actually cast the shadow onto the independent blades of grass--the way it would work in the real world. And I'm not going to get that effect if I work with the Feather value here. So I'm going to reduce that value back to zero. If you're interested for a more naturalistic effect, then I should warn you it's a static modification, but again, it's more credible. Then here's what you do.
The first step is to go up to the Filter menu and choose the Blur command and then choose Gaussian blur. And this time around we're not to apply as much blur, just 15 pixels, so half of what I applied a moment ago from the Masks panel, and then click okay. And now we need to distort this shadow using a displacement map. And in order to do that, we need to create the displacement map, and here's how: you Alt+Click or Option+Click on the eyeball in front of the Background layer in this case, because it's the one that contains the grass. Then I'll go up to the Image menu, and I'll choose the Duplicate command.
And I'm going to go ahead and say duplicate merge layers only, so that we get a flat file. I might as well go ahead and call this new image Background. Click okay. Now I want to find the channel that contains the most contrast, where the grass is concerned. So I'm going to go ahead and zoom in on the grass, switch over to the Channels panel, and let's check out the channels. Here's the Red channel; here's the Green channel, which gets pretty blown out, as you can see; and here's the Blue channel in which the grass is very dark. So it appears that, where the grass is concerned anyway, the Red channel provides us with the most contrast.
So I'm going to go ahead and click on that Red channel, and then I'll go up to the Image menu, choose Mode, and choose Grayscale. Now, you may end up seeing a message asking you if you want to flatten the image--in which case you would say OK. Then you'll see this alert message, which says, "Discard other channels?" Go ahead and click okay to it as well. So you end up with a grayscale image. Then go up to the File menu and choose the Save As command. And you want to save the image to the native PSD format, as I'm doing right here. And then go ahead and give the image a name, save it out.
I've already saved an image in advance; it's called Red channel.psd. So I'll go ahead and cancel out of this dialog box, switch over to the image in progress, switch back to the Layers panel as well. And I'm going to scroll down to the bottom of list and Alt+Click or Option+Click on the eyeball in front of the Background layer to turn all the other layers back on. Make sure that the layer mask for the shadow layer is active. Then go up to the Filter menu, choose Distort, and choose Displace. Inside the Displace dialog box, I've set the Horizontal Scale value to zero because I don't want the shadow wandering back and forth; I just want it to wander up and down.
And I've set the Vertical Scale value to 30. Then I'll click OK. And you want to select that file you just created--in my case, Red channel.psd--and then click the Open command in order to apply that displacement map to the image. And you can see that now the shadow is wandering up and down with the blades of grass. And you can get an even better sense of what's going on if you turn that Background layer off. Notice how organic that shadow is. It's just amazing. But I think it could be even better still, so I'm you bring back my background layer, and I'm going to double-click on an empty portion of the shadow layer to bring up the Layer Style dialog box.
And I'm going to drop the shadow off of the brightest blades of grass by pressing the Alt key on the PC, or the Option key on the Mac, and then dragging the left half of that white slider triangle--for the Underlying Layer slider incidentally-- all the way down until that value before the slash is 170. And as I say, that goes ahead and reveals some of the brightest grass blades. Then I'll click OK in order to accept that affect. All right. Now I'll press Ctrl+0, or Command+0 on the Mac, to center the zoom. And I'm going to reduce the opacity of this layer to 35% by pressing 35 on my keyboard.
This assumes that one of your selection tools is active, incidentally. And that is the final version of the cast shadow, created by flipping the selection from the shark layer, converting that to a layer mask, and then applying a combination of Gaussian Blur and the Displace filter here inside Photoshop.
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