Photoshop.CS.Bible [Electronic resources] نسخه متنی

Layer Basics

Regardless of how you create a new layer, Photoshop lists the layer along with a little thumbnail of its contents in the Layers palette. The new layer appears highlighted to show that it's active, and the layer's name appears in bold. The little paintbrush icon in front of the layer name also indicates an active layer.

To the left of the paintbrush icon is a column of eyeballs, which invite you to hide and display layers temporarily. Click an eyeball to hide the layer. Click where the eyeball previously was to bring it back and redisplay the layer. Whether hidden or displayed, all layers remain intact and ready for action.

Switching between layers

You can select a different layer by clicking its name in the Layers palette. This layer becomes active, enabling you to edit it. Note that only one layer may be active in Photoshop — you can't Shift-click to select and edit multiple layers, I'm sorry to say. So although you can link multiple layers and combine them into sets — as I explain in the section "Moving, Linking, and Aligning Layers" — you cannot select, paint, filter, or otherwise change the pixels on more than a single layer at a time.

Why Ctrl+Alt-right-clicking (z -Option-Control-clicking on the Mac)? Here's how it breaks down:

Ctrl (z on the Mac) gets you the move tool. (If the move tool is already selected, you don't have to press Ctrl or z; Alt-right-clicking or Option-Control-clicking works just fine.)

Right-clicking (Win) or Control-clicking (Mac) alone brings up a shortcut menu. When you right-click or Control-click with the move tool — or Ctrl-right-click (z -Control-click on the Mac) with any other tool — Photoshop displays a pop-up menu that lists the layer that the image is on and any other layers in the image, as in Figure 12-6. (If a layer is completely transparent at the spot where you right-click or Control-click, that layer name doesn't appear in the pop-up menu.) Select the desired layer to go there.

Figure 12-6: Ctrl-right-click (Win) or z -Control-click (Mac) an image to view a pop-up menu. The menu lists all the layers in the image that contain pixel data on the spot where you clicked.

The Alt key (Option key on the Mac) bypasses the pop-up menu and goes straight to the clicked layer.

Add them all together, and you get Ctrl+Alt-right-click (Win) or z -Option-Control-click (Mac). It's a lot to remember, but believe me, it's a great trick once you get the hang of it.

Switching layers from the keyboard

You can ascend and descend the layer stack also from the keyboard:

Alt+] (Win) or Option-] (Mac): Press Alt+right bracket (Win) or Option-right bracket (Mac) to go to the next layer up in the stack. If you're already at the top layer, Photoshop takes you back around to the lowest one.

Alt+[ (Win) or Option-[ (Mac): Press Alt+left bracket (Win) or Option-left bracket (Mac) to go down a layer. If the background layer is active, Alt+[ or Option-[ takes you to the top layer.

Shift+Alt+] (Win) or Shift-Option-] (Mac): This takes you to the top layer in the image.

Shift+Alt+[ (Win) or Shift-Option-[ (Mac): This activates the background layer (or the lowest layer if no background exists).

Understanding transparency

Although the selection outline disappears when you convert a selection to a layer, no information is lost. Photoshop retains every nuance of the original selection outline — whether it's a jagged border, a little bit of antialiasing, or a feathered edge. Anything that wasn't selected is now transparent. The data that defines the opacity and transparency of a layer is called the transparency mask.

To see this transparency in action, click the eyeball icon in front of the Background item in the Layers palette. This hides the background layer and enables you to view the new layer by itself. In Figure 12-7, I hid the background woman from Figure 12-6 to view the mask and frame on their own. The transparent areas are filled with a checkerboard pattern. Opaque areas look like the standard image, and translucent areas — where they exist — appear as a mix of image and checkerboard.

Figure 12-7: When you hide the background layer, you see a checkerboard pattern that represents the transparent portions of the layer.

If you apply an effect to the layer while no portion of the layer is selected, Photoshop changes the opaque and translucent portions of the image but leaves the transparent region intact. For example, if you press Ctrl+I (z -I on the Mac) or choose Image Adjustments Invert, Photoshop inverts the image but doesn't change a single pixel in the checkerboard area. If you click in the left column in front of the Background item to bring back the eyeball icon, you may notice a slight halo around the inverted image, but the edge pixels blend with the background image as well as they ever did. In fact, it's exactly as if you applied the effect to a selection, as demonstrated in Figure 12-8. The only difference is that this selection is independent of its background. You can do anything you want to it without running the risk of harming the underlying background.

Figure 12-8: Applying the Invert command to the mask layer inverts only the mask without affecting any transparent pixels. The woman and frame remain every bit as visible as ever.

Only a few operations affect the transparent areas of a layer, and most of these are limited to tools. You can paint on transparent pixels to make them opaque. You can clone with the clone stamp or smear pixels with the edit tools. To send pixels back to transparency, paint with the eraser. All these operations change both the contents of the layer and the composition of the transparency mask.

When a portion of the layer is selected, pressing plain old Backspace (Win) or Delete (Mac) eliminates the selected pixels and makes them transparent, revealing the layers below.

Modifying the background layer

At the bottom of the layer stack is the background layer, the fully opaque layer that represents the base image. The background image is as low as you go. Nothing can be slipped under the background layer, and pixels in the background layer cannot be made transparent, unless you first convert the background to a floating layer.

To make the conversion, double-click the item labeled Background in the Layers palette. A dialog box appears. Enter a name for the new layer — Photoshop suggests Layer 0 — and press Enter or Return. You can now change the order of the layer or erase down to transparency.

In Figure 12-9, I converted the background woman to a layer. This particular image included a predrawn path that encircled the scared subject. I Ctrl-clicked (z -clicked on the Mac) on the path to convert it to a selection outline and then I pressed Ctrl+Shift+I (z -Shift-I on the Mac) to reverse the selection. Finally, I pressed Backspace (Delete on the Mac) to erase the pixels outside the woman, as the figure demonstrates. From this point on, I can reorder all the layers or add layers behind the woman. I can also introduce a new background layer.

Figure 12-9: After converting the image of the scared woman to a layer, I Ctrl-clicked (z -clicked on the Mac) on the path, inversed the selection, and pressed Backspace (Delete on the Mac) to reveal the transparent void below.

To establish a blank background, create an empty layer by pressing Ctrl+Shift+N (z -Shift-N on the Mac) and then choose Layer New Background From Layer. In Chapter 14.)

Figure 12-10: I added a background layer behind the woman and applied a paper texture and drop shadows to give my composition a l ittle false depth.

Photoshop permits only one background layer per image. If an image already contains a background layer, the command Layer New Background From Layer changes to Layer From Background, which converts the background layer to a floating layer, as when you double-click the Background item in the Layers palette.

Reordering layers

What good are layers if you can't periodically change what's on the top and what's on the bottom? You can reorder layers in two ways. First, you can drag a layer name up or down in the scrolling list to move it forward or backward in layering order. The only trick is to make sure that the black bar appears at the point where you want to move the layer before you release the mouse button, as illustrated in Figure 12-11.

Figure 12-11: Drag a layer between two other layers to make the all-important black bar appear (left). Then release the mouse button to change the hierarchy of the layer (right).

The second way to reorder layers is to choose a command from the Layer Arrange submenu. For example, choose Layer Arrange Bring Forward to move the active layer up one level; choose Layer Arrange Send to Back to move the layer to above the background layer.

You can move faster if you remember the following keyboard shortcuts:

Ctrl+Shift+] (Win) or z -Shift-] (Mac): Press Ctrl+Shift+right bracket (Win) or z -Shift-right bracket (Mac) to move the active layer to the top of the stack.

Ctrl+Shift+[ (Win) or z -Shift-[ (Mac): This shortcut moves the active layer to the bottom of the stack, just above the background layer.

Ctrl+] (Win) or z -] (Mac): This nudges the layer up one level.

Ctrl+[ (Win) or z -[ (Mac): This nudges the layer down one level.

Automated matting techniques

When you convert an antialiased selection to a layer, you sometimes take with you a few pixels from the selection's previous background. These fringe pixels can result in an unrealistic outline around your layer that cries out, "This image was edited by a hack." For example, Figure 12-12 shows a magnified detail from one of my original attempts to add a pair of glasses to the frightened woman we met earlier in the chapter. Although the selection outline was accurate, I managed to retain a few white pixels around the edges, as you can see around the outline of the glasses.

Figure 12-12: This enlarged detail of the glasses against the face shows the fringe pixels left over from the white background that was originally behind the glasses.

You can instruct Photoshop to replace the fringe pixels with colors from neighboring pixels by choosing Layer Matting Defringe. Enter the thickness of the perceived fringe in the Width option box to tell Photoshop which pixels you want to replace. To create the image shown in Figure 12-13, I entered a Width value of 1. But even at this low value, the effect is pretty significant, leaving gummy edges in its wake.

Figure 12-13: Here I used the Defringe command set to a Width value of 1 to replace the pixels around the perimeter of the glasses layer with colors borrowed from neighboring pixels.

It's not that Defringe never works; sometimes the results will be satisfactory. But keep in mind that it's not available when a selection is active or when the layer has a layer mask or vector mask.

Photoshop provides two additional commands under the Layer Matting submenu: Remove Black Matte and Remove White Matte. Frankly, it's unlikely you'll have much call to use them, but here's the scoop:

Remove Black Matte: This command removes the residue around the perim-eter of a layer that was lifted from a black background.

Remove White Matte: This command removes a white ring around a layer.

Adobe tells me that these commands were designed for compositing a scene rendered in a 3-D drawing program against a black or white background. But for other purposes, they almost never work. For example, my glasses are a prime candidate for Remove White Matte — they originated from a white background — and yet the command leaves behind more white pixels than the Defringe command set to its lowest setting.

Figure 12-14 shows the results of applying this technique to my glasses. By setting the Contract command to 1 pixel and the Feather command to 0.5 pixel, I managed to remove the edges without harming the layer itself. And the effect looks better than that produced by the Defringe command (as you can compare for yourself with Figure 12-13).

Figure 12-14: Here I removed the edges manually using the Contract, Feather, and Inverse commands. This looks way better than anything Photoshop can do automatically.

Blending layers

Photoshop lets you blend layers like no other program in the business. In fact, Photoshop does such a great job that it takes me an entire chapter — Chapter 13 — to explain these options in detail. I offer this section by way of introduction so that you're at least aware of the basics. If you have bigger questions, Chapter 13 is waiting to tell all.

The Layers palette provides four basic ways to blend pixels between layers (see Figure 12-15). None of these techniques permanently changes as much as a pixel in any layer, so you can always return and reblend the layers at a later date.

Figure 12-15: The blend mode pop-up menu and the Opacity and Fill option boxes enable you to mix layers without making any permanent changes to the pixels.

The Opacity value: Enter a value in the Opacity option box near the top of the Layers palette to change the opacity of the active layer or floating selection. If you reduce the Opacity value to 50 percent, for example, Photoshop makes the pixels on the active layer translucent, so the colors in the active layer mix evenly with the colors in the layers below.

The Fill value: The Fill option lets you adjust the opacity of pixel information in the layer — anything painted, drawn, or typed — without affecting the opacity of any layer effects that might be applied. For instance, if you have a text layer with the Drop Shadow layer effect applied, lowering the Fill slider to 0 fades out the text itself, leaving just the ghostly drop shadow behind. As with all other blending-related options, I explain the Fill option in excruciating detail in Chapter 13.

The blend mode pop-up menu: Choose an option from the blend mode pop-up menu — open in Chapter 5 (in fact, the two terms are sometimes used interchangeably). But you can accomplish a lot more with blend modes, which is why I spend so much time examining them in Chapter 13.

Blending Options: Choose Layer Layer Style Chapter 13, you can hide one or more color channels, specify which colors are visible in the active layer, and force other colors to show through from the layers behind it. Select an item from the left-hand list to apply a layer style, as discussed in Chapter 14.

Although far short of the whole story, that should be enough to prepare you for anything I throw at you throughout the remainder of this chapter.

Fusing several layers

Although layers are wonderful and marvelous creatures, they have their price. Layers expand the size of an image in RAM and ultimately lead to slower performance. And as I noted in Chapter 3, only four formats — PDF, TIFF, the new PSB, and the native PSD — permit you to save layered compositions.

In the interest of slimming the size of your image, Photoshop provides the following methods for merging layers:

Merge Down (Ctrl+E or z -E): Choose Layer Merge Down to merge a layer with the layer immediately below it. When generating screen shots, I use this command 50 or 60 times a day. I paste the screen shot into the image window, edit the layer as desired, and then press Ctrl+E (Win) or z -E (Mac) to set it down. Then I can save the screen shot to the smallest possible file on disk, essential when e-mailing the screens to my editor.

Merge Visible (Ctrl+Shift+E or z -Shift-E): Choose the Merge Visible command to merge all visible layers into a single layer. If the layer is not visible — that is, if no eyeball icon appears in front of the layer name — Photoshop doesn't eliminate it; the layer simply remains independent.

Flatten Image: This command merges all visible layers and throws away the invisible ones. The result is a single, opaque background layer. Photoshop does not give this command a keyboard shortcut because it's so dangerous. More often than not, you'll want to flatten an image incrementally using the two Merge commands.

Dumping layers

You can also throw a layer away. Drag the layer name onto the trash can icon at the bottom of the Layers palette. Or click the trash can icon to delete the active layer.

Saving a flattened version of an image

As I mentioned, only four file formats — PDF, TIFF, PSB, and the native Photoshop format — save images with layers. If you want to save a flattened version of your image — that is, with all layers fused into a single image — in some other file format, choose File Save As or press Ctrl+Shift+S (z -Shift-S on the Mac) and select the desired format from the Format pop-up menu. If you select a format that doesn't support layers — such as JPEG, GIF, or EPS — the program dims the Layers check box.

The Save As command does not affect the image in memory. All layers remain intact. And if you select the As a Copy check box with the Layers option deselected — which I recommend you do — Photoshop doesn't even change the name of the image in the title bar. It merely creates a flattened version of the image on disk. Nevertheless, be sure to save a layered version of the composition as well, just in case you want to edit it in the future.