Basic Transparency in Creative Suite

Transparency comes in many different flavors so many that sometimes you might not even realize that you're using transparency effects. For example, feathering is a transparency effect, and so are drop shadows, glows, bevels, blends, layer masks, and overlays. We'll talk about how each of these work in the Creative Suite applications in this chapter. There's not necessarily a right or wrong application to choose when applying transparency, and many of the results appear the same. But when there's a better way to do it, we'll tell you.

Some effects require that a pixel layer or object be on top of another in order to display the transparency effect, because without another object below the first, there is no way to know that a blend mode has been applied to an object. Other transparency effects, such as feathers and glows, can be seen without any other objects below. Still other, such as bevels and embossed edges, use elements of transparency, although the effects themselves may not look very transparent.

Taken together, there are hundreds of menus, sliders, and fields in Photoshop, Illustrator, and InDesign where you can create or control some form of transparency. Rather than try to go through every example of those fields, we've broken them down by categories: opacity, blending modes, shadows and glows, special effects, and transparency masks. Table 11-1, at the end of this chapter, gives you a summary of the transparency effects found in Photoshop, Illustrator, and InDesign.

Table 11-1. Availability of transparency features

Effect		Photoshop	Illustrator	InDesign
Opacity for entire object		Y	Y	Y
Opacity for parts of objects		N	Y	N
Transparency Mask		Y (called Layer Mask)	Y (called Opacity Mask)	N
Blending modes		23 types	16 types	16 types
	Normal	Y	Y	Y
	Dissolve	Y	N	N
	Darken	Y	Y	Y
	Multiply	Y	Y	Y
	Color Burn	Y	Y	Y
	Linear Burn	Y	N	N
	Lighten	Y	Y	Y
	Screen	Y	Y	Y
	Color Dodge	Y	Y	Y
	Linear Dodge	Y	N	N
	Overlay	Y	Y	Y
	Soft Light	Y	Y	Y
	Hard Light	Y	Y	Y
	Vivid Light	Y	N	N
	Linear Light	Y	N	N
	Pin Light	Y	N	N
	Hard Mix	Y	N	N
	Difference	Y	Y	Y
	Exclusion	Y	Y	Y
	Hue	Y	Y	Y
	Saturation	Y	Y	Y
	Color	Y	Y	Y
	Luminosity	Y	Y	Y
Drop Shadows		Y	Y	Y
Bevels And Emboss		Y	N	N
Inner Shadow		Y	N	N
Outer Glow		Y	Y	N
Inner Glow		Y	Y	N
Feather		Y (but not live)	Y	Y
Transparency in gradients		Y	N	N

Pixels vs. Object Transparency

Photoshop applies transparency to the pixels in a layer or the pixels created by a painting tool. Illustrator and InDesign apply transparency to objects. These objects are the fills or strokes in Illustrator documents or the frames in InDesign layouts.

Though these differences are significant, for the purpose of describing how you apply transparency, we'll use the term "object." This term covers the pixels in Photoshop as well as the fills, strokes, and frames in Illustrator and InDesign.

Object Opacity

If you want to make an object less opaque (or more transparent), you need to change the object's opacity. The lower the opacity, the more transparent the object will become. When the object gets down to 0% opacity, it has disappeared. Photoshop, Illustrator, and InDesign offer opacity tools with some differences between them.

Opacity in Photoshop

Photoshop has the most options for adjusting the opacity of elements and layers.

• Layer opacity. Located in the Layers palette, this control lets you adjust the appearance of all the elements in the layer. This means that the images and any layer effects applied to that image change together.

• Fill opacity. Also in the Layers palette, this settings lets you control the appearance of the image in the layer, but not the entire layer. If you lower the opacity of the fill, the image in the layer changes, but no change is applied to any layer effects.

• Painting tools opacity. You can change the opacity for painting tools such as the Brush, Pencil, History Brush, Clone Stamp, etc. When you lower the opacity of a painting tool, each stroke allows you to see through the paint stroke to the pixels below. However, the transparency is applied only during the creation of the stroke. Afterwards, the transparency of each brush stroke is controlled by the opacity setting of its layer.

• Effects opacity. When you apply effects such as drop shadows, gradient fills, and strokes, you get to choose an opacity setting for that effect. This opacity setting is independent from the opacity of the fill or the layer. This makes it possible for an image that has no opacity applied to still cast a semi-transparent drop shadow.

These are also the same areas where you can apply the blending modes to layers, fills, tools, and effects. We'll look at those blending modes later in this chapter.

Erasing Pixels

Photoshop also has an Eraser tool that lets you delete pixels or lower their opacity. We rarely use this tool because it permanently destroys the pixels in an image. We would much rather use layer masks as discussed in the next section.

Photoshop Layer Masks

Another way to get transparency is to apply a layer mask to a Photoshop layer. Layer masks allow you to apply transparency to selected portions of the image on a layer. The benefit of using a layer mask is that you get the appearance of transparency without actually deleting any pixels in the image. (See the sidebar "Save the Pixels!" in this chapter.)

A layer mask is an editable grayscale channel that is added to a layer. You can use any of the painting or imaging tools to create the grayscale areas on the mask. Wherever the mask is white, the pixels in the layer have 100% opacity. Wherever the mask is black, the pixels in the layer have 0% opacity. Any shades of gray are equivalent shades of opacity. Figure 11-1 shows the various opacity controls for layers in Photoshop. (For more information on working with layers, see Chapter 12, "The Flexibility of Layers.")

Figure 11-1. Opacity controls for layers in Photoshop.

Here are the steps to create a layer mask.

1. Select the layer on which you want to add the layer mask.

2. Click the Add Layer Mask icon in the Layers palette. The layer-mask thumbnail appears next to the thumbnail for the image.

3. Click the layer-mask thumbnail. A highlight appears. Use any of the painting or editing tools to modify the appearance of the layer mask. For example, you can create a black-to-white gradient in the layer mask that will cause the image to fade from 100% opacity to 0% opacity along the length of the gradient.

Photoshop also has a setting that allows you to lock the transparent pixels on a layer. With this setting enabled, you can edit only the opaque pixels of that layer.

Tip: Look for the Transparency Grid

As you work in Photoshop, look for the checkerboard pattern, which indicates that there is some form of transparency applied to that layer. We'll discuss how to view and understand the transparency grid in Photoshop as well as the other Creative Suite applications in the section "Viewing the Transparency Grid" later in this chapter.

Save the Pixels!

Whenever you are about to erase, delete, or otherwise destroy the pixels of an image or layer, stop and consider. Could you achieve the same effect by using some sort of opacity mask or opacity setting? If so, use that technique pixels are precious bits of information that you should not delete willy-nilly.

Opacity in Illustrator

Like Photoshop, Illustrator also offers layer-based opacity, but in addition to using layers, you can control opacity object by object. Illustrator applies opacity to the following items:

• Parts of objects. This includes the individual fills and strokes that are available through the Appearance palette.

• Objects. Instead of breaking opacity down to individual fills and strokes, you can also apply it to the object as a whole.

• Groups. You can apply one opacity setting to a single item in a group, and then a different opacity to the group as a whole.

• Layers. If all this isn't enough, you can apply opacity to an entire layer.

Tip: Watch out for multiple levels of opacity

Illustrator makes it very easy to get lost in a maze of confusing opacity settings. For instance, you can have one opacity assigned to a single object, then another opacity assigned to the group that the object is within, and then yet another opacity setting for the layer as a whole. Each of the opacity settings add together.

The opacity controls in Illustrator are in the Transparency palette. If you simply select an object, the opacity setting is applied to all the appearance attributes of the object. However, you can use the Appearance palette to target a single object attribute, such as the stroke. You can then change the opacity setting so that it is applied just to that single attribute. Figure 11-2 shows how you can use the Appearance palette to change the opacity for just one object attribute.

Figure 11-2. The left image shows an opacity setting applied to the entire object. The right image shows how targeting the stroke in the Appearance palette applies opacity to just the stroke.

Illustrator also has a transparency feature called an opacity mask (Figure 11-3). An opacity mask is very similar to a layer mask in Photoshop; where the opacity mask is white, you can see the object. Where the mask is black, you do not see the object. Here are the steps to create an opacity mask in Illustrator.

1.	Select the object that you want to modify.
2.	Make sure that Show Thumbnails is chosen in the Transparency palette menu. The selected object appears as a thumbnail image in the palette.
3.	Double-click the area to the right of the object's thumbnail or choose Make Opacity Mask from the Transparency palette menu. A thumbnail for the opacity mask appears. The name for the Layers palette also changes to be Layers (Opacity Mask). This indicates you are working on the opacity mask, and not the object itself.
4.	Create the object for the opacity mask. The opacity mask can be a vector object created in Illustrator or a placed image created in Photoshop.
5.	Choose Invert Mask if you want to swap the white and black controls for the opacity mask so that white will be the color that masks the object instead of the color that allows you to see the masked object.
6.	Deselect the Clip option if you want to see the masked object outside the boundaries of the opacity mask.

Figure 11-3. An opacity mask applied to a placed image.

Clipping Mask or Opacity Mask?

Illustrator has two types of masks. A clipping mask is the term applied to objects that are used to hide parts of objects that fall outside the contours of the clipping mask object. The area that is masked (hidden) by a clipping mask is solely dependent on the shape of the clipping mask object. The colors of the mask neither its interior colors nor blacks nor whites do not affect the parts of the object that are seen. Opacity masks use the grayscale values of the masking object to determine what parts of the object are visible.

If you're familiar with the masks of Photoshop, and want to make comparisons, opacity masks in Illustrator are most similar to the layer masks in Photoshop; clipping masks in Illustrator are most similar to the clipping masks in Photoshop. Use an opacity mask if you want intermediate levels of opacity in the mask. Use a clipping mask if you want a simple shape to outline the visible areas of an object.

Opacity in InDesign

InDesign has very basic transparency controls compared to Photoshop or Illustrator. As in Illustrator, the opacity and blending mode controls are in the Transparency palette (Figure 11-4). You can change the opacity of an object, but you can't apply opacity to just the fill or the stroke. Also, InDesign doesn't have any sort of opacity-mask feature.

Figure 11-4. Blending options for Photoshop (left), Illustrator (top right), and InDesign (bottom right).

Blending Options

All three programs have options that let you control how the blending and opacity controls work between layers (in Photoshop) and between objects (in Illustrator and InDesign). As befits its more sophisticated controls, Photoshop's blend options are the most complex (Figure 11-4). We won't dare to try to cover all the intricacies of the Photoshop Layer Style dialog box except to call attention to the Blend If controls at the bottom. If you change the settings for the top layer (This Layer), you can easily hide portions of the image. Figure 11-5 shows how setting the blending options hides the white area around an image.

Figure 11-5. Blending options allow you to hide the white background in the top layer (left) so that the bottom layer shows through (right).

Illustrator and InDesign share similar blending options. The Knockout Group option allows you to apply opacity or blending modes to the objects on the layers below, but not between the objects on the same layer, as shown in Figure 11-6. The Isolate Blending command allows the blending modes to function only between selected objects and not any others below, as shown in Figure 11-7.

Figure 11-6. With Knockout Group turned off, the stars show through to each other and to the image below (left). With Knockout Group turned on, the stars do not react to each other (right).

Figure 11-7. With Isolate Blending turned off, the circles blend with other as well as the image below (left). With Isolate Blending turned on, the circles react only to each other, not to the image below (right).

Opacity in Gradients

One of the most popular requests from designers working with the Creative Suite applications is to create gradients that change opacity as well as colors. This is possible in Photoshop, where you use the Gradient Editor to set opacity stops, which allow you to control the opacity of the color at that location in the gradient (Figure 11-8). You open the Gradient Editor by choosing the Gradient tool in the Tools palette and then clicking the gradient that is displayed in the Options bar.

Figure 11-8. Controls for gradients in Photoshop (left), Illustrator (top right), and InDesign (bottom right).

Sadly, neither Illustrator nor InDesign allows you to assign opacity to gradients. In these applications the gradients contain only color stops, not opacity stops (Figure 11-8). There are some blending modes that can be applied to gradients that simulate some form of opacity (see the section "Blending Modes" below), but they are not as useful as true opacity in a gradient.

Blending Modes

Blending modes are more complicated than simple opacity. When you change the opacity of an object, you change the image without any interaction from the images below. When you change the blend mode for an image, the image interacts with the objects below, and the results vary depending on the qualities of those objects. Each blending mode creates a different appearance for the top image.

Understanding Blending Modes

You can apply blending modes fairly similarly in Photoshop, Illustrator, and InDesign, through the transparency controls, as shown in Figure 11-9. However, Photoshop has the most types of blending modes. We won't try to explain them all here (we also won't try to explain why the InDesign engineers changed the order of the blending modes from how it was in Photoshop and Illustrator). Instead, we'll talk about their groupings. The blending modes are arranged in Photoshop and Illustrator into groups that give you some idea of what the modes in the groups do.

Figure 11-9. Blending modes in (from left to right) Photoshop, Illustrator, and InDesign.

Understanding the groups for the blending modes in Photoshop and Illustrator can help you remember which blending modes do what. We've taken the names that our friends David Blatner and Bruce Fraser, who wrote Real World Adobe Photoshop CS2, have used for naming these groups of modes:

• Independent modes. This group contains the Normal blend mode plus the Dissolve mode. Both of these replace the colors below with the pixels above at 100% opacity. When the opacity is lowered, the Normal mode changes the top colors by combining them with the bottom based on the opacity levels. The Dissolve mode replaces the colors in a random fashion that simulates noise in the image.

• Darken modes. As the group name suggests, all these modes (Darken, Multiply, Color Burn, and Linear Burn) will combine with the underlying pixels to darken the top colors.

• Lighten modes. As the group name suggests, all these modes (Lighten, Screen, Color Dodge, and Linear Dodge) will combine with the underlying pixels to lighten the top colors.

• Contrast modes. The modes in this group (Overlay, Soft Light, Hard Light, Vivid Light, Linear Light, Pin Light, and Hard Mix) combine colors based on a mixture of the Darken and Lighten groups. If the top color is darker than 50% gray, that color will darken the image below. If the top color is lighter than 50% gray, that color will lighten the image below. A fill of 50% gray does nothing to the underlying colors; it is neutral.

• Comparative modes. The Difference and Exclusion modes combine colors based on the color values, and subtract either the underlying colors from the overlying colors or the overlying colors from the underlying colors based on whichever will create the brightest color. These two modes work similarly, except the Exclusion mode works with a lower contrast for the results. Sandee uses the Difference mode to line up patches she creates to correct screen shots. When the Difference mode highlights disappear, she knows the top layer is positioned correctly over the bottom.

• HSL modes. As the name suggests, the modes in the final group (Hue, Saturation, Color, and Luminosity) work by using the hue, color saturation, and luminosity of the top color compared to the bottom.

Some blending modes are more obvious than others, depending on the colors in the top and bottom images. For example, the Multiply blend mode is very obvious when a 50% gray object is over any color. The gray adds to the color below. But when a 50% gray object is set to Overlay, it disappears when positioned over any other color not what you'd expect.

See the Color Insert pages C12C16 for color examples of how the blending modes appear.

When Blending Modes Don't Seem to Work Correctly

Sandee remembers when blending modes were first introduced in Illustrator. There seemed to be a problem with how the Overlay mode worked compared to how it worked in Photoshop. A few years later, when InDesign added blending modes, it also seemed to work differently from Photoshop. Could it be that the blending modes in Photoshop had different appearances than the same modes in Illustrator or InDesign? Not at all, as she eventually found out. But the reason behind the discrepancy demonstrates an important point about blending modes.

As shown in Figure 11-10, we've set a 100% magenta object to Overlay and placed it over a 100% yellow object. On the far left, you can see that when the magenta object is set to Overlay in Photoshop, it disappears. However, in Illustrator (center), the Overlay setting only changes the display of the object where it overlaps the yellow area. Outside that area, the magenta color is visible.

Figure 11-10. Overlay example in Photoshop (left), Illustrator (middle), and Photoshop with white background turned off (right).

Is there really a major difference in how the blending modes work in the applications? Not at all! Look carefully at the Layers palette of the Photoshop file. Notice that two shape layers are over a white background layer. Now look at the Layers palette of the Illustrator file. Notice there is no object with a white background below the others.

The magenta color in the overlay mode turns transparent when over a white background. But if you take away the white layer in the Photoshop document, as seen in Figure 11-10 on the right, the magenta color behaves identically to how Illustrator and InDesign work. Alternately, you could place a white object behind the paths in Illustrator to achieve the same effect as in Photoshop. The most important thing to remember is that the blending modes react with all the colors in the file.