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Brush Dynamics

Photoshop has long permitted you to vary the size, opacity, and color of paint according to input from a pressure-sensitive drawing tablet. Available from companies such as Wacom (www.wacom.com), pressure-sensitive drawing tablets respond to how hard you press on the stylus, as well as the angle of the stylus and other attributes.

I happen to be an old fan of drawing tablets. I believe I have roughly a dozen sitting around in one form or other. So it's hardly surprising that I consider them every bit as essential as mice and keyboards. Alas, despite my advice, you may not own a tablet. Fortunately, Photoshop permits mouse users to enjoy much of the same flexibility as their stylus-wielding colleagues. Whether you use a stylus, a mouse, or even a finger on a notebook trackpad, you can introduce an element of spontaneity into what seems at times like an absolute world of computer imaging.

Photoshop calls these imaginative options brush dynamics, and they open up a lot of opportunities for faking pressure sensitivity. For example, you can make a brush shape twirl as you paint. You can add noise to the edges of a stroke. You can spray shapes, add texture, combine brushes, or even paint in rainbows. And most of the settings work every bit as well with, say, the sponge tool as they do with the brush tool. If you're a creative type, prepare to get lost inside Photoshop and lose track of reality for a few hours or maybe even days.

Brush dynamic basics

Chapter 2.

So there's your general overview; now let's plunge headlong into the specifics. To give you a sense of what's going on, we start with a detailed look at the options in the Shape Dynamics panel, which are arguably the most interesting, useful, and representative of all the brush dynamics. Then we take a more cursory look at the other options, which often follow in the same vein. After that, I encourage you to explore the options on your own.

So have fun. And when I say "have fun," I mean, have a blast, go nuts. By which I mean, wowsers, this stuff rocks. Goodness, how I envy you, so young and naive, embarking upon brush dynamics for the very first time. You're about to be amazed, astonished, and then once again amazed. Or, after this buildup, horribly disappointed. I guess it all depends on how much of a thrill you get from drawing wiggly, splattery, rough, colorful brushstrokes. Me, I love it. But you, who knows? Okay, I'll shut up now.

Shape dynamics

Inside the Brushes palette, click the Shape Dynamics option — the name, not the check box — to display the panel of options illustrated in Figure 5-24. Notice that the panel is divided into three sections, which start with the words Size Jitter, Angle Jitter, and Roundness Jitter. These options permit you to vary the diameter, angle, and roundness, respectively, of the brush over the course of a single stroke. But the repetition of the word "Jitter" may be misleading. It implies (to me, at least) that each group of options is related to jittering — Photoshop's word for random brush shape fluctuations — when in fact, jittering is a minor element of shape dynamics.

Figure 5-24: The Shape Dynamics panel along with a quick cartoon I drew using the brush shape described in the palette and a Wacom Intuos II tablet.

If I had designed this panel, it would look more like the one in Figure 5-25, with clear headlines for each section followed by the single most important option, the Control pop-up menu. Meanwhile, I'd put the least important option, Jitter, at the end. Because I believe this is the most logical way to present these options, I explain them in this order.

Figure 5-25: My suggestion for a redesign of this panel that would help it to make more sense. (It seems to make more sense to my cartoon, anyway.)

The diameter settings

The first group of options control the thickness of the brushstroke. The most important of these is the Control pop-up menu, which links the diameter of the brush to one of several variables. If you own a pressure-sensitive tablet, the most obvious setting is Pen Pressure, which is the default. This turns the brush into a traditional, pressure-sensitive painting tool, growing when you bear down on the stylus and shrinking with you let up.

In addition to Pen Pressure, the Control pop-up menu lets you select between the following options:

Off: Select this option to turn off the capability to vary the thickness of the brushstroke. You can still add random variations to the thickness using the Size Jitter value.

Fade: This option works every bit as well whether you use a mouse or tablet. Select Fade to reduce the size of the brush over the course of the drag, and then enter a value in the option box on the right to specify the distance over which the fading should occur. This distance is measured in steps — that is, the number of spots of color the brush plops down before reducing the size of the brush to its minimum (defined by the Minimum Diameter setting). The default value is 25#, which means 25 spots of color. Exactly how long such a stroke is in, say, inches depends on the Diameter and the Spacing values in the Brush Tip Shape panel. In other words, be prepared to experiment.

The Fade option can be most useful in the creation of a specular reflection, or in layman's terms, a sparkle. Figure 5-26 shows a highly polished, gold-painted egg. To add the sparkle in the second example, I painted a series of white strokes outward from the center using the brush tool. I Shift-dragged to make each of the four horizontal and vertical strokes, using a soft brush with a diameter of 20 pixels and a Fade value of 100 steps. To make each diagonal stroke, I clicked in the center and Shift-clicked farther out, using a diameter of 10 pixels and a Fade value of 50 steps. To complete the effect, I clicked once in the center of the sparkle with a very large, very soft brush.

Figure 5-26: A shiny golden egg from the Corbis library (top), and that same egg with a sparkle created using the Fade setting (bottom).

Pen Tilt: As illustrated in Figure 5-27, the tilt of a pen is its angle with respect to the tablet. Straight up and down, the pen communicates no tilt; at a severe angle, the pen communicates maximum tilt. When you set the Control option to Pen Tilt, you do two things. First, you vary the size of the brush according to pressure, just as you do when using Pen Pressure. Second, you add an element of vertical scaling so that the brush shape is oblong during a tilt. This scaling is defined by the Tilt Scale slider. All in all, it's an interesting idea, but for my money, Pen Tilt works more predictably when applied to roundness.

Figure 5-27: Most Wacom tablets are sensitive not only to how much pressure you apply to a stylus, but also to the angle of the stylus with respect to the tablet, known as the tilt.

Stylus Wheel: If tablet owners account for 10 percent of Photoshop users, airbrush owners account for about 1 percent of tablet users. But heck, that's still enough folks to populate a small town, so Photoshop might as well support them. Figure 5-28 shows what an electronic airbrush looks like, complete with wheel. Unlike the scroll wheels included with many PC mice — which are exceptionally useful for scrolling Web pages and Word documents — the wheel on an airbrush locks into position. This means you can nudge it higher or lower and leave it there. Although typically associated with properties such as Flow (which you can set from the Other Dynamics panel), the airbrush wheel is surprisingly useful for diameter as well. Move the wheel up, the brush gets thick and stays thick; move the wheel down, and you lock in a fine line, all in the middle of painting a brushstroke. Downside: A Wacom airbrush costs $99, not including the tablet. So it's not a stocking stuffer. She gets earrings, he gets an airbrush. Or vice versa. Heck, send me the earrings — I already have an airbrush. And no, I'm not interested in a trade, just give me the earrings!

Figure 5-28: The airbrush stylus includes a wheel that you can permanently set to increase or decrease the flow of paint, as with a traditional airbrush.

Accompanying the Control pop-up menu are three slider bars:

Minimum Diameter: Use this option to determine the thinnest a brushstroke can go. Me? I say go all the way to 1 percent baby. Why settle for more?

Tilt Scale: I don't admit this very often, but this option puzzles me. Yes, it's available only when you set the Control option to Pen Tilt, and yes, it stretches the height of the brush to make it elliptical when you tilt the stylus. But why? You can do this just as well with the roundness options, as I explain shortly. My guess is that a thoughtful engineer at Adobe wanted you to get confused by this option so you'd go out and buy this book. Really, that's my best guess. Now for those of you who did buy this book for a lucid description of the Tilt Scale option, sorry I couldn't help. Check out the other pages, though — they're really great.

Size Jitter: Use this slider to add an element of randomness to the thickness of a brushstroke. It doesn't matter whether you use a mouse or a stylus; the brush will jitter every bit as well either way. Higher values produce a wider range of jitter. Keep an eye on the preview at the bottom of the palette to get a sense of what different settings will do.

Angle and roundness

Now that you understand the diameter settings, the angle and roundness settings are pretty simple stuff. But to confirm your knowledge and ensure that we're all on the same page, here's how they work:

Angle Control: As with diameter, you can link the angle of the brush to such variables as Pen Pressure, Pen Tilt, and Stylus Wheel. More pressure or tilt equals more rotation of the brush. Naturally, the changes show up best with elliptical or asymmetrical brushes. You can also link the angle to Fade, which rotates the brush over the course of a specific number of steps, and then returns the brush to its normal angle (as specified in the Brush Tip Shape panel).

But this Control pop-up menu adds two more settings, Direction and Initial Direction. The first rotates the brush according to the direction of your drag. A horizontal drag is considered the normal angle; when dragging vertically, the brush rotates 90 degrees. For maximum effect, after setting this option to Direction, go to the Brush Tip Shape panel and set the Angle value to 90 degrees (or something close) with an elliptical brush. Then raise the Spacing value to something higher than 100 percent.

Meanwhile, the Initial Direction option rotates the brush according to the very start of your drag and then locks it into position. It's a nice idea, but the angle is locked down about 2 pixels into your drag, which means Photoshop is aware of your initial direction before you are.

Angle Jitter: This option rotates the brush randomly as you paint. As always, be sure to adjust the roundness of the brush so you can see the randomness at work.

Roundness Control: Set this option to Fade to reduce the roundness to its minimum over the course of a specified number of steps. You can also associate the roundness with Pen Pressure, Pen Tilt, or Stylus Wheel. Of these, Pen Tilt makes by far the most sense to me because that's what pen tilt does in real life.

Minimum Roundness: This value determines the minimum roundness, or maximum flatness, of the brush available to the Control and Jitter settings. If the Control option is set to Off and the Roundness Jitter is 0 percent, the Minimum Roundness slider is dimmed.

Roundness Jitter: Use this option to introduce random variations in roundness to your brushstroke.

Additional brush dynamics

For many, the Shape Dynamics settings will be enough. They certainly permit you to achieve an enormous range of effects. But if you're feeling ambitious, you can venture deeper, much deeper. Fortunately, the other panels of options — Scattering, Texture, and so on — follow the same logic we've seen thus far. So I'll breeze through them fairly quickly.

Figure 5-29 demonstrates several dynamic permutations as applied to the Scattered Leaves predefined custom brush. Here's how these options work:

Figure 5-29: Several brush dynamics applied to Scattered Leaves, one of Photoshop's predefined custom brushes.

Scattering: Highlight the Scattering option to spread the position of the spots of color around the brushstroke. When using a custom brush, such as Scattered Leaves in Figure 5-29, the effect is like spraying a pattern of images. Raise the Scatter value to increase the spread. Select Both Axes to scatter the brush spots along the stroke as well as perpendicularly to it. Use the Control pop-up menu to link it to stylus pressure or some other variable. Finally, use the Count options to increase the population of brush spots.

Texture: Select this option to apply a texture to a brushstroke, useful for conveying a surface such as paper or canvas. After selecting a predefined texture, set the Scale and Depth values to determine the size and degree of texture applied. Use the Mode option to define how brush and texture mix. (I discuss modes in the "Brush Modes" section near the end of this chapter, but for now, just experiment with an eye on the preview.)

If you want to vary the depth of texture throughout a stroke, turn on the Texture Each Tip check box. Then use the Control option to vary the depth according to, say, stylus pressure, or add some random Depth Jitter.

Dual Brush: The Dual Brush panel lets you mix two brushes together. Select the second brush from the list of thumbnails and use the Mode option to specify how the brushes intermix. You can also throw in settings such as Spacing, Scatter, and Count, all of which affect the second brush.

Figure 5-29 includes a couple of examples, mixing the Scattered Leaves brush with the Maple Leaves and Grass brushes, respectively. Figure 5-30 shows another example, complete with settings in the Brushes palette. Notice how by mixing a standard round brush with one of Photoshop's predefined Dry Brush options, I'm able to generate a complex brush that imparts its own texture.

Figure 5-30: I used the Dual Brush options to combine a soft round brush and a predefined custom brush to create a fairly convincing chalk effect. I also scaled and rotated the brushes to create the light eraser stamps in the upper-left and lower-right corners.

Color Dynamics: Use these options to vary the color of the stroke between the foreground and background colors depending on a fade or stylus pressure. You can also apply random changes to the hue, saturation, and brightness. The final slider bar, Purity, increases or decreases the saturation of colors throughout the brushstroke.

Other Dynamics: The final set of brush dynamics permit you to associate the opacity, strength, flow, or exposure of the brush, depending on what tool you're using. I discuss each of these attributes in more detail in the upcoming section, "Opacity and Strength, Flow and Exposure." If you happen to own an airbrush, settings such as the Flow and Exposure are what the wheel was originally designed for.

Noise, Wet Edges, and the rest

The list along the left side of the Brushes palette ends with five check boxes that you can use to add highlights and constraints to your brushstrokes. Not all options work with all tools — none are compatible with the smudge tool, for example — but when available, they're as effective as they are easy to use. And they work equally well with a mouse or a tablet.

Noise: This option randomizes the pixels along the edge of a brushstroke. Because the option affects only the edge, softer brushes result in more noise. The middle line in Figure 5-31 shows an example.

Figure 5-31: Three lines painted in black with the brush tool. The first was painted without dynamics, the second was painted with Noise, and the third, with Wet Edges. The enlarged details show how the edges of the strokes compare.

Wet Edges: When you select the Wet Edges check box, the brush creates a translucent line with darkened edges, much as if you were painting with watercolors. Soft brush shapes produce more naturalistic effects. The final example in Figure 5-31 shows a soft brushstroke painted in black.

Airbrush: This check box duplicates the airbrush icon in the Options bar. When turned on, paint builds up even when you hold the cursor in place, as if you were spraying color from a real airbrush. The Airbrush option is not available when using the pencil tool or any of the three focus tools (blur, sharpen, and smudge).

Smoothing: If you have difficulty drawing smooth lines and curves, turn this check box on to even out the rough spots. It slows down Photoshop's tracking time a little, but it may be worth it in many cases. Adobe recommends this option when using a stylus, but I've found it most helpful when using optical mice, which are notoriously bad at tracking evenly on patterned surfaces, such as wood tabletops.

Protect Texture: If you plan on painting a lot of textured lines and you want your textures to match, select this check box. It maintains a consistent pattern from one brushstroke to the next. The effect can be subtle, but I usually advise working with this option turned on.

Undoing pressure-sensitive lines

In the old days, pressure-sensitive lines were a pain to undo. Because a stylus is so sensitive to gradual pressure, you can unwittingly let up and repress the stylus during what you perceive as a single drag. If, after doing so, you decide you don't like the line and press Ctrl+Z (z -Z on the Mac), Photoshop deletes only the last portion of the line because it detected a release midway.

This is why it's a good idea to get in the habit of using Ctrl+Alt+Z (z -Option-Z on the Mac). Each time you press this shortcut, you take another step back in the history of your image, permitting you to eliminate every bit of a line regardless of how many times you let up on the stylus. (See Chapter 7 for complete information on Photoshop's multiple undos.)