Written By Steve Patterson

As I mentioned in the introduction to this series of tutorials, all six of Photoshop's Brush Dynamics categories share similar types of controls so once we've taken a look at how the Shape Dynamics work, which we'll do in a moment, we'll already have a good understanding of how the rest of them work. Unfortunately, controls are not the only thing they share. As we'll see, the way the controls are laid out makes understanding them a bit more of a challenge than it should be. Don't worry, though. We'll figure it out.

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To access the Shape Dynamics options, click directly on the words Shape Dynamics on the left side of the Brushes panel. We need to click directly on the words themselves for the controls to appear (clicking inside the checkbox to the left of a category's name will turn those options on but won't give us access to their controls):

As soon as you click on Shape Dynamics, the controls for the various Shape Dynamics options will appear on the right side of the Brushes panel. The preview area on the bottom of the panel remains so we'll be able to see the effect we're having on the brush stroke as we make changes:

Shape Dynamics allows us to dynamically control the size, angle and roundness of the brush as we paint with it. In fact, with just these three controls alone, we can make our digital, lifeless Photoshop brushes behave as if we were painting with real brushes on paper!

I mentioned that the way the controls are laid out makes things more confusing than they should be, so let's clear this problem up right now. The Shape Dynamics options are divided into three sections - Size, Angle, and Roundness. Unfortunately, this isn't really clear because to the right of each of these headings is the word Jitter with a slider bar below it. For the moment, ignore the word "Jitter" (and the slider bar). The only thing we're interested in right now is the word that comes before "Jitter". This is the name of the section (Size, Angle, and Roundness):

Below each of these three headings is a Control option. Each Control option is tied directly to the heading above it. So, for example, the Control option at the top should be labeled Size Control (it isn't, but it should be). The middle one should be labeled Angle Control (again, it isn't but it should be), and the bottom one should be labeled Roundness Control (which of course it is... oh wait, no it isn't, but it should be):

These Control options give us various ways to dynamically control the size, angle and / or roundness of the brush as we paint. Most of the choices we're given require us to have a pen tablet installed, but there are some choices available if you don't have one (although you're seriously missing out if you don't have one). By default, each one is set to Off, which means we currently have no control over anything. Let's gain control by taking a closer look at each section individually.

Size

The Size section gives us different ways to dynamically change the thickness of the brush stroke as we paint. To see a list of all the various ways we can choose from to control the brush size, simply click on the drop-down list to the right of the Control option. Click on any of the options in the list to select it:

Fade
The Fade option is the only choice we have for dynamically controlling the thickness of the brush that does not require a pen tablet. In fact, it works exactly the same way whether you're using a pen tablet or not. Fade gradually reduces the size of the brush as you drag out a stroke.

If you recall from our Create Your Own Custom Photoshop Brushes tutorial, if we were painting on paper with a real brush, the brush would lay down a continuous coat of paint on the paper, but that's not how Photoshop works. What Photoshop does is it "stamps" a series of brush tips along the path of your brush as you drag it inside the document. The Fade option gradually makes each new stamp smaller than the previous one until the brush is no longer visible.

Exactly how long it takes for the brush stroke to fade out completely is determined by the number of steps we set for it in the input box to the right of the Control option. The default number of steps is 25:

Think of "steps" as stamps, with each new stamp of the brush tip being one step. With the default value of 25, Photoshop will gradually reduce the size of the brush stroke over the course of 25 stamps. The easiest way to see this is by increasing the spacing between each stamp. Let's exit out of the Shape Dynamics controls for a moment by clicking on the words Brush Tip Shape directly above Shape Dynamics on the left side of the Brushes panel:

This gives us options for adjusting the brush tip itself. You'll find the Spacing option near the bottom of the panel, just above the brush stroke preview area. The Spacing option allows us to adjust the distance between each stamp of the brush tip as we paint a stroke. I'm going to drag the Spacing slider towards the right to increase the amount of space between each new brush tip, which will make it easy for us to see how Fade is working. I still have one of Photoshop's standard round brushes selected. Notice how each new stamp of the brush tip is smaller than the previous one. If you count each stamp, you'll find that there's exactly 25 of them from the largest one on the left to the smallest one on the right. After that, the stroke disappears into oblivion:

I'll click back on the words Shape Dynamics on the left of the Brushes panel so I can once again access the Size controls and I'll lower the number of Fade steps to 15:

If we look at the preview of the brush stroke at the bottom of the panel, we see that the stroke is now shorter since it's taking only 15 stamps of the brush tip for the size of the brush to fade out to nothing:

For best results when using Fade to control the size of the brush, you'll usually need to adjust the Spacing option as well to fine-tune the length and smoothness of the brush stroke. A smaller Spacing value will give you a smoother looking stroke. Larger values make the individual stamps more obvious and result in a more ridged appearance.

Minimum Diameter
If you don't want the brush size to fade out completely, you can use the Minimum Diameter option to set a limit for how small the brush can get. Once the brush is reduced to the minimum size, it will remain at that size for as long as you continue dragging out the stroke. You can adjust the Minimum Diameter option either by dragging its slider or by entering a specific value into the input box. The default value is 0%, which means the brush will fade out completely. I'm going to increase the minimum diameter of my brush to 10% so that once the brush reaches 10% of its original size, it won't go any smaller:

If we look at the preview of the brush stroke at the bottom of the panel, we see that the stroke now continues on and never drops below its new minimum size:

Pen Pressure
By far the most common and natural way to dynamically control the thickness of a brush stroke as you paint is with Pen Pressure:

With Pen Pressure selected for the size Control option, the harder you press the pen into the tablet, the larger the stroke thickness becomes. Easing up on the pressure makes the brush stroke thinner. The preview area at the bottom of the Brushes panel will change to show the brush stroke tapered off at both ends when Pen Pressure is selected:

Of course, you can only use this option if you have a pressure-sensitive pen tablet installed on your computer. Photoshop won't stop you from selecting Pen Pressure even if you don't have a pen tablet installed, but it will display a small warning icon to let you know that even though you've selected it, it's not going to work:

Pen Tilt
If you do have a pen tablet installed and want even more dynamic control over the size of your brush stroke, try out the Pen Tilt option:

Pen Tilt includes all of the pressure-sensitive abilities of the Pen Pressure option and adds the ability to control the size of the brush by tilting the pen as you paint. The further you tilt the pen, the larger the stroke becomes. You can control how much of an impact tilting the pen has on the brush stroke with the Tilt Scale option, which is only available when Pen Tilt is enabled. Drag the slider left or right to adjust the scaling percentage:

Personally, I find that using Pen Tilt to control the brush size is more frustrating than anything so I usually stick with the Pen Pressure option, but that's just me. And by "just me", I mean probably you, too.