The Shape
Dynamics settings are: Size Jitter - This slider determines how
much variation there will be in the individual instances of the
brush's tip. At the maximum of 100% variation, instances of the
brush tip can be as small as 10% (or smaller) of the diameter that
you have set. In no case will Size Jitter create instances of the
brush tip larger than the Diameter selected in Brush Tip Shape or
the Master Diameter selected in Brush Presets. Minimum Diameter -
You can constrain the size of the smallest instances using the
Minimum Diameter slider. Tilt Scale - When the Control pop-up
menu is set to Tilt, this slider regulates how much the angle of
the stylus will affect the brush stroke. Angle Jitter - With
non-round brush tips, the angle of application can be varied. The
Angle Jitter setting determines the degree of variation. At a
setting of 25%, the orientation of the brush tip with vary from -90
degrees to +90 degrees Remember that, by default, the angle is
relative to orientation of the page rather than the path of the
stroke - even if you drag a circular stroke, the variation in angle
remains relative to the top of the image. Orient the brush tip to
the path by changing the Control menu under Angle Jitter to
Direction. (You don't need to change the Angle Jitter from 0%.)
Roundness Jitter - The Roundness slider controls variation in the
proportion of a brush tip. When set to 0%, each instance of the
brush has the same width-to-height relationship. As you increase
Roundness Jitter, you add variation. At 100% jitter, the height of
the brush instances will vary between approximately 5% and 100% of
the size specified in the Brushes palette. Roundness never
increases the height beyond that selected with the Diameter or
Master Diameter sliders. Minimum Roundness - You can constrain
the Roundness variations using this slider. It sets the smallest
instance that the brush will produce when Roundness Jitter is
activated. Examples of the shape dynamics are shown here. For ease
of identification, custom brushes were defined using numerals. In
all cases, Spacing was set to 110%. 
Number 1:
The stroke has no shape dynamics applied. Number 2: Size Jitter
is 50%. Number 3: Size Jitter is 100%. Number 4: Size Jitter is
100% combined with a minimum diameter of 50%. Number 5: Angle
Jitter is set to 10%. Number 6: Angle Jitter is 50%. Number 7:
Roundness Jitter is 50%. Number 8: Roundness Jitter is set to
100%, with a Minimum Roundness of 20%. Note the difference between
Roundness and Size jittering. With Roundness, the width of each
brush instance remains the same - only the height is varied. When
working with the dynamic brush options, think of the slider as
representing the amount of variation or variety or change in the
individual brush instances along the stroke, and the pop-up menu as
the control for that variation. Combining Shape Dynamics settings
produces more complicated patterns. However, once you understand
what each option does, their interaction is more predictable. This
stroke was created with the settings shown. 
SCATTERING Scattering spreads copies of the brush tip as
instances along the path of the stroke. The next image illustrates
how Spacing affects Scattering and shows the influence of the Count
and Count Jitter options. 
In this image,
the following settings are used: 1. Spacing 25%, Scatter 220%,
Count 0, Count Jitter 0%. 2. Spacing 100%, Scatter 220%, Count 0,
Count Jitter 0%. 3. Spacing 100%, Scatter 220%, Count 3, Count
Jitter 0%. 4. Spacing 100%, Scatter 220%, Count 3, Count Jitter
60%. Using Spacing to create a specific density of brush instances
results in substantial overlap in places, as well as some areas of
"clumping," where many instances occur in a small space. Using the
Scattering and Count options, especially in conjunction with Count
Jitter, produces the appearance of random distribution, while doing
a better job of preserving individual brush instances. The
Scattering pane of the Brushes palette also offers the check box
Both Axes. In the first set of examples, only one axis is used for
distributing the brush instances. The scattering is perpendicular
to the path. Adding the second axis enables you to randomize the
scattering along the path as well. 
These five
examples, all set to Spacing 100%, do not use the Count option in
order to better display the effect of adding a second axis of
distribution. The settings used in image are: 1. No scattering. 2.
Scatter 100%, one axis. 3. Scatter 100%, both axes. 4. Scatter
250%, one axis. 5. Scatter 250%, both axes. Enabling the Both Axes
option produces a result much like using a reduced Spacing setting
- some clumping of the brush instances occurs as the distribution
is varied along the path of the stroke. TIP: When Count and
Count Jitter are used and Scatter is set to Both Axes, a very
random pattern can be produced, but you're likely to see brush
instances bunched together in groups. Add some Roundness Jitter
(Shape Dynamics) to produce an illusion of depth.
Read the previous article in the Brushes Palette series by here. Previously featured Planet Photoshop articles are archived under Featured Columns. Special thanks to www.planetphotoshop.com for allowing us to reprint their Photoshop tutorials here at Renderosity. You can e-mail Pete Bauer, the author of this article, at peterbauer@columbus.rr.com.
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