Opacity Brush

Tool Location and Cursor Appearance

The Opacity Brush tool appears in Illustrator’s main toolbar (which must be in Advanced mode: View > Toolbars > Advanced).

Opacity Brush Tool Location

The Opacity Brush tool’s cursor is a crosshair. When the tool is not actively brushing, or when brush previews are disabled, it also displays a dark gray, dashed circle (or ellipse) indicating the size and shape of the brush:

Opacity Brush Tool Cursors

A minus sign symbol indicates that the brush is in “erasing” mode.

Tool Operation

As the Opacity Brush tool has several keypresses which can add or change its functionality, we suggest installing the free Astute Graphics plugin Astute Buddy, which creates a panel that dynamically updates to inform you of the various keys which can be pressed in the tool’s current context.

While the Opacity Brush tool can be used without its panel, some functionality, such as adjusting the amount of noise, requires the panel to access.

To use the tool, simply brush over selected artwork to make it “fade out” in those areas. Opacity Brush automatically creates a raster opacity mask for each selected art object that is not part of the same group. The raster has a default resolution of 72ppi, but the value can be changed in the tool Preferences dialog (see Opacity Brush: Preferences).

If the artwork already has an opacity mask, the raster object will be added to it, at the bottom of the stacking order. If the existing mask was set to invert, this setting will be retained and the brush will appear work in an inverted manner.

Opacity Brush Example

The Opacity Brush tool’s preview can be changed in its preferences; by default, it is white and shows its size, hardness, and opacity faithfully, similar to how a Photoshop brush would draw. Due to technical limitations of Illustrator, this requires CPU preview to be enabled in order to display properly when brushing long distances.

If the Option/Alt key is held down before brushing, the tool will be set to “erasing” mode, whereby each brush stroke adds opacity to the artwork (up to a maximum of 100%), instead of removing it. Like other brush tools, the diameter of the brush can be changed at any time it is active by pressing the keys assigned in the native Keyboard Shortcuts dialog to “Decrease Diameter” and “Increase Diameter.” For English language installations, these default to the open square bracket and close square bracket keys ([ and ]).

Another way to change the brush diameter (and hardness) is to hold down Shift-Option/Alt and click-drag the mouse; this adjusts the diameter. After releasing Shift-Option/Alt (and with the mouse button still down), a second drag will adjust the hardness.

While brushing (i.e., with the mouse button down), several keypresses can be used:

Shift: Constrains the brush motion to the nearest increment of 45° around the general constrain angle.

Left/Right Arrow: Decreases or increases the brush diameter.

0–9: Sets the brush opacity. 1 sets the opacity to 10%, 2 to 20%, etc.

D: Changes the drawing annotation color, cycling through red, blue, magenta, green, black, and white.

E: Changes the erasing annotation color, cycling through red, blue, magenta, green, black, and white.

To reset, invert, or remove the opacity mask created by the Opacity Brush tool, use the Opacity Brush panel.

The menu item to show and hide the Opacity Brush panel can be found in the main menu under Window > Astute Graphics > Opacity Brush.

Opacity Brush Panel

1. Flyout menu

See Opacity Brush Panel: Flyout Menu.

2. Panel banner

The help button on the right opens the help documentation in the Astute Manager. If this does not automatically appear, please ensure your Astute Manager is running first.

Click on the other area of the color bar to activate the Opacity Brush tool. This is a quick method of locating the tool within the default Advanced toolbar or a custom toolbar.

3. Size Specification

The size (diameter) of the brush, from 1pt to 1000pt.

4. Hardness Specification

The hardness of the brush, from 0% to 100%.

5. Opacity Specification

The opacity of the brush, from 0% to 100%.

6. Noise Specification

The amount of noise in the brush, from 0 (no noise) to 100 (maximum noise).

7. Roundness

The roundness of the brush, from 10% (highly elliptical) to 100% (circular).

8. Angle

When the brush is not at 100% roundness, the angle of the major axis of its elliptical shape.

9. Size Control

Visible when the panel is expanded. When using a mouse as the input device, it should be set to Fixed; otherwise, enables the brush size to be controlled by either the pressure or wheel setting of a stylus-like device.

10. Opacity Control

Visible when the panel is expanded. When using a mouse as the input device, it should be set to Fixed; otherwise, enables the brush opacity to be controlled by either the pressure or wheel setting of a stylus-like device.

11. Roundness/Angle Control

Visible when the panel is expanded. When using a mouse as the input device, it should be set to Fixed; otherwise, enables the brush opacity to be controlled by either the tilt/bearing or tilt/rotation setting of a stylus-like device.

12. Reset Mask

Visible when the panel is expanded. The value input specifies the base opacity of the entire mask when it is reset (or first created, if the tool preference Base Opacity Applies to New Masks is enabled), with a default of 100%. The Reset Mask button resets the mask, removing all existing brush strokes that may have been made to it and filling it with the base opacity specified in the value input box.

13. Invert Mask

Visible when the panel is expanded; inverts the raster portion of the opacity mask.

Opacity Brush Panel Invert Mask

Opacity Brush Panel Flyout Menu

1. Expand/Compact Panel

When expanded, the panel shows the size control, opacity control, roundness/angle control, reset mask area, and invert mask button.

2. Reset Mask

Resets the opacity mask(s), just as clicking the Reset Mask button on the panel would.

3. Invert Mask

Inverts the opacity mask(s), just as clicking the Invert Mask button on the panel would.

4. Extend Mask to Fit Art

By default, Opacity Brush automatically extends an raster opacity mask if the art to which it belongs is made larger. However, if that preference is turned off, choosing this menu item will manually extend it.

5. Remove Mask

Removes the currently selected opacity mask(s). If the art had an existing opacity mask before being brushed by the Opacity Brush, only the raster portion of the mask that was created by the tool will be removed.

7. Opacity Brush Preferences...

Brings up the Preferences dialog (see Opacity Brush: Preferences).

Using the flyout menu of the Opacity Brush panel, doubleclicking the Opacity Brush tool in the toolbox, or pressing the Enter key when the tool is selected will bring up the Opacity Brush preferences dialog:

Opacity Brush Preferences Dialog

1. Resolution

Specifies the resolution of any new opacity masks which are created by brushing with the Opacity Brush tool (existing masks are not affected). The value can range from 1ppi (pixels per inch) to 2400ppi, with a default of 72ppi.

2. Preview Type

Specifies the type of preview which the Opacity Brush tool will display, from among None, Radius Only, Radius and Hardness Only, Full (Medium Resolution), and Full (High Resolution). Full previews may be somewhat slower than the other options, depending on brush size and computer capability.

3. Brush Preview Warning

Due to technical limitations of Illustrator, previews will not display correctly when brushing long distances when GPU Performance is enabled. It is recommended to use CPU preview when brushing with the Opacity Brush tool.

4. Drawing Annotation Color

Specifies the color of the brush preview when drawing normally, from among red, blue, magenta, green, black, and white.

5. Erasing Annotation Color

Specifies the color of the brush preview when in erasing mode, from among red, blue, magenta, green, black, and white.

6. Decrease Spacing at High Hardness

When enabled, brush spacing will be lowered when its hardness increases, in order to avoid scalloping along the edges of the brush’s path.

7. Hide Edges While Brushing

When enabled, Illustrator’s annotations indicating the edges of the selection will be automatically hidden during the brushing operation.

8. Base Opacity Applies to New Masks

When enabled, the base opacity value from the reset mask area of the panel will be used not just when resetting masks, but also when a new mask is initially created (that is, when the art is first brushed).

9. Extend Masks Automatically

When enabled, and a piece of art that has been brushed with the Opacity Brush is enlarged, the opacity mask will automatically be extended such that it completely covers the new bounds of the artwork.

10. Informational area

Shows a brief description of each preference control when the cursor is being hovered over it.