How to Link GIMP Brush Opacity to Pen Speed

GIMP allows you to control brush behavior using your drawing tablet's physical input through its Paint Dynamics engine. By creating a custom paint dynamic preset, you can map brush opacity directly to the velocity (drawing speed) of your stylus rather than standard pen pressure. This guide walks through opening the Paint Dynamics dialogs, creating a new preset, mapping opacity to speed, and applying the custom dynamic to your painting tools.

1. Open the Paint Dynamics Dialogs

To configure custom dynamics, you need access to the Paint Dynamics dockable dialogs:

  1. Go to the top menu and select Windows > Dockable Dialogs > Paint Dynamics.
  2. Go to Windows > Dockable Dialogs > Paint Dynamics Editor.

2. Create a New Dynamics Preset

GIMP's default dynamics presets are read-only, so you must create a new profile:

  1. In the Paint Dynamics dialog, click the Create a new dynamics button (the paper icon) at the bottom.
  2. Name your new dynamic preset (e.g., "Velocity Opacity").

3. Map Opacity to Velocity

The Paint Dynamics Editor displays a matrix where rows represent brush outputs and columns represent tablet inputs:

  1. In the Paint Dynamics Editor, locate the Opacity row.
  2. Find the Velocity column (which tracks the speed of your pen stroke).
  3. Check the box at the intersection of Opacity and Velocity.

4. Fine-Tune the Response Curve (Optional)

By default, moving the stylus faster increases brush opacity linearly. To modify how sensitive the opacity is to your speed:

  1. Expand the Dynamics Curves section at the bottom of the Paint Dynamics Editor.
  2. Select Opacity from the dropdown menu.
  3. Choose Velocity from the input selector.
  4. Click and drag the curve to adjust the response. For example, inverting the curve will make faster strokes more transparent and slower strokes more opaque.

5. Apply the Dynamic to Your Brush Tool

  1. Select the Paintbrush (or any other brush-based tool) from the Toolbox.
  2. In the Tool Options panel, locate the Dynamics section.
  3. Click the dynamic icon/dropdown and select your newly created preset.
  4. Draw on the canvas at varying speeds to test the dynamic opacity response.