GIMP Ink Tool Velocity Sensitivity Explained

The Velocity sensitivity curve in GIMP’s Ink tool controls how the speed of your drawing hand directly impacts the width and behavior of your stroke. By fine-tuning this graphical curve, digital artists can mimic traditional calligraphy pens, produce dynamic tapered line art, or eliminate line variation entirely for clean, uniform sketching.

How the Velocity Curve Works

In GIMP, the Ink tool simulates traditional liquid ink, where movement speed dictates ink flow. The Velocity sensitivity curve plots movement speed along its horizontal axis (from completely still to rapid movement) against the resulting stroke size on the vertical axis (from minimal thickness to full width).

By default, the curve slopes downward from left to right. This produces realistic physical pen physics:

• Slow strokes: The virtual nib rests longer in one place, saturating the area and producing a wider, heavier stroke.
• Fast strokes: Swift hand movements pull the virtual nib across the canvas quickly, reducing the ink deposit to create thin, sharp, and tapered lines.

Customizing the Curve for Sketching

You can manipulate the shape of the curve in the Ink Tool Options panel under the Sensibility settings to drastically alter your drawing feel:

• Linear Negative Slope (Standard Inking): A straight diagonal line from top-left to bottom-right ensures predictable line variation. Rapid flicking motions produce clean, hair-like tapers, which is ideal for sketching dynamic outlines, eyelashes, or organic textures.
• Steep Drop-off (Expressive Tapering): Pulling the curve down sharply on the left side ensures that only the slowest deliberate marks are thick, while regular sketching speeds instantly snap to fine detail lines.
• Flat Line (Uniform Weight): Flattening the curve horizontally decouples stroke size from your drawing speed entirely. This is useful for technical sketching, contour tracing, or cartooning where consistent line weight is preferred regardless of hand movement velocity.
• Inverted Slope (Stylized Effects): Sloping the curve upward from bottom-left to top-right reverses physical reality, causing slow strokes to produce thin lines and fast sweeps to produce wide, heavy slashes.

Fine-Tuning Considerations

The Velocity curve works in tandem with the tool's Size slider and the other sensitivity curves (such as Tilt or Pressure). If your sketch lines feel unpredictable, flattening or softening the slope of the Velocity curve provides greater stability without completely removing the expressive, hand-drawn character of the Ink tool.