Adjust GEGL Lens Distortion in GIMP

This guide explains how to locate and configure the GEGL Lens Distortion filter in GIMP, focusing specifically on the Curvature and Refraction Index controls. These parameters allow you to simulate physical camera lens effects or correct optical warping such as barrel and pincushion distortions in your digital images.

Accessing the Filter

  1. Open your image in GIMP.
  2. Select the target layer in the Layers dialog.
  3. In the top menu, go to Filters > Distorts > Lens Distortion...
  4. Ensure the Preview checkbox is enabled to view real-time changes directly on the canvas.

Adjusting the Curvature

The Curvature setting controls the primary spherical distortion of the simulated lens:

  • Positive Values: Move the slider to the right to create a "barrel" distortion. This expands the center of the image outward, resembling the effect of a wide-angle or fisheye lens.
  • Negative Values: Move the slider to the left to create a "pincushion" distortion. This pulls the center inward and pushes the corners outward, which is useful for correcting wide-angle camera artifacts or creating inverted warps.
  • Neutral (Zero): Keeps the geometric structure completely flat without spherical curvature.

Adjusting the Refraction Index

The Refraction Index setting simulates the physical density and light-bending properties of the glass element:

  • Lower Values (closer to 1.0): Simulates a lens material with light refraction similar to air, producing minimal optical compression and subtle edge displacement.
  • Higher Values: Increases the bending angle of light passing through the simulated lens. This intensifies the magnification around the focal center and dramatically stretches or pinches elements toward the image margins, enhancing the depth of the chosen Curvature setting.
  • Fine-Tuning: Use numerical entry rather than large slider movements, as small decimal shifts in the refraction index produce noticeable shifts in spatial perspective.

Applying the Effect

Once you have balanced the Curvature and Refraction Index values to achieve your desired optical effect, click OK to render the GEGL operation directly onto your active layer.