How to Fix Vignetting in GIMP Using Gradient Masks

Optical vignetting occurs when camera lenses fail to distribute light evenly, causing the edges and corners of an image to appear visibly darker than the center. This guide outlines how to neutralize unwanted corner falloff in GIMP by combining an exposure adjustment layer with a manual radial gradient mask. This technique gives you precise, non-destructive control over exposure falloff, allowing you to restore balanced lighting across the entire frame.

Step 1: Duplicate and Brighten the Exposure

  1. Open your image in GIMP.
  2. Duplicate your base layer by right-clicking it in the Layers panel and selecting Duplicate Layer (or press Ctrl + Shift + D).
  3. Select the duplicated layer and navigate to Colors > Exposure or Colors > Curves.
  4. Increase the exposure or raise the curve until the darkened corners reach the target brightness of the center of the image. Disregard the fact that the center of the image will appear overexposed at this stage.
  5. Click OK to apply the adjustment.

Step 2: Add a Layer Mask

  1. Right-click the newly brightened layer in the Layers panel.
  2. Select Add Layer Mask.
  3. In the dialog that appears, choose Black (full transparency) and click Add.
  4. The brightening effect will vanish, as the black mask conceals the entire adjusted layer.

Step 3: Draw a Radial Gradient

  1. Click on the black layer mask thumbnail in the Layers panel to ensure it is active.
  2. Select the Gradient Tool from the toolbox or press G.
  3. In the Tool Options panel:
    • Set the gradient type to FG to BG (RGB).
    • Set the foreground color to White and the background color to Black.
    • Set the Shape option to Radial.
  4. Click at the optical center of your image and drag outward toward the outer corner, then release the mouse.
  5. Invert the gradient logic if necessary: the center should remain black (masked/original exposure) and the outer edges should become white (revealing the brightened exposure). If the center is white, click the Reverse button in the Tool Options or swap the gradient stops.

Step 4: Refine the Falloff

  1. Drag the gradient control line handles to match the natural curvature and falloff point of your lens.
  2. Move the midpoint slider along the gradient line to control how gradually the brightening takes effect.
  3. Press Enter to commit the gradient once the transition appears seamless.
  4. If the edges become too bright, select the layer and lower the Opacity slider in the Layers panel until the exposure matches naturally.
  5. If the lens falloff is asymmetrical, select a soft Paintbrush tool with black or white paint at low opacity to manually paint over specific corners on the layer mask.