Remove Hot Pixels in Long-Exposure Images with GIMP

Long-exposure photography often pushes camera sensors to their limits, generating heat that produces bright red, green, or blue artifacts known as hot pixels. GIMP (GNU Image Manipulation Program) provides powerful, built-in tools to remove these defects without degrading the fine details of your photograph. This guide outlines the most effective automated and manual methods to clean up hot pixels in GIMP.

Method 1: Automated Removal Using the Despeckle Filter

The Despeckle filter is the fastest way to remove hundreds of scattered hot pixels across an entire image.

  1. Duplicate the Background Layer: Open your image and press Ctrl + Shift + D (or Cmd + Shift + D on macOS) to duplicate your base layer. This ensures non-destructive editing.
  2. Open the Despeckle Filter: Navigate to Filters > Enhance > Despeckle... in the top menu.
  3. Adjust the Settings:
    • Radius: Set this to a low value (typically 1 or 2). A larger radius will blur fine details like stars or sharp edges.
    • Black Level: Increase slightly to remove dark dead pixels.
    • White Level: Decrease slightly to remove bright hot pixels.
  4. Apply a Layer Mask (Optional but Recommended): If the filter softens important details, add a black layer mask to the filtered layer (Layer > Mask > Add Layer Mask > Black (full transparency)) and use a soft white brush to paint only over the areas where hot pixels appear.

Method 2: Manual Removal with the Healing Tool

For isolated, high-intensity hot pixels that automatic filters miss, manual retouching provides pinpoint accuracy.

  1. Select the Healing Tool: Choose the Heal Tool from the toolbox or press H.
  2. Configure the Brush: Set the brush to a small size (just slightly larger than the hot pixel) with soft edges (hardness around 50–75%).
  3. Set the Sample Point: Hold Ctrl (or Cmd) and click on a clean area directly adjacent to the hot pixel with similar color and texture.
  4. Click the Hot Pixel: Click directly on the defective pixel. The tool will blend the texture of the sample point with the surrounding color, seamlessly removing the artifact.

Method 3: Dark Frame Subtraction

If you captured an in-field dark frame (a photo taken with the lens cap on at the same exposure time and ISO):

  1. Open as Layers: Open your raw photograph, then go to File > Open as Layers... and select your dark frame.
  2. Align the Layers: Ensure both layers are perfectly aligned in the Layers panel.
  3. Change the Blend Mode: Set the blend mode of the dark frame layer to Subtract. This will automatically cancel out the thermal sensor noise recorded at those specific pixel coordinates.