Remove Sky Sensor Dust with GIMP Heal Selection

Eliminating stubborn sensor dust spots and rings from smooth sky gradients can be challenging without introducing visible smudges, banding, or color inconsistencies. This guide walks you through using the Heal Selection tool—powered by the Resynthesizer plugin in GIMP—to seamlessly analyze the surrounding tones and synthesize new pixels that match the natural color progression of your sky.

Step 1: Install and Verify the Resynthesizer Plugin

The Heal Selection feature is part of the third-party Resynthesizer plugin suite. Ensure it is installed in your GIMP plug-ins folder. When installed correctly, the tool is accessible under Filters > Enhance > Heal selection....

Step 2: Highlight the Dust Rings

Faint sensor dust rings can be hard to see clearly against a subtle gradient.

  1. Duplicate your image layer by pressing Shift + Ctrl + D.
  2. Go to Colors > Curves or Colors > Levels on the duplicate layer.
  3. Drag the black point up and white point down aggressively to stretch the contrast. This will clearly reveal the faint outer halos and rings of the dust spots.

Step 3: Select the Dust Ring

  1. Select the Ellipse Select Tool (E) or Free Select Tool (F).
  2. Set a small feather radius in the Tool Options (typically 2 to 5 pixels) to ensure the healed edge blends naturally into the gradient.
  3. Draw a selection that completely encloses the dust spot and its surrounding shadow ring, keeping the selection as tight to the defect as possible.

Step 4: Run the Heal Selection Tool

  1. Switch back to your original, unadjusted image layer (you can hide the high-contrast helper layer by clicking its eye icon).
  2. Go to Filters > Enhance > Heal selection....
  3. Configure the dialogue settings for gradient areas:
    • Context sampling width (pixels): Set this high enough (e.g., 15–30 pixels) to sample clean pixels beyond the ring.
    • Sample from: For horizontal or vertical sky gradients, select the direction matching the gradient line. For a standard horizontal sky gradient where tone varies vertically, choose Above and below or Sides depending on which axis has the most consistent color values. In most cases, All around works well if the selection is tightly fitted.
    • Filling order: Set to Random or Inwards towards center.
  4. Click OK to process the heal.

Step 5: Verify the Result

Press Ctrl + Shift + A to deselect the area. Turn your high-contrast curve layer back on to confirm that the dust ring has been fully eradicated without leaving behind bright halos, dark patches, or broken gradient lines. Once verified, delete the high-contrast helper layer and export your image.