How to Do HDR Exposure Blending in GIMP

Exposure blending is a technique used to combine multiple bracketed photographs into a single image with a balanced dynamic range, preserving details in both the brightest highlights and darkest shadows. This guide explains how to manually blend bracketed exposures in GIMP using layers, layer masks, and gradients to produce natural-looking high dynamic range results without the artificial artifacts of automated tone mapping.

Step 1: Import and Align Your Exposures

  1. Launch GIMP and go to File > Open as Layers.
  2. Select all your bracketed shots (typically an underexposed shot for highlights, a correctly exposed midtone shot, and an overexposed shot for shadows) and click Open.
  3. If the images were shot handheld, align them by selecting the layers and navigating to Filters > Combine > Align Layers or using an external alignment tool like Hugin before importing.

Step 2: Organize the Layer Stack

Arrange your layers in the Layers Dialog (Ctrl + L) from darkest to brightest:

  • Top Layer: Underexposed image (preserves highlights, such as the sky).
  • Middle Layer: Base/normal exposure image (midtones).
  • Bottom Layer: Overexposed image (preserves shadow details, such as foreground foliage).

Step 3: Blend the Highlights

  1. Select the top (underexposed) layer.
  2. Right-click the layer in the Layers Dialog and choose Add Layer Mask.
  3. Select Black (full transparency) and click Add. This hides the dark layer entirely.
  4. Select the Paintbrush Tool (P) or the Gradient Tool (G).
  5. Set your foreground color to White.
  6. Paint over or apply a gradient across the blown-out areas (e.g., the sky) on the mask. Painting white reveals the darker exposure only in those specific bright areas.

Step 4: Blend the Shadows

  1. Select the middle (normal exposure) layer.
  2. Add a layer mask by right-clicking and selecting Add Layer Mask > White (full opacity).
  3. Select the Paintbrush Tool with the foreground color set to Black.
  4. Set the brush opacity to a lower value (around 20% to 40%) for soft transitions.
  5. Paint over the dark shadow areas. Painting black will mask out the midtone layer and reveal the brighter bottom layer beneath it.

Step 5: Advanced Blending with Luminosity Masks

For complex edges like tree lines or architectural details:

  1. Duplicate the layer containing the detail you want to isolate.
  2. Go to Colors > Desaturate > Desaturate to convert it to grayscale.
  3. Go to Colors > Levels and increase the contrast to create a high-contrast black-and-white silhouette.
  4. Copy this grayscale image (Ctrl + C), select the layer mask of your target layer, and paste it (Ctrl + V).
  5. Click the anchor icon to anchor the floating selection into the mask, creating a precise luminosity mask.

Step 6: Final Adjustments and Export

  1. Adjust the Opacity slider on each layer to ensure transitions between exposures appear seamless and natural.
  2. Create a merged copy of your work by right-clicking any layer and choosing New from Visible.
  3. Apply any final global adjustments to color, contrast, or sharpness using Colors > Curves or Colors > Color Temperature.
  4. Go to File > Export As, choose your desired file format (e.g., JPEG or TIFF), and save your finished image.