HDR with the gimp

Basic HDR can be handled in for example the gimp.

We start off with this image:



The areas where the leaves are in the shadow are underexposed, so no details are visible. The sand in the foreground is overexposed, so hardly any details are visible. It would be very difficult to find a setting where the camera captured everything correctly.

Luckily two other pictures were taken at the same time. One was had a longer shutter speed, so it is even more overexposed:



The other picture had a shorter shutter speed, so it was more underexposed:



The trick is to use the good parts of the overexposed pictures and the good ones from the underexposed picture and put them together with the good bits of the original picture.

1. Open all three pictures in the gimp.
2. Copy the underexposed picture, and paste it as a new layer on top of the original. (Click on the underexposed picture > ctrl+A > ctrl+C > click on original > ctrl-L to display the layers > click on the New layer icon.)
3. Copy the overexposed picture, and paste it as a new layer on top of the original. (Click on the overexposed picture > ctrl+A > ctrl+C > click on original > display the layers > click on the New layer icon.)
4. Save the original image in a new xcf file, in case something goes wrong.



In the image above I have also renamed the two pasted layers.

We now want to hide the overexposed areas of the overexposed picture. To do this we use a layer mask.

5. Highlight the overexposed layer.
6. Go to the menu Layer > Mask > Add Layer Mask.
7. Select "Grayscale copy of layer" and "Invert mask".

We now want to hide the underexposed areas of the underexposed picture with another layer mask.

8. Highlight the underexposed layer.
9. Go to the menu Layer > Mask > Add Layer Mask.
10. Select "Grayscale copy of layer" but not "Invert mask".

We now have a picture where the sand no longer is overexposed and the leaves no longer are underexposed.



To change it further, we can apply curves to the layer masks, to fine tune which parts of the picture are hidden by the layer.

11. Click on a layer mask.
12. Menu Colors > curves.



Of course other changes, like increasing saturation can also be applied.