Blended Exposures

Introduction

When the scene you are photographing has a very high dynamic range (it has very bright areas and relatively dark areas also) it can be useful to take multiple shots of the same scene, each exposed for a different area, and combine them in post-processing.

This technique is a digital equivalent of the traditional graduated neutral density filter, although it does have a number of disadvantages.

Example

Blend_sky Blend_mask Blend_ground

Here we have one exposure for the sky (left, making the ground too dark), one for the ground (right, making the sky too light) and a sample mask that was used to control the blend between the two images (middle).

Using the mask to blend between the images gives the following result:

Blend_complete

Whilst not the most arresting photograph ever taken it should serve as a demonstration of the basic technique.

Conclusion

Traditionally the photographer would have worked around scenes with high dynamic range through the use of a graduated neutral density filter. This is a semi-transparent filter placed in front of the lens, partially transparent and partially grey to help balance the exposure between light and dark areas.

Blended exposures have a number of disadvantages to the graduated neutral density filter:

  • You really should be using a tripod, as you need two identically set shots.
  • The technique doesn't work well with moving objects.
  • When objects cross between different blended areas or if the delineation between areas of different exposure is non-trivial then more work is needed to perform the blend.