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2012.10.30

This is the first of a series of posts comparing hardware and software ways of getting a photographic effect.

During the glory days of film, the Graduated Neutral Density filter was considered an essential part of a landscape photographer’s toolbox. Even as photographers take on landscape photography digitally, it remains widely used.

Simply, a Graduated Neutral Density Filter (GND) is a filter which is clear at one end and dark at the other. Between the two levels of transparence, there is a transition which can be hard or soft, depending on the filter. Square GND filters are more common because they can slide to adjust the point of transition but they are much more cumbersome. Round GND filters always transition at the same point but they can be rotated.

There are two ways to simulate a Graduated ND filter by software and they both have different advantages and disadvantages compared to a physical filter. Here is how all three approaches compare:

Hardware Filter

  • Pro: Gives you results immediately which you can see while you compose.
  • Con: The effect is fixed in gradation and shape. There is always a straight transition between transparency levels. It is also recommended to meter manually since camera meters are not made to accommodate GND filters.

Software Effect

A software effect, such as the one present in Adobe Photoshop Lightroom, processes a single image to make one side darker than the other. It does so by darkening one side of an image and leaving the other untouched.

  • Pro: Adjustable in strength, size, shape and direction.
  • Con: Cannot recover clipped details. Blown out areas cannot get details back while a hardware filter may prevent over-exposure.

Exposure Fusion / HDR

Exposure fusion is a software algorithm that blends multiple exposures of the same subject to produce an image that holds details from a wider dynamic-range. For a list of exposure-fusion software, read this question at Photo.StackExchange.

HDR is another multi-exposure technique which produces an image which holds a huge dynamic range. This image is impossible to view directly on typical displays and cannot be printed, so it must be tone-mapped into an image of standard dynamic-range. This is more complex than Exposure-Fusion but allows to produce surreal images using different tone-mapping algorithms.

  • Pro: Completely adjustable. Can simulate any strength, shape and size of ND filter.
  • Con: Anything that moves between exposures can cause problems and requires more work.
As usual  in photography, with great power comes great amounts of work! The software solution is extremely easy to use but cannot cope with dynamic-range exceeeding the camera or film’s capability. Exposure fusion requires an exposure bracket but is otherwise mostly hands off. HDR requires both an exposure bracket and parameter tuning. It can give the wildest results if overdone though!

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