Monday, 15 July 2013

Understanding Dynamic Range in Digital Photography

digital photography dynamic range
Photo By Pedro Szekely

Dynamic range or tonal range is the range between the darkest and the lightest parts of an image. A composition that has very bright areas such as a bright sky and very dark areas such as deep shadows is a good example for a scene with wide dynamic range. Another term used to denote such a scene is ‘high contrast’.

An understanding of dynamic range is important in photography as there is a limit to the dynamic range which our digital sensors could capture. They fail to capture contrast beyond a certain level which is far less than what the human eye is capable of.

That is why you could clearly see details (objects) in the shadows and the sky with whatever little colour’s available there at the same time. but when the same scene is photographed, either the sky is completely blown out (highlight clipping) or the shadows are rendered pure black with little or no detail.

On most occasions, depending upon many factors; the photographer chooses to retain details in either the highlights or shadows compromising the other. If he exposes for shadows then highlights are irreparably blown out and if he exposes for highlights then shadows are totally clipped; a real Hobson’s choice for the poor soul!

dynamic range
Photo By Trey Ratcliff

However there are ways to overcome the limitations of the digital camera sensors and capture the entire dynamic range of the scene in your photographs they are:

1. Use RAW

Photograph the scene using the RAW format and in post processing convert the photo twice. Convert one using exposure settings to properly expose highlights and the other using exposure settings to properly expose the shadows. 

Finally combine both the images together to get a photograph which has details in both shadows and highlights.

This is the easiest option available but the downside is that you only have limited capabilities and so is not suited for scenes with very wide dynamic range.

2. Try Graduated Neutral Density Filter

A graduated neutral density filter also known as split neutral density filter is one which gradually changes from light to dark with variable light transmission. They make it possible to even out the dynamic range of the scene and thus pulling the contrast to a range which is within the capabilities of the digital camera sensor. 

However photographs captured using graduated neutral density filters often appear less dynamic than photographs created by combining multiple exposures.

This option requires one to carry along a graduated neutral density filter and align it properly along the horizon or where the light and dark transitions happen in their composition. It is also not possible to use this filter when you have subjects in the foreground that extend in to the sky above.

3. Combine Two or More Exposures into One

dynamic range photography
Photo By Skunkworks Photographic

This technique requires one to set up the camera on a solid tripod so the composition does not change between exposures. First capture the scene with an exposure setting that would properly expose the highlights and then taking another with exposure settings to properly expose the shadows. The two photos could be later combined together using an image editor.

This method allows you to take as many different exposures as you wish and provides complete control over the way your final image is rendered. However one major limitation of this technique is that it is not possible to use this technique if there are moving elements in your scene such as fast-moving clouds or wildlife.

Did You Know?

photography dynamic range
Photo By Phil Snyder

You may have a more visible dynamic range in your digital photos than you can see. A good-quality computer monitor that has been carefully calibrated to show a wide dynamic range is essential to seeing and properly editing digital photos. 

Photo Tip!

dynamic range in digital photography
Photo By Trey Ratcliff
You can expose a scene with a wide dynamic range to get excellent silhouettes. You can also shoot to capture detail in the shadow area of a landscape photo; not bothering about the sky above getting blown out. In one way it is better to completely overexpose the sky so that it is easier to selectively replace it with sky from another photograph.