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High Dynamic Range Imaging

Achieving proper exposure for all areas of a scene.


A variety of different exposures of the same scene is the first step in creating a High Dynamic Range image.
A variety of different exposures of the same scene is the first step in creating a High Dynamic Range image.

A picture containing very bright areas and very dark areas has a "wide" dynamic range or tonal range. Cameras are typically unable to properly expose such a scene's complete range (all areas between the lightest and darkest areas of an image) in a single picture.

You have probably taken a photograph in which the sky is so much brighter than the land that your camera was unable to expose both areas properly. The sky may be washed out due to overexposure or, if the sky is properly exposed, the land is underexposed and therefore dark.

The inability to capture a scene’s full dynamic range is a limitation common to all cameras, whether traditional (film) or digital. However, digital cameras are most severely prone to the problem because of their sensors' limited exposure latitude.

There are several solutions photographers can employ to overcome or partially overcome the problem, including the use of a gradated neutral density filter on your lens, or afterwards using the Shadows/Highlights command on the image file in Adobe PhotoShop. Many photographers prefer to use the High Dynamic Range technique because they feel their pictures become much more realistic in appearance as a result – that is, they can be viewed by the human eye to give the same impression as when looking at the actual scene itself.

High Dynamic Range (HDR) or High Dynamic Range Imaging (HDRI) refers to a series of techniques enabling you to correctly expose all areas of a scene in one image. Many HDR images have a look to them that is stunning when properly done. Others can look unnatural. You want to achieve a balance that appears to be natural.

HOW IS IT DONE?

The High Dynamic Range process begins with you and your camera, making a number of different exposures, usually through exposure bracketing, to properly expose the brightest areas, the mid-tones and the darkest areas. The images (in this case, three) are combined or merged using an image-editing application like Adobe PhotoShop into one image that shows detail in each of the areas. (Note: PhotoShop CS2 or a later version is required for HDR merging.)


Many photographers prefer to take more than three differing exposures, often as many as five, six or seven, to be sure that the scene’s full dynamic range is captured in the photographs. Some bracketed images appear to be generally underexposed and others are generally overexposed, but each should contain at least one area that is acceptably exposed.

The idea, then, is to extract from each individual photo its properly-exposed areas and combine them skillfully into one final photograph, where all areas appear to be properly exposed, or at least exposed to give the effect the photographer wants. The final assembled image contains details throughout, even in the brightest and darkest areas.


HDR is not suited to all pictures. A scene that shows sufficient detail throughout will stand to benefit little, if at all, from the technique.
HDR is not suited to all pictures. A scene that shows sufficient detail throughout will stand to benefit little, if at all, from the technique.

WHAT YOU SHOULD HAVE

  • A scene that has very dark and very bright areas that your camera is unable to properly expose so that detail will be seen in all areas.
  • A camera with auto exposure bracketing capability, or a camera which you can manually set to bracket exposures or manually over-expose and under-expose pictures.
  • A tripod or other solid camera support, and preferably a shutter release cable to avoid camera shake.
  • Adobe PhotoShop CS2 or one of the later versions of PhotoShop. (Other image-editing programs may also be capable of HDR assembly.)

Ideally, the scene will not contain a lot of movement, since you will want its elements to be in the same locations in all exposures. Highlight and shadow areas should contain details that you want to appear in your final image. If there is no sky detail or if a shadow area will look better in complete darkness, there is no point trying to bring out unneeded details.


LET’S BEGIN

1. When you feel you have found the perfect scene to photograph, one that has a dynamic range too wide for your camera to capture in one exposure, select a shooting location that will provide a pleasing composition.

2. Attach your camera to a tripod or another solid support that will keep it from moving, and frame the image. (If possible, set your camera to shoot in RAW format, and use image stabilization, if you are able to.)

3. Select Aperture Priority (so that bracketing will be achieved using different exposure times) and choose an aperture for the depth of field you wish to show. If your camera doesn’t have aperture priority capability, select manual exposure and manually set the aperture for the depth of field you want.

4. Select Auto Exposure Bracketing if your camera has that mode as an option. If you can set the number of stops to bracket, you can choose the maximum range for the most variety of under- and over-exposures. For your first effort, though, you may wish to keep things simple and choose the camera’s default setting, which is usually three exposures – one deemed to be proper exposure, one over-exposed and one under-exposed. The light source should be behind you or off to one side to avoid, for example, shooting into the sun, in which case, the dynamic range would be very wide, and three exposures would be insufficient. On your next go-around, having a greater number of images at different exposure settings will give you more detail to work with.

5. Trip the shutter release to make the exposures.

6. Open the bracketed image files in Adobe PhotoShop or another image-editor that has HDR capability.

7. Use PhotoShop’s “Merge to HDR” feature to merge all of the individual pictures into one image file that shows properly-exposed tonal detail throughout the entire scene.

8. You will be presented with several options for adjusting and fine-tuning the image. You will want to experiment with them to achieve the effect you want.

A scene that has wide dynamic range is suited to HDR imaging.
A scene that has wide dynamic range is suited to HDR imaging.

That's it. Your final picture after using HDR imaging techniques should show detail not just in mid-tone areas, but also in highlight and shadow areas.


This is the kind of scene that would benefit from HDR imaging techniques. The upper area in direct sunlight is overexposed.
This is the kind of scene that would benefit from HDR imaging techniques. The upper area in direct sunlight is overexposed.
Related topics...

Exposure latitude

Bracketing exposure

Gradated neutral density filter