April 11 2013
High Dynamic Range imaging, or HDR, is a process for creating photos with a greater range of brightness from light to shadows than a digital camera can record in a single photo.
Photographers take the limits of dynamic range in their stride. There are a number of metering options allowing photographers to select the area of the photograph to be properly exposed, and what is to be over or underexposed.
Then there is the option of adding artificial light to brighten the shadow areas using techniques such as fill flash. Another option is to use neutral density filters in front of the lens to reduce the light from the bright part of the scene, typically the sky in landscape photography.
These techniques were developed in the film era indicating dynamic range is a problem for photographers using film or digital cameras.
Dynamic range limitations are the reason the DxOMark dynamic range tests are a feature of aviewfinderdarkly’s digital camera reviews.
Central to the HDR process is creating multiple photos so each part of the scene is correctly exposed in at least one of the photos. This allows HDR processing to reveal details in shadows or highlights that are often lost in a normally processed single photograph. The common practice is for to take three to five photos of the same scene with exposure settings to capture the shadows, the highlights, and the mid tones.
The other way is to process a raw photo file with different exposure settings to create the source photo files for HDR. This technique is useful for creating HDR photos from candid and action shots.
The source files are combined in HDR photo software such as Photomatix so all areas are correctly exposed, in one large HDR photo. The HDR photo is stored in a 32 bit file, two to four times the size of normal photo files.
Unfortunately, current display and printing technology cannot portray full HDR photos. This is the role of the Tone Mapping process in the HDR software. The tone mapping process reduces the HDR image file from 32 bits to 16 bits so it can be displayed and printed using current technology.
Tone Mapping does not undo all the work done in creating the HDR photo. Although it compresses the dynamic range the photo still displays more detail in the shadows and highlights than a conventional single image. This can make the image look slightly surreal, depending on the tone mapping settings used by the photographer. Overdoing some of these tended to create an impression of gimmickry, and belong in the over photoshopped league. Although, done well on the right image it can be breathtaking. As well all these things, it is the creative flair and skill of the photographer that is important.
Limitations Of High Dynamic Range Imaging
Movement of the subject or the camera is a problem when the HDR photo is a composite several photos. Anything not in exactly the same place between photos is either blurry, or for significant movement shadowy – called ghosting. This makes HDR photography more suited to genres where the subjects do not move such as landscapes and interiors.
For landscapes this present problems with wind in the trees and plants as well as water surfaces with ripples.
As movement of the camera while taking multiple shots produces a blurry final image a good tripod is recommended, and carrying the extra gear makes the process more time consuming.
This is taking a set of photos with varied exposure for HDR processing