I am sure you have heard of HD in relation to televisions and DVDs. HDR
is not the same as HD. HDR stands for High Dynamic Range.
HD stands for High Definition.
HD is about getting a higher
resolution picture, thus improving image sharpness.
HDR is not about image sharpness. It is about image detail.
Specifically, it is about getting detail in the light and dark areas where you used
to get blown out whites and flat blacks.
HDR is the use of one of more techniques to increase the dynamic range of an
image. What is dynamic range? It is how much detail you can capture
from the deepest blacks to the brightest whites. It is related to
brightness and contrast. Brightness refers to how bright or dark something
is. Brightness can be used to describe a single pixel or an entire image.
Contrast is the difference between the brightest area in an image and the
darkest. The bigger the difference, the higher the contrast. High
dynamic range consists of lowering the brightness of whites and increasing the
brightness of blacks so you can see detail in both areas. The result is an
image richer in detail, but lower in contrast.
Figure 1. Conceptual diagram of Contrast
Range and Dynamic Range. Contrast ranges from the darkest to the brightest.
Dynamic Range is from darkest with detail to brightest with detail.
Some of you have probably been increasing dynamic range long before you
heard of digital cameras or HDR. Do you prefer to take your outdoor
pictures on a cloudy day? Ever use fill flash? Or use a split
neutral density filter? Ever use the shadow/highlight enhancement feature
of your image editing software? If so, then you have been practicing
techniques to increase the range of detail in your images.
Even with fill flash and special filters, the contrast range in a scene can
be too extreme to capture detail throughout a photograph in a single exposure. This
is where we use HDR techniques. The concept of HDR is to take multiple photographs of the same scene.
The first photograph is
exposed to render detail in the shadows. Then each succeeding
photograph has its exposure decreased by increasing shutter speed by 1
take as many photographs as needed until the last photograph has captured detail in the
highlights. These photographs represent the full range of detail in the scene.
You then combine the photographs in your computer into a single image.
This results in a single photograph that has a broader dynamic range than any of the
Figure 2. These six images were taken in the
field. The aperture was f/8 for all six images. The shutter
speeds, from left to right, were 1/3, 1/6, 1/13, 1/25, 1/50 and 1/100.
All six images were used to create the final HDR image shown in Figure 4.
Figure 3. Click a thumbnail above to see the larger version.
Figure 4. The final HDR image.
You do not need a digital camera to create HDR images. Digital cameras and
the Raw format have not made HDR possible. They have made it easier.
However, you do need a digital darkroom.
In the field, you will need the following.
- A film or digital camera. If using a film camera, you do not need
special film. Use the film, color or black and white, that you typically use. For print film users,
please note that print film naturally has a broader dynamic range than slide
film. If using a digital camera, shoot Raw or Raw + JPEG. The Raw files
will be used to create the HDR image.
- A tripod. If you hand hold the camera, it will be very difficult
to get the multiple images to align properly when combining them into a
- A cooperative subject. Objects that are moving will not be in the
same position in each of the photographs.
- An understanding of exposure and how to set it on your camera.
In the digital darkroom, you will need the following.
- If you use film, you will need access to a film or drum scanner.
Scanning prints on a flat bed scanner will give poorer quality results.
- Software that can process multiple images into a single HDR image.
This can be Photoshop's Merge to HDR feature or third party software.
- Patience. More often than we wish, the software will create an
image with visible defects that will have to be fixed.