High Dynamic Range

Increasing detail throughout an image

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What HDR is and what it is not

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.

Non-HDR ways of increasing dynamic range

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.
 

What makes true HDR different?

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 f-stop.  You 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 individual photographs.

What you need

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.
 

Field Requirements

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 single image.
• 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.

 

Digital Darkroom Requirements

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.