HIGH DYNAMIC RANGE (HDR) By Philippe Clabots
H
igh-dynamic-range (HDR) imaging is a technique used in photography to reproduce a greater range of luminosity than what is possible with standard digital imaging or photographic techniques. Standard techniques allow differen�a�on only within a certain range of brightness. Outside this range, no features are visible because in the brighter areas everything appears pure white, and pure black in the darker areas. The ra�o between the maximum and the minimum of the tonal value in an image is known as the dynamic range. HDRI is useful for recording many real-world scenes containing very bright, direct sunlight to extreme shade. High-dynamic-range images are o�en created by capturing and then combining several different, narrower range, exposures of the same subject ma�er.
All images ©Philippe Clabots
When is it, and when is it not, useful to use HDR ? HDR is useful when the ligh�ng condi�ons will make impossible to capture details in the highlights and in the shadows at the same �me. The histogram on your camera is key to detect such a situa�on. If you cannot adjust the exposure to avoid clipping in the highlight and in the shadow at the same �me then HDR will probably help you to get an image with details in all the tonal range.
Dynamic Range (in EV)
Tone Mapping When we create an HDR image we take a range of brightness that’s beyond what can be displayed using conven�onal display equipment. Producing an image file where the image can’t be seen is of li�le value so a process is required where we turn this into an image that can be displayed.
Keep also in mind that, If your camera is quite recent and you’re using RAW, the dynamic range of your digital image is larger than the medium used to show your image whatever it is. A typical usage is a sunset on the sea having the sun in the frame.
This is where tone mapping comes in as it will take the extended dynamic range and compress it into a range that allows it to be displayed, or printed. If you’re pushing the tone mapping too far you will end up with an unnatural (and, for me, ugly) picture. This kind of pictures has given a bad reputa�on to HDR imaging.
As HDR means taking mul�ple shots of the same scene and combining them together in post-processing it’s really not appropriate for moving subjects. The deghos�ng op�on helps but this is defini�vely not for shoo�ng sports. Mostly it will be used for landscape photography. 6
