What is HDR?



I’ve had a few messages asking what is HDR? and how is it done?

HDR (High Dynamic Range) is a process that provides the opportunity for a greater dynamic range of exposures through digital imaging techniques. It captures the full range of luminosity between light and dark in a single scene. What this means in terms of photography is that the processing of HDR captures every detail from dark shadows to bright highlights and combines them into a single image.  For example, assuming the standard digital camera has a range of 10 exposure (or ‘f’) stops for a single shot, if the start position is reduced by 2 stops then a second shot taken, then the start shot is advanced by 2 stops and a third shot taken, we will now have 3 images of the same scene but with a 14 stop range as opposed the the original 10 stop range. These images are then combined with, for example, Photoshop or Photomatix and then we have a single shot with all the information from the 3 individual shots.

Unfortunately, pc monitors are unable to present this HDR information correctly so the HDR software has to run a second process called tone mapping to make the detail visible to us. That may or may not sound simple to you, but there are about 20 different controls for tone mapping to tweak the process to deliver the results you prefer. If you are considering using HDR then I suggest that you always use your camera’s RAW setting for image quality if it is available to you.

So the benefit of HDR processing is that when confronted with a choice about exposing your shot  for shadows or lighter areas you are not restricted as you can bracket your shots for both then merge them to get all the detail you want.

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