HDR means High Dynamic Range. It’s a way of processing a photograph so that it captures the fullest range of highlights and shadows in the original scene. All camera film and digital sensors have restricted dynamic range: the difference between the whitest white and blackest black on the screen or print is less than real life. HDR is a trick to increase the spread between shadows and highlights in an image by taking more than one picture of the same scene — one shot maximizing shadows, one mid-tones and one highlights — and then merging them into one unified picture with tremendous range. Of course, in practice it is not that simple or direct, thus the need for this very clear PDF book which will tell you step by step how to produce an HDR photo using Photoshop.
The trick is useful especially for capturing photos of interiors, where, say, there is both a bright window and shadows on a face in one scene. With HDR you can see the patterns outside the window and details in the shadowy face. HDR is also used for twilight landscapes, and anywhere else where there is “tricky” lighting. My guess is that about half of the “best of Flickr” photos are ones that have been HDR processed. Indeed, the look of a high dynamic range is so common now that it is easy to detect, and some fuddy-duddies object to its “artificialness,” although all photos are artificial. Like any tool it can be overused and abused. Someday HDR may be built into cameras. Now, it’s a hack. A few websites, such as Stuck in Customs, give basic intros to the procedure, although the process described at that site requires an additional software package called Photomatix, which automates the method.
The better tutorial is available from O’Reilly publishers as a Short Cuts paid PDF. It gives superior step by step instructions, and does not require Photomatix software — it’s all done in Photoshop CS.
[This post was originally part of Cool Tool's Five Good eBooks. ]
Why try HDR imaging? Imagine you’re visiting a cathedral with great stained glass windows, but there is low available light inside the building to show the ornate interior designs. There is also a sign stating “No Flash Photography.” Checking your meter, you see that there is a seven stop difference between the brightest highlight area and the deepest shadow detail. With traditional imaging, you are forced to choose and expose for the stained glass windows-turning all the interior to muddy shadows with little or no detail-or you can expose for the interior details, but overexposing the stained glass, which eliminates most of their detail and color. The final option is to pick a middle-range exposure and attempt to twist the single flat image into something that resembles your impression of the scene.
The three bracketed exposures (over, under and normal) on the left are combined to make the well-balanced, very detailed image on the right.