Today’s Question: Why use HDR [high dynamic range] when you can adjust shadows and highlights in Lightroom or Camera Raw?
Tim’s Quick Answer: High dynamic range (HDR) techniques enable you to retain full tonal detail in a photo, even when the contrast in the scene is too great to be contained within a single capture. If highlight and/or shadow detail is completely lost in a single photo, the Highlights and Shadows adjustments will not be able to recover that information.
More Detail: Many software tools for optimizing digital photos include controls that enable you to focus adjustments on just the brightest or darkest areas of a photo, including darkening bright areas and brightening dark areas. However, these adjustments will not provide a solution if all information was lost in the brightest or darkest areas of a photo.
In other words, HDR photography is not first and foremost about how you adjust the final image, but rather how you retain detail in the image is retained in the first place.
If a scene you are photographing exhibits significant dynamic range, such as having the sun in the frame but also having foreground subjects backlit, a single photo will not be able to contain the full range of tonal values. If you expose for the sun, the dark shadows will be completely blocked up. If you expose for the shadows the sun will be completely blown out.
In this type of situation, you can bracket the exposure and then blend those bracketed exposures into an HDR result. That HDR image can then be adjusted to determine how you interpret the final result, such as by adding a little contrast so the image doesn’t exhibit a strong “HDR look”.
Many HDR software applications are also capable of applying similar adjustments to single captures rather than only HDR images created from bracketed exposures. But the key is that if the scene exhibits greater contrast than can be contained within a single photo, you’ll need to use HDR techniques to retain full tonal range in the final image.