The Principles of HDR Imaging

The term HDRI (or HDR for short) often educes strong reactions from photographers; it’s one of those photographic techniques that has been bastardised by amateurs to the extent some professional photographers shun it as new-fangled and gimmicky, or else argue that it portrays an unnatural photographic result.

It’s no surprise. A quick Google search for HDR images or a gander through photo sharing sites such as Flickr reveals the majority of photos tagged with HDR are hyper-real and over saturated at best, and vulgar, tasteless renditions of a scene at worst.

The real reason HDR is hated by some is because you can spot a bad HDR from a mile off, but it’s harder to spot a good one. This leads most people to assume HDRI generally makes for horrid images. Of course, many enthusiasts can’t spot even a bad HDR – but that’s another matter.

But isn’t the same true of any post-processing? Professional photographers tinker with saturation, contrast, crop, and toning all the time. When it’s done badly, you think “that has been tampered with”; when it’s done well, you concentrate on the actual image giving no thought to its production.

Like any photographic tool in the toolkit, it’s how you use it that matters. And as for the argument that it produces ‘unnatural’ images, this argument could be extended to any photographic technique; artificial lighting, post production, filters, cross processing, etc. In fact, a true art philosopher would argue that all photography is an unnatural rendition of reality, but maybe I’ll save this discussion for another day.

There’s no use arguing for or against HDR. It’s an image processing technique. If you believe in image processing, (and neither film nor digital photography would exist without), then you see HDRI as another tool in the toolkit. And it’s a tool that is here to stay.

Basic principles of HDRI

  1. A high dynamic range image (an HDR) is created from three or more impressions of the exact same scene. That’s three physical camera clicks (each image taken with different exposures), and three image files combined into one using HDR software. It’s possible to duplicate one photograph and edit each to produce three source files to input into your HDR software; that’s not a true HDR.
  2. The technique may be used to artistic effect, or for technical reasons. The best HDR images are constructed according to a rigorous technical process, and the same tenets of post production should define the aesthetics when it comes to combining the photographs.
  3. If HDRI is used to fulfill a technical objective (for example, showing the detail a viewer sees through a window in a room which would otherwise be washed-out on camera), the three images used must appear as close to carbon copies of one another as possible. No movement of objects in frame must occur, however small. For this reason HDRI is best suited to static scenes, and it is unsuitable for portrait photography.  It must be made using a tripod to ensure absolutely no movement of frame. Even a moving tree in the distance can ruin an HDR image.
  4. If HDRI is used for aesthetic effect, movement can add to the interest, especially where the source images are long exposure, or where it’s desirable to trace the movement of an object (e.g. light trails, moving crowds, etc.)
  5. HDRs are usually produced from three RAW images, which were made at exactly two stops apart from one another. (-2EV, 0EV, +2EV).

These principles can be applied in hundreds of different ways.

In my next HDR article to follow, I will give you a step-by-step guide to the way I make an HDR.

St Pancras Commercial Shot HDR HDRI high dynamic range image example

St Pancras Commercial Shot, HDR example