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What is HDR?

HDR (High Dynamic Range) is a method of allowing us to see an image more as we would in real life (not to be confused with the surreal look, which is more of a cartoony representation,  and tends to give HDR a bad reputation), giving detail in the highlights and shadows where a normal photographs are unable to do so.

Have you ever taken a photo where you can see details with the naked eye, but on viewing the resultant image it looks nothing like you remember, with deep featureless shadows and blown highlights, the phrase “You had to be there” comes to  mind.

A typical situation is where you are in a room with one window at the opposite end, you can see texture in the walls and furniture, and a lush green garden with a blue sky and white fluffy clouds. Your eyes and brain can process all this information and  render a balanced view giving us all the available visual information. But even with the very advanced Digital Cameras available today, they can still only process information in relatively narrow bands of the dynamic spectrum. Therefore in a single image,  you can expose for information in the Highlights, Midrange or Shadows but not all three, and the brighter the highlights or darker the shadows the worse the situation becomes.

If you shot the scene for each extreme of the dynamic range however you at least have the information available to you in the camera. This is where HDR processing comes into play.

To process for HDR you need the following:

1.  A series of images exposed for the differing dynamic ranges in the scene, typically this will take
a minimum of three and a maximum of nine, although there is no actual upper limit.

2.  A computer with software capable of processing the images to produce a blended image
containing all the required elements. Also required will be regular photo processing software to
tweak the image to obtain a finalised image to your own requirement.

3.  Time and a modicum of learned skills, there is plenty of free help in the form of E-books and
Videos available on the internet.

How is a HDR image achieved?

The process is actually very straightforward, you just need the concept straight in your mind first.

To capture the required images you first need to take a series of shots using a method called Exposure Bracketing.

To achieve the bracketed shots you need to establish the midrange for the scene, this will be the baseline or 0EV. From this you then take a number of progressively underexposed images for the highlight information, and the same number overexposed images  for the shadow information, the norm is usually between three to nine shots although it is possible to use only one.

Typically the result for three shots will be -2EV 0EV +2EV (or 1EV equals one stop), and for nine -4EV, -3EV, -2EV, -1EV, 0EV, +1EV, +2EV, +3EV & +4EV, the number of shots necessary depends on just how wide a dynamic range there is to be recorded.

There are an increasing number to cameras on the market these days that have a bracketing function built in, but few with the ability to capture more than three shots per bracket, there are however ways to overcome this limitation.

It will obviously take longer to obtain a number of bracketed shots than just one, so there are three important points to remember.

Firstly it is desirable to use a tripod to keep the camera still between each shot, or there could be alignment issues during processing.

Secondly it is a good idea to use off camera activation or the built in timer function to reduce the likelihood of vibration.

Thirdly (unless you wish to make a feature of ghosting in the image) moving objects are difficult subjects, but there are features in some software programs designed to combat this.

The images then need to be uploaded to your computer and brought into the HDR processing program. In general, the program can be tweaked to produce a balanced image containing all the information and detail in the whole dynamic range.

This will produce a rather flat image for further processing, if a realistic result is required. But if your taste is more for the surreal there is scope to achieve this by essentially over processing the image at this point.

The program will then perform Tone Mapping, this is where the program takes the information contained in the image data, selects the best pixels, and compresses it to a form visible for the output device, be it a monitor or printer.

The resultant image can then be further processed by any of a number of photo processing programs to adjust the Contrast, Brightness and Colour etc.

Below is an example of an image before HDR processing (the processed image will appear when you pass the mouse pointer over the image), notice the difference in the general detail, sharpness and vibrancy in the image.

I know this is a moving subject, but I used the cheat to make a single shot into a bracket for HDR processing, it is however not as good as processing purposely taken RAW images. This image is one of my favourite equine images and I think it works well  as a HDR illustration.

What can HDR be used for?

Obviously HDR is useful where ever a High Dynamic Range causes a problem. In Landscape work it can enhance many types of scene, especially dawn and dusk shots, water be it  flowing or still and reflective, in forests and more.

On the commercial side it can be used to enhance Architectural, Estate Agency, Promotional and Product shots, where ever clarity and great detail is required.

Basically HDR is only limited by our vision of the world we live in, and I will be looking for chances to extend my use of this style of photography where ever I go.