28 Mar 2012

High Dynamic Range (HDR)

Submitted by Roger

As photographers, we are in the business of creating images. We are often faced with difficult lighting, poor composition, limited time and no co-operation, yet we are expected to produce images that leap off the page and capture the attention of the viewer. In such cases we often reach into our bag of tricks. HDR is definitely one of those tools we can pull out to rescue our shoot.

There are many excellent tutorials on HDR, and I will not try to duplicate what they offer. Most are dedicated to showing you how to use HDR to enhance a photo, without the surreal quality that HDR can create. My goal here is to show you the extreme, and what that effect looks like.

To begin, you need a high contrast scene, and bracketed exposures. A tripod and cable release are essential. All camera settings must be manual, and the only setting to change is shutter speed in most cases. As you will be merging two exposures of the same photo, you will want focus and depth of field to remain constant. If your camera is capable of automatic exposure bracketing, it will create the exposures for you without your having to touch the camera and risk moving it between exposures.

These two photos were taken through the front window of my studio, using a Canon 135mm soft focus lens at f16 and maximum softening to enhance the blur in the background. Focus was on the window bars. The exposures were 1/4 sec for the inside and 1/125 sec for the outside.

Each image, as a CR file, was preprocessed to maximum saturation and vibrance, and imported into photoshop. They were combined using ImageMerge Exposure.

The combined image can then be manipulated to look like a watercolor drawing, or you can apply whatever post-processing effects you wish. The actual goal here is the effect, creating a usable image in the face of adversity.

If you shoot in camera raw format, HDR techniques can be used on a single frame. During a 'Fall Colours' shoot, I came across a ruined mill with a pair of archways where the old millrace ran. The ground beyond the archways was lit with the warm miday sun, while the ruined interior was bathed in soft, cold light from the northern sky. However there were healthy green sprigs emerging from the bed of yellow and red leaves. The whole scene looked to me like the eyes of time watching life reclaim its place in the ruins.

To show what my minds eye saw, I loaded the raw image into Photoshop twice, first reducing the exposure by one stop, and then increasing the exposure by one stop. I combined the images with PhotoMerge exposure, maximizing both highlight and shadow detail, and saturation.

This is HDR in its purest form.

After combining the layers ('flattening') the image into a background layer, I created a duplicate layer. As an increase in saturation was the goal, I did not remove colour, but rather I used Adjust Color to increase the saturation slightly, and Adjust Lighting to fine tune the highlight and shadow detail, as well as midtone contrast. This is what I saw.

Most HDR tutorials go into so much detail that the readers are discouraged. The basic steps are simple, and not every image will exhibit the artifacts common to HDR. The most important thing is to get started, and to understand what the tool can acheive. Eventually you will see images in front of you and you will shoot with the understanding that postprocessing tools will complete the image creation process. HDR is just one of those tools. Play and learn!

digital photography