High Dynamic Range

Introduction

High Dynamic Range (HDR) images are very popular discussion in photographic books and magazines. It is also a very old procedure almost old as photography. Nowadays with availability of digital cameras and image editing software, this technique is very commonly used by photographers. For successful use of the procedure, a common sense is essential. Difficulty level is from very easy (dodging and burning in Photoshop) to hard (combining an image of the sky through branches on an image intended for large print photograph).

History

The first photographer to use this technique was Gustave Le Gray in his images shown in London in 1856. At the time negatives were more sensitive to blue light then to red and green. As a result, the sky would be rendered in white and subjects on earth in shades of grey. So he exposed one photograph for sky and the second one for subjects on the ground. When making prints two negatives were masked. One was used for sky and the other one for the ground.

Overview

Visible light, that’s what we see, can be rendered with camera with ability to capture Dynamic Range of 30 f stops. Nowadays, cameras can capture roughly 5-10 f stops in one image depending of the sophistication of a camera. As a result, a camera can capture only a window of the visible light in one single image. The intent of HDR technique is to widen this window. In simple words burned highlights and unexposed shadows in an image need to be revealed.

When to Use It

Use of HDR technique is to be avoided unless it is necessary. For example, at noon on a sunny day shadows are harsh. That means a part of rock facing the sun and part of the same rock in the shade will have different intensity of light. This difference can be several f stops. In order to photograph this subject one would need to adjust exposure for sunny side of the rock and the second exposure for the part in shade. In the office these two exposures would be combined using image editing software to create one image. The better option would be to come at the location early in the morning or late in the evening and photograph the same subject. This time only one exposure is needed because the light does not create harsh shadows.

To conclude, in some instances choosing appropriate lighting conditions gives better results than applying the HDR technique.

Application

HDR technique is a tool available to a photographer in creating a desired image. As mentioned earlier it is to the photographer‘s common sense to decide to use it or not. Some other procedures one can use instead or in combination with HDR technique:
- Chose appropriate lighting condition. Come on the location at the dusk or down when shadows are soft.
- Acquire an advanced camera which wider dynamic range.
- Use artificial light (flash) or reflector to lighten the detail in the shade.

Depending on your subject and type of photography, the photographer chooses the appropriate approach.

Revealing Highlights

In some cases we can avoid HDR procedure by choosing appropriate lighting conditions, but in others this is the only way we can present a subject. For example, at sunset and sunrise sky gets spectrum of warm colors. In order to catch warm colored sky and the ground, it is necessary to use HDR technique. So take one shot for sky and the other for the ground and then combine them in an image editing software. The image (Figure 1) shows sunset, where I could not avoid HDR technique.

Figure 1: Zion Sunset

Reviling Shadows

When subject with lot of shadows is photographed, some shadows lose detail and become plain black. The best way to render such subject is to photograph it in optimal lighting condition. Sometimes we can’t camp on location, drive late in the evening or can’t afford camera with high dynamic range, so remedy is to use HDR procedure. In Figure 2 is shown example of such situation.

Figure 2: Sands of Time

How To

The simplest way to combine two images in photo editing software is to use eraser. Load up the image with most of the detail on the top layer. In the bottom layer load up an image adjusted for shadows or highlights, which ever you want to reveal on the top layer image. Make your top layer active and choose eraser soft brush with opacity 5-10%. Now go over area which you want revealed a few times. When you are happy with outcome flatten the image.

This is not the best way to combine images, but it will get you going in no time.

Summary

HDR procedure is a tool in the tool box of a photographer. At the end of the day is personal preference to use it or not and when to use it. The most important aspect is your imagination.