Everyone who has experience in photography realizes that the wider the dynamic range of the lighting in the scene, the more difficult it is to get a properly exposed image. If the photographer exposes for the shadows, the highlights are blown. If the shot is exposed for the highlights, the shadows are dark, featureless and lacking detail. Metering is used to establish the light readings at any point in the scene, and metering multiple times is used to find the optimum exposure for any combination of highlights and shadows.
In the SLR, such metering is both science and art. It is a science when the on-camera processors measure light intensity at multiple points of the scene and then combine the results to determine the appropriate exposure. This is called matrix metering and can include information other than light intensity – whether part of the image is in focus or not, whether part of the image is backlit, etc. Some proprietary processing is required to take this information and provide a proper exposure for any combination of ISO and aperture. Metering is an art when the photographer makes judgments about the overall tone of the scene and exposes in order to achieve a specific tonal effect.
After establishing the exposure parameters of a shot, the photographer has two choices: to use additional light sources to “balance” the image, or use the natural lighting and employ post processing techniques to achieve that balance.
High Dynamic Range Photography (HDR) is a post-processing method of combining multiple exposures of a scene in order to provide a more balanced image and capture more of the contrast.
HDR is a technique, not a style, although there are clearly masterful photographers who use HDR to create superb stylized images. Others, unfortunately, use HDR on images of no particular distinction and call that a style.
We are not concerned with HDR as a style, but as a solution to a pervasive problem. The churches that we shoot represent such a wide dynamic range that conventional photography is challenged to capture them adequately. The problem is exacerbated when you take into account that we typically take very long exposures. This image of Sainte Radegonde in Poitiers shows bright windows, an unlit crypt, a statue lit by artificial light, a dark oven vault, and shadowed areas behind the hemicycle of columns in the background. The image shown has been conventionally processed but is a good representation of the challenges found in photographing these structures.
When we use post-processing techniques, our objective is to create an image that is otherwise impossible to represent with a camera but reflects what we see with our eyes. We have three basic techniques that we use to achieve that objective – HDR, layer masking, and simple, elegant editing in Lightroom (this is PJ’s specialty).
The intent in using HDR is to capture the dynamic range while keeping the image as natural as possible. There are no hard and fast rules – a tripod is necessary, of course, and we use the number of exposures necessary to capture the various light levels within the scene. The “three shot/two stop” rule often will not work in our environment. I routinely shoot six stops at 1-stop intervals, but have shot up to 24 in a complex situation. However, I don’t think that any finished image has required more than six or eight source images.
We have used both the Photomatix Pro and Photoshop software, but prefer to use Photoshop in conjunction with Lightroom. We create the base HDR image in Photoshop and then edit that image in Lightroom, just as we would edit the RAW image from the camera.
This shot at Saint Michel-de-Cuxa is an amalgam of five of nine exposures that were taken of the cloisters. The trick was to balance the dark underside of the wooden roof with the extreme brightness of the exterior scene, while maintaining the natural look of the pink stones of the cloister itself. In addition, it was necessary to preserve the detail in the cloister on the far side of the grass.
It is not always necessary to merge the entirety of different versions of a shot. In some cases there may be a very good overall photograph that contains only a limited number of elements to be improved. This image of the Cathedral of Saint Peter and Saint Paul in Providence is an example of using layer masking to replace elements from one exposure with those from another. In this case, the side windows and rose window were the underneath layer that was revealed. The only difficulty was to get the windows to be the right intensity compared to the rest of the scene. In actuality, I set the opacity to 92% on the windows to achieve the right balance between the two layers.
This photograph of the Basilica of Saint Hilaire in Poitiers was processed in Lightroom by PJ. She has created a wonderful balance of light and shadow. This is a work of great skill that gives a true representation of the space without any special processing.
It should be clear that we are not trying to use these techniques to create artistic visions in themselves. We are trying to use photography to illuminate the artistic visions of the builders, and like them, we use the tools available to us to achieve our ends.