Digital Darkroom

Raw Exposure Techniques
When you switch from JPEG to Raw Capture mode, the camera records raw data from the sensor. Data on aspects such as exposure are recorded but not locked in. Later, using a raw converter program you’ll be able to modify exposure or tonal value. This is a non-destructive process. The raw data file can handle fairly major brightness modifications because it contains 4096 levels of tonal information.

Since a raw data file is quite different than a JPEG, it also calls for a different approach in terms of light metering and exposure control. The best technique is based on a principle called expose to the right, first publicized by Michael Reichmann on his website: www.luminous-landscape.com. After using this approach extensively while shooting in Raw Capture, I can provide the following practical advice that you should try while experimenting.

An example of an optimal JPEG image, this photo is well exposed. The overall effect is pleasing and there is no loss of detail in important highlight or shadow areas. This exposure was achieved by taking the light meter reading from a midtone area, setting a +1⁄3 exposure compensation factor and using Auto Exposure Lock while recomposing. Only minor fine-tuning would be required in image-editing software before making a print. (Evaluative metering; JPEG capture.)

1. If practical, start by metering a mid-tone such as grass or a gray card, in the same light as your primary subject. This is only a preliminary step and will not often provide the ideal exposure.

2. Be sure to activate your camera’s highlight/shadow warning feature or
the histogram.

3. Take a photo and evaluate exposure in Playback mode.

4. If it seems to be fine, increase exposure; try a +1 setting while experimenting; make another photo that’s brighter than ideal.

5. When viewing the second photo, check the histogram and any warning about loss of highlight detail.

6. If important highlight areas are blinking, set a lower level of plus compensation and re-shoot. This may take several attempts, at different exposure levels, until you get one photo that is “ideal”: as bright as possible but not triggering a loss of highlight detail warning. With experience, you’ll learn to predict the suitable amount of exposure compensation for many scenes.

When using JPEG capture it’s worth bracketing exposures when you must shoot quickly and are not sure as to the amount of compensation that’s required. Often, that will produce one image that’s technically accurate or appropriate for the scene as it did in this case. However, in serious photography, it’s preferable to start by taking a meter reading from a midtone before bracketing exposures or setting exposure compensation at an estimated amount. That will increase the odds of getting one image that’s close to perfect.

Exposing to the right in Raw Capture provides a significant benefit. Because you won’t need to do much (if any) lightening of shadow and midtone areas in the converter program, digital noise (a grainy or mottled color effect) will rarely be problematic. Before converting the raw data to a TIFF file try to maximize detail in all important areas, using the available software tools. After conversion, use your conventional image-editor to slightly tweak brightness, contrast and midtone detail until the photo looks perfect.

Even the best raw converter program cannot recover highlight or shadow detail that was not actually recorded by the camera’s sensor. This image for example was seriously overexposed due to an excessive compensation level. While the Shadow/Highlight tool (available in some Adobe programs) could be used to improve the overall look of the photo, no software can work miracles. Hence, it’s worth getting the exposure close to “correct,” in camera even in Raw Capture. That will also minimize the amount of time and expertise required to make adjustments in the converter software.

The Bottom Line
While many digital cameras include an “intelligent” light metering mode (Matrix, Evaluative or Multi-Segment), no such system will always produce optimal exposures. So plan to exert some control. Use Auto Exposure Lock and exposure overrides as necessary to achieve optimal results as confirmed by your camera’s exposure feedback features. Then spend a few minutes perfecting the image in your computer. All of that may seem complicated at first but it merely calls for some practice with new concepts and tools. Based on my experience, the extra effort will definitely pay dividends, with accurate exposures that will make excellent prints.

Exposing to the right is recommended only with Raw Capture, to produce photos like this one: specifically intended for tonal value manipulation in the converter software. With JPEG capture, use less exposure than you might in Raw Capture; sacrifice shadow detail if necessary to avoid unnaturally bright midtone and highlight areas. (Image made with Raw Capture and converted without adjustment; Evaluative light metering; +1 exposure compensation.)

A long-time Shutterbug contributor, Peter K. Burian (www.peterkburian.com) is a freelance stock photographer and a digital course instructor with BetterPhoto.com. He is the author of “Mastering Digital Photography and Imaging, Magic Lantern Guide To The Sony A100 and Pentax K10D,” and co-author of “Photoshop Elements 5 Workflow.”

Each brand of raw converter software varies substantially in terms of the exposure control tools provided. However, most programs offer at least a couple of options for modifying the tonal values. It’s worth experimenting with features such as Levels, Curves, Exposure, Brightness and Contrast in order to develop some expertise with exposure optimization. (The screens shown are from Canon Digital Photo Pro 2 and from Adobe Camera Raw in Photoshop CS3.)