Coping with Highlights and Shadows
Recover Digital Image Detail in Post-Processing
by Wes Kisting
Some folks claim it is better to shoot RAW instead of JPG in order to prevent blown highlights, but in my experience, it makes little difference. If you blow out your highlights, they're gone for goodwhether you were shooting RAW at the time or not. For single-exposure, high-contrast scenes, the best practice is to deliberately underexpose the shot and instead, "expose for the highlights." To do so, set your camera to "Histogram" or "Highlights" mode, then reduce exposure just enough to eliminate highlight blow-out.
Whereas blown highlights are usually lost for good, most of the detail obscured by dark shadows can be recovered (often quite easily) with a capable photo editing program like Adobe Photoshopassuming, of course, the shadows are not so underexposed that they get blown to flat black. You do lose some color by underexposing, but color can be easily restored if you have a basic knowledge of layers and layer-based adjustments in Photoshop.
Below is a photograph of a barn with severe backlighting. To capture the shot, I took an exposure reading from the sky just to the left of the sun (without including the sun in the frame), locked this exposure value, re-composed, and released the shutter. By doing so, I minimized the amount of blow-out on the sun (I allowed some blowout for effect) and radically underexposed the barn, the adjacent farmhouse, and the surrounding grass and treescreating a typical silhouette effect. The image was shot at the "normal" JPG quality setting, loaded into Adobe Photoshop CS2, converted to a PSD (Photoshop) file, and modified in layers to preserve detail and maintain greater control over the final result.
For underexposed shots like this one, I usually begin by balancing out the exposure using Photoshop's "Levels" tool (Image --> Adjustments --> Levels) or "Shadow/Highlight" tool (Image --> Adjustments --> Shadow/Highlight). Either tool works, but depending on the picture, one tool may produce better results than the other. In my experience, the "Levels" tool generally offers a quicker, easier fix. It also preserves color and smoothness better during the adjustment process. On the other hand, the "Shadow/Highlight" tool can cope with a wider range of light/dark values and encourages a slightly grainier, but aesthetically-pleasing "film" look. Both tools can be combined to "finesse" an especially difficult image, so it pays to get familiar with both.
The Shadow/Highlight Tool
With the Shadow/Highlight tool, there is no "right" setting for every shot, so I play with the "shadow" slider until the dark areas appear more evenly balanced with the rest of the image. A common novice mistake is to make the shadows appear as bright as the highlights, which not only destroys the aesthetic richness of the original lighting, but produces a very artificial-looking image. In real life, shadows are noticeably darker than midtones, so don't try to bring the shadows up to a "normal" exposure. Brighten them just enough to approximate what the human eye sees (instead of what the camera records with its more limited exposure range).
For demonstration's sake, I've brought the shadows up much higher than necessary to show two things: First, much of the original color has been washed out by the underexposureespecially in the grass and the barn, but also in the sky. That's one "downside" to deliberate underexposure, but it's easy to remedy as I'll show in a moment. Second, the amount of detail preserved is superbthe solid black "mass" of silhouetted shapes has given way to a clearly-defined barn, farmhouse, and vegetation.
At this point, I could warm up the whole image very easily using Photoshop's "Photo Filter" option as a quick fix (Image --> Adjustments --> Photo Filter), but I prefer to have control over the individual colors. So instead, I created three separate, colored layersone green, one yellow, and one redto adjust the color of the grass, the sun, and the barn, respectively. Photoshop's "Color Source" option (Select --> Color Source) and "Magnetic Lasso Tool" make it very quick and easy to select isolated portions of the image to "localize" the colors (apply them only to specific portions of the image). Here, the colors have been exaggerated to make them more visible. These effects could be intensified much further, but they already look ridiculously artificial to my eye.
Since I prefer photo-realism and try to alter my images as little as possible, I softened the effects of the colored layers (by adjusting the opacity of the layers) and lowered the brightness of the shadows to create a much better balanced, true-to-life imagevery closely approximating how the original scene looked to my eye. I'm quite satisfied with this result, but a more creatively-inclined photographer could go on to manipulate the image further to produce a vast range of effects. What you see here took only a few minutes of editing. The visual and creative possibilities are limited only by your knowledge of proper exposure and your skill at photo-editing.
Not bad, right? With just a little tweaking, you can produce some really striking shots with nicely balanced exposures under tricky lighting conditions. That's exactly what makes digital photography so appealing! Here's one last, quick look at the progression of the image from start to finish:
I always perform editing operations in layers, rather than modifying the original image directly. Then I save the image as a .PSD (Photoshop Document) file to preserve the layers. (Saving as a JPG automatically merges all of the layers into one, permanently altered image.) By preserving the layers, I can go back to tweak, modify, or undo any of the effects I've applied at any point in the editing process. Thus, from a single file, I can print (1) the original image, (2) the final, edited image, or (3) any "in-between" version of the image at any point during the modifications applied by each layerall with a few simple mouse-clicks! Trust me, working in layers is a huge time saver. It also saves you space: You don't have to save and store multiple copies of the same image to apply or remove edited effects!
© 2006, Wesley Kisting