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Tuesday, April 8, 2008

Expanding Photography’s Tonal Range

HDR photography lets you capture images of great brightness range that are closer to the reality you see

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What makes Photomatix work so well is that it not only puts the tonalities from multiple shots together into one image, but also offers excellent control over those tones in something called Tone Mapping. You can adjust the strength, color saturation and, very important for my interpretation of the HDR file, light smoothing (this can go from a rather funky look to something totally real). In addition, you can set white and black points, which I consider key to good digital photos.

I can’t say that every “shot” (made of multiple exposures) looked great—Photomatix can only deal with what it gets from the photographer! But I was hooked, and now I’m always looking for HDR types of images in locations where I shoot so I can get photos that actually capture something closer to what we see. I usually do a little added work in Photoshop to give the image more structure by selectively darkening and lightening parts of the photo as done in traditional photography in the darkroom.

If you want to explore the idea of working a scene so that you capture more tonal range than a single shot normally does, you also can try two techniques that I still use and can be quite effective—double-processing RAW and shooting two exposures of the same scene to be combined in Photoshop. Both use Photoshop in the same way to combine two versions of the same scene showing different tonalities (you can do even more than two versions, but I rarely find a need to do that).

The double-processing RAW technique is fairly simple. You process a RAW image with challenging dark and light areas by processing once for the dark areas and a second time for the light areas. You can do this in any RAW-processing program, from Camera Raw to Lightroom.

Often with scenes with extreme tonal ranges, you end up compromising when you try to process it all at once, and neither the dark nor the light areas look their best. By processing each version focused purely on first dark and then light tones (and ignoring what happens to the opposite tones), you can more easily get the best from both tonal ranges.

photoshop screenshot
With the other technique, you have to shoot two photos of the scene (camera on a tripod)—one for the dark areas, one for the light areas—and then process each specifically for those tones. I find this easy to do by using autobracketing and exposure compensation. The brightest photo is good for the light areas—I keep the brightest and darkest exposures and throw out the middle shot. By autobracketing, I avoid having to move anything on the camera (such as shutter speed or ƒ-stop) that can make the camera move slightly between exposures. If the camera moves, it can make it harder to line up these shots in Photoshop.

Either way, you end up with two separate images in Photoshop—one light, one dark. Keep both open and visible on your monitor and then, using the Move tool, press the Shift key, click on the better-looking image and drag it over and onto the other photo. If you get an error message, it means you didn’t drag your cursor far enough onto the other photo. Release the mouse button and then the Shift key. The Shift key means the two photos will align exactly on the edges.

This literally puts two photos in a stack, one on top of the other as layers. If you had two real photos in such a stack, you’d cut holes in the top one to reveal the one underneath. You do exactly the same thing in the computer. You can do this by using a soft eraser brush (easy to do) or a layer mask (better because it gives you more control).

If the top photo is the darker one that favors the light parts of the photo, just go in and remove the darkest areas, which allows the better dark-processed or exposed tonalities to appear. If you use an eraser, you have to use the History palette to back up if you make a mistake.

Try adding a layer mask (found in the Layer menu or click on the little rectangle and circle icon at the bottom of the Layers palette). Paint black with a soft brush over the areas you want to remove. Black blocks whatever is on that layer, revealing what’s underneath. Any techniques (and there are several that require more space than I have here) that put black in specific areas will help combine these images.

Regardless of how you do this, bringing a larger range of tones into a photograph than is possible using traditional techniques gives the nature photographer a powerful tool to create images closer to reality. You gain some great possibilities for your photography that go beyond the limits of what a sensor or film is capable of seeing.


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