expose to the right

expose to the right

Exposing to the right is a practice that many people don’t follow precisely because RAW files do stand up so well to post-processing. But shooting RAW doesn’t give us an excuse to be sloppy, and exposing to the right is important for two reasons. The first is simple. If you underexpose an image and then have to pull out shadow detail from the darker areas of an image, you’re going to be introducing noise. But darkening slightly overexposed areas will not give you a loss in quality. This is true because of the second reason
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This second reason is even more compelling but requires a bit more explanation. DSLR cameras in general have about five stops of dynamic range. Recall from above that a 12-bit RAW file has 4,096 possible tonal values in each color channel. If we array the stops of dynamic range along our monochromatic or luminance histogram, we’ll notice that each stop (from left to right) contains two times more information than the previous stop. And notice also that most of the possible color values are in the brightest areas. That is, our camera can capture only a relatively few dark tonal values and lots of bright tonal values
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As the figure above illustrates clearly, fully half of the tonal values are in the brightest fifth of the histogram. So, if you don’t have at least some pixels heading out into that rightmost fifth of the histogram, you’re wasting half of the potential tonal information that your camera can capture!

Exposing to the right does not mean overexposing to the extreme though. It simply means that you should expose your image so that the brightest tones in your scene display out into the right fifth of the histogram. If you want detail in the whitest or brightest parts of the scene, however, you need to take care to take them just to the edge of the histogram but not over.

Take the image of a Montezuma oropendola below. This is one of the tougher birds in Costa Rica to expose properly because of the white skin on the face and the black feathers around the head and neck. Underexpose this one, and you’ll have no feather detail in the blacks. Overexpose too far, and the white skin will be blown out white with no detail at all.

Below is a screen shot of my untouched RAW file and the resulting histogram. Notice that there is some space on the left edge of the histogram. This means that the dark feathers are not pure black. And notice that the brightest pixels go right out to the right edge but not past. This means that I made the image as bright as I could in order to capture feather detail in the blacks but without blowing out the white skin. You’ll note also that there is a large amount of pixels clustered toward the middle right of the histogram. This is the background, which is represented by brighter than average mid-tones. The background in this shot was distant forest but there was some fog moving through, which meant that the background was indeed a bright but fairly dull green.



In terms of exposing to the right, there is a caveat that applies especially to the rainforest, where light is usually scarce. Let’s say that I’m shooting a monkey that’s moving around a bit. I have my lens aperture set wide open, I’m getting only 1/60 of a second, and I’m already at ISO 3200. That is, I’m doing everything possible to get just barely enough light for a sharp image. I take a shot and check my histogram and find that I really should be pushing my exposure one stop to the right to get good detail in the monkey’s dark fur. I have a bit of a dilemma now — how to get that extra stop of light.

I can’t open up my aperture any further; it’s already wide open. If I adjust my shutter speed to let in one stop more light, I drop to 1/30. I think that’s going to make it hard to get a sharp image in this situation, and it’s also placing me into the territory where mirror vibration becomes a concern. So, I don’t want to take my shutter speed any slower. I could take my ISO from 3200 to 6400 but, even though my Mark IV is quite good at high ISOs, I’m not enamored of 6400. So, this is a case where not exposing to the right and brightening the exposure in post-processing may actually be a better or at least equally valid choice. I want a sharp image so I need that shutter speed. And going to ISO 6400 will introduce noise, perhaps just about as much as taking the image at ISO 3200 and brightening it by one stop in post-processing.

This, of course, is a fairly extreme situation but it’s worth noting because there are some potential tradeoffs involved when exposing to the right. Still, it’s a good habit to have and will help you to get the cleanest image files possible in the vast majority of shooting situations.

The above was taken from http://www.deepgreenphotography.com/2012/01/top-5-tips-for-quality-image-files/ -- you definitely need to read the whole article!