There is an anomaly in digital capture that seems to defy logic and knowing it now will save you a lot of heartache in the editing room. Exposure doesn’t work the same way in digital as it does in film. Want to know the secret?
Here it is:
You can get more detail from a slightly overexposed photo than from a slightly underexposed photo.
Yes, that’s right. I’m not talking about blowout but slightly overexposing without blowing out your photo will result in more detail. Here’s why.
How exposure is calculated in digital cameras
Digital cameras record images with math algorithms. Let’s look at the numbers in RGB’s digital tones. Absolute black is the absence of light and it registers at 0 in RGB – no colour information, none. Shadow areas can range from 0 to 128 which is the midpoint but most fall at around 64 and under. White, on the other hand, contains red, green, and blue fully saturated in equal amounts and registers at 255. Most very light areas in a photo range from 192 to 255 and numbers at the higher end of the scale contain a lot more information. That’s why it works. If you have any doubt and need to err on one side or the other, choose overexposure for much better results.
Think about it. If you underexpose your photo and an area that should have information reading 64 now has far less and is actually reading at 34, where are the details? Nowhere. You’ve lost 30 tonal points before you even start. Trying to boost it later results in a computer guesstimate and the pixels are manufactured. The real details aren’t there and the end result is often very poor.
Overexposing does the opposite. Let’s suppose I have a light-coloured wall with some sort of etching. Exposing correctly in camera results in no blowout and a large expanse of wall rendered at say, 192. Overexposing slightly boosts the amount of colour information that I have to work with in editing. Instead of working with 192 I may have 225. That’s a lot of detail I can bring out by adjusting the exposure from there. I don’t need to manufacture pixels at all. I have more than I need.
When to increase exposure beyond what your camera indicates
Increase the exposure when there are a lot of light objects in the photo and you want to ensure good detail. Yes, it is the opposite of what you would think is logical but that’s the beauty of a new technology applied to an older craft. Digital is not film. It’s the application of light in red, green and blue on a sensor. RGB is additive colour. The more light, the higher the number. It makes sense when you think about it. The reason people are inclined to underexpose is they don’t understand what happens at the high end. Once a colour reaches its saturation point, it is at 255 and can’t increase. Information beyond that point is not recorded and that’s what blowout is all about. However, everything at 255 and under can be manipulated very nicely so it leaves a lot more room to play. More information means more detail.
Shoot in RAW
This gives you room in image editing that you won’t have with a JPEG. If you have very light areas in your photo that you want detailed, increase your exposure by one stop.
Fig. 1 shows the image that was exposed normally. Camera was set manually. Tonal range was adjusted exactly the same in both images, creating a black point and a white point. In Fig. 1 some of the red channel exceeded 255 and resulted in some clipping. All colour adjustments are identical in both. Notice how although the images are nearly identical in the lightest areas (top right), there is considerable shift throughout the rest of the image in Fig. 1 while Fig. 2 is able to handle much more adjustment at the high end of the tonal range. This results in more accurate tones throughout.
There is no clipping at either end of the tonal range in Fig. 2 even after all the adjustments. You will see the same phenomenon occur when shooting street scenes that include white or very light coloured signs. Overexposing slightly will allow you to retrieve detail from these areas to a much greater degree than if you exposed normally.
Once you know how to manipulate light and exposure, you may come up with some interesting results. Experiment. See what happens with different settings