1. Overexposing can in fact be the ideal approach, but only if you’re capturing RAW files. After capture, adjusting the image to make it look “normal” in the RAW processor is a crucial step, and to reap the benefits of overexposure it has to be carried out in RAW rather than JPEG shooting mode.
2. Overexposing RAW images works because it increases signal-to-noise ratio. More image-forming detail is contained in the brightest areas of the image than in dark areas. If you think of a pixel as a bucket, and light as the water filling that bucket, the more water in the bucket, the more information you have. All that “water” is the equivalent of a stronger signal, thereby improving s/n ratio. And you always can eliminate excess water from the bucket later, which is the principle at work when you overexpose RAW.
4. Overexposing appropriately requires checking the histogram on the back of the camera. The process is sometimes called “exposing to the right” or ETTR, because it involves moving the peaks on a luminance histogram toward the right side of the graph (representing the brighter portion of the image file). If the peaks move all the way to the right edge and go beyond it, that’s when detail has been lost due to clipping. So move the peaks toward the right side of the histogram without going too far.
5. Overexposures should be brought down to “normal” in postprocessing of the RAW file without increasing noise. In fact, noise is minimized (especially in the shadow areas of the image) with subtle overexposure. It actually produces a cleaner, more noiseless signal than the “correct” exposure indicated by the light meter. That is, as long as you don’t overexpose so much as to clip the highlights!
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