Expose to the Right (ETTR) is a digital photography technique which is used to optimize image quality by obtaining an exposure with the least amount of noise and the most detail possible. This is done by exposing a digital photo so that the histogram is biased toward the right side, regardless of what the “standard” exposure would be, then bringing the exposure down as needed in post-processing. The reasons for exposing to the right are: To increase the SNR (Signal-to-Noise Ratio) on the digital sensor image, thereby minimizing noise and increasing detail. To increase tonal range. To have cleaner, truer colors in darker areas. To get more control over the previously mentioned areas in editing, and to allow an overall higher final image quality.
Expose to the right technique is especially effective for images that have dark areas and shadows, where the typical SNR would be lower and noise therefore more prevalent.
When determining whether or not to expose to the right, one major consideration should be the highlights; if there is a possibility of blowing out the highlight detail, ETTR may not be the best option. Other considerations may include, but not be limited to: Available light, desired shutter speed and subject motion, shooting ISO, dynamic range of the scene.
Always judge your exposures based on the LCD Histogram, NOT the image preview. I recommended checking the separate R, G, B histograms, as well as the luminosity histogram.