Exposing to the right
ETTR images requiring increased exposure may appear to be overexposed (too bright) when taken and must be correctly processed (normalized) to produce a photograph as envisaged.
The principle is also applied in film photography in order to maximize the negative's latitude and density and achieve richer blacks when the image is printed slightly down.
ETTR was initially espoused in 2003 by Michael Reichmann on his website, after purportedly having a discussion with software engineer Thomas Knoll, the original author of Adobe Photoshop and developer of the Camera Raw plug-in.
[1] Their rationale was based on the linearity of CCD and CMOS sensors, whereby the electric charge accumulated by each subpixel is proportional to the amount of light it is exposed to (plus electronic noise).
It has since been demonstrated that the benefit of more exposure lies not really in the better quantization, because the noise always present in photographic captures renders it invisible to the human eye,[5] but solely in the better SNR, particularly in the shadows of a high-contrast scene that need some pushing.
[7] This problem can often be mitigated by using camera tonal settings that allow the JPEG histograms and highlight-clipping indictors to best reflect the underlying raw data.
With the advancement of digital image sensors, the same ETTR technique may be applicable to scenes with a relatively high dynamic range (HDR) (high contrast within both bright highlights and dark shades in harshly lit scenes), previously in the domain of HDR techniques involving multiple exposures.
[9][10][11] A complication to using ETTR with higher DR is the fact that the vast majority of photographic cameras can only display a histogram produced by its JPG processing engine.
Typical examples of unimportant highlights include the Sun, other very bright light-sources, and sharp-edged specular highlights like chrome car bumpers in sunlight; however, one should avoid blowing areas with smooth luminosity gradients, for instance the sky around the Sun, because these likely lead to visible sensor saturation artefacts (banding).
Rather, it uses and depends on the exposure indicators, either the histograms and/or the highlight indictors (blinkies/zebras), which, ideally, have been set to reflect as well as possible the maximal values of the underlying raw data.
