the greatest signal-to-noise (and therefore the greatest image quality). In both cases, the practice of ETTR does not use or depend on the camera's meter. 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. Background 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. 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). Although a camera may have a dynamic range of 5 or more stops, when image data is recorded digitally the highest (brightest) stop uses fully half of the discrete tonal values. This is because a difference of 1 stop represents a doubling or halving of exposure. The next highest stop uses half of the remaining values, the next uses half of what is left and so on, such that the lowest stop uses only a small fraction of the tonal values available. This may result in a loss of tonal detail in the dark areas of a photograph and posterization during post-production. By deliberately exposing to the right and then stopping down afterwards (during processing) the maximum amount of information is retained. Limitations The ETTR exposure is, by its very nature, established with a camera ISO setting that allows the exposure indicators (right edge of histogram or blinkies/zebras) to indicate when the sensor is at or near saturation for desired highlights. Most people will find this to be the camera's base (lowest, not false) ISO. However, depth of field requirements may demand such a high f-ratio, and motion-blur/camera-shake issues may demand such a fast shutter speed, that ETTR is not possible at this ISO setting. When this happens, one retains the spirit of ETTR (maximizing signal-to-noise) by making the exposure as high as possible subject to the shooting conditions. ISO may then be increased to bring the image up to a desired brightness. But, since increasing ISO does not actually increase sensor exposure (instead the sensor's signal gain is increased), it should be applied only after the actual exposure