Subject: Re: Exposure to the right and tone placement
What I do know from experience is that if I shoot RAW I get much cleaner
results in the shadow areas by taking shots with the histogram shunted
as far to the right as it can go, without clipping anything that I don't
want clipped, and then shunting it back to the left in post procesing
to get the mid tones where I want them. Any further discussion is purely
technical explanation of why this works so well...
The explanation for your observation is really simple. The darker f/stops in a digital image are noisy because the sensor is collecting fewer photons and the resultant sampling error leads to noise. By exposing to the right, you are collecting more photons. It is similar to taking a poll of likely voters: the larger the sample, the better estimate of predicted vote.
Look at this image of a step wedge photographed at ISO 1600 with the Nikon D200. The steps are in 0.1 density units, so 3 steps = 1 f/stop. If you expose to the right by 1 f/stop, you are in essence shifting the noise 3 steps to the left-- big difference.
Bruce Fraser is overly concerned with the brightest f/stop because it contains half the levels of a digital capture. Normally, the highlights contain an excess of levels over what is needed in the image, and the real advantage of ETTR is in the shadows.
Roger Clark gives a good analysis of counting noise on his web site:
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Exposure to the right and tone placement =>
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