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Subject: Re: Exposure to the right and tone placement

In an interesting discussion on the Luminous Landscape forum Bernard Languillier raises some interesting points in the Expose To The Right (ETTR) dogma. He points out that the digital sensor is not linear at high values approaching saturation, but rather exhibits a "hockey stick" appearance. Furthermore, this non-linearity varies among the three channels of the sensor.

This non-linearity is demonstrated in Roger Clark's experiments in comparisons of the dynamic range comparison of film to digital.

These observations support my original contention that ETTR is a good thing, but should not be overdone to the extent that clipping occurs. With this information, we also have to be concerned with non-linearity just below clipping, where a color cast can be inmparted from the variations in linearity among the channels.

This goes back to the advice of Norman Koren concerning ETTR:

"I mostly agree with the Luminous-Landscape.com article, Expose (to the) Right, which recommends setting the exposure to the maximum value that doesn't burn out highlights. (This applies only to images saved in RAW format.) However I wouldn't go too far. A little margin doesn't hurt; there are plenty of levels in 12-bit A-to-D converters"

This non-linearity could be compensated for with camera profiles, but I wouldn't count on it. Highlight recovery in ACR is great, but IMHO it is no substitute for proper exposure in the first place.


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