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Cameras could do ETTR quicker and more accurately than humans, and without the risk of actually clipping any pixels. The camera could then write a field to the RAW metadata telling the viewer home much to under-expose to restore the natural exposure.

Most cameras don't have an ETTR metering mode. Is there any reason why — anything I'm missing?

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    \$\begingroup\$ Checkout magiclantern.fm \$\endgroup\$ Commented Jun 27, 2015 at 4:54
  • \$\begingroup\$ Some recent Nikon bodies have a highlight-weighted metering mode that prevents clipping and can be driven to do ETTR with exposure compensation. Nikons tend not do well with ETTR, but the bodies that have HWM have enough dynamic range that you can pull quite a bit out of the underexposed parts. \$\endgroup\$
    – Blrfl
    Commented Jun 28, 2015 at 0:51

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Cameras could do ETTR quicker and more accurately than humans

No, because it is a judgement call what highlights need to be clipped. There is no agreement as to what is photographic dynamic range; and much here depends on the intended use and personal tolerance to noise and artifacts.

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    \$\begingroup\$ There are different definitions of ETTR. The one I had in mind is increasing exposure until just before the brightest pixel clips. Increasing exposure beyond that is a judgement call. But until this point, it's fine to automate, again as a metering mode, to be used when desired. \$\endgroup\$ Commented Jun 28, 2015 at 7:29
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    \$\begingroup\$ @Kartick Vaddadi : sorry, that is a wrong definition, it does not work, and it results in the opposite to what ETTR tries to achieve. However if a camera has a spotmeter, there is no problem in doing it; but at least in doing so one is aware what exactly happens. \$\endgroup\$
    – Iliah Borg
    Commented Jun 28, 2015 at 14:51
  • \$\begingroup\$ I disagree that my definition is wrong. photo.stackexchange.com/a/23010/22575 , for example, says: "The technique works provided you don't increase the exposure to the point where it hits the maximum possible value and gets cut off, as this will result in a loss of information (known as clipping/blowing the highlights)." Nothing prevents you from manually increasing the exposure at the cost of clipping. But not wanting to do so, especially automatically, is perfectly valid as well. \$\endgroup\$ Commented Jul 2, 2015 at 4:39
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    \$\begingroup\$ @Kartick Vaddadi The goal of ETTR is to decrease noise, not to hold the specular highlights or light sources. What you are suggesting is cross purpose. \$\endgroup\$
    – Iliah Borg
    Commented Jul 2, 2015 at 15:19
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    \$\begingroup\$ @ Kartick Vaddadi : > I know that the goal of ETTR is to decrease noise, and that's achieved by having the camera automatically increase exposure until a pixel clips -- No. Specular highlights and light sources mostly need to be clipped. Or the noise is increased. Please familiarize yourself with the reasoning behind exposure meter calibration constants. \$\endgroup\$
    – Iliah Borg
    Commented Jul 2, 2015 at 17:42

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