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05/22/2012

Comments

Jim Bullard

I may have sent this to you before but I addressed the ETTR idea in a post back in 2010.

    http://jims-ramblings.blogspot.com/2010/02/right-idea-wrong-reason.html

The notion that there is somehow more information in the brightest pixels is the result of a misunderstanding of how digital files work. ETTR proponents seem to be under the misconception that bright pixels are recorded with more data bits than dark ones. That idea apparently comes from the geometric increase in brightness of increasing exposure. Unfortunately it doesn't work that way. Your gut feeling serves you well.

Chuck Kimmerle

"ETTR proponents seem to be under the misconception that bright pixels are recorded with more data bits than dark ones."

I guess that depends on who you ask. Most of the ETTR proponents I know do so to increase the signal to noise ration in the shadows, and nothing else.

As for more "data bits" that is, as you infer, incorrect. Data "bits" are nothing more than the numerical result of the A/D conversion. However, brighter pixels DO receive more information during capture in the form of photons, which IS the point of ETTR.

Still, I have found that ETTR can, if done over-zealously or on images with very large amounts of highlights, actually be a detriment. Like all things, it must be used in moderation.

Elmar

As Chuck says, the main reason for ETTR is the lesser noise in the image. Especially the shadows (darker image areas) will benefit from ETTR.

In practice I'm observing the blinking highlights on the camera LCD: I know, as soon as the highlights are beginning to blink, I can add 1/2 to 1 f stop whithout losing details in the brightest RAW file areas. The blinking highlights are more important to me than the histogram, because they are telling me where the image has white pixels. If these areas are not important, they can be white.

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