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Subject: Re: raw 3.1 professional custom profiles for highend digital cameras

Bill Janes wrote:

"Linear recording wastes many bits in the highlights by recording more gradations that our eyes can differentiate and not enough in the shadow areas where our eyes can detect small realative differences in intensity. A log scale is more efficient."

Jeff Schewe Replied:

"Wastes? Well, if the user doesn't do anything with the additional date, yes, it's wasted. But if you tone map it correctly then those higher density of levels at the higher range become useful. A log scale is what you end up with _AFTER_ conversion and tone mapping. But there's nothing one can do to CHANGE the nature of sensors-they are linear, so you have to adapt the way you capture and process to bring out the tonality you want/need."


How many levels do you need in Zone I? Twelve bit encoding will give you 2048, but the eye can differentiate only about 60. This derives from the Weber-Fechner law which states that the eye is not sensitive to absolute differences in luminance but to proportional differences, with the perceptible difference amounting to about 1 percent. For details see the link below;

The fact is that the highlights contain ample data for any practical purpose even if you place them 1 or 2 stops low. However, as Bruce points out a low placement can get you into trouble with shadow noise and posterization.


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