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Subject: Re: Exposure to the right and tone placement

Bill Janes wrote:

-->Nonetheless, the point of my post discussing digital counting statistics (and on which you made no comment) was that doubling of exposure decreases noise by only a factor of 1.4, whereas blowing the highlights can cause a loss of thousands of highlight tones (if your camera does not have lossy compression).

Bruce Fraser replied:

-->6 weeks off does wonders for clearing the mind. You've got it exactly backwards.

-->Blowing the highlights doesn't cause a loss of tones. It simply renders everything above the clipping point as white. The camera devotes the full range of tones it can capture to everything darker than the blown highlights. If it's a 12-bit camera, it'll use 1 bit to describe white (the blown highlights), and the remaining 4095 bits to describe everything in the scene darker than that.

In all due respect Bruce, please read my assertion again. I stated that blowing the highlights would cause loss of HIGHLIGHT TONES, not the total number of tones. With overexposure, the vital highlight tones in the SCENE are lost through clipping.

Of course it would be nice to place the highlights at 4096, but you have already admitted that the tools to so so reliably are not available. You can either bracket or leave yourself a little headroom at the top.

Overexposure will give you 4096 tones, but they will not be the 4096 that you need. Most agree that for final output 256 tones is all that the eye can differentiate, but they had better be the right 256 tones.



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