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Subject: Re: Exposure to the right and tone placement


Leaf certainly does make some fine digital equipment. I have played with both the Valeo and Aptus backs. I wish that I could afford one.

I reviewed the Aptus 25 and 75 a few weeks ago. Unfortunately, I did not get a usable Color Checker image but I did get some shots of jewelry and flowers. With the Leaf software, the jewelry is simply brilliant. With ACR the gems have severe chroma around the facets. They look like plastic. Without calibration I cannot rule this out as the source of the problems. The Adobe histogram indicates a tendency for rather severe clipping in the red channel. The Leaf histogram did not. But clearly different software does different things with the same raw data. Clearly the Leaf software is world class.

In the example shown in your earlier post, 12 f/stops are mapped into 12 of 14 available bits. Naturally, by this definition each bit is one f/stop. Following this logic an 8-bit image can only hold 6 f/stops of light. This is a hard concept for my feeble mind. It doesnít look that different to me. If I repeat it often enough it should become a fact. One bit equals one f/stop. One bit equals one f/stop. One bit equals one f/stop. I got it.

I donít have this software but the exposure adjustments and curves operation seem similar to others. The ability to mark five points (zones?) on a tone curve is useful but not unique. Wouldnít that be mapping the recorded dynamic range into the desired tones and dynamic range? Oops, probably not. Tones, f/stops, bits, they would be all messed up.

I am not confusing raw data and rendered images. It is apparent that I cannot make myself understood. So be it.

My point has been simply that we should not assume that the histogram is a micrometer and a total replacement for exposure metering. ETTR and histograms are excellent tools for sanity checking and can keep you out of trouble. But all histograms are not created equal and they can mislead you.

Gravity is not just a good idea, itís the law.

Cheers, Rags :-)


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