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

This is a very interesting thread and I especially appreciate the participation in the thread by experts such as Bruce and Jeff. However, experts sometimes get tangled up in minutia that some of us can not follow. The following observations are offered for comment.

Ansel Adams' approach was to expose for the shadows and develop for the highlights. However, he was working with negatives. With transparency film the situation is reversed and the situation with respect to digital is similar to transparency film. You should expose in digital so that the important highlight detail is at the right end of the histogram. If the contrast of the subject is greater than the dynamic range of the camera, you have to make a reasoned compromise.

For a given reading from a Gossen or any other light meter, the response of the digital sensor is quite predictable if the proper calibration has been carried out. In the studio you can take a reading from the highlights with your Gossen meter, but with a distant scene you can not isolate the highlights with the Gossen meter and a spot meter is needed to do this.

The characteristic curve of film is log with a toe and shoulder and the digital sensor is linear. However, in practice we always apply a gamma correction to the raw data and the digital capture is now in log format. Gamma in digital is similar to contrast in film and the linear portion of the H&D curve is also called gamma. If you want to approximate the toe and shoulder of film, you can apply a curve in ACR 3.X. Norman Koren has a good essay on how to do this on his web site (however, he does not use camera raw).

In summary, the concepts we learned with film are equally applicable to digital.


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