Subject: Re: raw 3.1 professional custom profiles for highend digital cameras
"Again what you are missing is the linear nature of digital and the fact that SO MUCH CRITICAL data is recorded in that brightest stop. Yes, you can meter for the highlights and then open up, but how much? 3-4 stops is simply too imprecise. Is it 3 stops or 4 stops for your sensor to record a textured highlight? If is 4 and you only open 3 stops then you've lost a full 1/2 of all the levels your sensor can capture. "
No Jeff, I am perfectly aware of the linear nature of digital sensors (if you read my post :) ).
When you apply the gamma correction, the linear data becomes log--no one prints pictures with a gamma of 1. If you want to place the highlights, of course you must first calibrate to find the proper amount to open up. Isn't the highlight value on your Minolta meter merely based on standard zone system assumptions (Metered + 3 stops = zone 8, +4 stops = zone 9 as I stated in my post; I did not say open up 3 or 4 stops). I am quite aware of exposing to the right from Michael Reichman's essay on the Luminous Landscape. He was personally advised by Thomas Knoll on this matter.
Throwing away half of the levels that the camera can capture sounds dire, but you must remember that most digital cameras capture 12 bits of data (4096 levels) and only 8 bits (256 levels) are needed for a good print and we can afford to throw some away with seeing posterization in the shadows. If we could capture 16 bits or more (already possible with some high end backs) good exposure would be quite a bit less critical, much like the situation with black and white film (which can withstand quite a bit of overexposure but little underexposure). Sometimes exposing to the right is more important to avoid the noise in the lower pixel levels than preserving the maximum number of levels.
Personally, I find the in camera histogram is a pretty good guide if you previsualize the nature of the highlights and take specular highlights into account (yes, I know the histogram shows the gamma corrected data with a tone curve applied). If in doubt, bracket.
However, even with the best technique the tolerances are within 1/2 or 1/3 stop. In practice, you will either have to waste some of those precious bits, bracket or run the chance of blowing your highlights. That is no different from Kodachrome. Indeed, the Nikon digital slr metering is from the F5 film camera--the same principles apply to film and digital once you account for the characteristics of each medium. Nikon did not develop a special meter for digital
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