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Subject: Re: ACR Calibration



Les,

I think the touchstone for any existing or new calibration procedure is to risk an unbiased numerical comparison with Camera Raw’s native state. It requires to process the captured target in two different ways:

1.) in any preferred way which represents your new calibration.

2.) whitebal the second gray, set Exposure to minus 1, stay with the preset tonecurve from Shadows, Brightness and Contrast (shipping default, without auto-correction), Saturation 0, Luminosity curve linear and all Calibration tab sliders in their zero position.

After Raw processing, run a moderate Gaussian blur to average noise. Then, measure & calculate the difference to Bruce’s chart, respectively, in terms of deltaHSB-hue and deltaHSB-saturation for every single color patch. Take care to have everything in the same working space.
Key indicators are the sum of all deviations (ignoring +/-) as well as the number of patches which deviate by 5 steps or more; the troublemakers.

Would you like to support your proposal by adding the results of this test?

To be clear, I have no doubts that more pleasing results (‘observational in nature’) can be achieved by a fortune redistribution of all color errors involved. Also, ACR calibration allows you to rededicate the coloring to a different tonal state (tonality and color are intimately connected with each other).
However, the core question is, if batch deviations of cameras can occur to a measurable extend, so that ACR calibration would effectively lead to a reduction of the total error.

Peter

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