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Subject: Re: ACR Calibration

(*) Famous comparisons “before vs. after / calibrated state vs. simulated
target” can create the polite fiction of an improvement via calibration.
It ignores the side effect from tonal changes on color saturation. IMO,
it’s more reasonable to assume that Adobe’s profiling software aims to
balance the whole coloring – hue and saturation - under consideration
of the default tone curve from Shadows, Brightness and Contrast settings.

Peter, good point. But I've found that saving one's initial tonal calibrations as a new default (along with color calibration) effectively overcomes this problem. Indeed, running Rags' (and Tom's)script(s) gave substatntially different color profiles depending upon the initial exposure and tonal settings. Clearly, tonal changes do have an effect on color with ACR, especially saturation.

I now leave shadows, contrast, saturation and curves at their new defaults (0,15,-9 and linear for my Canon 300D and 17-40 lens, for example) when applying the new color calibration(s). These values were obtained via an initial neutral patch calibration process. Occasional tweaks to white balance, exposure and brightness are now generally all that are needed prior to conversion using ACR.

I used to rely heavily on a time consuming process using curves and hue/saturation in PS to achieve correct color balance for routine work but now all that is generally needed (aside from the usual sharpening and occasional shadows/highlight adjustment) is a slight curves tone adjustment (in luminosity mode) to get things "right" in order to balance tone with accurate color. Noise problems for certain images have been substantially reduced, as well. And "default" skin tones are truly awesome for a change!

I have found that the further a given file deviates from the white balance used to shoot the color chart (5200K in my case) the more that hue or curves color adjustments are needed but it does appear that the reasonably accurate range for this given calibration temperature is from 4800K up to 5600K or so. Outside of this range corrections become increasingly necessary but still far short of that needed when using an uncalibrated RAW conversion.

Color (and tone) calibration has proven to be a substantial time saver for me even though I struggled to figure things out initially. But selectively using bits and pieces of advice from both Rags and Bruce Fraser in particular have been extremely helful. I'm also finding the ongoing technical discussion quite informative, as well.

It certainly would be beneficial if Adobe would provide more information so that others might profile their cameras/lenses more easily. It can be an intimidating process but I am beginning to suspect quite strongly that perhpas the outcome of Adobe's calibration process we see in ACR's initial defaults may simply represent an average for all cameras supported.


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