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Subject: Re: ACR Calibration


This is just my two cents on your post.

First, I would disagree with starting from the white patch and adjusting the exposure slider. This would mean that your defaults would always need exposure compensation. White is at the extreme of the luminosity range. Not a very good calibration target. An analogy would be driving on the shoulder of the road at 80mph. Most safe drivers try to keep the hood ornament in the middle of a driving lane.

That is why I recommend shooting a proper exposure and setting brightness to the middle tone. That is calibrating ACR to your camera instead of calibrating your camera to ACR. The exposure tab should play no role in calibration.

Your color calibration steps are sound and match Bruceís suggestions or any others. My only comment would be that if Adobe provided optional watch point metrics in HSB you would not need to do any of the mental or manual calculations. HSB metrics describe these relationships with easily understood numbers. This was proposed as an ACR feature request over two years ago. So far, no response from Adobe.

Finally, it is my belief that tone curves should have no place in calibration. I recommend setting the tone curve to linear. There are two different objectives at play here. Color matching is the objective for calibration. Tone curves alter the contrast in different areas of the image for aesthetic objectives. They alter the color relationships differently at different luminosities. If you had different curves for each channel, you might be able to emulate color matching to some extent. But currently within ACR you donít.

Properly calibrated I find that the color relationships remain consistent within plus or minus one or two exposure stops. This does not seem to hold true with corresponding changes in the ACR exposure slider. And things go all out of kilter with any changes in the tone curves.

This does not mean that the ACR exposure slider is useless. It is very useful when the original exposure was wrong for whatever reason. And it does not mean that the tone curves are useless. Au contraire they are very useful for aesthetic or artistic goals. The same is true for the master (global) saturation slider. Base them all on artistic objectives, not as part of the calibration procedures.

Anyway, that is my personal opinion. Others are free to disagree. The most important point of all is that you took some action to calibrate ACR to your camera. The defaults do not seem to match any camera I have encountered. As long as you are happy with the results of your efforts, nothing else matters.

Cheers, Rags :-)


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