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Subject: Re: ACR Calibration





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




Certainly. Sounds like a reasonable approach. And many thanks to you and Rags for the continuing input.

I've manually compared the before and after calibration RGB values but never simply set the exposure to minus 1 as you suggest. Just left everything at defaults with exposure at 0. Any suggestions for numerically measuring saturation?

I've run Rags' color checker script on the default vs. my settings and noticed some glaring differences (but will reprocess defaults as you suggest and blur). I'm not much at authoring javascript so will just recalculate numbers provided in Rags' color checker given the values are slighlty different for the GM prophoto chart (115 vs. 122 for red in the red patch, for example). A quick look at previous results from Rags' script indicates the largest single hue deviation (RGB) in my calibration to be +7 (corrected value) with all others well within 5 levels whereas the ACR defaults produced a great many "deviants" as high (low) as -55. Obviously, I was not happy witht the default settings and the numbers confirmed why. Faces were coming out way too red, greens too yellow and well saturated colors (particlarly red) often contained lots of unexplainable noise.

I see you and Rags have different ideas about the role of the exposure slider but I found that the histogram for the color chart capture only occupies about one half of the available dynamic range of my camera. So a "proper" exposure is really a bit more subjective than ideal for our purposes. This is why I took four different exposures, progressively moving the narrow histogram to the right. Didn't seem to make much difference, though the exposure with the histogram furthest right visually appeared overexposed at ACR defaults. But I'll try Rags method, too.

At this point, this is all for fun so will first fetch some Oregon micro brew and chips - will report back as time allows!

Cheers,

Les

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