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Subject: Re: ACR Calibration

For example, here are the results for three different exposures from my
300D, with Exposure and Brightness adjusted to get the white patch to
around 245 and the green value in the green patch to 124.

Bruce I assume you are first using the exposure to get the white patch to 245 and then using the brightness slider to get the green patch to 124. Further assuming contrast at 25, shadows at 5 and saturation to 0 with linear tone curve and all calibration sliders to 0.

My results:


White balance 5200K Tint -16 (you didn't provide this info. for your files)

Red: 131 64 53
Light Skin: 164 139 118
Green: 86 124 74
Yellow green: 145 169 77
Blue: 50 46 114
Blue Sky: 90 100 132

If the variation in strobes can make for this large a variation between our two cameras then it might be safe to assume that calibration is a useless concept unless one calibrates to a specific light source, brand, model #, etc. Obviously outdoor lighting would make calibration a nightmare at best.

Furthermore, I find that I consistently need to apply a +2 parameter color correction when shooting jpeg in order to avoid browns with a pronounced reddish tone and/or realistic skin tones with this particular camera.

I am now inclined to think the significant variation is perhpas inherent to the sensor in the Digital Rebel - I'm unconvinced that there is enough of a variation in commercial strobes to produce this great a difference.

But if you would provide your white balance/tint values, it would be helpful in assesing this hypothesis.


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