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Once you have initially roughed in the RGB channels for the White ColorCheck square, it its time to look at the dark side .
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3) Move the camera over the black square on the ColorChecker standard.
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6) Adjust the Red Black and Blue Black Gains until the ratio are close to 1 +/- 0.0105
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The issue with black is that there is very little energy at this level and noise makes up a significant % of the value. The next issue is that the cameras response from bright to dark objects is non-linear. The ColorChecker value is actually near 50 but do not try to obtain that value by jacking up the gain. It just doesn't work! By convention we aim for ~15. Getting a white balance is also difficult. Once you set the green to 15 move the camera so that you are view the next color just above the dark and use the red and blue black gains to get a good white balance. |
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