Monday, October 8, 2007
Curving RGB Color
Color correcting by numbers is a combination of art and science
The image is looking pretty good at this point (Figure 15). Can we improve it even more? Look at the CMY values for the skin color again. We haven't looked at Cyan yet, and in this image it's a bit lower than the ideal one-third of the average between Yellow and Magenta. Sampling the CMY values at a different point on her skin, it looks like Cyan is low by an average of 10 to 15 points in the highlights and only 3 to 8 points in the shadows.
The opponent of Cyan is Red, so return to the Red Channel and place a point on the curve for the skin. Since I've already balanced the values for her red satin robe, I want to place a point on the curve to lock it down. Reselect the skin point, move the cursor back to the forehead and move that point down with the arrow key (Figure 16).
The Cyan value will increase, but the Yellow and Magenta values also will increase a bit because subtracting Red will make the area brighter. The ratio of Magenta to Yellow also will change a bit because there's more Magenta in Red than Yellow. You'll have to bounce back and forth between Blue and Red to adjust the ratios until you get the values where you want them. Keep watching the black and white points—make small adjustments in the points to keep everything in place while you adjust the skin color.
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