Applying the Subtract command

To create the first example in Figure 13-26, I selected the Subtract option from the Blending pop-up menu, once again accepting the default Scale and Offset values of 1 and 0, respectively. This time, the thinker turned pitch black because I subtracted the light values of his face from the light values in the sky, leaving no brightness value at all. Meanwhile, the thinker's hair had virtually no effect on the sunset because the hair pixels were very dark and in some cases black. Subtracting black from a color is like subtracting 0 from a number — it leaves the value unchanged.

Subtract, Scale: 1, Offset: 0

Figure 13-26: Two applications of the Subtract command on the images from Figure 13-25, one subject to Scale and Offset values of 1 and 0 (top) and the other subject to values of 1.2 and 180 (bottom).

Subtract, Scale: 1.2, Offset: 180

Figure 13-26: Two applications of the Subtract command on the images from Figure 13-25, one subject to Scale and Offset values of 1 and 0 (top) and the other subject to values of 1.2 and 180 (bottom).

The result struck me as too dark, so I lightened it by raising the Scale and Offset values. To create the second image in Figure 13-26, I upped the Scale value to 1.2, just as in the second Add example, which actually darkened the image slightly. Then I raised the Offset value to 180, thus adding 180 points of brightness value to each pixel. This second image is more likely to survive reproduction with all detail intact.

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