From the course: Photoshop for Designers: Color

Additive and subtractive color - Photoshop Tutorial

From the course: Photoshop for Designers: Color

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Additive and subtractive color

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- [Instructor] In this movie, I'm going to talk about Photoshop's color modes. They're all up here on the image mode menu. I'll begin with a discussion of additive and subtractive color and the differences between the RGB and CMYK color modes. Our images begin in the RGB color mode. RGB is the color mode of monitors, digital cameras, and scanners. If you're creating an image for off-set printing at some point that image will need to be converted to the CMYK color mode. At exactly what poin in the work flow is debatable. And I'll talk about that in the movie on color management. But for now, what we have is a diagram of the additive or RGB color mode. RGB colors are the colors of light. So if I come to my layers panel, and open this layer group and select by holding down the shift key these three shape layers, and change the blend mode to lighten, what we see is an interaction of the red, the green and the blue and where they interact. Where the red and the green interact we have yellow. Where the green and the blue interact, cyan. Where the blue and the red interact, we have magenta. So here within the center, we have our subtracted primaries, as cyan, magenta and yellow. Since RGB is the color of light, where all of them interact, where the red, the green and the blue interact at their maximum level, we have white at the center of our three circles. What I'm going to do now is come to the top of my layer stack and add an invert adjustment layer. Now when I invert, what we see is the subtractive color model, the cyan, magenta and the yellow. And where the cyan and magenta overlap we have blue. Magenta and yellow, the red. The yellow and the cyan we have the green. Where all three overlap, where we have the maximum ink, not light, we have black. Now in practice with offset printing, because of ink impurities, cyan, magenta, yellow at 100% results in a muddy brown. So that's why there is a fourth color channel, the K. And the K stands for key, and it's the black channel or key channel that provides contrast in CMYK images.

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