color.slides.printing.6

color.slides.printing.6 - Light and Wavelengths CS 450...

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CS 450: Introduction to Digital Signal and Image Processing Color Processing Light and Wavelengths Visible light is in the range 400 nm (blue) to 700 nm (red). Perception of Light Cones have three different kinds of color-sensitive pigments, each responding to a different range of wavelengths. These are roughly “red”, “green”, and “blue” in their peak response but each responds to a wide range of wavelengths. The combination of the responses of these different receptors gives us our color perception. This is called the tristimulus model of color vision. Cones and Wavelengths (From G&W, individual cone responses normalized) Relative responses of the three different cones Cones and Wavelengths The sensitivity and number of the three types of cones are different More sensitive overall to green and red than to blue Luminous Efficiency Function • The luminous efficiency function combines the responses of all three to measure perceived brightness for different wavelengths
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RGB Color Model Simplest model is just to store red, green, and blue values Colors can be thought of as points in a RGB cube RGB Color Channels “Web Safe” Colors Primaries and Secondaries Primary colors: ones mixed to make other colors Secondary colors: pairwise combinations of primaries Can be additive or subtractive CMY Model Subtractive media absorb rather than emit light Real-world objects – Paint Printing ink The perceived color is what is not absorbed (reflected) CMY based on subtractive primaries: cyan (C), magenta (M), and yellow (Y) CMYK Model Problem with CMY model: – Because of imperfect primaries, can’t entirely absorb all colored light (i.e., make black) – Usually produces a dark greyish brown Solution: add black (K) as a fourth primary CMYK most common model for printers
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