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CS 101 – Sept. 16

CS 101 – Sept. 16. Finish color representation RGB √ CMY HSB Indexed color Chapter 4 – how computers think Begin with basic building blocks. Color rep’ns. RGB – system based on light CMY – based on printing HSB – based on art Indexed color – a swatch to save space. RGB system.

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CS 101 – Sept. 16

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  1. CS 101 – Sept. 16 • Finish color representation • RGB √ • CMY • HSB • Indexed color • Chapter 4 – how computers think • Begin with basic building blocks

  2. Color rep’ns • RGB – system based on light • CMY – based on printing • HSB – based on art • Indexed color – a swatch to save space

  3. RGB system • Based on primary colors for light • Each pixel has (red, green, blue) values. • Examples black = (0, 0, 0) purple = (75, 0, 100) white = (255, 255, 255) • How about (x, x, x) or (0, 0, x) ?

  4. RGB examples

  5. CMY system • Based on primary colors of printing • Each pixel has (cyan, magenta, yellow) values • In contrast to RGB: white = (0, 0, 0) black = (255, 255, 255)

  6. CMY examples

  7. Practical notes • Printout may look different to screen • Ex. RGB blue = (0, 0, 255) but CMY blue = (255, 255, 0) In other words, in color printer, 2 different toners required to produce blue. • CMY, a.k.a. CMYK

  8. HSB system • From artistic standpoint, neither RGB nor CMY makes much sense to people  • More intuitive color definition: • Hue = what color you want • Saturation = how much of that color • Brightness

  9. Hue = which direction on color wheel Saturation = how far from center Brightness = how far up or down HSB geometry

  10. brightness Trade-off between saturation and brightness hue saturation

  11. Indexed color • Do we really need 16,777,216 colors? • ~ 200 is more practical • Indexed color is like RGB: • 6 values of each primary color, not 256 • Hex values: 00, 33, 66, 99, cc, ff • 1 byte per pixel instead of 3 • Dithering to simulate in-between colors

  12. Chapter 4 Begin chapter on computer organization • Logic gates • Used to perform math operations • Later: finite automata • basic model of computation

  13. Basic building blocks Usually 2 inputs X, Y could be 0 or 1. 1 = true 0 = false By combining 2+ gates, you get more sophisticated functions Logic Gates

  14. ‘AND’ and ‘OR’

  15. Adder • We can teach the computer how to add using just a few logic gates. • However, we need to look at one more gate, the XOR.

  16. XOR basically says “either, but not both” The output is 1 if both inputs are different. Exclusive or (XOR)

  17. Adder • Here is the logic to add, one bit at a time.

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