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 ColorRGB black000 white255 red25500 green02550 blue00255 cyan0255 magenta2550 yellow255 0

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 ColorCMY white000 black255 cyan25500 magenta02550 yellow00255 red0255 green2550 blue255 0

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

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

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. Logic Gates 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

14. ‘AND’ and ‘OR’ AND XYans 111 100 010 000 OR XYans 111 101 011 000

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. Exclusive or (XOR) XOR basically says “either, but not both” The output is 1 if both inputs are different. XOR XYAns 110 101 011 000

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