1. Digitization Informatics INFO I101 January 26, 2004 John C.Paolillo

2. Mars “Anomalies” Are the photos from various Mars missions faked? Do the existing photos show evidence of civilized life? Do the photos show evidence of martians? Etc.

3. http://rush.digitalchainsaw.com/marspath.html

9. Raster Image Digitizaztion Grid –Resolution Quantization –Bit-depth –Color cf. Vector Graphics

10. 1280  960 Great Sand Dunes, Colorado (IRS satellite image; www.spaceimaging.com)

11. 640  480

12. 320  240

13. 160  120

14. 80  60

16. 256 Grays

17. 16 Grays

18. 4 Grays

19. Black and White

20. Digital Artifacts Pixelation (“jaggies”) –From discretization of the analog signal shape color/gray level Resolution mismatches –cause geometric distortions as error accumulates Fix: digital interpolation –dithering –anti-aliasing (especially with fonts)

21. Color

22. Color Perception 3 Electron guns, aimed at 3 different colors of phosphor dots — analog signals 3 types of retinal sensor cells, sensitive to 3 different bands of light

23. Color: Response Patterns red cones green cones blue cones Wavelength 

24. The Eight-Color World Eight colors: black, yellow, magenta, red, cyan, green, blue, white Three color tubes on a TV monitor: Red, Green, Blue 2 3 =8 Additive color relations: red+green+blue=white

25. A Psycho-Physical Encoding Wavelength  110 RGB 101100110010011001101 000111

26. More Colors Recognize more levels in each channel –2 bits per channel: 2 6 = 64 colors –4 bits per channel: 2 12 = 4096 colors –8 bits per channel: 2 24 = 16,777,216 colors Except for 3-bit and 24 bit colors, most standard colors are not in multiples of 3 bits –8 bits (256 colors) –16 bits (32,768 colors) (8 bits is a convenient storage unit)

27. The Color Table A table of some convenient number of values –4, 16, 256, etc. Each location in the table is mapped to some higher resolution color value (24 bit) –Some locations may be unused (mapped to black) A monitor typically uses only one color table at a time

28. Signal Levels Intensity is analog Levels are digital How do we convert analog intensity to digital levels? Quantization: convert analog signals to digital numbers

29. Quantization 1 0 1 0 1 0 1 0 1 0 1 0 1 0 Black White Med Gray 1.Evenly divide signal levels 2.Assign a unique binary number to each recognized level 3.Match signal with recognized levels and round any intermediate signal level to the nearest recognized level 4.Report the signal as a list of binary numbers 000 111 100 011 010 001 110 101

30. Counting in Binary Two values: 0, 1 Each digit is a power of 2 –1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024,... –Fractions: 0.5, 0.25, 0.125, 0.0625, 0.03125,... –positive, negative, rational, real, imaginary... We’ll stick to whole numbers for now

31. Binary counting Start with zero: 00000 Add 1:00001 Adding 1 more carries:00010 Add 1:00011 Adding 1 more carries 2x:00100 Add 1:00101 Etc. OR: Divide the full range into 2 halves, 0 (low) and 1 Divide each range again for each next bit Stop with the last bit

32. End