What about multimedia P hotos audio and video Same principles Color and the Mystery of Light Color image Grid of pixels Pixel is formed from three primary colors RGB Showing Colors Colors formed by using 3 ID: 1044364
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2. Digitizing DataText is easyWhat about multimedia?Photos, audio, and videoSame principles
3. Color and the Mystery of LightColor imageGrid of pixelsPixel is formed from three primary colorsRGB
4. Showing ColorsColors formed by using 3 intensities of primariesFull intensity red, green, or blueFull intensity of red, green, and blue?No intensity of any color?Other combinations
5. LCD Display TechnologyClose-up of white arrow pointerNote subpixels
6. Black and White ColorsIntensity of light color stored in byteNeeds 3 bytes/pixelSmallest intensity is 0000 0000Decimal?Largest value is 1111 1111Decimal?
7. Black and White ColorsBlack is absence of light:0000 0000 0000 0000 0000 0000White is full intensity of each color:1111 1111 1111 1111 1111 1111
8. Color IntensitiesConsider blue (0000 0000 0000 0000 1111 1111)8 bits have position valuesTo cut intensity in half128643216842111111111128643216842110000000
9. Color Intensities
10. Decimal to BinaryHow to convert decimal to binary?Look for powers of 2 and subtractE.g.: Convert 365 to binary
11. Lighten Up: Changing Color by AdditionWhat color does this represent?1100 1000 1100 1000 1100 1000It’s RGB (200, 200, 200), a grey#C8 C8 C8 in hexAll grays of form (x, x, x)
12. To Increase Intensity: Add in BinaryIncrease common value to lightenE.g., add 0001 0000 (decimal 16) to each color1101 1000 1101 1000 1101 1000 RGB (216,216,216)
13. LighteningAdding another 16… 1101 1000+ 0001 0000----------------- Check using decimal!
14. Lighter Still: Adding with Carry DigitsBinary addition is similar to decimal additionWork from right to left0 + 0 = 0, 0 + 1 = 1, 1 + 0 = 1No carry1 + 1 = 0Carry of 1
15. Binary Addition
16. Binary Addition
17. Binary Addition
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19. Computing on RepresentationsExample: changing the brightness and contrast of a photo
20. Brightness and ContrastBrightnessHow close to whiteContrastDifference b/w darkest and lightest portions of imagePhoto manipulation software often gives values of pixels in a Levels graph
21. Levels Graph0 percent is black point (0, 0, 0)100 percent is white point (ff, ff, ff)Midpoint of pixel range is gamma point
22. BrightnessShift pixels closer to whiteAdd 16 to each pixelE.g.:(197, 197, 197) =>(213, 213, 213)
23. ContrastScale pixel rangeStretch toward rightAdd to each pixel, butadd a smaller amount for dark pixelsadd a larger amount for light pixels
24. New Levels Graph
25. Adding ColorColor => (x, y, z), all 3 differExampleColorize image of moon
26. Making the Moon OrangeTint white regionsPick a shade of orange, say (255,213,132)Tint light grayRed byte: leave unchangedGreen byte: reduce green slightly (subtract 42)Blue byte: reduce blue significantly (subtract 123)
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28. Digitizing SoundVibrating object creates soundVibrations “push” air to form pressure waveWave vibrates our eardrums
29. Digitizing SoundIntensity of push determines volumeFrequency (# of waves per second) of pushes determines pitchcontinuous (analog) representation of the wave
30. Analog to DigitalNeed to digitize to bitsUse binary # for amplitude of waveAt what point do you measure? Infinitely many possible
31. Analog to DigitalSample at regular intervalsSamples/second is sampling rate
32. Nyquist Rule for SamplingSampling rate is keyNyquist rule Sampling rate must 2x highest frequencyRange of human hearing 20 Hz – 20 KHzDigital audio sampling rate is 44.1 KHz
33. Digitizing Process
34. Digitizing ProcessRecording (digitizing) processSound => micSignal sampled by ADCSamples encoded in binary
35. Digitizing ProcessPlaying processNumbers read by DACElectrical wave created by interpolationElectrical signal => speaker
36. How Many Bits per Sample?Perfect accuracy requires unlimited bits/sampleMust handle both +/- valuesMore bits => more accuracy
37. How Many Bits per Sample?More bits yields a more accurate digitizationDigital audio uses 16 bits
38. Advantages of Digital SoundKey advantage is ability to compute on representationRemove noiseCompressionLossless LossyFrequencies outside our range
39. Advantages of Digital SoundMP3 formatAllows for compression ratio > 10:1Another key advantage of digital representations is exact reproduction
40. Digital Images and VideoImage is grid of RGB pixelsStored as linear sequenceCan take up a lot of space
41. Digital Images and VideoExample8 × 10 image scanned at 300 ppiHow many bytes to store?Sending across 56 Kb/s phone connection requires how many minutes?
42. Image CompressionTypical monitor has fewer than 100 ppi9x space saving over 300 ppiStill requires more than 5.5 min to send
43. Image CompressionCompression changes rep to use fewer bitsExample: faxesFaxes are a sequences of 0’s and 1’sUse run-length encoding
44. CompressionRun-length encoding is “lossless”Opposite is “lossy compression”
45. CompressionMP-3Lossy schemeHighs and lows lostJPG (or JPEG)Lossy scheme for imagesExploits limits of human perceptionLuminance sensitivityChrominance insensitivity
46. JPEG CompressionJPEG is capable of 10:1 compression w/o detectable loss of clarity
47. JPEG CompressionRatios higher than 10:1Smaller filesPossible artifacts (pixelation)
48. MPEG CompressionMPEG used for videoVideo is sequence of stillsEach image/frame is not seen for long
49. MPEG CompressionJPEG used to compress frames“Interframe coherency” is usedMPEG compression only transmits “deltas” b/w framesResults in significant compression
50. Optical Character RecognitionOCRConverts images of characters to charactersUsed by U.S.P.S.Used in bankingUsed in automatic license-plate recognition
51. Virtual RealityVRSimulates real-world environmentDigitizes 3D space, soundUses head-mounted displaysTraining: surgeons, military
52. Haptic DevicesHaptic devicesUsed in VRInput/output technology for sense of touchGloves can apply forces
53. LatencyChallenges with VRLatencyTime it takes for info to be recv’dBandwidthInfo per unit timeFundamental limit: speed of light
54. Bits Are It!4 bytes can represent different infoNumber 4 charactersColoretc. Bias-Free Universal Medium PrincipleBits can represent all discrete infoBits have no inherent meaning
55. Bits: Bias-FreeWhat does this bit sequence represent? 0000 0000 1111 0001 0000 1000 0010 0000 In hex: 00 F1 08 20 Depends on context
56. Bits are bits…
57. SummaryRGB colorManipulating imagesBinary numbers and arithmeticDigitizing sound, images, videoCompression
58. SummaryOCRVirtual RealityLatency and BandwidthBias-Free Universal Medium Principle
59. QuizHow many colors can 9 bits represent?1010 + 0110 = ?Convert C7 to binary