VA1160 Class 05

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VA1160 Class 05

  1. 1. VA1160 Class 05 Introduction to Computer Graphics
  2. 2. Computer Graphics “ Perhaps the best way to define computer graphics is to find out what it is not. It is not a machine. It is not a computer, nor a group of computer programs. It is not the know-how of a graphic designer, a programmer, a writer, a motion picture specialist, or a reproduction specialist. Computer graphics is all these – a consciously managed and documented technology directed toward communicating information accurately and descriptively.” Computer Graphics, by William A. Fetter, 1966
  3. 3. Topics Photo-taking (self portrait) Short history Terminology Exercise 1 Understand a computer image Exercise 2 Source of images
  4. 4. History A very brief history of computer graphics.
  5. 5. Ben Laposky – 1950
  6. 6. Oscilloscope Art – Robin Fox
  7. 7. Steve Russell
  8. 8. Spacewar
  9. 9. Early computer graphics Computer graphics as science Plotter based graphics Karl Sims Manfred Mohr Frieder Nake Georg Nee Harold Cohen
  10. 10. Early computer graphics
  11. 11. Karl Sims
  12. 12. Manfred Mohr
  13. 13. Manfred Mohr
  14. 14. Frieder Nake
  15. 15. Frieder Nake
  16. 16. Georg Nee
  17. 17. Georg Nee
  18. 18. Roman Verostko
  19. 19. Harold Cohen - Aaron
  20. 20. Harold Cohen - Aaron
  21. 21. TRON
  22. 22. Contemporary computer graphics Network art Software art Interactive art Music video Parody
  23. 23. Vuk Cosic http://www.ljudmila.org/~vuk/ascii/film/
  24. 24. Alexei Shulgin http://www.c3.hu/collection/form/
  25. 25. Mark Napier http://www.potatoland.org/
  26. 26. Casey Reas
  27. 27. Autechre
  28. 28. Radiohead
  29. 29. Thriller
  30. 30. Digital Graphics Vector graphics Raster graphics
  31. 31. Vector Graphics – examples from VA2650
  32. 32. Raster Graphics – Vanity Fair, Nick Knight
  33. 33. Raster Graphics
  34. 34. Grid A raster graphics image is a 2 dimensional rectangular grid. Its dimensions are defined by its width and height . Each cell in the grid is a pixel (picture element). It is the smallest visible element of a digital image. Each pixel contains a piece of colour information.
  35. 35. Digital Colour There are different ways to describe a colour. By name: red, orange, cobalt blue, brown, lilac, …
  36. 36. Digital Colour There are different ways to describe a colour. By name: red, orange, cobalt blue, brown, lilac, … It is, however, not exact. We need to have a systematic way to describe it.
  37. 37. RGB
  38. 38. RGB A colour is uniquely defined by three numbers. Usually, the range of the 3 numbers are from 0 to 255. R: 0 – 255 G: 0 – 255 B: 0 – 255 For example, yellow is defined as R=255, G=255, B=0. It is mainly used in computer screen display.
  39. 39. RGB – colour wheel
  40. 40. RGB Try to experiment with RGB colour information in Photoshop.
  41. 41. CMYK
  42. 42. CMYK A colour is uniquely defined by four numbers. Usually, the range of the 4 numbers are from 0% to 99%. C: 0 – 99 M: 0 – 99 Y: 0 – 99 K: 0 – 99 For example, yellow is defined as C=0, M=99, Y=99, K=0. It is mainly used in printing, i.e. process colour.
  43. 43. Others There are other ways to specify colours, HSB (Hue, Saturation, Brightness) Lab (Lightness, a, b) Indexed colour
  44. 44. Web Safe Index Colour
  45. 45. Size of Colour Information To calculate the size of colour information, say, a 800 x 600 image: Number of pixels: 800 x 600 = 480,000 Each pixel has R, G, B. Each colour number ranges from 0 – 255. To represent a number within this range, we have to use 1 byte. For each pixel, we use 3 bytes to store the colour information. The total size of colour information is: 480,000 x 3 = 1,440,000 bytes, i.e. 1.4 Mb.
  46. 46. Size of Colour Information It will take too much memory to store an image. Usually, we’ll use some compression methods to store the image in memory.
  47. 47. Compression Compression will reduce the file size of an image, by removing redundancy in colour information. There are 2 types of compression: Lossy compression (loss of information when de-compressed) Lossless compression (without loss of information)
  48. 48. Lossy Lossy compression, e.g. JPEG Take a look of the file size in JPG.
  49. 49. Lossless Lossless compression, e.g. TIF, PNG Check the file size of your photos compressed in TIF, PNG.
  50. 50. Transparency For a digital image, we can also include the 4 th colour number, transparency or alpha channel. In this case, each pixel contains, Alpha (A), Red (R), Green (G), Blue (B). It is similar to the use of mask in photography. A white pixel will reveal the image, while a black pixel will mask it. We test the use of transparency in Photoshop.
  51. 51. Example – gray scale
  52. 52. Example - bitmap
  53. 53. Example - bitmap
  54. 54. Example – indexed colour (256)
  55. 55. Example – indexed colour (256)
  56. 56. Example - duotone
  57. 57. Example – inverse colour
  58. 58. Example – 4 colours
  59. 59. Exercises Experiment in Photoshop on colour mode, layer, etc.
  60. 60. flickr
  61. 61. gettyimages
  62. 62. stock.xchng
  63. 63. Google images
  64. 64. Sources http://images.google.com http://www.sxc.hu/ http://www.gettyimages.com/ http://www.flickr.com/

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