CS 3121 Study Questions: Exam 2

Fall 2009

Revisions:

11/9/09; 12:46pm; Added in chapters covered from Williams book into "Material covered".
11/9/09; 12:55pm; Removed Chapter 9 from Exam 2 coverage-- not covered yet in lecture.
11/11/09; 9:15am; Slight edit to question 25.
11/11/09; 9:17am; In the Chapter 11 review questions, ignore questions other than 65, 69, 70, and 73.

Material covered:

Chapter 4: Bitmap graphics
Chapter 5: Color
Chapter 6: Video
Chapter 8: Sound
Chapter 11: Visual Design
Williams book: Chapters 1-6

Homework questions due: Wednesday, November 11th, 2009 [15 pts]

Homework is due at the start of class on the due date. Late homeworks will not be accepted. Homeworks must be type-written, and not hand-written. Keep a copy of your homework, and bring this with you the day of the quiz/exam review (i.e., the day the homework is due). This should help you in the review session.

Remember: Some of the questions on the exams will be drawn purely from the textbook, and will not have been covered in the class lectures or class lecture notes. Be sure to read the textbook chapter material and other assigned reading!

For the homework, solve only the following 15 problems:

Q #1 [1 pt]
Q #2 [1 pt]
Q #5 [1 pt]
Q #12 [1 pt]
Q #15 [1 pt]
Q #21 [1 pt]
Q #23 [1 pt]
Q #33 [1 pt]
Q #34 [1 pt]
Q #35 [1 pt]
Q #36 [1 pt]
Q #40 [1 pt]
Q #47 [1 pt]
Q #48 [1 pt]
Q #50 [1 pt]

    Chapter 4: Bitmap graphics

  1. What is a pixel? What is a "dot"? How does a dot relate to a pixel?
  2. What is usually intended by "dots per inch" on a computer display?
  3. Why is lines per inch a useful measure for some devices?
  4. Why is samples per inch a useful measure for some devices?
  5. What is special about 72 dpi resolution for images? How does 72 dpi relate to computer monitor resolution?
  6. An image is 1024x720 pixels in size and is rendered on a 100 dpi output device (e.g., a computer monitor). What is the area on the output device covered by the image? What area would be covered if the output device was 300 dpi (assume dots still mean pixels here)?
  7. What is upsampling with respect to images? What is downsampling, also with respect to images?
  8. What does interpolation mean in the context of scaling images?
  9. Which of nearest-neighbor and bicubic scaling take more computational time? Why (give as much specific explanation as you can)?
  10. Is Run-Length Encoding (RLE) lossless or lossy compression? Explain. Does RLE work equally well with all images? Explain.
  11. Briefly explain the algorithm used with dictionary-based compression.
  12. The Discrete Cosine Transform (DCT) compression method makes use of concepts related to spatial frequency in images. Explain what is meant by high versus low spatial frequency in an image. In what way is the concept of spatial frequency useful in compressing images?
  13. What is quantization in the context of images?

    14. Chapter 5: Color

  14. What is a spectral power distribution?
  15. Can RGB represent any possible visible color? Explain.
  16. What is color depth? How does color depth relate to quantization?
  17. Explain dithering in terms of graphical output. Why is a high resolution display (or other visual output device) important if dithering is going to be used?
  18. Clearly distinguish between additive and subtractive color processes. When is a additive color model used? When is a subtractive color model used?
  19. What does it mean for a color space (or model) to be perceptually uniform?
  20. What is YUV? What is the meaning of the Y value? What is the meaning of the U and V values?
  21. If we use 3 bits to represent red, 3 bits to represent green, and 3 bits to represent blue, how many distinct colors can we potentially represent in this color space?
  22. What is a color lookup table (CLUT)? How can it be considered to provide a form of compression?
  23. Consider an image that uses three different "colors": White, Black, and Gray (mid-way between Black and White). Suppose this image uses a CLUT. How many entries would the CLUT have? How many bits would be used in the image to represent a pixel? How wide would the CLUT entries be? (i.e., how many bits per CLUT entry)? Clearly state any assumptions you are making.
  24. How are black & white pixels most efficiently represented in a CLUT? What is the minimum number of entries needed for the CLUT in this case?
  25. For a color-depth of 4 bits, give the layout of a CLUT for a BMP file. Label the parts of your CLUT. Give some possible values for the contents of the CLUT. Be as specific as you can.
  26. What is the sRGB color space?
  27. Explain how a program like Photoshop creates (e.g., saves) an image in an sRGB color space.
  28. Explain how a browser that doesn't know about sRGB renders an image using the sRGB color space.
  29. Explain how a browser that does know about sRGB render an image using the sRGB color space.
  30. What is color management?

    Chapter 6: Video

  31. Define frame rate for motion video.
  32. What is a key frame? What is the key frame rate for motion video?
  33. What is interlacing?
  34. Explain what is meant by 4:2:2 chrominance subsampling. Why is chrominance subsampling used?
  35. With a 360x240 frame resolution, 16 bit color, and 29.97 frames per second, give the exact theoretical (i.e., without compression) video data rate in Mbits/sec (Mbit = 1024*1024 bits).
  36. Given a data rate of 400 Kb/sec (Kb = 1024 bits) where that data rate includes all audio and visual tracks, how large will a video file be that is 60 minutes in duration?
  37. Explain the following sentence: "Perceptual quality is often related to data rate, but perceptual quality is not necessarily proportional to data rate." Also: What would you expect if perceptual quality was proportional to data rate?
  38. A given DV video file contains 461 seconds of video at 29.97 frames per second, has frame resolution 640x480, with 24 bits per pixel, and stereo audio tracks (with 48 kHz sampling, 16 bit samples). The actual DV file stored on disk is 1.55 GB in size. Explain, based on calculations, how you know that DV format is using compressed, as opposed to raw, video.
  39. Explain the textbook distinction between streaming and progressive download video.
  40. How can frame differencing be used in compressing video?
  41. What is generational loss?
  42. What bit rate (Mbits/s) should you select if a video clip is 60s in duration and you desire an end video clip that is 25 Mbytes? (Mbyte = 1024 * 1024 bytes; Mbit = 1024*1024 bits). Assume that all video and audio tracks are included in the bit rate.

    Chapter 8: Sound

  43. Define: cycle, hertz, and amplitude in regards to acoustic waveforms.
  44. Define sampling in terms of analog to digital conversion of an analog audio waveform.
  45. Define quantization in terms of analog to digital conversion of an analog audio waveform.
  46. Sampling and quantization may introduce errors or inaccuracies into the process of analog to digital conversion of an analog audio waveform. Explain.
  47. We talk about a digital sample of sound in a sampling-based representation of sound. What is a digital sound sample?
  48. The units used for sampling rate and sound frequency are both "Hz" (Hertz). Clearly distinguish between audio sampling rate and sound frequency in an audio signal.
  49. In a sampling-based representation of sound, we have to choose a sampling rate. Given that the highest frequency component of sound we have to process is 3,000 Hz, what is the lowest reasonable sampling rate that will accurately represent the sound information? Why? Why do we want the lowest reasonable sampling rate, and not a rate that is higher than this?
  50. How do abrupt changes in sound play into sampling rate? E.g., some instruments have a sudden attack of sound that is very abrupt.
  51. Generally explain the idea of the Nyquist rate in regards to digital audio.
  52. What is the general acoustic range (in Hz) of human sound perception, and what implications does the Nyquist Limit have regarding this?
  53. With a 44,100 Hz sampling rate, 24 bit sound samples, and one channel (mono) recording, give the exact theoretical (i.e., without compression) sound data rate in Kb/sec (Kb = 1024 bits).
  54. Both WAV and MIDI files have a binary file format, and yet WAV is sample-based, and MIDI has (in part) an abstract or language-based format (i.e., it's analogous to vector graphics in its structure). How is it that an abstract format of sound can be represented in a binary file format?
  55. Can sample-based audio file formats be stored in ASCII text files? Explain.
  56. Give examples of the kinds of information stored in a MIDI file.
  57. Sometimes we talk about "statically linked" media versus "dynamically linked" media. Statically linked media is contained within the file we are working with. E.g., WAV files are often statically linked in Macromedia Flash-- the WAV files are contained within the Flash presentation. Dynamically linked media is not contained within the file we are working with. E.g., An "A HREF" tag (without the use of #labels) is often used to link to media outside of the current file. Is the <EMBED> tag used for statically or dynamically linked media?
  58. 16 bit audio samples (as opposed to 8 bit audio samples) work well in CD quality audio because of the Nyquist limit or Sampling Theorem. True or False? Explain.

    Visual layout (Williams)

  59. Name and define Williams' four basic principles of design.
  60. Give a concrete example of each of Williams' four basic principles of design.
  61. There seems to be a relationship between the concept of inattentional blindness and Williams' four basic principles of design. What is the relationship?
  62. Here is a previous (9/15/08) front page for Qwest.com. Using Williams' four basic principles of design, analyse this design. Comment on any existing uses of these principles, and also determine where they might be better or more extensively applied.

    Chapter 11: Design

  63. The textbook mentions four different systematic web site structures. What are these structures? Along with their names, give a brief definitions of the site structures.
  64. Would a purely hierarchical structure be useful for a web site? Yes, No, or Maybe (circle one). Explain.
  65. In a multimedia context, what is a breadcrumb?
  66. The textbook discusses the implications of the following three factors on web page design: (a) download time, (b) hardware & software configuration, (c) user background. Briefly consider (discuss) each of these three issues.
  67. What tangible (i.e., concrete, clearly specified or described) end products do you expect from a design process in interactive multimedia?
  68. What intangible (i.e., ephemeral or less clearly specified or described) results do you expect from a design process in interactive multimedia?
  69. What is meant by usability evaluation of software? How can this be important?
  70. What are user interface guidelines for interactive multimedia design? What advantages can result from using user interface guidelines? What disadvantages can result? (see also Chapter 1 when answering this question).
  71. The textbook suggests that web browsing is not purely a goal-directed activity. What does this mean?
  72. The textbook suggests that a web site should transform gracefully. What does this mean?
  73. Why might it be important to not rely on color exclusively for communicating particular information on a web page?
  74. Is correctness more important than the appearance of a web site? Yes or No? Explain.
  75. How are text-only browsers related to blind computer users?
  76. Why might it be better to use a h1 or h2 (header) tag for a web page heading rather than a p (paragraph) tag?
  77. What is provided by an HTML validation service?
  78. What is contingent motion? How does it differ from animated motion?