CS248 Midterm Review - PowerPoint PPT Presentation

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CS248 Midterm Review

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Mon, November 5, 3-5 pm, Gates 392. Mostly 'short answer' questions ... Sensitivity highest in fovea. Frequency sensitivity. Phase sensitivity (Vernier acuity) ... – PowerPoint PPT presentation

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Title: CS248 Midterm Review


1
CS248 Midterm Review
2
CS248 Midterm
  • Mon, November 5, 7-9 pm, Terman Aud
  • Mon, November 5, 3-5 pm, Gates 392
  • Mostly short answer questions
  • Covers through Thursdays lecture

3
Raster Displays, Resolution, Perception
  • Measures of spatial resolution
  • physical vs. addressable resolution
  • CRTs
  • 3 phosphors for red, green, and blue
  • Triads and shadow mask

4
Human spatial frequency sensitivity
  • Sensitivity highest in fovea
  • Frequency sensitivity
  • Phase sensitivity (Vernier acuity)
  • Temporal sensitivity
  • Flicker (50-70Hz)
  • Perceived motion
  • 12 Hz cartoons, 24 Hz film, 60 Hz video

5
Raster Displays, Resolution, Perception
  • Human intensity sensitivity
  • Response to intensity is nonlinear
  • Gamma in cameras, CRTs
  • Gamma correction
  • Dithering
  • Trade off spatial resolution for intensity res.

6
Raster Displays, Resolution, Perception
  • Sample (easy) questions
  • A scene is photographed with a TV camera with
    gamma0.5 and displayed on a CRT with gamma2.4.
    If we want system gamma to be 1.0, we should do
    gamma correction with what exponent?
  • You are doing clustered-dot dithering on an image
    for output on a 300 dpi laser printer. If you
    need at least 75 dpi effective resolution, how
    many shades of gray can you output?

7
Color
  • Perception of color
  • Humans are trichromat
  • Three cones sensitive to red, green, and
    blue
  • Overlapping response curves
  • Color matching
  • Color matching experiment
  • Metamers

8
Color spaces
  • Linear colorspaces
  • ?, ?, ? space (perceptual stimulous)
  • R, G, B space
  • X, Y, Z space
  • Non-linear colorspaces
  • HSV
  • Spectral locus
  • Gamut of reproducible colors

9
Color
  • Sample questions
  • Can your printer necessarily reproduce all colors
    that your monitor can reproduce if they both use
    RGB primaries?
  • You are wearing glasses that block all light from
    the lower third of the visible spectrum, what
    color does the world look tinted?

10
Sampling and Antialiasing
  • The sampling and reconstruction pipeline
  • Prefiltering
  • Sampling
  • Resampling
  • Reconstruction
  • Aliasing
  • Frequency domain interpretation

11
Sampling and Antialiasing
  • Filtering and convolution
  • Prefiltering vs. postfiltering
  • Desirable filters for antialiasing
  • Box, pyramid, gaussian, sync
  • Methods of antialiasing
  • Supersampling
  • Analytic antialiasing

12
Sampling and Antialiasing
  • Sample questions
  • What is the result of convolving a 1-D box filter
    with itself?
  • If we want to be sure to avoid aliasing, should
    we choose a filter slightly narrower or slightly
    wider than a pixel?

13
Digital Compositing
  • The compositing approximation
  • Conditions for validity
  • Deriving alpha mattes
  • Blue screen
  • Computing while rendering
  • Compositing algebra

14
Digital Compositing
  • Sample question
  • You are doing the special effects for a movie,
    and need to composite a computer generated object
    over a live background. Why should you use an
    8-bit alpha matte rather than a binary (1-bit)
    matte, even if the computer-generated object is
    fully opaque?

15
Rasterization
  • Rasterization of lines
  • Definition of one-pixel-thick line which
    points get rasterized?
  • Rasterization of polygons
  • Only pixels in the polygon
  • Supersampling
  • Patterns

16
Rasterization
  • Sample question
  • If you rasterized this line, which pixels would
    get turned on?

17
Transformations
  • Homogeneous coordinates why?
  • Matrices rotation, translation, scale, shear in
    2D, 3D
  • Know the form of each kind
  • Composing transformations
  • multiply matrices in reverse order

18
Transformations
  • Sample question
  • What is the transformation between vector1 and
    vector2?
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