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Computer Graphics > 02 - Perception and Color > Flashcards

02 - Perception and Color Flashcards

1
Q

How does a “Cathode Ray Tube (CRT)” work? What’s a technique used by the CRT?

A
  • cathodes shoot electron beams through focusing and deflection coils
  • shadow mask places beam at fluorescent coating with RGB pixels
  • it uses a “frame buffer”
    -> independent of computational cost
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2
Q

How does a “Liquid Crystal Display (LCD)” work

A
  • two coated glass plates with liquid crystals in between
  • voltage determines orientation of crystals
  • liquid crystals modify polarization of light
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3
Q

What’s the difference between “Vector Graphics” and “Raster Graphics”

A

Vector Graphics
- resolution independent representation

Raster Graphics
- image buildup independent of scene complexity
- finite pixel number -> “aliasing” and “Moiré effect”
- no object access

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4
Q

What is “Aliasing”? What causes it?

A
  • pattern that aren’t real in sampled images
  • caused by under sampling
    -> merging of highs and lows to an average value
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5
Q

What is the “Moiré Effect”?

A
  • super position effect
  • interference patterns
  • frequency depends on angle
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6
Q

What are spectral colors?

A
  • monochromatic light
  • only one wavelength
    -> appear bright and clear
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7
Q

What is a “Plane Angle”? How do you calculate it?

A
  • angle of a curve from a point
  • L/r
    -> L being the arclength of the projection of the curve onto the unit circle
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8
Q

What is a “Solid Angle”? How do you calculate it?

A
  • amount of field of view covered by an object from a point
  • F/r^2
    -> F being the projection onto the unit sphere
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9
Q

What’s illumination

A
  • consist of many wavelength
  • each wavelength with a certain intensity
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10
Q

What are the most important parts of the eye (3) and their characteristics

A

Retina:
- houses light sensitive cells

Fovea:
- sharpest vision

Foveola:
- sharpest vision of Fovea

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11
Q

What types of cells are in the eye? Where are they placed?

A
  • cones (few, central, colors -> trichromatic)
  • rods (many, peripheral, black-white-vision -> monochromatic)
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12
Q

What’s the “Opponent Process”? What’s the effect of this?

A
  • brains color scheme: 1 achromatic, 2 chromatic
  • red-green
  • blue-yellow
  • ganglion cells consist of these photoreceptors
  • when both parts are activated, they cancel each other out
    -> no reddish-green
    -> no blueish-yellow
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13
Q

What are “Mach Bands”? What causes them?

A
  • brighter or darker edges in gradient
  • caused by contrasts in receptive fields that amplify contrast
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14
Q

What is the “Trichromatic Color Vision”? How are colors formed? How can this effect perception?

A
  • perceptual response to different wavelength
  • colors are the integrals of the cone responses
  • different wavelengths / intensities can create same response
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15
Q

What is a “Metamerism”

A
  • two different spectra
  • cause identical response in receptors
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16
Q

What are the two types of “Color Mixing” and their colors? Where are each used?

A

Additive (e.g. screens, projectors):
- red
- green
- blue

Subtractive (e.g. printers, color pens):
- cyan
- magenta
- yellow

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17
Q

What is “Grassman’s Law”

A
  • every color representable by 3 basic quantities
    -> 3-dimensional quantity
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18
Q

How does the “RGB Color Space” work

A
  • 3 primary colors
  • C = rR + gG + bB -> (r,g,b) in [0,1]^3
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19
Q

How does the “CMY(K) Color Space” work

A
  • dual space to RGB
    C = 1 - R
    M = 1 - G
    Y = 1 - B

For CMYK -> covering + saving ink
K = min(C, M, Y)
C’ = C - K
M’ = M - K
Y’ = Y - K

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20
Q

How does the “HSV Color Space” work

A
  • neither additive nor subtractive
  • very intuitive

H = [0°,360°]
S = (max - min) / max
V = max(r, g, b)

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21
Q

Difference: “Color Model”, “Color Space”, “Tristimulus Values”

A

Color Model:
- mathematical model
- 3-4 tuples

Color Space:
- set of all colors describable by Color Model

Tristimulus Values:
- describe color in a Color Space
- without Color Space -> meaningless numbers

22
Q

What was the “Color Matching Experiment”? What’s its result?

A
  • try to match a given color with given primary colors

-> not all colors reproducible
-> “negative” primary colors needed

23
Q

What is a “Color Matching Function”? What’s special about it?

A
  • shows how spectral colors can be reproduced by primary colors
  • can have negative values -> can’t be realized
24
Q

What is the “XYZ Color Space”? What is special about it?

A
  • nonnegative color matching function

-> oversaturated primary colors

25
Q

What does the “Gamut” describe

A
  • contains all visible colors of human perception
26
Q

What are the colors and the ticks on the edge of the “Gamut”

A
  • spectral colors -> correspond to monochromatic light
  • ticks are wavelengths
27
Q

What is the bottom line in the “Gamut”?

A
  • line of purples
  • set of fully saturated colors that are NOT spectral colors
28
Q

What is the middle of the “Gamut”

A
  • white point
  • x, y, z = 1/3
29
Q

What colors lie on the line through a color and the middle of the “Gamut”?

A
  • color itself
  • white point
  • pure color (on the side of color)
  • complementary color (on the opposite side of white point)
30
Q

What does an area (e.g. a triangle) indicate in the “Gamut”

A
  • representable colors of output device
31
Q

What’s the “Dynamic Range”

A
  • difference darkest black / brightest white
32
Q

What are the “MacAdam Ellipses”

A
  • all colors within ellipsis are perceived same as its center
33
Q

What’s a “Raster Graphic”? What are its characteristics?

A
  • rectangular grid of pixels
  • resolution (width x height)
  • color depth (number of bits per pixel)
34
Q

What’s a “Framebuffer”

A
  • storage for an raster graphic that is to be displayed by the monitor
35
Q

What’s “Dithering”

A
  • simulation of missing colors
  • perception of mixed colors from available colors
36
Q

What’s the typical resolution and color depth of modern displays

A
  • 1920 x 1080 pixel
  • 24 Bit color Depth (3 x 8 -> RGB each 2^8 = 256)
37
Q

What’s the “Weber-Fechner Law”

A
  • subjectively perceived intensity
  • proportional to logarithm of physical intensity
38
Q

What is the “Gamma Channel”

A
  • declares opacity
  • 8 bits
39
Q

Why does “Aliasing” happen? What are its result?

A
  • sample frequency lower than frequency of signal
    -> frequencies in reconstructed signal that are not present in original signal
40
Q

What does the “Nyquist-Shannon Sampling Theorem” say

A
  • f_sample > 2 x f_max
    -> exact reconstruction possible
41
Q

What are “Jaggies”

A
  • type of aliasing at edges of objects
42
Q

What is “Image Manipulation”? What two types are there?

A
  • modification of pixel based on current color at this position
  • modification pf pixel also based on neighbors
43
Q

What is a “Convolution” in the Computer Graphics sense? How does it work?

A
  • image function
  • assigns color to each position
  • use a kernel matrix to sum over the products of the image and the kernel
44
Q

What is the “Kernel” for a “Convolution” that blurs

A
  • entries sum up to 1
  • most basic: 1/9 for 3x3 kernel
45
Q

What is the “Kernel” for a “Convolution” that detects edges

A
  • negative around middle (N, E, S, W)
  • positive in middle
    -> sum total: 0
46
Q

What is the “Kernel” for a “Convolution” that sharpenes

A
  • negative around middle (N, E, S, W)
  • positive in middle
    -> sum total: >0
47
Q

What are “Morphological Operations”

A
  • structurally changing operations
48
Q

How does a “Dilation” work

A
  • at least one 1 in B overlaps with a 1 in A -> 1
49
Q

How does an “Erosion” work

A
  • ALL 1s in B overlap with a 1 in A -> 1
50
Q

How does an “Opening” work

A
  • smoothing of contour
  • removing bridges and protrusions (bumps)
  1. Erosion
  2. Dilation
51
Q

How does a “Closing” work

A
  • smoothing of contour
  • closes smaller gaps
  1. Dilation
  2. Erosion

Computer Graphics (6 decks)

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