02 - Perception and Color Flashcards
How does a “Cathode Ray Tube (CRT)” work? What’s a technique used by the CRT?
- 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
How does a “Liquid Crystal Display (LCD)” work
- two coated glass plates with liquid crystals in between
- voltage determines orientation of crystals
- liquid crystals modify polarization of light
What’s the difference between “Vector Graphics” and “Raster Graphics”
Vector Graphics
- resolution independent representation
Raster Graphics
- image buildup independent of scene complexity
- finite pixel number -> “aliasing” and “Moiré effect”
- no object access
What is “Aliasing”? What causes it?
- pattern that aren’t real in sampled images
- caused by under sampling
-> merging of highs and lows to an average value
What is the “Moiré Effect”?
- super position effect
- interference patterns
- frequency depends on angle
What are spectral colors?
- monochromatic light
- only one wavelength
-> appear bright and clear
What is a “Plane Angle”? How do you calculate it?
- angle of a curve from a point
- L/r
-> L being the arclength of the projection of the curve onto the unit circle
What is a “Solid Angle”? How do you calculate it?
- amount of field of view covered by an object from a point
- F/r^2
-> F being the projection onto the unit sphere
What’s illumination
- consist of many wavelength
- each wavelength with a certain intensity
What are the most important parts of the eye (3) and their characteristics
Retina:
- houses light sensitive cells
Fovea:
- sharpest vision
Foveola:
- sharpest vision of Fovea
What types of cells are in the eye? Where are they placed?
- cones (few, central, colors -> trichromatic)
- rods (many, peripheral, black-white-vision -> monochromatic)
What’s the “Opponent Process”? What’s the effect of this?
- 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
What are “Mach Bands”? What causes them?
- brighter or darker edges in gradient
- caused by contrasts in receptive fields that amplify contrast
What is the “Trichromatic Color Vision”? How are colors formed? How can this effect perception?
- perceptual response to different wavelength
- colors are the integrals of the cone responses
- different wavelengths / intensities can create same response
What is a “Metamerism”
- two different spectra
- cause identical response in receptors
What are the two types of “Color Mixing” and their colors? Where are each used?
Additive (e.g. screens, projectors):
- red
- green
- blue
Subtractive (e.g. printers, color pens):
- cyan
- magenta
- yellow
What is “Grassman’s Law”
- every color representable by 3 basic quantities
-> 3-dimensional quantity
How does the “RGB Color Space” work
- 3 primary colors
- C = rR + gG + bB -> (r,g,b) in [0,1]^3
How does the “CMY(K) Color Space” work
- 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
How does the “HSV Color Space” work
- neither additive nor subtractive
- very intuitive
H = [0°,360°]
S = (max - min) / max
V = max(r, g, b)
Difference: “Color Model”, “Color Space”, “Tristimulus Values”
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
What was the “Color Matching Experiment”? What’s its result?
- try to match a given color with given primary colors
-> not all colors reproducible
-> “negative” primary colors needed
What is a “Color Matching Function”? What’s special about it?
- shows how spectral colors can be reproduced by primary colors
- can have negative values -> can’t be realized
What is the “XYZ Color Space”? What is special about it?
- nonnegative color matching function
-> oversaturated primary colors
