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Visual Sensation and Perception > Midterm 2: Color Vision > Flashcards

Midterm 2: Color Vision Flashcards

1
Q

What color cone was the first to evolve?

A

Blue cones were the first to evolve

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2
Q

What is the relationship between the opsin molecules of red and green cones?

A

The red and green cones are very similar. There are only a few differences in amino acids between the two. This is what causes the green and red to be located closely to one another on a spectral sensitivity graph.

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3
Q

What is the Principle of Univariance?

A

The absorption of a long wavelength (low frequency, low energy) quantum has the same effect on a receptor as the absorption of a short wavelength (high frequency, high energy) quantum. Once a quantum of light is absorbed, all information about wavelength is lost.

The probability of absorption changes with wavelength and with photoreceptor class.

Ex. Blue cones absorb short wavelength photons more easily than long ones.

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4
Q

Wavelength is a _______ attribute. 
Color is a __________ attribute.

A

physical; perceptual

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5
Q

Color is to __________ as brightness is to _________.

A

wavelength; intensity

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6
Q

Illuminant color is related to the wavelengths of light ________.

A

emitted

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7
Q

Object color is related to the wavelengths of light ________ from an object.

A

reflected

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8
Q

The two main ways colors can be combined. What colors are associated with both? What law does this relate to?

A

Color addition- Red, Green Blue (RGB)

Color Subtraction- Cyan, magenta, yellow ( CMYK) K=whiteness?

Relates to Abneys Law- “total luminance of light composed of several wavelengths is equal to the sum of the luminances of its monochromatic components.”

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9
Q

Describe color subtraction

A

Start with yellow, cyan, and magenta. When subtracting colors, you take away what they don’t have in common. What’s left is what they have in common.

Example, yellow (R+G) and magenta (R+B) have a Red in common. Take away what they don’t have in common (G and B) and you are left with red.

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10
Q

How is spectral color obtained?

A

By prismatic decomposition of sunlight

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11
Q

How is non-spectral color obtained? What color is non-spectral?

A

ONLY by mixing spectral colors. Not present in sunlight.

-purples are non spectral colors

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12
Q

What are metamers?

A

Two or more stimuli that have the same color but have different wavelengths.

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13
Q

Describe the 3 Grassman Laws

A

Scalar Property of Metamers:
If you increase the intensity of two metamers, they will still be metamers.

Additive Property of Metamers:
Add same wavelength to two metamers and the results will still be metamers.

Associative Property of Metamers:
If a 3rd metamer is created for one of a pair of metamers, all three will be metamers.

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14
Q

Describe Newton’s color circle and the information you can get from it.

A

Newton had 3 points on a circle that were equally separated and labeled them blue, green, and red with lines connecting them. If you were to add 2 of the colors along the line, the resulting color would be desaturated. As you move that desaturated color to the outside of the circle, the saturation would increase.

  • Provides qualitative description of color matches.
  • Shows why there needs to be more than 2 colors to make all the color matches.
  • Shows the need to use negative colors.
  • To saturate the color, add red (color not used for initial mixture)
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15
Q

__________ colors are any two colors that, when added together, produce a “neutral” (i.e. black-gray-white) color.

A

Complementary

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16
Q

On a color circle, complementary colors always lie on _________ sides of “white”. Where is white?

A

opposite

White is in the center of the circle

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17
Q

Perceptual color attributes associated with wavelength

A

Hue

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18
Q

Perceptual color attribute that gives perceived intensity of the color

A

Brightness (Munsell “value”)

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19
Q

Perceptual color attribute that gives degree to which a color appears to differ from an equally bright gray.

A

Saturation (Munsell “chroma”)

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20
Q

What gives perceptual attribute gives a color’s perceived colorimetric purity?

A

Saturation

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21
Q

What are the tree types of cones? What color is associated with each?

A

S: Blue
M: Green
L: Red

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22
Q

How do each cone type respond to a given wavelength?

A

Each cone type responds to a wide range of wavelengths. Depending on the wavelength, some cones overlap and the intensity of each response is different depending on the wavelength.

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23
Q

Describe the Relative Cone Sensitivity Function graph. (also x and y axis)

A

This graph shows the sensitivity to a given wavelength by each cone (S,M and L)

On the x-axis, you have the wavelength in nanometers.
On the y-axis, you have relative excitation level

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24
Q

What is colorimetric purity? What does it describe? What is the equation?

A

Colormetric purity is the physical correlate of saturation.
It describes the proportion of pure, dominant spectral wavelength energy relative to the amount of achromatic (white/gray) luminance objectively present in a color sample.

cp = Lλ / (Lλ + Lw)

Lw= luminance of white

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25
Q

What are MacAdam Ellipses?

A

MacAdam Ellipses are regions on the CIE chromaticity diagram that show the normal just noticeable differences regions. They are not uniform in shape. Some regions have larger ellipses than others.

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26
Q

Describe wavelength discrimination. What wavelengths provide the best discrimination from other wavelengths?

A

The ability to distinguish differences in the hue of two spectral (mono-chromatic) lights that differ ONLY in wavelength.

The best discrimination is at 495 nm and 590 nm.

27
Q

What color is both the least saturated and and has the poorest saturation discrimination?

A

Yellow (570 nm)

28
Q

Describe the Bezold-Bruke Effect. What wavelengths do not follow this effect. What are they called?

A

Changing the value (intensity) also changes the hue for most wavelengths.

The wavelengths that don’t follow this are called invariant wavelengths and have unique(invariant) hues. They are wavelengths 478 nm, 503 nm, and 578 nm.

29
Q

Describe the graph the Bezold-Burke Effect uses.

A

On x-axis, you have wavelength.
On y-axis, you have Log luminance.

Used different intensities of monochromatic light and plotted the results. The lines are called “hue contour lines”. The lines for wavelengths 478, 503, and 578 were straight vertical while all other values were bent.

30
Q

What is Benham’s disk? What does it indicate?

A

Benham’s disk is a disk made up of black lines of different lengths. When you spin it, you can see colors like red, green, and blue. The colors are referred to as Fechner colors.

It indicates that the different wavelength-opponent neural channels have different temporal response and recovery characteristics.

31
Q

The value and hue of most lights are
_____ entirely independent

A

not

32
Q

Describe simultaneous color contrast

A

Hue is influenced by its surround in complementary fashion.

Differs from an aftereffect by in that, here, the inducing and illusory colors are visible simultaneously.

33
Q

Describe the McCollough Effect

A

Complementary hues perceived, but the McCollough Effect is not due to simple receptor adaptation.
It exhibits “binocular transfer” (requires cortical processing).
It lasts (way) too long!

34
Q

What is color assimilation?

A

lighter pattern elements cause the background colors to appear brighter.
Differs from an simultaneous contrast by the similar (rather than complementary) influence of context.

35
Q

What is color constancy?

A

Color constancy refers to the tendency of objects to retain the same color appearance despite changes in the spectral composition of their illumination.

Allows a color to be a stable property of an object despite changes of the object’s illumination

36
Q

Describe Ed Land’s demo of color constancy by looking at a Mondrian Pattern

A

1) 3 light sources: red, green, blue.
2) Measure the amounts of red, green, and blue light reflected by
a green rectangle.
3) Adjust each of the red, green, and blue illuminants so that a blue rectangle now reflects the same amounts of red, green, and blue light as the green rectangle reflected before.

The blue rectangle still looks blue even though it now reflects the same light that made the green rectangle appear green.

37
Q

How do rainbows work?

A

The light hits water droplets in the sky. Each beam of light is refracted into a prismatic effect. Depending on where you stand, the refracted beams will present you with different colors for the different angles at which the beam was refracted.

38
Q

How does lightning work?

A

Specific atoms in gas present a vapor or a gas when excited, which have their electrons raised into higher energy levels by a variety of excitations; light is then emitted when the excess energy is released as photons.

39
Q

Why is water blue?

A

The absorption that gives water its color is in the red end of the visible spectrum, one sees blue (the complementary color of orange) when observing light that has passed through several meters of water.

40
Q

How are Auroras formed?

A

The light is emitted when charged particles from the sun are guided by the earth’s magnetic field into the atmosphere near the poles. When the particles contact atmospheric molecules, primarily oxygen and nitrogen, at altitudes from 300 down to 100 km, a part of the energy of the collisions transforms to visible light.

41
Q

Describe the Munsell Color System

A

Has 3 values: Hue, Chroma (saturation), Value (brightness/lightness)

Hue:

  • has 10 sectors (R, YR, Y, GY, G, BG, B, PB, P, RP)
  • each sector broken down into 10 more values labeled 1-10

Chroma (saturation):

  • Visually uniform scale
  • 0-30+
  • Increases as fluorescent colors are added

Value (Lightness/ Brightness)

  • scale 0-10
  • black > white
42
Q

Explain the RGB color matching function

A

A person can add the 3 different primary colors to match any color. The proportion of tristimulus values are plotted on a graph.
Y- value on graph = proportion of primary
X-value on graph = wavelength of sample color

43
Q

What are the real primary wavelengths

A
  1. 8 nm (blue)

  2. 1 nm (green)

  3. 0 nm (red)
44
Q

Explain XYZ color matching function

A 
Y-Axis = tristimulus value
X-axis = wavelength of given

Uses imaginary primaries.
XYZ (RGB) tristimulus values are plotted instead of proportions. To find tristimulus value, divide the tristimulus value
or each primary by the sum of the 3 tristimulus values.

45
Q

True or false:

Chromaticity coordinates are always decimals that add up to one.

A

true

46
Q

Can tri-stimulus values be greater than 1?

A

Yes

47
Q

2-dimensional plot of human color space

A

CIE Chromaticity Diagram

48
Q

What is a spectral locus?

A

Any point on the outside of the CIE chromaticity diagram

49
Q

What is the planckian locus?

A

path or locus that the color of an incandescent black body would take in a particular chromaticity space as the blackbody temperature changes.

50
Q

Where are the non-spectral purples on a CIE chromaticity diagram?

A

On the flat part of the diagram at the bottom between red and violet.
Also called the purple locus

51
Q

Describe excitation purity and how to find it on a CIE chromaticity diagram

A

Correlates to saturation.
From W (White in center) to a given point on the graph (S) represents the value “a”.
From S to the D (most saturated form of S, located on edge in same direction) represents value “b”

Excitation purity = a / (a+b)

52
Q

What is a color gamut?

A

All possible outcomes of combining certain colors.

CIE diagram is a color gamut of the primary colors (RGB)

53
Q

X and Y components of CIELUV diagram

A

Y- axis = v’

X-Axis = u’

54
Q

What is the purpose ff the CIE (u’, v’) diagram?

A

Attempts to make perceived chromaticity differences more uniform across the whole diagram.

55
Q

What is the color temperature, source, and function of CIE illuminant A?

A

Color temp = 2856° K

Source = gas-filled coiled-tungsten filament lamp with a fused-quartz envelope or window operating at 2854° K

Function = Serves as standard for illuminants B & C


56
Q

What is the color temperature, source, and function of CIE illuminant B?

A

Color temp = 4874° K

Source = Illuminant A + 1 cm thick double cell optical glass container (Davis-Gibson filter) filled with liquid chemical solutions B1 and B2

Function = Mimics direct sunlight at noon (poorly).


57
Q

What is the color temperature, source, and function of CIE illuminant C?

A

Color temp = 6774° K

Source = Illuminant A + 1 cm thick double cell optical glass container (Davis-Gibson filter) filled with liquid chemical solutions C1 and C2

Function = Mimics average direct Northern sunlight but lacks power in near UV range important for fluorescent materials.
-Illuminant C is the illuminant for which nearly all clinical color vision tests were designed.

58
Q

What is illuminant C best approximated by? (name of lamp)

A

Macbeth Lamp

59
Q

Describe CIE D illuminants. What does it correct for? Source? Which is acceptable for Illuminant C substitute?

A
  • Represent measured spectra under different conditions of natural daylight
  • Correct for weaknesses of the other standard illuminants (A, B, & C) in near UV
  • no standard source
  • Illuminant D65 is an acceptable substitute for Illuminant C for color vision testing.
60
Q

What is the color temperature, source, and function of CIE Illuminant D65? What is recommended for?

A

-recommended for natural daylight

Color temp: 6500° K , fluorescent sources

Source: No standard source.

Function: Acceptable substitute for Illuminant C in clinical color vision testing.

61
Q

Describe Matching color test (Anomaloscopes)

A
  • based on work by Rayleigh (red+green=yellow)
  • most accurate; expensive; difficult to use
  • Patient mixes colors to obtain the color of regard
  • Traditionally, for red/green defects only
  • Sloan Achromatopsia Test
62
Q

Describe the arrangement test for color vision

A

(testing distance-50cm)
Farnsworth Munsell 100 Hue Test (FM 100)
uses the chromaticity diagram/takes a long time
Farnsworth Dichotomous Test for Color Blindness (Panel D-15). Good screener for congenital and acquired defects
L’Anthony desaturated D-15
Adams desaturated D-15

63
Q

Describe the Pseudoisochromatic plates (color confusion) “PIC Test” for color vision testing. The 2 types and what they are good for.

A
  • Distance 75 cm
  • Different strategies on various plates (ex. Vanishing vs. Transformational designs)
  • Ishihara. Good screener for congenital defects
  • HRR. Acquired and congenital.
64
Q

What test is useful for red/green defects? Describe it.

A

Nagel Anomaloscope is useful for red/green defects. It distinguishes from proton and Deutan only. Not Tritan.

Bipartite field
670 nm (red) + 546 nm (green) (or 664 & 549, or 679 & 544)
Variable ratio (0 to 73, arbitrary units)
Constant (CIE) luminance
590 nm (yellow) (or 579nm)
Variable radiance

Change radiance until they appear equal.

Visual Sensation and Perception (19 decks)

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