Color Vision slide set 2

Planckian Locus

a collection of points on the chromaticity diagram representing blackbody radiation of various temperatures (represented as an arc of 'white' formed by these different color temperatures within the CIE diagram)

x+y+z

always equals 1

Primary Colors (Red, Green, and Blue)

are combined to match a monochromatic test primary light (λm)

No Spectral Compliments

are found between 490 and 570

All Physically Realizable Colors

are on the CIE diagram

Standard Illuminant C (Overcast Sky)

bluish white, has a higher color temperature (6,774 K)

Dominant Wavelengths and Excitation Purity of Color

can be calculated via color mixing (because an additive mixture of 2 wavelengths lies on a line connecting the 2 wavelengths)

Amount of Primaries Needed to Match a Color

can be determined from the CIE diagram

Equal Energy White

can be found at coordinates 0.33, 0.33 (5,600 K)

Spectral Compliments

can be found from 380 to 490 and 570 to 700

Specification of White

can be in terms of color temperature of a black body radiator (an opaque object)

x, y, z

chromaticity coordinates (relative units on the CIE diagram, are derived from the imaginary primaries)

CIE Color System

color system that is more precise than the Munsell system, is based on the trichromatic theory of color vision, and relies on parameters based on spectral power distribution of light from a colored object and sensitivity curves that have been measured for the human eye

What three attributes are described by the Munsel Color System?

hue chroma - similar to saturation value - related to brightness (reflectance)

Since you can't technically add the real negative primary colors, the CEI system mathematically changes R, G, and B to ___.

imaginary primaries called: - X - Y - Z *no negative tristimulus values*

X, Y, Z

imaginary primaries (arise when red, green, and blue are mathematically transformed) are not on the CIE chromaticity diagram because they are not real

Practical Applications of the Munsell Color System

include the Munsell color tree, Munsell color book, Munsell atlas, etc.

How do you add a negative red primary color?

instead of mixing in red with the green and blue, you have to add red to the monochromatic test light side - this defeats the purpose - CEI primaries are not real

CIE Color Matching Function (CMF)

is formed when the amounts of each primary needed to match the monochromatic test light are plotted by test light wavelength on the horizontal scale

Correlated Color Temperature of White Light

is represented by points along the plackian locus

Hue

is used to described colors in the Munsell color system and is related to wavelength

Value

is used to described colors in the Munsell color system, is related to brightness (reflectance), runs along the vertical dimension, and falls between 0 and 10

Chroma

is used to described colors in the Munsell color system, is similar to colorimetric purity (saturation), is represented as a radius from the center, and falls between 1 and 14 (14=highest purity)

Additive Mixture of 2 Wavelengths

lies on a line connecting the 2 wavelengths (can be used to calculate dominant wavelengths and excitation purity of color)

Purple Line

line connecting 380 to 700 that includes non spectral purples

What is the spectral locus?

location on the chromaticity diagram that represent color stimuli across the entire visual spectrum

Imaginary Primaries

mathematically transformed real primaries that serve to locate primary reference points in a CIE chromatic diagram

What are spectral hues?

monochromatic hues found along arches of the perimeter of chormaticity diagram

Spectral Hues

monochromatic hues that are located along the arc of the perimeter

3D graph of imaginary primaries

no light at point of origin points X, Y, and Z are outside solid shape because they are imaginary colors

Black Body Radiator

opaque object that emits electromagnetic radiation as it is heated (when it is heated high enough it begins to emit visible radiation)

What is the excitation purity of a sample 'M' with a dominant wavelength of 520, where a = 3 and b = 1?

p = a/(a+b) p = 3/(3+1) p = *0.75*

Complimentary Colors

pairs of colors that match a specific white light when mixed in proper proportion (on a CIE diagram you can connect the wavelength through white to find the other wavelength)

Red, Yellow, Green, Blue, Purple

primary hues in the Munsell color system

Munsell Color System

provides a system to accurately determine 'what color blue is it' involves describing colors based on 3 attributes: hue, chroma, value

CIE Chromaticity Diagram

provides the amount of each imaginary primary (X, Y, and Z) needed to match any real color

What color cannot be produced with monochromatic light on the CEI diagram?

purple - purple is actually a combo of red and blue

How is the chroma identified in the Munsell color system?

radius from the center - 1 to 14 14 = highest purity

490-570

range in which there are no spectral compliments

1-14

range of values for chroma in the Munsell color system

0-10

range of values for value in the Munsell color system

450-550 nm

range of wavelengths for which negative amounts of a primary color are needed to make a match

380-490 and 570-700

ranges of spectral compliments

R, G, B

real primaries (will be mathematically transformed into imaginary primaries)

What are the primary hues in the Munsell Color system?

red yellow green blue purple - intermediary hues in between

Standard Illuminant A (100 W Incandescent Bulb)

reddish white, has a lower color temperature (2,855.6 K)

Chromaticity Coordinates

relative units on the CIE diagram (x, y, z)

CIE 1931 Chromaticity Diagram

represents perceptual attributes of hue and saturation, separated from luminance

How do you use the CIE to determine the purity of combined wavelengths?

take the ratio of distance from *whitest point - midpoint* to *whitest point - spectral locus* *a/(a+b)* max purity = 1

What are color matching functions?

the actual amount needed of the three primaries to match a given monochromatic light

Spectral Locus

the arc or location of points on a chromaticity diagram that represent color stimuli across the entire visible spectrum

Excitation Purity

the extent to which a color stimulus differs from white or its dominant wavelength (as determined by its location between them on a chromaticity diagram) distance of the sample (M) along the line connecting W to the perimeter of the arc

Dominant Wavelength

the wavelength that can be mixed with a reference white to find a match to that color

0

value that represents the least bright colors in the Munsell color system (least reflectance)

10

value that represents the most bright colors in the Munsell color system (most reflectance)

What color is in the middle of the CIE digram?

white

How can you calculate the 'z' value if only the x and y axes are shown?

x + y + z = 1 z = 1 - (x+y)

How do you convert the imaginary colors (tristimulus) values X, Y, and Z to the chromaticity coordinates x, y, and z?

x = X/(X+Y+Z) y = Y/(X+Y+Z) z = Z/(X+Y+Z) where x + y + z = 1

On the CIE diagram, if x = 0.3 and y = 0.2, what is z?

z = 1 - (0.3+0.2) z = 1 - (0.5) *z = 0.5*

Hue, Chroma, Value

3 attributes used to describe colors in the Munsell color system

From ___ to ___ nm, negative amounts of the *red* primary color are needed to match a monochromatic test light.

450 to 550

What is the complimentary color of 580?

480 nm

What is the CIE color system?

Commission Internationale de I'Eclairage - more precise than Munsell system

.33, .33

coordinates for equal energy white

Arc

curved boundary

How do you find complimentary colors (spectral complimentson the CIE diagram?

draw a line from the given spectral locus through the white point only works from: 380 to 490 570 to 700

White

falls in the middle of the CIE chromaticity diagram

True or false. There are spectral compliments for wavelengths 490 to 570.

false - no spectral compliments

True or false. The CIE color system is based on the theory of color opponency.

false - trichromatic theory - the amount of each of the 3 primary colors needed to match a monochromatic light

How do you know which is the dominant wavelength using the CIE diagram?

first draw a line connecting wavelengths on the spectral locus then put a dot at the midpoint of the line. then draw a line connecting the whitest point of the diagram to the midpoint of the first line then continue out the line to the spectral locus to see what wavelength of light will be produced (called the *dominant wavelength*) picture shows mixture of 510 and 560 making 530nm.

a/a+b

formula for excitation purity

Standard Illuminant B (Direct Sunlight)

has a medium color temperature (4,874 K)

Tristimulus Values of Pure Spectral Colors

have the maximum saturation