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Chapter 5

PSYC 363 Chapter Notes - Chapter 5: Spectral Power Distribution, Reflectance, Color Solid


Department
Psychology
Course Code
PSYC 363
Professor
Michael Lantz
Chapter
5

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Chapter 5 : Perceiving Color
Color Vision
1. The ability to see differences between lights of different wavelengths.
LIGHT AND COLOR
The Visible Spectrum
1. The portion of the electromagnetic spectrum in the range of about 400 to about 700 nm:
a) Within this range, people with normal vision perceive differences in wavelengths as
differences in color.
Spectral Power Distribution
1. For any light, we can conduct a graph that depicts the light's
spectral power distribution (SPD):
a) The intensity (power) of a light at each wavelength in
the visible spectrum.
b) Important determinant of the perceived color of the light.
2. Heterochromatic (hetero: different; chromatic: light) Light:
a) Light that consists of more than one wavelength.
3. Monochromatic (mono: single; chromatic: light) Light:
a) Light that consists of only one wavelength.
4. Achromatic (a: without; chromatic: light) Light (white light):
a) Light containing wavelengths from across the visible spectrum, with no really
dominant wavelengths.
b) Perceived as more or less colorless (i.e. shades of gray).
c) The SPD of sunlight is quite close to that of an idealized white light.
d) Achromatic colors:
i. Contain no hues (white, gray, or black).
Spectral Reflectance
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Chapter 5 : Perceiving Color
1. The proportion of light that a surface reflects at each wavelength:
a) Example:
i. A tomato will reflect the red wavelength more than any other.
DIMENSIONS OF COLOR: HUE, SATURATION, AND BRIGHTNESS
The Perceptual Experience of Color
1. Explained with three dimensions:
a) Hue:
i. The quality usually referred to as ''color'' (i.e. blue, green, yellow, red, etc.)
without specifying whether the color looks:
Vivid.
Washed out.
Bright.
Dim.
ii. The perceptual characteristic most closely associated with the wavelength of light.
b) Saturation:
i. The vividness, purity, or richness of a hue.
c) Brightness (or intensity):
i. The amount of light.
Color Circle and Color Solid
1. Color circle:
a) A 2D depiction in which:
i. Hue varies around the circumference.
ii. Saturation varies along any radius.
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Chapter 5 : Perceiving Color
2. Color solid:
a) A 3D depiction in which:
i. Hue varies around the circumference.
ii. Saturation varies along any radius.
iii. Brightness varies vertically.
Color Mixtures
1. Subtractive Color Mixtures (Mixing Substances):
a) Recall:
i. The perceived color of a substance depends on its reflectance (i.e. the percentage
of light it reflects at each wavelength; what we see) with the rest being absorbed.
b) Subtractive color mixtures:
i. A mixture of different-colored substances:
-Called “subtractive” because the light reflected from the mixture has certain
wavelengths subtracted (absorbed) by each substance in the mixture.
ii. Consider the mixture: Blue paint + Yellow paint = Green paint:
-Blue paint:
oReflects Purple, and Green light.
oAbsorbs Yellow, Orange, and Red light.
-Yellow paint:
oReflects Green, Yellow, Orange, and Red light.
oAbsorbs Purple light.
-Green paint:
oReflects Green light.
oAbsorbs Purple, Yellow, Orange, and Red light.
iii. Each substance in the mixture subtracts certain wavelengths:
-In the Blue and Yellow example:
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