Task 3 - True Colors Flashcards
Reflectance curve
plots of the percentage of light reflected versus wavelength
Chromatic colors, or hues
this property of reflecting some wavelengths more than others, which is a characteristic of chromatic colors
Achromatic colors
When light reflection is similar across the full spectrum—that is, contains no hue—as in white, black, and all the grays between these two extremes
Selective transmission
things that are transparent, such as liquids, plastics, and glass, chromatic color is created - selective transmission - only some wavelengths pass through the object or substance
Additive color mixture
mixing lights
Subtractive color mixture
mixing paint
Trichromatic theory of color vision
color vision depends on the activity of three different receptor mechanisms
Color-matching experiments
observers adjusted the amounts of three different wavelengths of light mixed together in a “comparison field” until the color of this mixture matched the color of a single wavelength in a “test field.”
Young-Helmholtz theory of color vision
central idea of the theory is that color vision depends on three receptor mechanisms, each with different spectral sensitivities –According to this theory, light of a particular wavelength stimulates the three receptor mechanisms to different degrees, and the pattern of activity in the three mechanisms results in the perception of a color. Each wavelength is therefore represented in the nervous system by its own pattern of activity in the three receptor mechanisms
Metamerism
This situation, in which two physically different stimuli are perceptually identical
Metamers
the two identical fields in a color-matching experiment
Dichromats
people with just two types of cone pigment
Trichromats
they see fewer colors than people with three visual pigments
Color deficiency
most problems with color vision involve only a partial loss of color perception – are associated with problems with the receptors in the retina
Daltonism
another term for protanopia – another form of color blindness
Ishihara plates
color vision test
Monochromat
can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. Thus, a monochromat needs only one wavelength to match any color in the spectrum and sees only in shades of gray
Unilateral
a person with trichromat vision in one eye and dichromatic vision in the other
three major forms of dichromatism:
- protanopia
- deutoranopia
- tritanopia
Opponent-process theory of color vision
this theory states that color vision is caused by opposing responses generated by blue and yellow and by red and green – responsible for afterimages
Simultaneous color contrast
an effect that occurs when surrounding an area with a color changes the appearance of the surrounded area
Opponent neurons
in the retina and lateral geniculate nucleus that responded with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
Cerebral achromatopsia
color blindness due to damage to the cortex
Color constancy
we perceive the colors of objects as being relatively constant even under changing illumination
Chromatic adaptation
prolonged exposure to chromatic color. Adaptation to the red light selectively bleaches your long-wavelength cone pigment, which decreases your sensitivity to red light
Partial color constancy
the perception of the object is shifted after adaptation, but not as much as when there was no adaptation – This means that the eye can adjust its sensitivity to different wavelengths to keep color perception approximately constant as illumination changes
Memory color
the effect of our knowledge about the usual colors of objects in the environment
Lightness constancy
The fact that we see whites, grays, and blacks as staying about the same shade under different illuminations is called
The visual system’s problem is that the amount of light reaching the eye from an object depends on two things
(1) the illumination: the total amount of light that is striking the object’s surface—and
(2) the object’s reflectance - the proportion of this light that the object reflects into our eyes
Ratio principle
as long as this ratio remains the same, the perceived lightness will remain the same
Reflectance edge
an edge where the reflectance of two surfaces changes
Illumination edge
an edge where the lighting changes
Penumbra
the fuzzy border at the edge of the shadow – the penumbra provides information to the visual system that the dark area next to the cup is a shadow, so the edge between the shadow and the paper is an illumination edge. However, masking off the penumbra eliminates that information, so the area covered by the shadow is seen as a change in reflectance
Principle of univariance
one and the same visual receptor cell can be excited by different combinations of wavelength and intensity, so that the brain cannot know the color of a certain point of the retinal image
