Color + vision perception

Asynch lecture 10/14/2025, pgs 200-210

What are the chromatic colors? aka hues

Blue Green Red

What is Selective Reflection?

where colors (like chromatic colors) occur when some wavelengths are reflected more than others

Achromatic colors + how do they occur

White, gray, black

occur when light is reflected equally across the spectrum

How do we see certain wavelengths of lights?

We see whatever is reflected

What is selective transmission?

only some wavelengths pass thru object/substance 

ex. for cranberry vs lemonade in bottle

How does mixing paints work

both paints still

absorb the same wavelengths they absorbed when alone, so the only

wavelengths reflected are those that are reflected by both paints in common.

Subtractive color mixture

what occurs when u mix 2 paints/color together. You subtract all wavelengths except the ones associated with mixed color (ex. blue and yellow stay for green)

Additive color mixture

Mixture of lights

What happens when you project blue and yellow light on a white surface?

The white surface absorbs all light

“all of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed.”

so when you shine the blue and yellow (they reflect blue and yellow lights alone respectively that why we see blue and yellow), they both get reflected and you see a white spot!

Spectral colors are

the ones that appear on spectrum (ex. rainbow colors)

Non spectral colors are 

opposite of spectral colors, don’t appear on spectrum bc they are a mix of the spectral colors

(ex. red + blue → magenta which is a non spectral color)

How do we perceive all colors when visible spectrum is only a few colors?

we have 3 perceptual dimensions

3 perceptual dimensions

1. hue

2. saturation

3. brightness (luminosity/value)

Saturation 

intensity of color

Value/lightness

light-to-dark dimension of color

Color solid 

a way to relate the 3 perceptual dimensions

this one is called Munsell color system jm               

Trichromacy of color vision (Young-Hemholtz theory)

color vision depends on activation of 3 different receptor mechanisms

Color matching

A psychophysical procedure that proved this trichromacy theory

Given a reference light, and asked to match that wavelength using 3 RGB lights

3 RGB light = 3 receptor mechanisms w/ diff spectral sensitivities

Microspectrophotomentry

direct a narrow beam of light into

a single cone receptor of eye

How many types of cones are there?

3!

1. short wavelength pigment (S) absorbed maximally at

   419-nm

2. the middle-wavelength pigment (M), at 531-nm

3. the long-wavelength pigment (L), at 558-nm

what’s special between L and M cones

There’s a large overlap!

Adaptive optical imaging

look into a person’s eye and take pictures that showed

how the cones are arranged on the surface of the retina.

creates cone mosaic images!

Aberrations

imperfections in eye’s cornea and lens which distort light on the way to retina

How do we know which receptor are signaled given a certain light?

Ex. for a  blue (short wavelength) light, here’s a large response in S receptor, smaller response in M, and even smaller response in L

white = equal signaling in all receptors!

Metamerism

2 physically different stimuli are perceptually identical

Metamers

2 identical fields in color matching experiment

Why do metamers look alike?

The reason metamers look alike is that they both result

in the same pattern of response in the three cone receptors.

EXAMPLE

when the proportions of a 620-nm red light that

looks red and a 530-nm green light that looks green are ad-

justed so the mixture matches the color of a 580-nm light,

which looks yellow, the two mixed wavelengths create the

same pattern of activity in the cone receptors as the single 580-

nm light

Monochromatism

form of rare color blindness where they don’t have functioning cones, so they are only able to see through the rods

only needs 1 wavelength of light to match all others

Isomerization

when light is absorbed by the retinal part of the visual pigment molecule, retina changes shape

lower wavelgth of light isomerizes (more/less) visual pigment molecules?

More

Can change this relationship by adjusting intensity of the light

Principle of univariance

once a photon of light is absorbed by a visual pigment molecule,

the identity of the light’s wavelength is lost.

receptor doesn’t know wavelength of light absorbed, only the TOTAL AMNT that has been absorbed

Takeaways from monochromat experiment

can take any wavelength of light and match by adjusting it’s intensity

need more than 1 type of receptor to perceive chromatic color

Dichromacy

color vision with 2 pigments in retina

dichromats see chromatic colors, but can confuse some colors

Ishihara plates

a way to diagnose color deficiency

Unilateral dichromat

a person with trichromatic vision in one eye and dichromatic vision in another

we use this person to see what colors dichromat perceives compared to trichromat

they look through dichromat eye, see what color that is, and see what color it reports in the trichromatic brain

3 different forms of dichromatism

1. protanopia

2. deuteranopia

   1. tritanopia

2 common kinds of dichromatism

protanopia and deuteranopia, inherited thru gene located on x chromosomeWh

y are males more susceptible than females to being dichromats?

they have XY vs XX, so stronger effect on males

Protanopia

missing long wavelength pigment

short wavelength light is blue, as wavelength is increased blue becomes less and less saturated until 492 nm where it’s gray (neutral pt)

Neutral point

when the person perceives gray

Deuteranopia

missing medium wavelength pigment

perceives blue @ short wvlgth

yellow @ long wvlgth

Neutral pt 498 nm

Tritanopia

missing short wvlgth pigment

blue as short wvlgth

red long wvlgth

neutral pt @ 570 nm

Anomalous trichromatism

another type of color deficiency

needs 3 wavelengths to match any wavelength

they mix it in diff and wrong proportions than trichromat and aren’t good at discriminating wvlgths that r close together