Lecture 4 - Color

What is a practical use of the CIE diagram?

understanding how LED lights would combine to create a certain color

Why are pigment/paints color mixtures different than light color mixtures?

color light adds together - which is why all the colors create white light

pigment subtractive mixtures - which is why all the colors create black eventually

what does this mean?

red light is just red light, if you add to other light colors eventually you'll get wavelengths ranging from 400-700 nm i.e. white light

paint colors are defined by what they reflect, so red paint is technically every color but red (because it is reflected), so if you add a bunch of paints together eventually no colors will be reflected - subtracting which light can get reflected

What are the additive primaries (light)?

red, green, blue

What are the subtractive primaries (pigment)?

yellow, magenta, and cyan

How would more cone types affect our color vision?

able to distinguish more spectrally distinct light i.e. metamers!

What is rod monochromacy?

no cones

What is the visual acuity of someone with rod monochromacy?

20/200

cones predominate the fovea

Why can someone with rod monochromacy only match using brightness?

rate of absorption (probability) for two different lights is different, that difference can be overcome by adjusting light intensity

What color does red look like to someone with rod monochromacy? Why?

black - Purkinje shifts!

What does the term "achromat" describe?

someone with no color vision - rod monochromacy

What is a big issue for individuals with rod monochromacy? And how it is fixed for?

glare - shorter wavelength light has a higher sensitivity under both scotopic and photopic conditions for rods (compared to long wavelengths)

red glasses will block a lot of light reducing the bleaching of their rods

What is the minimum number of photoreceptors required for color vision?

two

why? - need differences in spectral absorption probabilities

What are blue-cone monochromats?

s-cones and rods (no M & L cones), poor visual acuity

What photopigment are deuteranopes missing?

missing M-opsin

What photopigment are protanopes missing?

missing L-opsin

What photopigment are trianopes missing?

missing S-opsin

What is the replacement model of dichromacy?

deuteranopes and protanopes will replace their missing opsin by the remaining functional L or M cones

If a normal colored vision person matches a color, will a dichromat also see a matching color?

yes! remaining opsin are normal

What is the difference between dichromats and an anomalous type defect?

dichromat - missing photopigment, remaining are normal

anomalous - altered photopigment, normal number of each photopigment

new explanation "deuteranomalous patient LACK the MWS cone, but have TWO versions of the LWS cone"

How does each dichromat behave while using the nagel anomaloscope?

protanope - monochromat

deuteranope - monochromat

tritanope - dichromat

Why do tritanopes act like a dichromat while using the nagel anomaloscope?

only testing the Rayleigh region, still have both M and L cones

How do protanopes and deuteranopes behave differently while using the nagel anomaloscope?

protonopes will be very insensitive to red

What photopigments do protanomalous patients have?

all three cones, L cones with an atypical sensitivity

What photopigments do protanopes have?

S and M, missing L

What photopigments do deuteranomalous patients have?

all three cones, M cones with an atypical sensitivity

What photopigments do deuteranopes have?

S and L, missing M

How are anomalous cone spectral sensitivities shifted?

abnormal photopigment is shifted towards the normal photopigment

deuteranomaly - M-cone spectrum displayed towards L-cone (dashed line)

How does the greater overlap of the M and L cone sensitivities affect color vision (anomalous trichromats)?

color discrimination between green and red lights is reduced

What is the newest genetic explanation for anomalous trichomacy?

often more than one set of MWS or LWS photopigment genes is present

example - deuteranomalous patients lack MWS cone, but have two versions of the LWS cone

What is the only test that can diagnose an anomalous trichromat?

nagel anomalous scope

What differences between M and L peak spectral sensitivities outline mild, moderate, and severe anomalies?

severe - 3 nm

moderate - 6 nm

mild - 12 nm

normal - 30 nm

remember these are differences in spectral sensitivities

Which color defect has the highest prevalence in the male population?

deuteranomaly

What is the mode of inheritance for color vision defects?

x-linked

Why can only carrier (or technically diseased) mothers transmit color defects to their sons?

x-linked inheritance pattern

sons receive their x chromosome from their mother

What happens to a cone once it becomes bleached?

becomes transparent to light

lighter - bleached photoreceptors

What are the percentages of cone distribution in the retina?

L-cone ~60%

M- cone ~30%

S-cone 7-10%

but there's variation amongst the population - these differences don't translate to differences with the standard color vision test

What is the purpose of the absence of S cones from the central fovea?

maximize acuity by reducing chromatic aberrations

How does each color defect see color?

How can CIE color space help us understand color defects?

CIE color space can be used to inform us which color protans, deutans, and tritans are likely to confuse

What are confusion lines?

all the lights on each line match for that certain color defect

Where are protanopes color confusion lines centered (confusion/copunctual point)?

red

Where are deuteranopes color confusion lines centered (confusion/copunctual point)?

beyond red

Where are tritanopes color confusion lines centered (confusion/copunctual point)?

blue

What are neutral points?

monochromatic light that appears white - confusion line that goes through white (middle)