Topic 7 Flashcards
general principles of colour theory
not everyone perceives colour the same
we primarily see EMR from the sun
approx 400-700nm (what we can see)
colour detection: rods
sensitive to brightness changes
about 120 million
monochromatic vision
colour detection: cones
6-7 million
three types
red sensitive “L” cones
green sensitive “M” cones
blue sensitive “S” cones
Note: midpoints of cones sensitivities do not always match the wavelenght (ex. green highpoint is in yellow)
what is the macula
back of the eye
macula degeneration can no longer see straight
what is the fovea
used to collect colour information
higher concentration of cones
beyond the eye: colour reception
signals collected by bipolar and ganglion cells sent to optic nerve
processed by visual cortex
what is rhodopsin
proteins that transmit information
information sent to the visual cortex (back of head)
Craig Blackwell Video #1
Colour basics
spectro - rainbow (natural colours)
white = achromatic
sunlight contains perceptable light
blackwell additive colour mixing
255 = fully saturated
0 = full black
all 126 = grey
all 255 = white
blackwell subtractive colours
cyan, magenta, red, yellow, green
complimentary colours put together = white
blackwell difference between additive and subtractive colours
adding different wavelengths
subtractive is taking away wavelenghts
Craig Blackwell Video #2
colour matching
3 basic colours to create a match for all other colours
trisstimulus = 3 colours used to make a match
not all colours can be matched by RGB primarys
blackwell chromaticity diagram CIE
spectral locus - colour of spectrum mapped onto diagram allows for x,y graph
outside the triangle cannot be matched
can only match within the triangle or boundary
this boundary is referred to as the GAMUT
Craig Blackwell Video #3
colour mapping
where it intersects when mixing is the dominant wavelength
Craig Blackwell Video #4
cones to see colour
cones sense RGB
send to cortex (brain)
produces what we see
blackwell colour perception order
cornea/lens - retina - optic nerve
3 layers of nerve cells in retina (RGB)
rods do not contribute to colour
3 layers of cones
blue or S = short
green or M = medium
red or L = long
blackwell receptive field
bullseye
center surround
on center = positive
off surround = negative
both of these work vice versa
balckwell opponent colours
black / yellow
green / red
cones = 3 colours
opponent = 4 colours
opponent colours channels
black vs white
green vs red
blue vs yellow
unique hues
Blue, green, yellow, red (pure colours)
1 cone = 200 levels
2 cones = 10,000 colours
3 cones = 500K
Craig Blackwell Video #5
one cone wont get you colour vision
Craig Blackwell Video #6
humans and animals
when you are focused on something, other things are perceived differently
what is rod monochromad
1 rod
only functions in dim light
what is cone chromat
one one cone
only brightness
only blue working = gg
what is di chromat
only two cones working
what is trichromat
3 cones working
what type of colour mixing is CMYK
subtractive colour mixing
colour models (6_)
RGB
CMYK
HSV ( hue, saturation, value (lightness))
Munsell (hue, value, chroma (saturation))
HVC
CIE (international commission on illumination)
RGB colour model
additive colour theory
works well with computers and colours on monitors
has a few drawbacks
not linear
hard to deal with
colour is not linearily perceptable and depends on your output device
what controls RGB channel intensity
intensitites are based on numbers
255 different number of intensities
binary = 8 bit
can only be on or off
lowest = 0
highest = 255 (8 bit)
16 bit = 65535
what is “true colour”?
24 bit
3 - 8 bit layers (RGB)
describe additive colour mixing
0,0,255 = full blue
255, 255, 255 = all white
64,64,64 = grey
full intensity green and blue gives….
cyan
describe hue
relates to wavelenght of light, location along a colour wheel usually describes as an angle
describe brightness
visual perception of an area emitting or reflecting more or less light
describe lightness/value
perceived brightness of an area compared to a similarily illuminated white
describe colourfullness
the way we perceive the absolute amount of bias among the long, middle and short wavelenghts relative to daylight
describe saturation
colourfullness of an area judged in proportion to its brightness. how we perceive proportional amount of bias among the L,M, S wavelenghts relative to light
describe chroma
the perceived colour difference from a grey of the same lightness. how we perceive the objects efficiency as a spectrally selective reflector/transmitter of light
saturation in a RGB colour model
not linear perceptually
HSV characteristics
separate out the things we normally perceive
munsell colour model characteristics
designed for artists
different hues “around the circle”
bubbles out in the mid area of the diagram1
HSV vs RGB
RGB = convinient for colour production
HSV - attempts to mimic how humans perceive light
as value increases, more hues become perceptable
HSV vs HSL
cylinders but drawn into cone and bi-cone
Saturation: colourfullness of area judged against brightness
Chroma: the perceived colour difference from a grey of the same lightness
components of colour perception/detection
trichromatic - based on wavelength sensitivities of three cone types
Opponent-process
lightness-darkness channel
Cie colour models
objectives: to create perceptually uniform colour models
to measure and compare colours
CIE labusually found in softwares
chromaticity is the basis
A, b are colour opponents in CIE lab
what is a hexcode
unique number that applies to an absolute colour across all digital platforms
how many ways to quantify colour in photoshop?
5
colour-vision impairment
4-6% in Europe and NA
two main types:
anamalous trichromats
dichromats
Cause?
change in colours that cones are sensitive
links between cones and ganglion and bipolar cells
Cie xyz vision impairment
do not hold back A or B channels constant and move the other (they represent colour impairment controls)
arc GIS pro colour models
a/b channels need to move cooperatley
Why is K(black inserted)
people want to print in basic black
cant reproduce a perfect black with CMYK
Arc Gis pro colour vision simulator
protanopia (red blindness)
deutrernopia ( green blindness)
tritanopia (blue blindness) not sex linked
similar feature in colour brewer software
Where does RGB colour blindness occur
occurs on the x chromosome
what is successive contrast
colour production is “off” after being exhausted on something else
simultaneous contast (more important)
perception of colour difference dependeont on the background
figure/ground + colour
this is how the american flag opponent colours thing works
RGB vs CMYK
RGB is additive colour
CMYK is subtractive colour mixing
density of dots gives a pure and darker colour
how do printers and plots work
dots on the page merge together and we perceive as a whole
what is dithering
how the blotches are arranged on a page
colour vision impairments - protonopia
red blindness (L)
missing L cones - dichromats
less sensitive to red- anomalous trichromats
sex linked
colour vision impairments - deuteranopia
green blindness (M)
missing m cones = dicrohmats
less sensitive to green - ana=omalous trichromats
sex linked
colour vision impairments - tritanopia
blue blindess (S)
missing s cones - dirchromats
less sensitive to blue - anomalous trichromats
not sex related
