Percieving Colors Notes

Colors are not simple a function of differing wavelengths - are our response to visual stimuli via complexe processes that occur in our perceptual apparatus - involve the way our eyes register colors, classifying the inputs, transfer them to the brain, and the way the brain the decodes the signals

much of color perception can be described only theortically - don't yet know how we see colors - brain may override what the eye tells it

THE HUMAN EYE
light enters the eye through the cornea - the transparent outer covering

iris muscles expand and contract to admit more or less light through the pupil

admitted light is then focused on the back surface of the eye by 3 different kinds of refractors - the aqueous humor, crystalline lens, vitreous humor

back of the eye covered by retina - retina consists of many specialized cells arranged in layers

layer most important to color perception - photoreceptors called rods and cones

rods and conces are named because of their shapes

rods - allow us to distinquish forms in dim light, but only with black and white vision

cones - function under brighter lighting to allow us to percieve hues

we cannot perceive hues well at night

rods function in light as well as darkness

before light reaches the rods and cones through layers of nerve cells

only about 20% of the light that reaches the retina actually registers in the photoreceptive rods and cones, the rest in unseen

forea - at the center back of the eye is an area about 1mm in diameter - contains only cones - light falling on this area  gives the sharpest color definition - while examining details in images, we automatically move our eyes until what we want to see is center on the forea

in only about 2 of the 360 degress field surround us do we see most accurately

each eye has approximately 100 million rods and 6 million cones - communicate with the brain via the optic nerve

photoreceptors send electrochemical messages the optic nerve across synpases (gaps) in a complex network of optic nerve fibers

bipolar and ganglion cells thought to gather and pass on signals from rods and cones

horizontal and inner  associative cells seem to intergrate activities from across the retina

in the forea each cone is connected to a single bipolar cell and single ganglion cell where as signals from rods and cones on other parts of the retina are bundled together

information from the yes is transmitted to various areas on both sides of the brain, where it is somehow integrated to form a single image

almost 1/3 of the gray matter of the cerebral cortex is involved in this complex process

SEEING COLORS

scientists have no definite proof of how cones work

rods contain disks of a light-sensitive pigment called rhodopsin, or visual purple

when light strikes visual purple it bleaches, reducing the electrical signals for darkness otherwise transmitted by the rods

in the dark, rods have very large amounts of unbleached visual purple, allowing us to see forms with very little light present

rods can function at light ---? of up to 1000 x weaker than the visual system based on teh cones

cones contain light sensitive pigments called iodopsins - nature and functions still matters of conjectures

a theory is that there are 3 different kinds of cone pigments : one for sensing long (red range) wavelengths, one for middle (green range), one for short (blue-violet range). primary levels thought to mix to form all color sensations. red sensistive and green senssitve cones predominate in the retina. relatively few blue sensitive cones;

Trichromatic Theory - the icha?? of 3 different kinds of cones - first advanced in 1801 by English physicist Thomas Young. Developed mid-19th century by German physicist Hermann von Helmholtz

only explains what happens in the photoreceptors under direct light stimulation - electrochemical signals transferred from these receptors to the brain are handled somewhat differently and process may have more than 2 stages - colors may be discerned in pairs of opposing colors at this stage

Opponent theory - some response mechanism such as specialized cells in the visual cortex registers either gr or red, or blu-v or yellow. in each pair, only 1 kind of signal can be carried at a time, while the other is inhibited - pairs correspond roughly to complimentary colors on color wheel. another set of cells operating responding to variations between white and black is thought to operate in a non-opponent fashion, yielding a wide range of hues

AFTER IMAGES

opponent theory has been supported by electrical analysis of nerve cells in various animals - helps explain why we do not percieve reddish green or blueish yellow

also explains after images - visual sensations that occur briefly after a stimulus is gone

store at highly saturated color for a time and the neturally colored area, we see an illusory image of the color complimentary

may be that when signalling mechanism for 1 color is fatigued its opponent color is no longer inhibited

after image effect = successive contrast

COLOR CONSTANCY

described in 1959 - 1977 by EH Land, developer of Polaroid instant photography process - his methods and research discerned colors with much less information than was ever thought possible - both r and g and y and yellow combinations can be used to depicted colors

COLOR CONSTANCY - stange but familiar phenomenon by which colors subjectively seem to remain the same under different kinds of illumination

retinex theory - (retina plus cortex) - has been vindicated by neurobiological research that demonstrates a network of tiny peg-shaped blobs in the visual cortex at the back of the human skull - seem to compare visual information from an object with what is seen immediately surrounding it - colors in the immediate vicinity seem more important than colors seen at  a distance

NEODYMIUM underglaze - pottery, purple glass

VARIABLES IN COLOR PERCEPTION

color sensations occur in the responses of our perceptual apparatus - not inherent properties of objects

few animals other than human seem to see the world through trichromatic color vision

GENETIC AND CULTURAL DIFFERENCES

minimal genetic difference between 2 people in terms fo a particular amino acid effects their cone cells and the way they see color

COLOR BLINDEDNESS - major variations from the norm. most often found in men. 7% of men cannot distinguish between red and green

EMOTIONS

emotional states liekly influence color perception

depressed people may perceive dimmer colorings

pupils open wider when looking at something we like - allows more light in

narrow when looking at something we dont like

DESIGN FACTORS

a large expanse of colo appears brighter than a vey small area of teh same color

if a color field is very far away, it will dull and lose the sharpness of its edges

in some cases, a smaller area of color appears darker than a larger area - effect depends heavily on the color
of the background

all colors are affected by the colors around them

adjacent colors cann change each others apparent hues

OP ART MOVEMENT - artists fascinated with color interactions

LIGHTING

flourescent lighting - blue cast. expensive "full spetrum"  fl. are color corrected to approximate sunlight

incandescent - reddish yellow cast - redder than midday natural sunlight cast

color of sunlight continually varies - blue in the morning to white to red in the late afternoon - other factors can affect perception of this, though

we percieve colors as unchanging bc of visual memory

"The eye has evloved to see the world in unchanging colors, regardless of always unpredictable, shiftingm and uneven illumination." EH Land

Claude Monet (French impressionist 1840 - 1926) observed and painted exact same scenes under many different lighting conditions

colors may look brighter under strong museum lighting

in museums, walls are being opened up to let natural light in

in the Goodwin-stone building, Thermolux panels were installed, creating a luminosity of diffused light that extends from the 2nd to the 3rd floor galleries

SURFACE QUALITIES

color perception depends in teh case of pigments on the characteristics of the surgace from which it is felected

a 3d surface does not reflect lgiht uniformly

reflection of light from its outermost contours will be strongest making them appear very lgiht

a rough or porous matter surface will reflect lgiht in a more diffused mannner no extreme highlights of the glossy surface

materials have differing reflective qualities

REFRACTION - a ray of light passing through a transparent surface is refracted (bent) and then transmitted onward

REFLECTION AND TRANSMISSION - some light may be reflected from a transparent surface, depending on surroudnigns and the angle from which it is seen - if the surface is shiny, but not transparent, light is reflected, but not transmitted through

TRANSLUCENCE - translucent or semi-opaque surface transmits only a little light some light is reflected and some absorbed

ABSORBTION  the least flection occurs when light hits a dark matter surface - the lgiht is absorbed. in opaque materials, a bright white surface reflects the most lgiht and absorbs the least

WHITE GROUND - in painting, if a translucent layer of pigment and medium is spread over a white ground, some light is reflected back upward throught the paint, giving brilliance and luminosity to its colors, the more opaque the paint, the less this effect occurs

DARK GROUND - a dark ground beneath a layer of translucent paint absorbs rather than reflects light rays so there is no appearance of brilliance or luminosity

NONVISUAL COLOR PERCEPTION

ability to feel colors through hands not uncommon in blind people

some perople percieve colors when hearing sounds - so common that a body of research exists surrounding this kind of synthesia (combining 2 forms of perceptions)

Scribin - composer who associated musical keys with color

subjective associations

tend to experience rising pitch or quickening temp with lighter colors
sombre passages - dark colors

females much more likely to experience