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Theories that take color constancy into account are based on a large body of anatomical evidence as well as perceptual studies. There are nerve connections among the light receptors on the retina, and there are far fewer nerve connections to the brain than there are rods and cones. This means that there is signal processing in the eye before information is sent to the brain. For example, the eye makes comparisons between adjacent light receptors and is very sensitive to edges as seen in [link] . Rather than responding simply to the light entering the eye, which is uniform in the various rectangles in this figure, the eye responds to the edges and senses false darkness variations.

An image of black and gray gradient in stripes pattern is shown in first figure. A step graph in increasing order below the image shows actual light intensities of the above pattern. The graph appears uniform as the grey strips are also uniform, but they are not. Instead, they are perceived darker on the dark side and lighter on the light side of the edge as depicted in the graph below it, which shows a step graph with spikes at the beginning of the next step.
The importance of edges is shown. Although the grey strips are uniformly shaded, as indicated by the graph immediately below them, they do not appear uniform at all. Instead, they are perceived darker on the dark side and lighter on the light side of the edge, as shown in the bottom graph. This is due to nerve impulse processing in the eye.

One theory that takes various factors into account was advanced by Edwin Land (1909 – 1991), the creative founder of the Polaroid Corporation. Land proposed, based partly on his many elegant experiments, that the three types of cones are organized into systems called retinexes . Each retinex forms an image that is compared with the others, and the eye-brain system thus can compare a candle-illuminated white table cloth with its generally reddish surroundings and determine that it is actually white. This retinex theory of color vision     is an example of modified theories of color vision that attempt to account for its subtleties. One striking experiment performed by Land demonstrates that some type of image comparison may produce color vision. Two pictures are taken of a scene on black-and-white film, one using a red filter, the other a blue filter. Resulting black-and-white slides are then projected and superimposed on a screen, producing a black-and-white image, as expected. Then a red filter is placed in front of the slide taken with a red filter, and the images are again superimposed on a screen. You would expect an image in various shades of pink, but instead, the image appears to humans in full color with all the hues of the original scene. This implies that color vision can be induced by comparison of the black-and-white and red images. Color vision is not completely understood or explained, and the retinex theory is not totally accepted. It is apparent that color vision is much subtler than what a first look might imply.

Phet explorations: color vision

Make a whole rainbow by mixing red, green, and blue light. Change the wavelength of a monochromatic beam or filter white light. View the light as a solid beam, or see the individual photons.

Color Vision

Section summary

  • The eye has four types of light receptors—rods and three types of color-sensitive cones.
  • The rods are good for night vision, peripheral vision, and motion changes, while the cones are responsible for central vision and color.
  • We perceive many hues, from light having mixtures of wavelengths.
  • A simplified theory of color vision states that there are three primary colors, which correspond to the three types of cones, and that various combinations of the primary colors produce all the hues.
  • The true color of an object is related to its relative absorption of various wavelengths of light. The color of a light source is related to the wavelengths it produces.
  • Color constancy is the ability of the eye-brain system to discern the true color of an object illuminated by various light sources.
  • The retinex theory of color vision explains color constancy by postulating the existence of three retinexes or image systems, associated with the three types of cones that are compared to obtain sophisticated information.

Conceptual questions

A pure red object on a black background seems to disappear when illuminated with pure green light. Explain why.

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What is color constancy, and what are its limitations?

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There are different types of color blindness related to the malfunction of different types of cones. Why would it be particularly useful to study those rare individuals who are color blind only in one eye or who have a different type of color blindness in each eye?

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Propose a way to study the function of the rods alone, given they can sense light about 1000 times dimmer than the cones.

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Questions & Answers

what is mass
Victor Reply
is the amount of an object
mass is the measure of the inertia of a body
advantages of CRO over ordinary voltmeter
Dismas Reply
what is the difference between displacement and distance?!
Daniel Reply
what is equilibrium
Sade Reply
If a system is said to be under equilibrium whenever there is no force act upon it... And it remain in its initial stage..
what is velocity
time rate of displacement of a body is called velocity
What is conductivity
Saud Reply
It is the ease with which electrical charges or heat can be transmitted through a material or a solution.
how to find magnitude and direction
Arjune Reply
how to caclculate for speed
derivation of ohms law
Kazeem Reply
derivation of resistance
R=v/I where R=resistor, v=voltage, I=current
A puck is moving on an air hockey table. Relative to an x, y coordinate system at time t 0 s, the x components of the puck’s ini￾tial velocity and acceleration are v0x 1.0 m/s and ax 2.0 m/s2 . The y components of the puck’s initial velocity and acceleration are v0y 2.0 m/s and ay 2.0
Electric current is the flow of electrons
Kelly Reply
is there really flow of electrons exist?
Yes It exists
explain plz how electrons flow
if electron flows from where first come and end the first one
an electron will flow accross a conductor because or when it posseses kinectic energy
electron can not flow jist trasmit electrical energy
free electrons of conductor
electric means the flow heat current.
Serah Reply
electric means the flow of heat current in a circuit.
What is electric
Manasseh Reply
electric means?
electric means the flow of heat current in a circuit.
electric means the flow of electric current through conductor
the continuos flow of electrons in a circuit is called electric
electric means charge
electric means current
flow of current.
a boy cycles continuously through a distance of 1.0km in 5minutes. calculate his average speed in ms-1(meter per second). how do I solve this
Jenny Reply
speed = distance/time be sure to convert the km to m and minutes to seconds check my utube video "mathwithmrv speed"
d=1.0km÷1000=0.001 t=5×60=300s s=d\t s=0.001/300=0.0000033m\s
A puck is moving on an air hockey table. Relative to an x, y coordinate system at time t 0 s, the x components of the puck’s ini￾tial velocity and acceleration are v0x 1.0 m/s and ax 2.0 m/s2 . The y components of the puck’s initial velocity and acceleration are v0y 2.0 m/s and ay 2.0
D=1km=1000m t=5mins×60secs=300sec s=d/t=3.333m/s
I think Daniel Glorious is ryt
why we cannot use DC instead of AC in a transformer
kusshaf Reply
becuse the d .c cannot travel for long distance trnsmission
what is physics
Chiwetalu Reply
branch of science which deals with matter energy and their relationship between them
Life science
what is heat and temperature
Kazeem Reply
how does sound affect temperature
Clement Reply
sound is directly proportional to the temperature.
Practice Key Terms 6

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