Color vision PO LEC

• Light


  • Travels in a straight line with an approximate speed of (in a vacuum) 299,792,458 m/s
  • Speed of light in a space is slower
• Colors of visible light

  • Red (longest wavelength and lowest frequency)
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet (shortest wavelength and highest frequency)

  
• Photons


  Mass-less particles that are electrical fields traveling through space
• Properties of light


  • Wavelength - crest to crest or trough to trough, measured in meters
  • Amplitude - height of each crest or depth of each trough
  • Frequency - number of wavelengths within a period of time, measured in cycles per second
  • Energy - measured in electron volts (eV)

  
• Long wavelength, low frequency (inversely proportional)
• Electromagnetic spectrum


  • Infrared - wavelength longer than the red of the visible light
  • Ultraviolet, Gamma ray and X-rays - wavelength shorter than the violet wavelength

  
• Visible spectrum


  The narrow portion within the electromagnetic spectrum that can be seen by the human eye
• Newton identified the ROYGBIV colors (red, orange, yellow, green, blue, indigo, and violet) that make up the visible spectrum
• Effects of color


  • Sparks our emotions
  • Influences our moods
  • Gives symbolic meaning
  • Influences our purchases
  • Used to define contours
  • Helps us remember objects
  • Helps us judge properties
  • Part of our experience
• Color


  • That aspect of things that is caused by different qualities of the light reflected or emitted by an object, definable by the observer in terms of: hue, lightness and saturation
  • That characteristic of light by which an individual is made aware of the objects through the receptors of the eye, definable by the observer in terms of: wavelength, luminance and purity
• Qualities (properties) of color

  • Hue - the familiar color's name or family and directly linked to the wavelength
  • Brightness/Luminosity/Luminance/Value - the apparent intensity of color, the darkness (shade) or lightness (tint) of a color
  • Saturation/Chroma - the purity of a color, dilution of hue by white
  • Temperature - warm and cool colors

  
• Factors that determine the colors of objects

  • Physics of the object relative to the environment - the spectrum of the incident light, reflectance properties (material and its physical and chemical state, the surface roughness, and geometric circumstances - light angle of incidence) of the surface
  • Characteristics of the perceiving eye - Chromatic adaptation, Color constancy

  
• White light reflects yellow, other colors will be absorbed
• Characteristics of the human eye


  • Cortical level
  • Retinal Level - L-cones (long cones) sensitive to RED, M-cones (medium cones) sensitive to GREEN, S-cones (short cones) sensitive to BLUE
• We are able to see yellow because L-cones and M-cones combined together in order to perceived yellow
• Color vision


  • Ability to discriminate various wavelengths independent of light intensity
  • Ability to discriminate among stimuli on the basis of hue, independent of brightness or any other cue
  • Uses the effective energy of light and the properties of light to create color
  • Used to determine the location and shapes of objects and their identity and characteristics

  
• Factors for color vision

  • The wavelength after it is reflected it will be absorbed by the cones, and which cones will react on it (whether L,M,S cones), this nerve impulse will be transmitted to the retina (End of the retinal process/Cortical level)

  
• Aspects of color vision

  • Physiological Aspect (COLORIMETRY) - Measure of visual function at the photoreceptor level or the retinal level of color vision, Color encoding
  • Psychological Aspect (COLOR DISCRIMINATION & COLOR CONSTANCY) - Measure of cortical function at the later stages of visual processing, Color perception affected by surround stimulus, adaptation, and experience

  
• Factors affecting color perception

  • Color Context / Chromatic Contrast / Chromatic Induction / or Setting - The appearance of color is altered by introducing a second surrounding color
  • Prior Exposure to Stimulus - Processes of adaptation constantly adjust visual sensitivity according to the stimulus the observer is currently viewing

  
• Colorimetry


  The science and technology that quantifies and physically describes human color perception. It includes the perception of color by the human eye and brain, the origin of color in materials, and the physics of visible electromagnetic spectrum

  
• Color vision supports 2 distinct visual functions

  • COLOR DISCRIMINATION - the ability to determine that two spectra (wavelength) differ or the ability to match or detect differences between them
  • COLOR CONSTANCY - ability to identify objects on the basis of their color appearance. The color of the object remains the same despite changes in the properties of the object and light

  
• Color vision process


  • Chromatic Adaptation (surface based processing) - a process of favorable or useful adjustment of sensory processes to compensate for changes in the spectral quality of light source in order to keep visual perception of color approximately constant
  • Color Naming (category-based processing) - refers to the ability to identify colors based on memory, learning, and categorization

  
• Color mixing


  • Juxtaposition / Optical Color Mixing

  - based on the positioning of the colors, the arranging of different colors side-by- side to create optical effects in a viewer’s eye.

  • Physical Color Mixing - adding colors with the use of light (ex: in the auditorium in stage, spotlights), and subtractive - adding colors with the use of pigments (ex: watercolor, clays)
  • Physiological - based on positive after-image

  
• Afterimage


  The continuation of a visual sensation after removal of the stimulus
• Positive after-image


  The image has the same color as the original stimulus
• Color constancy


  The visual perception of color approximately constant despite changes in illumination or the ability of the visual system to preserve the appearance of an object under a wide range of light sources

  
• Color naming


  The ability to identify colors based on memory, learning, and categorization

  
• Color mixing


  • Physical color mixing (adding colors with light or pigments)
  • Physiological (based on positive afterimage)
  • Juxtaposition / Optical color mixing (based on positioning of colors)

  
• Positive afterimage


  Image has the same color as the original image

  
• Negative afterimage


  Image has the opposite color as the original image
• Trichromatic theory


  • There are three receptors in the retina responsible for color perception, and the combination of these three colors produces all perceived colors
  • Young suggested the eye contained different photoreceptor cells sensitive to different wavelengths
  • Helmholtz suggested cone receptors were short, medium or long wavelength and the strength of signals determines color interpretation

  
• Opponent process theory


  • The ability to perceive color is controlled by three receptor complexes with opposing actions: red-green, blue-yellow, and black-white
  • Assumes 4 "primary" colors
  • Works through excitatory and inhibitory responses, leading to negative afterimages

  
• Complementary color theory


  • Each receptor pairing registers complementary colors, and when complementary colors are added together, they make white

  
• Dual process theory


  • The color vision system contains an initial trichromatic stage and a later opponent-process stage

  
• Color vision classification


  • Normal - Trichromacy
  • Anomalous Trichomacy (Protanomaly, Deuteranomaly, Tritanomaly)
  • Dichromalous / Dichromacy / Dichromatopsia (Protanopia, Deuteranopia, Tritanopia)
  • Achromalous / Achromacy / Achromatopsia
  • Monochromalous / Monochromacy / Monochromatopsia (Cone Monochromacy, Rod Monochromacy)

  
• Most common color vision anomalies are red-green color blindness, more common in men than women, and can be genetic or acquired

  
• Color vision tests


  • Color naming
  • Reading color names
  • Holmgren Wools Test
  • Farnsworth Lantern Test
  • Farnsworth Panel D-15 Test

  
• Chromatic adaptation

  • ability to adjust to changes in illumination in order to preserve the appearance of object colors) and personal contextual cues
• Color constancy

  • ability to perceive colors as relatively constant over varying illuminations)
• • Red- (L-cones) are stimulated

  ● Yellow- L-cones and M-cones are stimulated

  ● Blue - S-cones are stimulated

  ● Purple- S-cones and L-cones are stimulated