Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Color Perception Mechanisms

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Color Perception u Trichromats u Humans have three cones that correspond to three ranges of the visible light in the areas of red, green, and blue light Wavelength (nm) Relative response BlueCyanGreenRed 490 ILS

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Human Color Vision Deficiencies u Normal Vision u Viewer requires 3 basic colors to match another color. u 91% Males u ~ 99% Females u Anomalous Trichromacy u Also requires 3 basic colors to match another color, but the ratios of those three basic colors differ from a person with normal vision. u ~ 6% Males

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Human Color Vision Deficiencies u Monochromacy u Requires one color to match any other color u Two types: u Cone monochromats: Only one type of cone (very small % of population) u Rod monochromats: Only the rods respond (.003% males) u Dichromacy u Requires two colors to match any other color; 8- 10% Caucasion males u Four types: u Protanopes: No L cones (1% males) u Deuteranopes: No I cones (1% males) u Tritanopes: No S cones (very small % pop.) u Tetartanopes: Lack chromatic channel (RG or YB, small %)

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Human Color Vision Deficiencies

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Temporal Perception u Negative Afterimages u A viewer stares at an image for a period of time. u The cones become desensitized. u Upon looking at a plain white surface, the viewer perceives the previous image with complementary colors.

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Temporal Perception u Positive Afterimages - Persistence of Vision u An intense flash of light allows a viewer to see a scene. u When the light goes out the signal from the cones persist. u The viewer still perceives the image.

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Motion Perception u Real Movement u An object physically moves. u Induced Movement u The background moves behind an object causing the perception that the object moved.

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Motion Perception u Stroboscopic Movement u Quick, sequential flashes of light / images that imply motion. u e.g. television, film, monitor u Autokinetic Movement u A still spot of light appears to move in an unlit background. u e.g. star in the night sky

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Aftereffects of Movement u Waterfall Illusion u After staring at water falling, look at a still object, and it will appear to move upward. u Spiral Aftereffect u After staring at a rotating spiral: u a still spiral appears to move in the opposite direction. u an object will appear to deform in the spiral motion opposite that initially observed.

Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Consequences of Movement u Perception of Causality u One event is seen after another, thus it may be interpreted that the 1st event caused the 2nd. u Personification u Human / animal characteristics given to inanimate objects. u Perception of Location u Object 1 is seen going behind object 2, thus causing the viewer to extrapolate the location of object 1. u Linking Successive Shots u e.g. television, film