COMPUTER GRAPHICS CS 482 – FALL 2015 SEPTEMBER 1, 2015 HUMAN VISUAL PERCEPTION EYE PHYSIOLOGY COLOR BLINDNESS CONSTANCY SHADOWS PARALLAX STEREOSCOPY

EYE PHYSIOLOGY CS 482 – FALL 2015 RODS & CONES SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 30 THE THIN LAYER OF NERVE CELLS AT THE BACK OF THE EYE IS CALLED THE RETINA. THE LIGHT SENSOR CELLS CAPABLE OF WORKING OVER A WIDE RANGE OF ILLUMINATION LEVELS AND OF PROVIDING QUICK RESPONSE TO CHANGES ARE CALLED RODS. THE SECTION OF THE RETINA THAT REACTS TO COLOR IS CALLED THE FOVEA. THE “TRISTIMULUS THEORY OF COLOR” HYPOTHESIZES THAT EACH CONE IS SENSITIVE TO EITHER RED, GREEN, OR BLUE. HIGH RESOLUTION COLOR IMAGING IS PROVIDED BY LIGHT SENSOR CELLS CALLED CONES, LOCATED IN THE FOVEA.

EYE PHYSIOLOGY CS 482 – FALL 2015 PHOTORECEPTORS SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 31 PHOTORECEPTOR CELLS ARE ARRANGED IN CIRCULAR REGIONS KNOWN AS RECEPTIVE FIELDS. ON-CENTER FIELDS HAVE A CORE OF LIGHT- SENSITIVE RECEPTORS SURROUNDED BY DARK-SENSITIVE RECEPTORS. OFF-CENTER FIELDS HAVE A CORE OF DARK- SENSITIVE RECEPTORS SURROUNDED BY LIGHT-SENSITIVE RECEPTORS. RECEPTIVE FIELDS ARE FULLY ACTIVE WHEN LIGHT IS RECEIVED BY THE LIGHT-SENSITIVE RECEPTORS BUT NOT BY THE DARK-SENSITIVE RECEPTORS. RECEPTIVE FIELDS ARE FULLY INACTIVE WHEN LIGHT IS RECEIVED BY THE DARK-SENSITIVE RECEPTORS BUT NOT BY THE LIGHT-SENSITIVE RECEPTORS. CENTER/SURROUND ANTAGONISM OCCURS WHEN LIGHT IS RECEIVED BY BOTH THE LIGHT-SENSITIVE AND THE DARK-SENSITIVE RECEPTORS.

EYE PHYSIOLOGY CS 482 – FALL 2015 LATERAL INHIBITION SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 32 THE HERMANN GRID PICTURED AT LEFT BELOW GIVES THE IMPRESSION OF GRAY SPOTS AT EACH INTERSECTION, UNLESS THOSE INTERSECTIONS ARE VIEWED DIRECTLY. THIS IS DUE TO LATERAL INHIBITION, IN WHICH ON-CENTER RECEPTIVE FIELDS HAVE THEIR LIGHT-SENSITIVE RECEPTORS RECEIVING LIGHT WHILE THEIR DARK-SENSITIVE RECEPTORS RECEIVE A MIX OF LIGHT AND DARK. MACH BANDING, THE CURVED APPEARANCE OF THE SOLID- COLORED BANDS ABOVE, IS CAUSED BY RECEPTIVE FIELDS LINED UP AT THE BORDER BETWEEN BANDS, WITH A CENTER RECEIVING MAINLY LIGHT OR DARK AND A SURROUND RECEIVING A HEAVY MIX OF BOTH LIGHT AND DARK.

COLOR BLINDNESS CS 482 – FALL 2015 COLOR VISION DEFICIENCIES SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 33 MALFUNCTIONING OR MISSING CONES OF A PARTICULAR COLOR SENSITIVITY (RED, GREEN, OR BLUE) RESULTS IN ABNORMAL COLOR PERCEPTION. NORMAL VISION (NO DEFICIENCIES) 92% OF MALES 99.5% OF FEMALES PROTAN (RED DEFICIENCY) 2% OF MALES 0.11% OF FEMALES DEUTERAN (GREEN DEFICIENCY) 6% OF MALES 0.33% OF FEMALES TRITAN (BLUE DEFICIENCY) 0.05% OF MALES 0.05% OF FEMALES AN ISHIHARA COLOR BLINDNESS TEST AND HOW IT IS PERCEIVED BY NORMAL AND DEFICIENT VIEWERS

CONSTANCY CS 482 – FALL 2015 COLOR CONSTANCY SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 34 ALTHOUGH THE SQUARES ON THE RIGHT APPEAR DARKER THAN THOSE ON THE LEFT... …THEY ARE ACTUALLY IDENTICAL. IF LIGHT IS DETECTED SOLELY BY THE CENTER PHOTORECEPTORS IN AN ON-CENTER RECEPTIVE FIELD, THEN THE FIELD’S RESPONSE IS PROPORTIONAL TO THE LIGHT INTENSITY. HOWEVER, IF LIGHT IS ALSO DETECTED BY THE DARK SURROUND PHOTORECEPTORS, THEN THE CENTER AND SURROUND REGIONS CONFLICT WITH EACH OTHER AND IT TAKES A GREATER AMOUNT OF LIGHT TO ACHIEVE A FIELD RESPONSE.

CONSTANCY CS 482 – FALL 2015 GAMMA CORRECTION SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 35 BECAUSE OF THE HUMAN VISUAL SYSTEM’S SENSITIVITY TO LIGHT CONTRAST, RGB VALUES ARE STORED AS GAMMA-CODED VALUES (R , G , B  ), USUALLY WITH   WITHOUT GAMMA CODING (0,0,0)(1,1,1) (0.5,0.5,0. 5) (0.75,0.75,0.7 5) (0.25,0.25,0.2 5) WITH GAMMA CODING (0,0,0) (1,1,1) (0.5,0.5,0. 5) (0.75,0.75,0.7 5) (0.25,0.25,0.2 5) THIS RESULTS IN A WIDER VARIETY OF BRIGHTER SHADES, PROVIDING GREATER ABILITY TO ACCOMMODATE THE HUMAN’S EYES SENSITIVITY TO LIGHT. WHEN TRANSFERRING THE STORED IMAGE TO THE DISPLAY, IT MUST BE GAMMA-DECODED, USING A POWER OF   2.2. GAMMA CODING GAMMA DECODING

CONSTANCY CS 482 – FALL 2015 SHAPE CONSTANCY SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 36 HUMANS PERCEIVE THAT AN OBJECT’S SHAPE AND SIZE HAVEN’T CHANGED, EVEN IF THE PERSPECTIVE FROM WHICH THE OBJECT IS VIEWED DOES CHANGE.

SHADOWS CS 482 – FALL 2015 VISUAL CUES SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 37 SHADOWS PROVIDE VISUAL CUES TO NOT ONLY AN OBJECT’S ELEVATION, BUT ALSO ITS DISTANCE FROM THE VIEWER.

PARALLAX CS 482 – FALL 2015 ILLUSION OF DEPTH SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 38 BY MODELING BACKGROUND IMAGES TO MOVE PAST THE CAMERA AT A SLOWER RATE THAN FOREGROUND IMAGES, GRAPHICS DEVELOPERS CREATE THE ILLUSION OF DEPTH. BEFORE THE DEVELOPMENT OF 3D COMPUTER MODELING, PARALLAX SCROLLING WAS IMPLEMENTED VIA MULTI-PLANE CAMERA SYSTEMS IN TRADITIONAL ANIMATION, VIA DEPTH BUFFERING IN RASTER-GRAPHIC GAMES, AND VIA HTML5 AND CSS ON WEB SITES.

STEREOSCOPY CS 482 – FALL 2015 VERGENCE VS. ACCOMMODATION SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 39 PROJECTING A 3D IMAGE ONTO A 2D SCREEN OR TELEVISION DISPLAY TENDS TO PLAY TRICKS WITH ONE’S VISUAL PERCEPTION. IN THE REAL WORLD, WHEN A PERSON TRIES TO FOCUS ON A DISTANT OBJECT, THE EYES EXPERIENCE VERGENCE, WHERE THEY BOTH ROTATE ON THEIR OWN VERTICAL AXES UNTIL THEY BOTH POINT AT THE OBJECT. MEANWHILE, THE EYES EXPERIENCE ACCOMMODATION, WHERE THEY REFLEXIVELY FOCUS ON THE OBJECT IN ITS DISTANT POSITION, CAUSING NEARBY OBJECTS TO GO OUT OF FOCUS. WITH 3D IMAGES, HOWEVER, THE EYES ROTATE SO THEY ARE POINTED TO WHERE THE OBJECT SEEMS TO BE, BUT THE REFLEXIVE FOCUS MUST ADJUST TO THE SCREEN’S ACTUAL LOCATION, ELIMINATING THE NATURAL BLURRING OF NEARBY OBJECTS. THIS RESULTS IN SERIOUS EYESTRAIN AND HEADACHES FOR MANY 3D AUDIENCE MEMBERS.

STEREOSCOPY CS 482 – FALL 2015 DIGITAL 3D SEPTEMBER 1, 2015: HUMAN VISUAL PERCEPTIONPAGE 40 ADVANCES IN DIGITAL PHOTOGRAPHY AND STEREOSCOPY HAVE ENABLED FILMMAKERS TO AFFORDABLY PRODUCE 3D FILMS AND THEATRE OWNERS TO AFFORDABLY SHOW THEM. A 3D DIGITAL CAMERA RECORDS VIDEO, CIRCULARLY POLARIZING THE RIGHT VIEWPOINT USING RIGHT- HANDED POLARIZATION......WHILE RECORDING THE LEFT VIEWPOINT USING LEFT-HANDED CIRCULAR POLARIZATION. BOTH IMAGES ARE PROJECTED SIMULTANEOUSLY ONTO THE THEATRE SCREEN, IN A MANNER THAT GUARANTEES THAT THE VIEWPOINTS ARE SYNCHRONIZED. THE MOVIEGOER WEARS POLARIZED GLASSES THAT ONLY ALLOW THE RIGHT-HANDED POLARIZED IMAGES TO PASS THROUGH THE RIGHT LENS AND THE LEFT-HANDED POLARIZED IMAGES TO PASS THROUGH THE LEFT LENS.