111Lec. 27, Tuesday, April 20Chapter 8: Binocular vision• Why two eyes• Binocular disparity• Conveying depth in art• Stereo images1We are here1Next homework is due Thursday, April 22. 2Why two eyes?1. Wider field of view: one eye sees 130 degrees, two eyes see 208 degrees2. Depth perception: the two images are not the same. The difference, binocular disparity, tells us the distance. Animal eyes:Predators: eyes in front, like catsPrey: eyes on sides of head, like cows, ducks, rabbitsExceptions: prey living in trees; monkeys, squirrels23How do we perceive distance?Accommodation:eye muscles must exert a force to focus more closely. You can feel the strain associated with accommodation.Convergence:your eyes must both orient toward the center of the field of view in order to focus on something close. Parallax:a different view is seen from different positions. Hold up a finger in front of your face. Look at a distant object through one eye and then the other. 34Convergence (again)45What is parallax?What is binocular disparity?5Left eye view Right eye viewThe items are a basketball and a grapefruit. The brain interprets the difference in the images as due to distance.The image difference is binocular disparity. 6Stereo Photographytwo cameras make two images to reproduces binocular disparity6The three-d view looks “just right” when the cameras have the same spacing apart as your eyes. Is this answer a surprise? The spacing of eyes is about 6.5 cm or about 2 ½ inches.7Viewing a stereo image7This 19thcentury device is a stereopticon or stereoscope. 8Lenticular screenLenticular screens were used for 3-d “baseball cards.”These have little lenses embossed in plastic (see diagram below) which send to the left and right eyes different images which are printed in small vertical strips under the lenses. 8PlasticlenticulesThere is an LCD version of the lenticular screen that shows 3-d. However, you must be standing in front at the right distance.999Lec. 27, Tuesday, April 20Chapter 8: Binocular vision• Why two eyes• Binocular disparity• Conveying depth in art• Stereo images9We are here9Next homework is due Thursday, April 22. 10Conveying 3-d in 2-d artSix ambiguous depth cues (having more than one interpretation)1.Size2.Perspective3.Light and shadow4.Low contrast5.Overlay6.Previous knowledge10111. SizeWe interpret bigger as being closer. Trickery: a gardener will but big leafed plants in front and small leafed plants in back to make the garden look deeper. 1112Thirteenth century artists tended to draw the most important person (the king?) the biggest. Later, more sophisticated artists used smaller size to indicate persons further away.12CIMABUEVirgin Enthroned with Angels1290-9513Pietro Perugino's usage of perspective in this fresco at the Sistine Chapel (1481–82) helped bring the Renaissance to Rome. Wikipedia142. PerspectiveThe convergence of parallel lines as they become more distant, as in railroad tracks. Also, buildings look less wide at the top. 14“Vanishing point”15Pieter Jansz Saenredam, Assendelft Church, 1649. 1615thcentury illustration lacking vanishing points. More distant persons are smaller, but inconsistently.17ARTIST Giorgio de ChiricoPAINTING Mystery and Melancholy of a Street 18Artist Name: John Grazier Title: Will Grandmother Be Home19"The Suitcase and the City" by John Grazier. 20Rays of light travel from the object, through the picture plane,and to the viewer's eye. This is the basis for graphical perspective WikipediaExtended linesConverge at two points21Two point perspective Used when the picture plane is not parallel to surfaces in the image.223. Light and shadowThe shadow shows the cross section of the object22Wall clock. Alarm clock on table. Ball on table.23Shadows also convey texture23Francisco de Zurbarán, Martyrdom of Saint Serapion, 1628.24Yrjö Edelmann25Artist Yrjö EdelmannTitle Lotta i sängen26Highlights• These are reflections of incident light.2627Matisse: The Painter’s FamilyNo shadow. No perspective. On purpose.284. Low contrast for distanceWhich mountain (or pine tree) is most distant?2829Hiroshige: Miyanokoshi305. Overlay30316. Previous knowledgeWhich bunny is closer than the cow? 31326. Previous knowledge (2)32Table top is not a parallelogram. Table top is not a trapezoid. Also demonstrates shape constancy.33Schroeder’s stairs Thiery’s figureAmbiguous figures34Victor Vasarely35M. C. Escher’sWaterfall363636Lec. 27, Tuesday, April 20Chapter 8: Binocular vision• Why two eyes• Binocular disparity• Conveying depth in art• Stereo images36We are here36Demo:37How do colored 3-d glasses work?The two images are in red and blue ink, printed on the same page.Red ink is black seen through the blue filter and is light seen through the red filter. The reverse is true for blue ink. So the red-filtered eye sees the blue image and vise versa. Problem: images do not have a full range of color. 373838Special screen that does not “scramble”polarization39How do polarized 3-d glasses work?1. The two images are projected onto a screen. 2. The light passes through polarizing filters leaning 45 degrees to the left and 45 degrees to the right.3. The person wears polarizing glasses so each eye sees just one of the images. 4. The projection screen must be special to preserve the polarization. 394040Special screen that does not