Visual Perceptionof PicturesThanks to W. Warren, Brown University, for many of these slides, and Jan Koenderink, Utrecht University, for other slides

Picture PerceptionHow do we perceive 3D spatial structure from cues in a photograph or painting?

The eye is NOT a cameraThere is NO homunculusVision is NOT veridicalWhat we see is NOT really there; the HVS transforms the raw data

Pictorial Space Structure CuesSize, texture, shading, occlusion, etc.But NOT stereo, motion parallax, accommodation, etc.

Layout of objects in scene is specified by their relative locations on ground surfaceGround texture provides intrinsic scale of relative distance and sizeHorizon ratios specify relative depth and sizeInformation is preserved in image from any viewpoint

Depicting Our World: The BeginningPrehistoric Painting, Lascaux Cave, France, ~ 13,000 -- 15,000 B.C.

Origins of Picture Making: ShadowsCorinthian MaidTraced an outline of her lovers shadow to create a permanent reminder of him before he left the countryFavored explanation for the origin of painting and drawing in 18th and early 19th centuriesJoseph Wright, The Corinthian Maid, 1783-84

Cimabue, Madonna in majesty (c. 1280)Depicting Our World: Middle Ages

The Empress Theodora with her court. Ravenna, St. Vitale (6th c.)Depicting Our World: Middle Ages

paintingmirrorbaptistryFilippo Brunelleschis Discovery of Linear Perspective, c. 1413

Reduction screen: monocular viewno stereopsisno convergenceno motion parallaxincreases depth of field, reduces accommodationoccludes frame/edgeseye at station pointUnified perspective & cuesMirrorblurs painting surface texturelittle mirror surface texturevirtual image behind mirrorBurnished silverreflects skymoving cloudsvirtual image at infinite distanceWhy Did It Work?

Albertis WindowLeon Battista Alberti, De Pictura, 1435 Look through a stretched gauze sheet (window) held at a fixed distance to see the distant scene. Note the location on the cloth corresponding to key points in the scene. Transfer to grid on painting canvas.Can be done with a frosted glass windowSame basis as in Drers perspective methods

Hieronomous Rodeem (1531) Johan II of Bavaria. Woodcut.First of all, on the surface on which I am going to paint, I draw a rectangle of whatever size I want, which I regard as an open window, through which the subject to be painted is seen.

-- Alberti (1435-6)Albertis Window

Albertis Reticolato (grid) (c. 1450)On table for stabilityPost to ensure stable viewing (eye position)Wires on wooden frame form gridPlace frame perpendicular to line of sight, at a distance to frame sceneDraw on separate pageProper viewing position: where the top of the post was

Drer, Draughtsman Drawing a Recumbent Woman (1527)Same basic principle as Albertis veilLeonardo used a related technique in 1510Geometrical (rather than orthoscopic) perspectiveProper viewing position: tip of rod

Masaccio, Trinity, c. 1427, Santa Maria Novella, FlorenceDepicting Our World: Renaissance

Carlo Crivelli (1486) The Annunciation, with St. Emidius

Perspective analysis of Crivellis Annunciation

Depicting Our World: RenaissancePiero della Francesca, The Flagellation (c.1469)

Painting as a cross-section of Euclids and Albertis visual coneThe light ought to come from the Picture to the spectators Eye in the very same manner as it would from the objects themselves. -- Brook Taylor, 1715Illusionism

Trompe LOeil

Deceiving the EyeA depiction of an object, person, or scene, which is so lifelike that it appears to be realA style of painting which gives the appearance of three-dimensional, or photographic realism. It flourished from the Renaissance onward. The discovery of linear perspective in 15th-century Italy and advancements in the science of optics in the 17th-century Netherlands enabled artists to render object and spaces with eye-fooling exactitude.

Samual van Hoogstraten (1662) Perspective illusionTrompe LoeilPaintingDeceive the eyeA completed painting is as a mirror of nature, where things that do not appear seem to appear, and which deceives in an allowably entertaining and praiseworthy manner.

Andrea Mantegna (1461-74) Ceiling fresco, Camera degli Sposi, Palazzo Ducale, Mantua

Richard Haas Mural, 1987, Madison, Wisconsin

Fra Andrea Pozzo (1691-4) The glorification of St. Ignatius. Church of St. Ignazio, Rome.Viewed from marble disk at CP

Wrong viewpointPozzos Drawing Technique

Made a detailed drawing of the false architecture, and transferred it onto a square grid.Suspended a matching network of strings from the top of the nave, just below the curved vault.Strings attached at chosen viewpoint on the floor.Visually project string onto cylindrical ceiling.

Rules of Successful Trompe LOeilShallow depthwide range of acceptable viewing positionsless conflicting motion parallaxNo element cut off by frameless conflicting dynamic occlusionLife sizeFits into surroundingsHard edges, dark shadows, strong reliefSmooth picture surfaceoil and colored varnish: no brushstrokes

Samual van Hoogstraten (1662) Perspective illusionLinear Perspective is only Correct when Viewed from the Center of Projection

It is impossible that your perspective should not look wrong, with every false relation and disagreement of proportion that can be imagined in a wretched work, unless the spectator, when he looks at it, has his eye at the very distance and height and direction where the eye was placed in doing this perspective.-- Leonardo, NotebooksPerspective Distortion

La Gournerie (1859) Treatice on Linear Perspective Back-project from incorrect viewpoint (assuming parallel edges) Shear: line to VP = center of corridor Expansion: smaller angle = farther distancePerspective Distortion

The Robustness of our Perception of PerspectiveYet its been observed that we dont often notice perspective distortions caused by the observer not being at CP!

Station Point Paradox: Perspective is geometrically correct only when viewed from the center of projection (CP), yet pictures dont look distorted from many other viewpoints. How?

Pierre-Etienne-Thodore Rousseau (1857) The village of Becquigny. Frick Collection

Rousseaus Village of Becquigny, viewed from about 45 to the left.

Leonardo Da Vinci (1495-8) The last supper. Refectory of the Church of Santa Maria della Grazie, Milan (restored 1999)

Leonardo Da Vinci (1495-8) The last supper. Refectory of the Church of Santa Maria della Grazie, Milan.

The Compensation Theory(Pirenne)We perceive the surface of the picture and use it to compensate for an incorrect viewing position, and thus for the geometric distortion.

When the shape and position of the picture surface can be seen, an unconscious psychological process of compensation takes place, which restores the correct view when the picture is viewed from the wrong position. -- Pirenne (1970)We see an ellipse as a tilted circleMust see the surface to see through the surface

The Geometer Theory(Kubovy)But how do you know where the correct viewpoint is?

The visual system acts like a geometer to reconstruct CPInverse perspective analysisRecover position and distance of CP

Then compensate for current viewing position and correct distortions

Warrens Non-Euclidean TheoryDistortions are present, but we usually dont notice themDont attend to Euclidean shape and distance, but to relative (local) layout of sceneSee distortions because projected shapes are wrong. Larger distortions are more noticeable.Same image specifies receding road from any viewpoint. Rotation is more noticeable with deep perspective.

Ascending and Descending, 1960 Waterfall, 1961M. C. Escher

Retinal SamplingDensity of receptors decreases exponentially from the center to the periphery of the retina

Visual AcuityWith one eye shut, at the right distance, all of these letters should appear equally legible

What Makes the Mona Lisa Smile?"The elusive quality of the Mona Lisa's smile can be explained by the fact that her smile is almost entirely in low spatial frequencies, and so is seen best by your peripheral vision-- Margaret Livingstone The smile only becomes apparent if a viewer looks at her eyes or elsewhere on her face; the smile disappears when looking directly at her mouth

Peripheral vision is low resolution and blurs, picking up shadows from the Mona Lisa's cheekbones, which suggests the curvature of a smile The actress Geena Davis also shows the Mona Lisa effect, always seeming to be smiling, even when she isn't, because her cheek bones are so prominent

Field of ViewHuman vision system uses narrow-field-of-view and wide-field-of-view naturally and intelligently2o, high-acuity fovea window of the world3 saccades per second and gaze movesHuman vision can integrate information seamlessly

Saccadic Eye MovementsWork by Russian psychophysicist Yarbus who traced saccadic eye movements

When is Perspective NOT Robust?Trompe loeilonly 1 correct viewpointother viewpoints often yield visual distortionsPictures of picturesAnamorphic art

Fra Andrea Pozzo (1691-4) The glorification of St. Ignatius. Church of St. Ignazio, Rome.View from end of nave.

Successful Trompe LOeilPrevents Robust PerspectivePictorial cues:Linear perspectiveInterposition, etc.No surface information:Stereopsis (too far)Convergence (>> 1 m)Accommodation (>> 1 m)Surface texture (too far)No picture frameLittle motion parallax (too far)3D Scene2D Surface

Time Magazine, 1968A photograph ofa photographWe cant see theorientation of the photo relative to the viewer, so no automatic correction occurs and the photo looks distorted

Anamorphosisana-mor-pho-sis: 1. a drawing presenting a distorted image which appears in natural form under certain conditions, as when viewed at a raking angle or reflected from a curved mirror. 2. the method of producing such a drawing. 3. Zoology, Entomology. the gradual change in form from one type to another during the evolution of a group of plants or animals 4. (in certain arthropods) metamorphosis in which body parts or segments are added to those already present.

Leonardo da Vinci, Codex Atlanticus, c. 1486

Hans Holbein (1533) The ambassadors. National Gallery, London

Hans Holbein the Younger,The Ambassadors, 1533

2 Centers of Projection:Orthogonal PPSlanted PP Anamorphic Projection

William Scrots (1533) Portrait of Prince Edward VI of England

Jan van Eyck, Portrait of Arnolfini and his Wife, 1434

Make your view at least 20 times as far off as the greatest width or height of the objects represented, and this will satisfy any spectator placed anywhere opposite to the picture.

-- LeonardoTo minimize noticeable distortion, use shallow perspective:Example: Leonardos Moderate Distance RulePainters have used Heuristics to aid in Robust Perception of Perspective

Mantegna, Lamentation over the dead Christ, 1480 Example: Extreme Viewpoints Perspective

Ogdens photo recreation of The dead Christ.

Extreme perspective is due to a very close CPBreaks Leonardos Moderate Distance RuleWhen viewed from CP, it doesnt look distorted!Therefore Goodman is wrongBut from a typical viewing distance, feet look too big, head too smallAs expected from geometric projection -- perspective is not robust!So Mantegna corrected for typical viewing conditionsGeometric reasons for correctionDoesnt undermine naturalness of linear perspectiveExtreme Perspective

Ucellos Battle of San Romano,c. 1435, Uffizi Gallery

Pinhole camera photo of a marginal sphereExample 2: Marginal View DistortionObjects that are close to the viewer and at edge of field of view, are elongated by perspective projection

Raphael, School of Athens, 1511

Detail of Raphaels School of AthensPtolomyZoroasterSpheres should be elongated to be perspectively correct, but they are not

Pirennes pinhole camera photo of marginal columnsLeonardos Solution to the ProblemMake your view at least 20 times as far off as the greatest width or height of the objects represented, and this will satisfy any spectator placed anywhere opposite to the picture. -- Leonardo

Pieter Jansz. Saenredam (1637) Interior of St. Bravo at Haarlem.

Analysis of. Saenredams St. Bravo

Out of Bounds Photography

Out of Bounds Photography

Escaping Criticism,1874, del CasoOOB Predates Digital Photography!

Whys the Person in that Painting Staring at Me?

Moon IllusionSize of moon appears larger when near the horizon than when it is far from the horizonApparent distance theory it looks farther away because of size cuesAngular size contrast theory large relative to other objectsOculomotor micropsia/macropsia theory eyes converge

************************Woodcut, 8 x 22 cmGraphische Sammlung Albertina, Vienna**********************************************************************