MariaLardi

Critical

Visual perception, interpreting what is seen

Visual system, the sensory mechanism of eyesight

Vision (spirituality), inspirational experiences

Hallucination, vivid conscious perception in the absence of a stimulus

• Derived terms

Double vision, personal vision, prevision, visible, visibility, vision statement, visionary, visioner, visual

• Parallax

Parallax is an apparent displacement or difference in the apparent position of an object viewed along two different lines of sight.Motion parallax is a depth cue that results from our motion. As we move, objects that are closer to us move farther across our field of view than do objects that are in the distance. Depth perception arises from a variety of depth cues. These are typically classified into binocular cues that require input from both eyes and monocular cues that require the input from just one eye. Binocular cues include stereopsis, yielding depth from binocular vision through exploitation of parallax.

Motion parallax – When an observer moves, the apparent relative motion of several stationary objects against a background gives hints about their relative distance. If information about the direction and velocity of movement is known, motion parallax can provide absolute depth information.

Depth from motion – One form of depth from motion, kinetic depth perception, is determined by dynamically changing object size. As objects in motion become smaller, they appear to recede into the distance or move farther away; objects in motion that appear to be getting larger seem to be coming closer. Using kinetic depth perception enables the brain to calculate time to crash distance.

• Perspective

Perspective, in context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes; or their dimensions and the position of the eye relative to the objects. There are two main meanings of the term: linear perspective and aerial perspective.

• Linear Perspective

The human eye judges distance by the way elements within a scene diminish in size, and the angle at which lines and planes converge. This is called linear perspective. The distance between camera and subject and the lens focal length are critical factors affecting linear perspective. This perspective changes as the camera position or viewpoint changes. From a given position, changing only the lens focal length, and not the camera position, does not change the actual viewpoint, but may change the apparent viewpoint.

• Vanishing Point Perspective

In vision, lines that are parallel to each other give the sensation of meeting at vanishing points. When parallel lines, either horizontal or vertical, are perpendicular to the lens axis, the vanishing points are assumed to be at infinity. Other lines, those which are parallel to the lens axis, and all other parallel lines at all other angles to the lens axis meet at definable vanishing points. Thus lines that are parallel to the lens axis, or nearly parallel, start in the front of the picture and meet at vanishing points within the picture or at finite points outside the picture.

• Atmospheric Perspective

For all practical purposes, air is transparent. For most photography, this is fundamentally true; however, when pictures are made of subjects at great distances, the air is actually less than fully transparent. This is because air contains very fine particles of water vapor, dust, smoke, and so on. These particles scatter light and change its direction. The presence of scattering shows distant subjects in pictures as having a veil or haze. The appearance or effect of this scattering is proportional to the distance of the objects from the viewpoint. The greater the distance, the greater the amount of veiling or haze. The effects of this scattering of light are additive, but vary with atmospheric conditions. In atmospheric perspective several factors must be considered:

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Contrast–The luminance of each object in a scene is a direct result of the objects reflective quality and the amount of light falling on it. When objects are far away, light from highly reflective objects is scattered; therefore, when viewed from a distance (or imaged on a print), the darker portions of these distant objects do not appear as dark and the contrast is reduced. When there are objects both near and far from the camera, the difference in contrast provides a perception of distance.

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Brightness–The particles in air that scatter light are also illuminated by the sun. This causes an increase in the overall brightness of the objects seen. This increase in luminance, coupled with a loss of contrast, causes objects in the distance to be seen and photographed as lighter in color than they would be at a closer distance.

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Color saturation–The scattering of light not only affects contrast and brightness but also color saturation.

Color is defined by three qualities: hue (the actual wavelength), saturation (intensity or chroma), and brightness (reflective). A pure hue is fully saturated or undiluted. When a hue is desaturated or diluted, it is no longer pure but has gray intermingled with it. The actual colors of a distant scene appear to have less color saturation, because the light is scattered and also because of the overall presence of the desaturated (diluted) blue light of aerial haze. The original scene colors appear less saturated or pure when seen or photographed from a distance than from close-up; therefore, color saturation or desaturation allows the viewer to perceive distance in a color photograph.

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Sharpness–Because of atmospheric haze, there is a loss of image sharpness or definition in distant objects.

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This loss of sharpness is caused both by the lowering of contrast and the scattering of light. The loss of sharpness contributes to a sense of distance. This can be enhanced by setting the far limit of the lens depth of field just short of infinity. This procedure throws the most distant objects slightly out of focus. This combined with the other effects of aerial perspective intensities the sense of distance

• Aerial perspective

Is the effect of atmosphere on the perception of depth and distance. As particulate matter in the air gradually builds up over distance, the light reflecting off a particular object is filtered out to a greater or lesser degree. As a result, bright objects become duller and sharp edges become less distinct. And at the same time changes also occur, due to light scattering by the atmosphere, also resulting that objects that are a great distance away have lower luminance contrast and lower color saturation.

[Basic Perspective Drawing: A Visual Approach, By John Montague, Chapter 12, page 201]

• The Panoramic Image

A panorama (formed from Greek πᾶν “all” + ὅραμα “sight”) is any wide-angle view or representation of a physical space, whether in painting, drawing, photography, film/video, or a three-dimensional model.

Applications

• Artists Use

The history of perspective, when considered as a defined artistic practice, began in the fifteenth century and many prominent artists and architects such as Filippo Brunelleschi, Piero della Francesca, Paolo Ucello, Leonardo da Vinci, Albrecht Du¨ rer and Rafael Santi, contributed to the exploration of its theoretical and practical implications. Leonardo da Vinci defined three concepts in the theory of perspective, and his considerations are still valid today:

. Linear perspective

. Perspective of air and light

. Analysis of the sharpness of contours and contrasts depending on the spatial depth

• Computer Graphics / OpenGL

In computer graphics, this is often called “distance fog“. The foreground has high contrast; the background has low contrast. Computer Images sometimes seem unrealistically sharp and well defined. Antiallasing makes an object presented more realistic by smoothing its edges. Objects differing only in their contrast with a background appear to be at different depths. And also that colours indicate the part of a form that curves away from the picture plane. Additionally, an entire image can be made to appear more natural by adding ”fog”. This makes objects fade in to the distance>fog.

[OpenGL Programming Guide: Version 1.4: The Official Guide to Learning OpenGL -Networking Technology-by OpenGL Architecture Review Board, Dave Shreiner, Mason Woo, and Jackie Neider (Paperback - 27 Nov 2003), page 255)]

Case Studies/References

• Palazzo Spada Perspective, Rome, Borromini

The Palazzo Spada in Rome, built in 1638 by Francesco Boromini, is an illuminating example of how perspective can be used to deceive the eyes. The Palazzo is famous for its illusionary corridor created by Borromini. The corridor which is in the inner courtyard appears to be at least three times longer that it is due to the clever use of perspective, a shrunken statue and shrinking columns.

It appears to disappear into the distance when in fact it is actually just 9m long and if you were stood at the end you would have to bend over double to fit in the space. It is possible to see the statue without entering the gallery but only from a distance.

• Piranesi

The eighteenth-century Italian artist Giovanni Battista Piranesi has manipulated the conventional rules of perspective in order to produce a more believable and compelling representation of reality and subtly to influence our understanding of it. Piranesi’s technique reveals a sophisticated approach to the perspective which he employed. he composed views by combining different viewing positions is noted in the RIBA catalogue: Piranesi, Rome Recorded.2 One of the entries in the catalogue briefly points out that topographic view painters would often ‘compose’ their image from a number of viewing points and also that the manipulation of perspective was a common practice amongst the Vedutisti painters. The RIBA catalogue goes on to explain that only occasionally is this issue addressed in modern accounts of his work. But despite being given relatively little attention, this device remains an important clue to understanding the sophisticated approach employed by Piranesi.

Piranesi designed his images to capture the entirety of complex

environments of architectural ruins, so as to represent the experience of the Roman landscape .He aimed to capture the visual and symbolic essence of those artifacts, and to accomplish this he frequently adjusted his vanishing points with lateral shifts of viewpoint, and at times also combined views from widely separated view points into a single plate.

His drawings show greater structural clarity and portray massiveness of individual forms more convincingly. At the same time, Piranesi is very precise in controlling his etching technique, using lines that vary in width, and creating a more natural atmosphere for the scene. This broad range of line widths and densities allows contrasts of black and white, light and shadow as well as the gradual fading of forms in the distance.

• Vedute Paintings

The predominant characteristic of Vedute painting was not only

linear perspective but also natural atmospheric and tonal perspective. This kind of painting is as realistic as possible, and so, in a sense, similar to modern photography in its primary objective. Indeed, Vedute and landscape painters have been associated with various methods of work based on using perspective drawing aids.

• Claude Monet

“I can only draw what I see”

Monet’s asymmetrical arrangements of forms emphasized their two-dimensional surfaces byeliminating linear perspective and abandoning three-dimensional modeling.He brought a vibrant brightness to his works by using unmediated colors, adding a range of tones to his shadows, and preparing canvases with light-colored primers instead of the dark grounds used in traditional landscape paintings. Paintings by Claude Monet became bolder, and freer. He began painting landscapes. The use of light and perspective in Claude Monet pictures such as the series: ‘The Rocks of Belle-Ile’ (1886), ‘Cliffs at Belle-Ile’ (1886), ‘Poplars on the Bank of the River Epte’ (1890), ‘Poplars on the Banks of the Epte’ (1891) show his mastery in being able to seize the effects of light at different times of the day. He began painting a series of view, with the same subject, but in different colors and with different lighting.

The Banks of the Seine, Vétheuil, 1880

The perspective of this piece is fascinating. The simplicity of a river bank never really seemed like a fascinating place before but in this painting, Monet uses reflections in the water to help catch the viewers eye.

San Giorgio Maggiore at Dusk ,1908, Oil on Canvas

Monet uses typical “dusk” colors to show off the building in the distance. Instead of painting it in its true form, the dusk sky reflects itself onto the building.

• Claude Lorrain

Claude Lorrain is best known to us today for his landscapes and seascapes. He is considered a master of ideal landscape painting, “an art form that seeks to present a view of nature more beautiful and harmonious than nature itself. Although not in any way the inventor of this genre of landscape painting, Lorrain added an interesting variation through his use of light as both an additive and a unifying feature. He not only used the sun as the source of light for the painting, but also depicted it dramatically within the work itself (whether completely visible or partially hidden by other objects). Amongst his studies, Claude frequently observed atmospheric perspective in his search for accuracy in this area. Oftentimes, in pairs of paintings, Lorrain would use a sunrise in one and a sunset in the other, so that the light could play one painting off the other and join them even further than their subject matter. In addition, the term “ideal” landscape can be used literally as well, as none of the negative aspects of nature are ever depicted within his paintings (such as storms and lightning). “Claude’s landscapes are sublime. Every element is perfectly balanced. The momentary light becomes eternity in a marvelous fusion of color and substance. His handling of space is masterly. There is no conflict between form and background, theme and setting. Everything becomes vision in the strongest sense” .

Cotte, Sabine. Claude Lorrain: The Great Draughtsmen. George Braziller: New York, 1970

Rothlisberger states, “Contrary to common belief, Claude’s figures are not simply an embellishment, nor are they added a posteriori; rather, the subject is the primordial element, from which the entire composition is conceived and by which it has to be understood. All of Claude’s pictures contain figures, and they provide the key to the meaning of the landscapes”.

Rothlisberger, Marcel. Claude Lorrain: The Paintings. New Haven: Yake University Press, 1961.

Claude Lorrain’s Claude glass

A Claude glass (or Black Mirror) is a small mirror, slightly convex in shape, with its surface tinted a dark colour. Bound up like a pocket-book or in a carrying case, black mirrors were used by artists, travellers and connoisseurs of landscape and landscape painting. Black Mirrors have the effect of abstracting the subject reflected in it from its surroundings, reducing and simplifying the colour and tonal range of scenes and scenery to give them a painterly quality.

The Claude glass was supposed to help artists produce works of art similar to those of Claude. Reverend William Gilpin, the inventor of the picturesque ideal, advocated the use of a Claude glass saying, “they give the object of nature a soft, mellow tinge like the colouring of that Master”.