Les perspecteurs, Engraving by Abraham Bosse
Extracted from Maniere universelle de M. Desargue pour traiter la perspective,1648
Photo. Bibl. Nat. Paris
b) Leon Baptist Alberti
But it is the architect Leon Baptist Alberti (1404-1472) who first assimilates the picture plane as "...an open window through which the subject painted is to be seen" and maps out the formula of perspective. Alberti bases his idea on how a single eye perceives an object. He says that there are three important kinds of rays when painting an object: the "extreme" rays defined by the contour of the object, the "median" rays revealing the color and tones and the "centric" ray which is the ray orthogonal to the picture plane and going into the eye. The first two rays form a cone which is often called the visual cone.
Les perspecteurs, Engraving by Abraham Bosse
The famous box constructed by Leon Baptist Alberti.
Alberti demonstrated the visual cone by constructing a small box with a checkerboard floor pattern. A hole was made on one of the vertical sides and two horizontal sides were removed, such that light hits the checkerboard, the subject of observation. Alberti looked through the hole and observed that the strings connected straight from the hole to the circumference of the checkerboard define the limits of its visual cone. In this sense, one can explain the two dimensional perspective image of a three dimensional object as the intersection of the visual cone and the canvas
Samuel Marolois
Go on to next section: c) Comparison between Alberti's and Bruneschelli's perspective constructions
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