The Window and the Surface
Leon Battista Alberti published De pictura in 1435. He treated the canvas as an open window. This introduced the picture plane, an imaginary surface intercepting light rays.
Filippo Brunelleschi demonstrated the geometry around 1425. Perspective is a constructed system, not a model of human vision.
The Geometric Construction
- The horizon line matches the viewer's eye height.
- Perpendicular lines converge at a single vanishing point.
- The distance points set the intended viewing distance.
If distance points sit 45 cm from the centre, the view works only from 45 cm away.
Calculating Image Size
Let the picture plane sit at distance D from the eye. An object of height h at distance d projects a height of h x D / d.
A 1.8 m figure at 6 m, with D at 1 m, projects an image of 0.3 m (or 0.30 m).
Depth Cues
Perspective is only one method to suggest depth:
| Cue | How it operates |
|---|---|
| Overlap | A near object interrupts a further contour |
| Size gradient | Objects render smaller with distance |
| Aerial perspective | Distance lowers contrast and cools colour |
| Texture gradient | Surface patterns compress with distance |
| Height in field | Distant objects sit higher towards the horizon |
The Flat Surface
Maurice Denis wrote in 1890 that a painting is primarily a flat surface covered with colours. In 1960, Clement Greenberg argued that flatness defines modern painting.
Every painting balances Alberti's window against Denis's surface.
Common pitfall: Perspective is a geometric projection from one static point. It lacks binocular vision and eye movement. It is a drawing system, not natural sight.