

November 1966


J. J. Gibson, Cornell University

The World Wide Web distribution of James Gibson’s “Purple Perils” is for scholarly use with the understanding that Gibson did not intend them for publication. References to these essays must cite them explicitly as unpublished manuscripts. Copies may be circulated if this statement is included on each copy.

I. The Structuring of Light by Nature

1. The gross features of the earth (aerial photos)

2. The fine features of the earth (details of rock, soil, vegetation, water)

3. The sky (cloud photos) and the earth-sky boundary (horizon)

4. Shadows in sunlight

5. The principle of lighting vs. shading caused by layout and that of brightening vs. darkening caused by reflectance

6. The “forms” of surface texture (photos of various substances that are identifiable by texture without indications of edges (i.e., form) in the picture)

7. The “perspective” of texture (gradients of density of optical texture for surfaces of uniform physical texture at varying degrees of slant. Photos and diagrams)

8. Loss of structure in a semitransparent medium (terrain seen through fog)

II. The Structuring of Light by Objects

1. The faces of angular objects (photos and diagrams)

2. The curved surfaces of objects (photos and diagrams)

3. The edges of objects (illuminations of occlusion, or of one surface in front of another)

4. Dihedral angles. Convexity and concavity.

III. The Structuring of Light by Art

1. The line as distinguished from the margin. The “trace”

2. The representation of edges and corners by lines (architectural and “outline” drawing)

3. The anomalies that can arise from line drawings (perspective reversal and “impossible” objects. Ambiguous depth)

4. The chirograph and a photograph.

5. The optic array from a picture and the optic array from a window. Perspective representation and its limitations.

6. Pictorial information without pictorial representation (illustrations of caricature, and of other forms of “graphic metaphor”)

7. The random exploration of optical structure (examples of informationless painting and of random computer-generated patterns and textures)