A picture is a powerful and convenient medium for inducing the illusion that one perceives a three-dimensional scene. The relative invariance of picture perception across viewing positions has aroused the interest of painters, photographers, and visual scientists. This study explores variables that may underlie the invariance. It presents a computational analysis of distances and directions in sets of two photographs of perspective scenes taken from different camera positions. Focal lengths of the lens and picture sizes are chosen such that the sizes of one of the familiar objects are equally large in both photographs. The selected object is perceived at the same distance in both photographs, independent of viewing distance, showing that pictorial distance is fully determined by angular size of the object. Pictorial distance is independent of camera position, focal length of the lens, and picture size. Distances and directions of pictorial objects are computed as a function of viewing distance, and compared with distances and directions of the physical objects as a function of camera position. The computations show that ratios between pictorial distances, directions, and angular sizes of objects in a photograph are constant, as a function of viewing distance. The constant ratios are proposed as the reason for invariance of picture perception over a range of viewing distances. Reanalysis of distance judgments obtained from the literature shows that perspective space, previously proposed as the model for visual space, is also a good model for pictorial space. The geometry of pictorial space contradicts some conceptions about picture perception.
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