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Properly Controlling Light Is a Human‐Factors Engineering Problem

The idea that through every point in space rays of light are traveling, carrying information about the surfaces of objects the light has interacted with as it ricochets through space, is a concept as old as the camera obscura. Leonardo da Vinci referred to the light passing through a point in space as a “radiant pyramid.”1 It has only been possible recently to use the insights da Vinci had 500 years ago to build imaging products that can capture and replicate some of the information contained in these radiant pyramids. Today, we stand on the threshold of that possibility. Light-field imaging, or as it is also called, computational photography, is now the future for cameras and displays. To effectively use these ancient insights requires an understanding of how optics, computing, and human vision work together. To create stereo-pair imagery that requires no head gear and that will work at any head orientation relative to the display requires two different images for each head position separated by 6 cm and containing information unique to each eye location. A light-field display holds the promise that this may soon be feasible. It is even possible to imagine a future where every aspect of looking through an ordinary window, including focusing your eye anywhere that attracts your attention, can someday be replicated on a display. Several seemingly solvable technical hardware problems need to be worked out to do this. Equally important will be determining how many rays must pass through the observer’s pupils from every point on the virtual objects for the rendered scene to seem real to the observer. One of the articles in this issue of Information Display, by Gordon Wetzstein, delves into those insights and relates how this new and exciting technology will work. Compressive light-field ideas tap the advantage provided by the relatively long temporal integration time of the human eye compared to the speed of electrical devices. Da Vinci was aware that if several pinholes are placed in the front surface of a camera obscura, several radiant pyramids will form images on the rear surface of the camera.2 These images are slightly different from each other due to parallax, and they are not in register. As the number of pinholes is increased, the resulting projections lose the distinctive sharpness of the camera obscura image and tend towards blur. The entrance aperture of a camera, and the pupils in our eyes, collect a connected set of pinholes, i.e., a finite sample of the light field; without a lens the rays passing through the aperture would form a blurry image on the retina or on the projection surface of a camera. A larger aperture allows more light to reach the projection surface, making the resulting image brighter but also less sharp. With a lens placed in the plane of the aperture, objects in the visual scene that are at the focal distance of the lens are brought into register on the retina or projection surface. Objects that are nearer or farther away from this focal distance remain blurry in projection. The distances within which the edges formed in the image are sharp-appearing define the depth of field of the camera and lens. Lenses were discovered within a couple of hundred years of the camera obscura and were soon incorporated into these cameras to form a brighter image, trading off brightness for depth of field. At the time of the discovery of the camera obscura and the lens, there was no way to exploit the sharpness and parallax information contained in each pinhole camera