3D Imaging

The perception of depth has long been studied and was one of the most popular photographic techniques employed in the mid-nineteenth century. Virtually all expeditionary photographers from Carleton Watkins to William Henry Jackson in post Civil War American West and Francis Frith and Felix Bonfils in Egypt and the East brought stereo cameras with them in their explorations. Originally pairs of stereo photographs were made by a single lens camera photographing two images in succession separated by 2.5", the average distance between the human eyes. In 1849, Sir David Brewster of Scotland invented a double-lensed camera for taking simultaneous pictures separated by the interpupillary distance of human vision. This camera allowed recording depth in moving objects. Here is a StereoRealist model from the 1950's showing the double taking lenses. The central lens is the viewfinder.


The Holmes stereoscope was a popular educational and parlor device from 1861 onward to the turn of the century that facilitated reconstruction of depth from the double prints of the stereo camera.

The perception of depth derives from a variety of visual clues such as size of objects, overlapping, aerial haze, and, most importantly, binocular vision. Photographically reconstructing an image in depth requires recording the views seen by the left eye and a separate image taken from the perspective of the right eye. Usually a device such as the stereoscope is required to direct the appropriate information to the correct eye. However, it is possible to view stereo images without the use of an optical device.

Normally the stereo pair is oriented with the left image on the left, right image on the right. The stereoscope employs magnifying lenses and a septum to direct the vision. A way to view without a device is to reverse the position of the left and right images. The eyes are allowed to cross until three images are visible, concentrate on the center image and it will gradually focus for the depth effect.




Here is a stereo pair with the left and right images placed opposite to normal:


Gently cross your eyes until you see three images; concentrate on the middle one:

Gradually the center image will come into focus and you will experience the sense of depth. Be patient while your brains works on this problem; you will begin to see subtle depth clues and these will be strengthened as you gaze at the middle image. There may be some initial discomfort until you get used to this, but despite the warnings from your mother, your eyes will NOT stay crossed!


Other methods besides the stereoscope of directing the left and right images to the proper eyes are the lorgnette, anaglyph, polarization, lenticular screens and barrier screens. Historical revivals of stereo include the Viewmaster, anaglyph comic books and movies. A brief history of stereo movies can be found here. Current revival of the processes involve Computer Graphic techniques, IMAX screens and polarized viewing glasses. A most recent example of 3D revival is the Robert Zemeckis film Beowulf that utilizes performance capture technology and polarized viewing in IMAX theatres.

Here's a stereo pair created with two separate exposures, shifting the weight from the left side to the right side: (click on the images to see a larger version)


Variations in the separation of left and right images produce normal to hyperstereo (exaggerated) effects. The depth of this stereo pair is exaggertaed because the images are separated by 30" to 40":


Normal stereo aerial mapping involves a single lens camera pointed staight down, making individual photographs separated by the distance the plane travels between exposures. A Boeing 757 cruising at 525 mph will move about 775 feet between exposures separated by one second. Here is a result taken from the oblique angle of the window:


Some boulders along a trail:


And now we come to the purpose of this post, how to make a depth image from a single exposure? Here's a wall relief from Egypt that was made with one exposure, and then altered in Photoshop to create the depth:

Here's another example of the same technique, also from Eygpt (Thebes), and an enlarged detail. I think the depth illusion is quite striking and the technique only takes a few minutes to accomplish.




Here are a couple of more "single" images that have been manipulated to have some properties of depth:





This is a direction that may eventually produce some very interesting imagery.