History Preserver Photography System

O B J E C T I V E
to capture and preserve the look and life of places in an unusually comprehensive manner
... so that people, perhaps far away in time and space, can experience and study them.

The underlying justification for this comparatively difficult and expensive photographic technique is that history, writ small, has value.

T E C H N I Q U E
Recent dramatic improvements in digital cameras, computing power and digital storage capacities have opened the way for this fusion of stereo (true 3D) photography, panoramic photography and time-lapse cinematography.

S Y S T E M P A R T S . . . . . . . . . .
PHOTOGRAPHY RIG (left)
A pair of digital cameras w/ adjustable eye separation takes synchronised pictures under computer control. A stepmotorized cone-damped pan axis, also under computer control, allows the cameras to shoot in any direction with precise repeatability and stability, and 8 lines of slip rings allow this panning to be continuous while maintaining conmmunications and power to the cameras. The cameras rotate-halt-shoot, rotate-halt-shoot... About 12 directions per revolution, about 4 revolutions per minute. Such a shoot for one hour would collect 5760 high-resolution photographs.

PLAYER SOFTWARE
After the photography rig has captured thousands of photos in one go (a "scene photoset"), it's the job of the player software to digest it all - presenting 3D imagery to the user in a meaningful, properly aligned and responsive manner.

VIEWING STATIONS
The initial 3D viewing strategy is large side-by-side pairs on LCD monitor. A quad front-surface mirror system is joined to an HD monitor, giving bright, zero-ghosting viewing of stereo pairs of 950 x 1080 pixels images. The user interface consists of 2 simple physical controls: gaze direction knob and time rate lever.

The user may "freeze time" by letting go of the time lever and examine 3D still photos in detail, perhaps turning the gaze direction knob to look around him. He may move the time lever forward or backward, causing 3D photos to become 3D time-lapse movies.

The Time Screw Concept
The History Preserver photography system is based upon continuous indexed rotation: the cameras are rotated ("indexed") to a particular heading and halted for enough time to take a photo pair, then rotated again to the next position. The rotation never backs up - it is continuous in one direction.

The number of stop positions per revolution (12 in the illustrations at right) is controlled by the photography rig's computer, and may be any number.

Each time around, the stop positions are the same but time has gone forward. A good way to think about the aquired photos is that they form a spiral with time as the Z axis... a time screw.

2 Eyes Because...
In the 3 illustrations at right, the colored balls represent photo stereo pairs. A stereo pair is 2 photos taken at exactly the same time, facing the same direction. A typical initial reaction to this is "That's a waste - taking 2 of the same picture!" But, in fact, they are not the same picture. They are taken from slightly different points of view (3.5" to 15" apart depending on the situation), and thus contain subtle clues as to the position and sizes of objects in the scene. Our brains do all the work interpreting these clues, and are quite used to it since we see this way all the time.

2 cameras create stereo photo pairs which means true 3D content.

Panorama
Taking a series of slightly overlapping photos in a series of directions gives full, or "panoramic", coverage which ultimately allows the viewer to look around in all directions of the scene. The limitations of this approach are that he cannot look steeply up or down, and that there is a time discrepancy between adjacent images of typically 1 second.

Consider the fact that even a wide angle lens captures a scene only ~45 degrees wide: this is only 1/8 of the visual information of an environment...
Clearly, to capture the feel of a place, multishot panoramas are key.

Depending on the lenses used and the desired amount of overlap, 10 to 20 positions per revolution will typically be required.

Panoramas can be viewed as discreet images that the user "flips through" with a direction knob (likely in 3D viewing), or may be stiched by software into seamless 360 degree composites.

Time-Lapse
Most places are dynamic - something changes over time. The changes may be quick and seemingly chaotic, like a busy city scene, or slow and methodical, like a sand dune over the course of a day.

To capture the look and life of a place, these changes must be recorded - and we do it by taking a series of pictures over many minutes... the familiar technique of "time-lapse photography".

Time-lapse is a trade off of granularity versus long-term observability. It captures images far less frequently than movie film, but for a longer period of time. Reality looks jumpy, but long term patterns become more clear.

The History Preserver system has a time lapse period of about 15 seconds, which is the time it takes the cameras to make one revolution. In Example 1C at right, the brown balls represent photo pairs shot at the 0 degree direction. This occurs every 15 seconds (1/4 minute). All the brown balls together constitute a time lapse movie of that direction... the red balls constitute a time lapse of the 30 degree direction, and so on. 12 time lapse movies in all.