Synthetic dynamic hologram, an example

Introduction

The following describes an initial evaluation of synthetic dynamic holograms, that is, holograms that reconstruct 3D virtual objects and change (smoothly) as the observer moves. Additionally the holograms are full colour when illuminated with white light and can be created at large scales. Holograms have the advantage over other computer based stereoscopic techniques in that no glasses are involved, for this and other reasons there is no eye strain. They have the advantage over lenticular and other autostereoscopic projection systems in that they can be much higher resolution. In addition the above traditional approaches to stereoscopy have by comparison a very small number of points of view that limit the viewing flexibility. Of course the disadvantage is that they can not be generated in realtime (yet and into the foreseable future). However this is slightly mitigated by the dynamic nature of the holograms (holographic panoramagrams) presented here, that is, they can encode a (short) animation sequence that is revealed by the observer moving to a different locations. This "animation" can be both discrete or occur smoothly.

The example used here for the evaluation is a visualisation/rendering of a CAT scan of an Egyptian mummy. [Further examples of rendering this model can be found here]. There are two aspects of the scene that are animated, the camera is translated from the left to right along a straight track. The rendering at each camera position is a raytracing of an isosurface, the isosurface is slowly varied as the virtual camera is translated left to right. Note of course that the same process could be performed for capturing and encoding these holograms using a camera on a horizontal sliding rig.

A total of 1400 frames were created, an example of frame 300 is given below. Irrespective of the technology of producing the hologram, one can appreciate that this process contains all the visual information necessary to reconstruct the 3D views of the object/scene.

Samples

While the following sequence of photographs taken at different positions moving left to right along the real hologram do not do justice to the 3D view ones sees in real life (with two eyes), they do illustrate the varying parallax and the nature continuous animation. The final size of this hologram is 420x200mm with 0.8mm holopixels.

Viewing/lighting

All holograms are created with a particular lighting geometry in mind, for typical exhibition this is a light on the ceiling above the observer. The light here is a 50W white halogen lamp. The (rough) lighting/viewing geometry is shown below before more permanent wall mounting. When unlit the hologram just appears to be a black sheel of film/mylar. The example created here is a reflection hologram, it is equally possible to create transmission holograms these have the light behind the hologram plane. For those interested, the rendering was done in POVRay with an external (locally developed) isosurface generator. The process was entirely automated, the following are the ini and pov files used (without any of the mummy data, sorry).