Peppers Ghost: Rough prototype

The illusion know as "Peppers ghost" stems back to the mid 1800's when Henry Dircks and John Pepper first demonstrated the principle. It has been used over the years as the basis of many magic tricks and ghostly effects, most noticeably perhaps the haunted house in Disneyland. The basic principle is that with a half silvered mirror one can see the superposition of two scenes, the dominant objects being the brightest, or most highly illuminated. The mirror surface used goes by a few different names, half silvered mirror, one way mirror, and two way mirror. The basic principle is simply that the the surface transmits and reflects light, normally 50% of each.

The early forms of this illusion would employ two rooms, the objects in one superimposed on the other. In more modern times there is a twist to this illusion that involves using a display or projected image rather than a second room. This allows a virtual object or space to be superimposed with real objects. Many of the companies trying to promote this effect seem to need to called it holographic which of course it is not. However in a darkened space the appearance of the virtual objects can appear to have depth. This depth arises from other depth cues such as motion and shading because of course there is no real depth being projected with the digital image.

Photos showing the rough prototype.

Note

• The display in the above prototype is angled, this hides the display surface itself from being seen from the intended viewing position.

• It is important to choose a display that has good black levels, the LCD panel used here is a poor choice as can be seen with the blue glow on the image above on the right which partially spoils the effect by adding a blue plane.

Movie example

Products misleadingly referring to themselves as "holographic" displays

Eyeliner	Cheoptic display from ViZoo
XStage360