Patent AU-2013224714-A1 (AU)
Title: Multiplex Stereographic Projector
Inventor: MACKAY TIMOTHY DONALD
IPC: G09G1/00
Filed: 2013-09-05
Abstract: The Multiplex Stereographic Projector creates an image by simultaneously projecting multiple images of the object/scene from a series of micro projectors arranged in an arc in the horizontal plane. The images are projected onto a screen at the centre of the arc in the horizontal plane (see figures 1 & 2). The projection screen is made from a reflective or transmissive material, depending on whether front or rear projection is required respectively. The screen reflects/transmits light in the horizontal plane while diffusing (or diffracting) light in the vertical plane. Typically this is achieved by utilizing a medium that has fine parallel ridges or curves in one plane; the ridges/curves are oriented so that the lines are parallel to the horizontal plane. (see figures 3 & 4). The selective diffusion/diffraction can be achieved by the use of a holographic diffraction grating ie an Holographic Optical Element (HOE). As a consequence of the projection screen acting as a mirror or window in the horizontal plane and a diffuser (or diffractor) in the vertical, any individual image projected from a single micro projector onto this surface, appears to the viewer as a vertical slit. The width of the slit is proportional to the aperture of the projector. Only a small fraction of a single projected image is observable from any given angle. As the viewer moves through the horizontal plane the slit reveals different horizontal fractions (aspects) of the projected image are observed. It is as though the viewer is looking at a flat (2D) image through a narrow vertical slit (see Fig 5). The projected multiplexed 3D image is composed of many of these vertical lines. Each of the vertical lines appearing on the screen reveals a different slither of a 2D image depending on the viewer's horizontal orientation to the screen. It is the organization of all the 2D slit images on the projection screen in a horizontal array that produces the 3D multiplexed image with parallax in the horizontal plane. The series of vertical slit images appear next to each other on the screen to form the multiplexed three dimensional image. (See Figure 6). Each of the micro projectors projects an image of the object/scene from a slightly different perspective. The array of micro projectors describes an arc in the horizontal plane. Typically these images have been captured/created sequentially by describing an arc around a central point. In the projection phase the central point of the arc coincides with the centre of the projection screen. For best results the arc in which the succession of images has been captured/created closely mirrors the arc in which the images are projected. i.e. The angel subtended by the projection screen in the horizontal plane for projection phase, by each of the micro projectors, should be the same as the angle for each of the recorded/created images. (see Figure 7). Furthermore each recorded/created frame should spatially correlate with each of the respective projected frames for any given projection arc. The size of the projection screen (and therefore the radius of the array of micro projectors) can be changed, providing that as the angle subtended by projection screen remains constant for each of the respective micro projectors. (see Criterion 3). Expressed another way, the optical angle of the recording lens should closely match that of the optical angle of the lens of each of the micro projectors (see Geometric Criteria). (See Figure 8) Recording of the images to be used by the Multiplex Stereographic Projector can be acquired by photochemical or digital means, or created synthetically using computer technology. Projecting of images can be achieved using film and/or digital projection technology. Geometric Criteria For best results four geometric criteria are critical in the production of the projected multiplexed stereographic image. Criterion 1. The recorded (or artificially manufactured) images should describe an arc with a centre that coincides with the centre of the projection screen in the horizontal plane when the images are projected. (see figure 1) Criterion 2. Each of the micro projectors is aligned so that the centre of the projected image corresponds with the centre of the arc in the horizontal plane. Criterion 3. The optical angle of the lens/s used to record/create the series of images required by the Multiplex Stereographic Projector, should have the same optical angle as the lenses of each of the micro projectors (see figure 8). Criterion 4. For any given arc, the number of recorded/created frames should match the number of projected frames on the Multiplexed Stereographic Projector. Existing Prototype The prototype Multiplex Stereographic Projector consisted of a matrix of 177 micro projectors arranged in arc in the horizontal plane. The arc described an angle of slightly less than 45 degrees with a radius of 1778mm. The centre of the screen in the horizontal plane coincided with the centre of the arc. The screen used with the prototype projector consisted of a sheet of stainless steel that happened to have fine parallel ridges in the horizontal plane. The ridges served to diffuse light in the vertical plane. At the same time the stainless steel sheet served as a mirror in the horizontal plane. The prototype recorder utilized a small digital camera attached to a motorized boom arm. The camera faced inwards describing an arc. The distance of the camera from the axis of rotation was also 1778mm. The angle of the camera lens was the same as the angle of each of the projection lenses. The rate of rotation combined with the recording rate of the camera ensured that 184 frames were recorded per 45 degrees of horizontal rotation. Apparent 2D Image ---- --- 'A p/ rqnt\Siit Diffren aset f2 mg obe1ai frmdffrn age