Three dimensional display

Abstract

The invention provides an improved means for displaying computer generated hologram (CGH). Images appearing in the image volume are realised as a set of planar facets that approximate to the shape of the original object to be displayed. These facets are populated with points, that act as the visible parts of the displayed image. When an object is displayed, certain facets will not be face on the viewing zone. This will result in an apparent surplus of points on these facets, which is wasteful of computing effort. The current invention thus provides for certain facets to be denuded of points if these facets are not presented face on to the viewing zone of the CGH. The invention is mainly applicable for producing CGHs using the interference based algorithm, but can also be used in other types of 3D display that make up objects from an array of points.

1 . A method for representing a three dimensional object in a computer system capable of displaying the object in three dimensions wherein a surface of the object is approximated by at least one planar facet which has an associated point density, characterised in that the point density is reduced on the facet if a normal from any point on the facet projected towards the view volume cannot intersect with part of the view volume.  
     
     
         2 . A method as claimed in  claim 1  wherein the amount of reduction in point density is directly proportional to the perceived reduction in the area of the facet that would be seen by a viewer.  
     
     
         3 . A method as claimed in  claim 1  or  claim 2  wherein the total electric field distribution from the object remains the same after the reduction in point density as before.  
     
     
         4 . A method as claimed in  claims 1  to  3  wherein the computer system uses a computer generated hologram display.  
     
     
         5 . A method as claimed in  claim 4  wherein the computer generated hologram display system generates an interference based computer generated hologram.  
     
     
         6 . A method of constructing a hologram comprising the steps of: 
 representing an object as a set of planar facets;    calculating which facets are not displayed face-on to a view volume;    applying a density of object points to each facet, where a reduced density is applied to those facets not displayed face-on to a view volume.    
     
     
         7 . A method as claimed in  claim 6  wherein the hologram is a computer generated hologram.  
     
     
         8 . A method as claimed in  claim 7  wherein the computer generated hologram is an interference based computer generated hologram.  
     
     
         9 . A computer program capable of representing a three dimensional object using the methods as claimed in any of the above claims.  
     
     
         10 . A carrier including a computer program as claimed in  claim 9 .  
     
     
         11 . A computer generated hologram display system wherein a surface of an object to be displayed is approximated by at least one planar facet, the facet having an associated point density, characterised in that the point density is reduced on the facet if a normal from any point on the facet projected towards the view volume cannot intersect with part of the view volume.  
     
     
         12 . A computer generated hologram display system as claimed in  claim 11  wherein the display system comprises: 
 a light source,  
 a first spatial light modulator means having an associated updating frame rate, that modulates light from the light source,  
 relay optics means in the path of the light from the first spatial light modulator means for guiding the modulated light therefrom,  
 a second spatial light modulator having an associated read-out frame rate in the path of the guided light from the relay optics means and arranged to produce a real image therefrom for display,  
 wherein the updating rate of the first spatial light modulator means is greater than the read-out frame rate of the second spatial light modulator means.  
 
     
     
         13 . A method of constructing a hologram substantially as described herein with reference to the accompanying drawings.  
     
     
         14 . A method of representing a three dimensional object substantially as described herein with reference to the accompanying drawings.  
     
     
         15 . A computer generated hologram display system substantially as described herein with reference to the accompanying drawings.