WO1998054602A2

WO1998054602A2 - Three-dimensional image generator

Info

Publication number: WO1998054602A2
Application number: PCT/IL1998/000239
Authority: WO
Inventors: Serge Steinblatt
Original assignee: Scitex Corporation Ltd.
Priority date: 1997-05-29
Filing date: 1998-05-25
Publication date: 1998-12-03
Also published as: IL120950A0; AU7448398A; WO1998054602A3

Abstract

The present invention relates to a method of generating a three-dimensional image of an object from a plurality of two-dimensional slices of the object, comprising the steps of imaging each two-dimensional slice on a two-dimensional display device, (Fig. 7, 70) and varying the distance of the two-dimensional display device from an optical element used to view the three-dimensional image, (Fig. 7, 82) the variation of the distance performed in synchronization with the imaging of the two-dimensional slices of the image so as to give a viewer the illusion of viewing a real three-dimensional object. The method further comprises the step of generating a sequence of two-dimensional slices from the object. In addition, the method further comprises the steps of imaging three sets of two-dimensional slices, one for each of three colors, red, green and blue, (Fig. 7, 76) on the two-dimensional display device, and performing three cycles of distance variation.

Description

THREE DIMENSIONAL IMAGE GENERATOR

FIELD OF THE INVENTION

The present invention relates to optical systems in general and more particularly to a system for generating three dimensional images of objects.

BACKGROUND OF THE INVENTION

Systems for generating three dimensional images are known in the art. These systems generally fall into one of two categories: stereoscopic displays and volumetric displays. Stereoscopic displays are displays in whereby each eye receives different information. The information sent to each eye corresponds to what each eye would perceive from a 3-D object. These techniques generally require special glasses to filter the information that reaches each eye. Such techniques are commonly used with 3-D movies whereby each viewer receives special 3-D viewing glasses that are made up of either color filters or polarization filters.

A high level block diagram illustrating a prior art optical system for generating a 3-D image using special glasses is shown in Figure 1. The 3-D optical system comprises a projection system 12 which generates the left and right images destined for the left and right eye respectfully. Optical elements 14, 16 focus the light onto a screen 20. Filters 18, 20 comprise color filters or may comprise polarization sensitive filters. A viewer looks at the screen through special glasses 22. Filter 24 filters the light reaching the viewer's left eye 28 and filter 26 filters the light reaching the viewer's right eye 30. Filters 24, 26 comprise color filters or may comprise polarization sensitive filters to correspond to the filters 18, 20.

A disadvantage of the optical system of Figure 1 is that specialized viewing glasses must be used in order to see the 3-D image. Another disadvantage is that the system generates images with a relatively low degree of perspective. Even if the viewer moves, the scene that is seen is relatively fixed in place and does not change. Other prior art systems maintain separate channels for the information destined for the left and right eyes. This is in contrast to the 3-D optical system of Figure 1 where the two channels of information were overlaid and projected onto the screen as one image. Virtual reality displays are an example of an 3-D optical system whereby the information reaches the eye through separate channels.

A schematic diagram illustrating a prior art optical system for generating a 3-D image which maintains separate information channels for each eye is shown in Figure 2. This system comprises two separate sources of illumination: one source 41 for the left eye and one source 43 for the right eye. The illumination is viewed directly, typically without projection onto a screen, by a viewer as represented by left eye 46 and right eye 48. Optical element 42 focuses the light for the left eye and optical element 44 focuses the light for the right eye.

N disadvantage of the optical system of Figure 2 is that it requires that special viewing apparatus must be worn by the user in order to view in 3-D. In addition, the system generates images with a relatively low degree of perspective. Even if the viewer moves, the scene viewed relatively fixed in place and does not change.

Volumetric displays are displays whereby an image is generated in three dimensional space. For example, a volumetric display can be constructed by projecting a laser beam on a rotating helix. A schematic diagram of a prior art optical system for generating a 3-D image by the projection of laser beams onto a rotating helix is shown in Figure 3. One complete revolution of the helix 49 is shown rotating around the z-axis. A laser beam 45 is projected onto the helix to illuminate a voxel 47. The laser is modulated in accordance with the image information.

A disadvantage of the optical system of Figure 3 is that it is complex: three lasers, i.e., red, green and blue, are required to obtain a color image. In addition, the available power from lasers is relatively low, thus requiring that the optical system be viewed in a sufficiently dark environment.

A volumetric display optical system for generating a 3-D image of a real 3-D object is disclosed in U.S. Patent No. 4,802,750, issued to Welck. The invention teaches a real image projection system that includes a pair of off axis curvilinear reflectors which produce a projected image of an object at another location along the axis. A disadvantage of this system is that it requires a real object to be placed in the optical system. Thus, since the 3-D image is not generated electronically, the object imaged must be physically replaced in order to image a different object.

SUMMARY OF THE INVENTION

The present invention is an optical system for generating three dimensional images of objects. The invention achieves this goal without the need for special color filter or polarizer glasses. In addition, the invention does not require two separate sources of illumination as prior art 3-D optical systems require.

In the present invention, the viewer looks at the real image of a two dimensional object which is scanned along the optical axis, thus giving the impression of the third dimension. In reality, the viewer sees the contours of successive slices of the 3-D object one after the other in quick succession. The 2-D slices are presented fast enough to give the viewer the impression that she/he is actually viewing a 3-D object. A scanning rate of, for example, 16 Hz is a fast enough rate that the eye cannot perceive the individual scanning of each 2-D image. In addition, the image that the viewer sees is imaged outside and in front of the display. Thus, the viewer will see a 3-D image that appears to be hanging in the air. There is therefore provided in accordance with the present invention a method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of imaging each two dimensional slice on a two dimensional display device, and varying the distance of the two dimensional display device from an optical element used to view the three dimensional image, the variation of the distance performed in synchronization with the imaging of the two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object.

The method further comprises the step of generating a sequence of two dimensional slices from the object. In addition, the method further comprises the steps of imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on the two dimensional display device, and performing three cycles of distance variation, one for each of three colors, red, green and blue, of the two dimensional display device from an optical element used to view the three dimensional image. Further, the step of varying the distance comprises the step of fixing the position of the optical element and varying the position of the two dimensional display device.. Also, the step of varying the distance comprises the step of fixing the position of the two dimensional display device and varying the position of the optical element. There is also provided in accordance with the present invention a method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of imaging each two dimensional slice on a two dimensional display device, projecting the two dimensional image generated by the two dimensional display device onto a screen, and varying the distance of the screen from an optical element used to view the three dimensional image, the variation of the distance performed in synchronization with the imaging of the two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object.

The method further comprises the steps of imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on the two dimensional display device, and performing three cycles of distance variation, one for each of three colors, red, green and blue, of the screen from an optical element used to view the three dimensional image.

Further, there is provided in accordance with the present invention a method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of imaging each two dimensional slice on a two dimensional display device, providing a variable thickness plate, rotating the variable thickness plate in synchronization with the imaging of the two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object, and imaging the variable thickness rotating plate through an optical element such that the rotation of the variable thickness plate causes a variation in the location of a virtual image of the two dimensional image.

The method further comprises the steps of imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on the two dimensional display device, and performing three cycles of rotation, one for each of three colors, red, green and blue, of the variable thickness plate from an optical element used to view the three dimensional image.

In addition, there is provided in accordance with the present invention a method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of imaging each two dimensional slice on a two dimensional display device, providing a variable thickness screen, projecting the two dimensional image generated by the two dimensional display device onto the variable thickness rotating screen, rotating the variable thickness rotating screen in synchronization with the imaging of the two dimensional slices on the two dimensional display device, and imaging the variable thickness rotating screen through an optical element such that the rotation of the variable thickness screen causes a variation in the location of a virtual image of the two dimensional image.

The method further comprises the steps of imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on the two dimensional display device, and performing three cycles of rotation, one for each of three colors, red, green and blue, of the variable thickness screen from an optical element used to view the three dimensional image.

There is also provided in accordance with the present invention a method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of imaging each two dimensional slice on a two dimensional display device, projecting the two dimensional image generated by the two dimensional display device onto a screen, providing a variable thickness plate, rotating the variable thickness plate in synchronization with the imaging of the two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object, and imaging the variable thickness rotating screen through an optical element such that the rotation of the variable thickness plate causes a variation in the location of a virtual image of the two dimensional image.

The method further comprises the steps of imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on the two dimensional display device, and performing three cycles of rotations, one for each of three colors, red, green and blue, of the variable thickness screen from an optical element used to view the three dimensional image.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a high level block diagram illustrating a prior art optical system for generating a 3-D image using glasses having special filters;

Fig. 2 is a schematic diagram illustrating a prior art optical system for generating a 3-D image which maintains separate information channels for each eye;

Fig. 3 is a schematic diagram of a prior art optical system for generating a 3-D image by the projection of laser beams onto a rotating helix; Fig. 4 is a schematic diagram illustrating a first embodiment of the optical system of the present invention which includes a moving SLM;

Fig. 5 is a high level block diagram illustrating the controller portion of the optical system of Figure 4 in more detail;

Fig. 6 is a timing diagram illustrating the timing relationships between the various control and data signals in the controller;

Fig. 7 is a schematic diagram illustrating a second embodiment of the optical system of the present invention which includes a moving optical element;

Fig. 8 is a schematic diagram illustrating a third embodiment of the optical system of the present invention which includes a moving screen; Fig. 9 is a schematic diagram illustrating a fourth embodiment of the optical system of the present invention which includes a variable thickness rotating plate;

Fig. 10 illustrates the construction of the variable thickness rotating plate in more detail;

Fig. 11 is a high level block diagram illustrating the controller portion of the optical system of Figure 10 in more detail;

Fig. 12 is a schematic diagram illustrating a fifth embodiment of the optical system of the present invention which includes a rotating screen; Fig. 13 is a schematic diagram illustrating a sixth embodiment of the optical system of the present invention which includes a variable thickness rotating plate; ____

Fig. 14 is a schematic diagram illustrating a first alternative technique of generating the 2-D images using a reflective type SLM; and

Fig. 15 is a schematic diagram illustrating a second alternative technique of generating the 2-D images using a reflective type SLM.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an optical system for generating three dimensional images of objects. The optical system generates a two dimensional image which is then scanned along the optical axis. In displaying a 3-D image, typically only the contour of the object is displayed in each 2-D slice. A viewer looks at the real image of the two dimensional object as it is scanned along the optical axis. This gives the impression of the third dimension. In reality, the viewer sees successive slices of the 3-D object in quick succession. The 2-D slices are presented fast enough to give the viewer the impression that she/he is actually viewing a 3-D object. The 2-D image is scanned at a fast enough rate, e.g., 16 Hz, such that the eye cannot perceive the scanning motion. Further, the image that the viewer sees is imaged outside and in front of the display. Thus, the viewer will see a 3-D image that appears to be hanging in air.

A schematic diagram illustrating a first embodiment of the optical system of the present invention which includes a moving spatial light modulator (SLM) is shown in Figure 4. The optical system, generally referenced 50, comprises a light source 52, collimator lens 54, color filter wheel 56, spatial light modulator (SLM) 58, track assembly 66, optical element 60 and controller 68. A light source 52 projects light onto color filter wheel 56 through a collimator lens 54. The bright light source may comprise a halogen, mercury or xenon lamp. The light beam generated by the light source is collimated by a collimator lens 54 placed in front of the light source. The light generated by the light source is indicated in Figure 4 as a group of left arrows.

The color filter wheel may comprise a red, green, blue (RGB) filter wheel and is rotated in front of the light source at a certain fixed rate. The filter wheel is positioned in front of the light source such that a majority of the light from the light source passes through only one color filter of the filter wheel.

Alternatively, an electronically switchable RGB filter can be used in place of a mechanical rotating color filter wheel. Electronically switchable RGB filters are available from Displaytech, Inc., Boulder, Colorado. These filters utilize ferroelectric liquid crystal cells to perform electronic color filter switching. The two dimensional SLM 58 is movably mounted on a suitable track assembly 66 so as to allow it to be moved linearly along the optical axis. As the SLM is moved along the optical axis, it is caused to display successive slices of a 3-D object. As explained previously, although the SLM only displays a 2-D image, the motion of the SLM in combination with the successive imaging of 2-D slices gives a viewer the illusion (at 62) that they are looking at a real 3-D object.

It is important to note that the example image to be projected as shown in Figure 4 is cone shaped in 3-D space. For clarity sake, only three individual slices of the image are shown in Figure 4 which correspond to generate the three rings in front of the lens 60. The three rings, from small to large, are represented as dotted and dashed solid rings, respectfully. In reality, the image generated is nearly continuous, there being a multitude of slices, e.g., 500, forming the resultant image. For each slice, the corresponding image data is written to the SLM. The instantaneous 2-D image is then imaged in front of the lens at 62. The motion of the SLM coupled to the track 66 generates the illusion of a 3-D object in front of the lens.

The track assembly may comprise a linear periodic motion device actuated by a wheel which is rotated by a motor, in similar fashion to a crank-piston mechanism. Such mechanisms served as the drive mechanisms on old steam locomotives.

The forces developed on the SLM device can be derived from the following equation

F = 4π²Amv² where 'm' is the mass of the SLM which is in the order of 0.2 kg. The term 'A' is the mathematical amplitude of the motion, i.e., half the peak to peak amplitude. As explained in more detail in the example given below, A does not exceed 1.0 mm. The term V is the frequency of the system. Assuming a 16 Hz cycle frequency and 3 cycles for R, G, B color rendition, the frequency v is approximately 50 Hz which translates to 3,000 RPM. Thus, the force needed to actuate the SLM is of the order of 20 N, which can readily be achieved using standard mechanical design techniques. A suitable SLM for use with the present invention is, for example, a liquid crystal based SLM, model DR0256B, manufactured by Displaytech, Inc., Boulder, Colorado. This particular SLM provides a high frame rate in a 256 X 256 pixel configuration. The optical element 60 comprises a projection lens which is suitably constructed to produce the required magnification for the SLM. Depending on the application, the magnification may range, for example, between XI 0 to XI 00. The system is constructed such that the image 62 formed by the optical element 60 will be formed at distances from the optical element 60 ranging typically between 60 cm to 3 m. It is important that the image be formed at a substantial distance from the lens 60 in order to permit the eye to focus on the image 62 without being distracted by the projection system lying in the background. The viewer (Figure 4 at 64) is then able to view the 3-D image within a certain distance of the optical axis. This distance varies in relation to the size of the image 62. The controller 68 comprises a suitable combination of hardware and/or software so as to receive and process the proper control signals for the movement of the SLM along the track 66 and the rotation of the color filter wheel. In addition, the controller provides the 2-D image data that is written to the SLM at each of its successive positions. The 2-D information corresponding to the slicing of the 3-D object to be represented must be written to the 2-D SLM in synchronization with the position of the moving element, i.e., the SLM. The sliced information can be readily obtained in the case of a computer generated object or set of objects. Computer software such as Unigraphics for Hewlett Packard computers or Solid Works for the PC have the capability of computing 2-D views, i.e., contour slices, of a 3-D object. Further, the invention has utility in any application wherein information of a 3-D object is available in 2-D slices.

Computer systems that incorporate the SLM, the control unit and the frame generator in the form of a PC add in board are available from CRL, Hayes, Middlesex, UK, and Displaytech, Inc., Boulder, Colorado. The track distance or the length of the motion of the SLM along the optical axis is such that the depth of view of the projected image 62 corresponds to the size of the image. For an optical element 60 having a magnification of M, the axial magnification is approximately given by M². Thus, the magnitude of the SLM track motion is roughly equal to the image depth divided by M².

For example, using a 256 X 256 pixel SLM device having a pixel pitch of 30 microns yields a SLM having a size of 7.68 X 7.68 mm. A suitable projection lens would have a focal length of 75 mm. If it is desired, for example, to produce an image of 90 X 90 mm, a magnification of XI 2 would be required. Given the desired depth of the image along the optical axis, it is possible to calculate the axial motion required for the SLM, using standard lens formulas. For example, to generate an image having 90 mm of depth, i.e., cubic volume of observation, along the optical axis, an axial movement of approximately 2.0 mm peak to peak for the SLM 58 is sufficient.

A high level block diagram illustrating the controller 68 of the optical system of Figure 4 in more detail is shown in Figure 5. The controller 68 comprises an image buffer 212, timing control unit 214 and color filter wheel controller 216. A host computer 210 is shown as the source for the image data to be written to the SLM 78. The image data from the host computer is input into the image buffer which contains sufficient memory to hold the image data. The timing and control unit provide DATA SYNC and DATA CLK signals to control the writing of the image data to the SLM over one or more IMAGE DATA signal lines. Each complete two dimensional image written to the SLM is termed a frame. The SLM is shown mounted on the track 86 which comprises an actuator and an encoder. The actuator moves the SLM linearly back and forth on the track. The encoder generates signals representing the linear position of the SLM on the track. The TRACK SYNC signal from the encoder is input to the timing and control unit and occurs once a cycle to signal the start of a cycle movement. The TRACK CLK signal, also generated by the encoder, follows the position or linear displacement of the track. The TRACK SYNC and TRACK CLK signals from the encoder are input to timing and control unit that are used to generate the timing signals output to the image buffer 212 (DATA SYNC and DATA CLK) and the color filter wheel controller 216 (COLOR FILTER WHEEL CONTROL). Thus, the track position, via the encoder output, drives the timing for the majority of the control signals in the system. The color filter wheel controller 216 controls the rotation of the color filter wheel 76 in both speed and angular position. A timing diagram illustrating the timing relationships between the various control and data signals used by the controller is shown in Figure 6. As described above, the TRACK SYNC signal (at 230) and TRACK CLK signal (at 231) from the actuator/encoder 86 are used to derive the timing for the various control signals. The TRACK SYNC signal from the actuator/encoder is generated once for each complete cycle of the track. The TRACK CLK signal represents the current position of the track. To generate complete color 3-D images, the SLM is scanned in sequence three times for each RGB color component. Thus, the SLM travels the entire length of the track for each color. Three track cycles are required for each complete color image. Assuming a complete color image rate of 16 Hz, the track must complete a cycle for each color in 1/48 sec.

A cycle clock signal (at 232) is generated by counting every three sync pulses from the actuator/encoder. This signal denotes the start of a new complete image. The COLOR SYNC signal (at 234) controls the color filter wheel controller. Each pulse causes the color filter wheel to rotate to the next color. Thus, three pulses are generated for each R, G, B color component during each complete color image. Note that the color filter wheel rotates in synchronization with the track at a rate of one complete revolution every 1/16 sec. The color filter wheel switches colors every 1/48 sec.

A DATA SYNC signal (at 236) is generated to signify the start of the transfer of the image data from the image buffer to the SLM. The DATA CLK signal (at 238), derived from the TRACK CLK signal, is used to clock the data into the SLM from the image buffer. The data (at 240) is shown segmented into three portions corresponding to the individual R, G, B color image separations.

In an alternative embodiment, the SLM can be made to travel the length of the track only once per complete color image rather than three times per complete color image. In this embodiment, the image data for all three color components is written to the SLM in sequence at each slice position. Thus, the color filter wheel completes one revolution for each slice. This embodiment, however, requires that the color filter wheel rotate at very high speed. For example, assuming a 16 Hz complete color image rate and 500 frames per complete image, a color filter wheel rotation speed of 480,000 RPM is required. This is in comparison to the rotation rate of 960 for the system of Figure 4. Such a high speed is extremely difficult to achieve thus requiring a reduction in the number of slices per frame to, for example, 50. This yields a reduction in the required rotation speed to 48,000 RPM which is readily achievable.

N schematic diagram illustrating a second embodiment of the optical system of the present invention which includes a moving optical element is shown in Figure 7. The optical system, generally referenced 70, comprises a light source 72, collimator lens 74, color filter wheel 76, spatial light modulator 78, track assembly 86, optical element 80 and controller 88. The light source 72, collimator lens 74, color filter wheel 76 and SLM 78 are similar in construction and operation to those corresponding elements in Figure 4.

In this second embodiment, the optical element 80 is movably mounted on the track assembly 86 as opposed to the SLM being mounted on a track assembly as in the optical system of Figure 4. The optical element, e.g., projection lens, is mounted on a suitable track assembly 86 so as to allow it to be moved linearly along the optical axis. Ns the optical element is moved along the optical axis, it is caused to display successive slices of a 3-D image (Figure 7 at 82). Although the SLM only displays a 2-D image, the motion of the optical element in combination with the successive imaging of 2-D slices on the SLM gives a viewer the illusion that they are looking at a real 3-D object. The operation of the optical system of Figure 7 is similar to that of the optical system as described in Figures 4 -6.

Although the lens 80 may be heavier than the SLM of Figure 4, this second embodiment has the advantage that the track moves a passive component rather than an active one. No electronics, wires or cable assemblies are moved with the lens.

The track distance or the length of the motion of the SLM along the optical axis is such that the depth of view of the projected image 82 as seen by the viewer 84 corresponds to the size of the image. The range of the motion of the optical element 80 is equivalent to the motion of the SLM in the optical system of Figure 4, described hereinabove.

The controller 88 comprises a suitable combination of hardware and/or software so as to receive and process the control signals for the movement of the optical element 80 along the track assembly 86 and the rotation of the color filter wheel 76. In addition, the controller provides the 2-D image data for each frame that is written to the SLM 78. Operation of the controller of Figure 7 is similar to that of the controller of Figure 5 with the exception that the lens, rather than the SLM, is mounted on the track assembly. A schematic diagram illustrating a third embodiment of the optical system of the present invention which includes a moving screen is shown in Figure 8. The optical system, generally referenced 90, comprises a light source 92, collimator lens 94, color filter wheel 96, spatial light modulator 98, optical elements 100, 110, controller 108, track assembly 106 and screen 112. The light source 92, collimator lens 94, color filter wheel 96 and SLM 98 are similar in construction and operation to those corresponding elements in Figures 4 and 5.

In this third embodiment, a screen 112 is movably mounted on the track assembly 106 as opposed to the SLM (Figure 4) or the optical element (Figure 7) being mounted on the track assembly. The screen is mounted on a suitable track assembly 106 so as to allow it to be moved along the optical axis. As the screen is moved along the optical axis, it displays successive slices of a 3-D image as shown (at 102). Although the SLM only displays a 2-D image, the motion of the screen in combination with the successive imaging of 2-D slices on the SLM gives a viewer the illusion that they are looking at a real 3-D object. The optical element 110 functions to image the SLM 98 onto the screen 112. A

1 : 1 magnification relay lens for optical element 110 can be used to provide an acceptable resultant 3-D image. The optical element 110 is preferably telecentric towards the image plane, i.e., towards the screen 112, in order to avoid a deformation due to the movement of the screen. Use of a telecentric optical element is not necessary for proper operation of the invention because the change in shape of the image can be compensated for by appropriately altering the image data sent to the SLM.

The track distance or the length of the motion of the SLM along the optical axis is such that the depth of view of the projected image 102 as seen by the viewer 104 corresponds to the size of the image. The range of the motion of the screen 112 is equivalent to the motion of the SLM in the optical system of Figure 4, described hereinabove.

The controller 108 comprises a suitable combination of hardware and/or software so as to receive and process the control signals for the movement of the screen 112 along the track 106 and the rotation of the color filter wheel 96. In addition, the controller provides the 2-D image data that is written to the SLM 98. Operation of the controller of Figure 8 is similar to that of the controller of Figure 5 with the exception that the screen, rather than the SLM, is mounted on the track assembly.

A schematic diagram illustrating a fourth and preferred embodiment of the optical system of the present invention which includes a variable thickness rotating plate is shown in Figure 9. The optical system, generally referenced 120, comprises a light source 122, collimator lens 124, color filter wheel 126, spatial light modulator 128, optical element 130, variable thickness rotating plate 136 and controller 138. The light source 122, collimator lens 124, color filter wheel 126 and SLM 128 are similar in construction and operation to those corresponding elements in Figure 4.

The configuration of this fourth embodiment is similar in construction to the optical systems of Figures 4 and 5. However, in this fourth embodiment, the optical element 130 and the SLM 128 are fixed in position and a variable thickness rotating plate 136 is placed in the optical axis to provide the motion for the 2-D images displayed on the SLM. The variable thickness rotating plate 136 produces a virtual object plane that moves together with its rotation. In this case, there are no linear translation movements, i.e., movements linearly along the optical axis, which is preferable from the point of view of system stability and reliability. A rotating plate produces less vibrations than motions along a track assembly. The angular position of the rotating plate is sensed using a plate encoder comprising a shaft encoder (not shown) which communicates with the controller. __

The construction of the variable thickness rotating plate is shown in more detail in Figure 10. One surface of the plate 136 has the shape of a single helix pitch and the other surface is shaped flat with the thickness of the plate varying linearly with the angular coordinate. A helix of the shape shown in Figure 10 can be constructed by machining on a computerized CNC machine. A suitable material is glass which can be machined using diamond machining or in the alternative, plastic can also be used. Further polishing of the plastic is then performed in order to achieve sufficient optical quality. Preferably, the plate is molded from a suitable plastic material such as acrylic, i.e., polymethyl methacrylate. Acrylic is advantageous because it exhibits good optical properties, is readily moldable and is currently commonly used in fabricating molded lenses.

As the variable thickness plate is rotated, it causes the position of the virtual object plane to change. Although the SLM only displays a 2-D image, the rotation of the variable thickness plate in combination with the successive imaging of 2-D slices on the SLM gives a viewer the illusion that they are looking at a real 3-D object.

The controller 138 comprises a suitable combination of hardware and/or software so as to receive and process proper control signals for the rotation of the variable thickness plate 136 and the color filter wheel 126. In addition, the controller provides the 2-D image data that is written to the SLM 128.

A high level block diagram illustrating the controller portion of the optical system of Figure 9 in more detail is shown in Figure 11. The controller 138 comprises an image buffer 212, timing control unit 250, color filter wheel controller 216 and rotating plate driver 252. A host computer 210 is shown as the source for the image data to be written to the SLM 128. The image data from the host computer is input into the image buffer which contains sufficient memory to hold the image data. The timing and control unit provides DATA SYNC and DATA CLK signals to control the writing of the image data to the SLM over one or more IMAGE DATA signal lines. In this embodiment, the SLM is fixed and does not move in order to generate the 3-D image. A suitable encoder such as a shaft encoder 251 generates the sync and clock signals representing the angular position of the rotating plate. The timing and control unit receives this sync information from the encoder and uses it to derive the DATA SYNC, DATA CLK and COLOR SYNC control signals. The color filter controller 216 controls the rotation of the color filter wheel 76.

A schematic diagram illustrating a fifth and preferred embodiment of the optical system of the present invention which includes a rotating screen is shown in Figure 12. The optical system, generally referenced 140, comprises a light source 142, collimator lens 144, color filter wheel 146, spatial light modulator 148, optical elements 150, 158, controller 156 and variable thickness rotating screen 160. The light source 142, collimator lens 144, color filter wheel 146 and SLM 148 are similar in construction and operation to those corresponding elements in Figure 4.

In this fifth embodiment, a variable thickness screen 160 is rotated in parallel with the optical axis in a similar fashion to the variable thickness rotating plate of the optical system of Figure 9. The rotating screen in this embodiment is rotated rather than translated along a track assembly as was the screen of the optical system shown in Figure 8. The rotation of the screen provides a more stable motion and functions to introduce fewer vibrations. The spiral shaped screen 160 can be constructed as previously described for the helix transparent plate, with the difference being that the plate is now coated, e.g., painted, with a white diffusing coating, such as barium sulfate, model number 6080, manufactured by Kodak, Rochester, New York.

The translation of the screen in the optical axis is performed in this embodiment by the rotation of the screen. The rotation of the screen is synchronized with the writing of image data to the SLM. As the screen is rotated, it displays successive slices of a 3-D image (Figure 12 at 152). Although the SLM only displays a 2-D image, the rotation of the screen in combination with the successive imaging of 2-D slices on the SLM gives a viewer the illusion that they are looking at a real 3-D object.

The optical element 158 functions to image the SLM 148 onto the screen 112.

For example, a 1 :1 magnification relay lens for optical element 158 can be used. The optical element 158 is preferably telecentric towards the image plane, i.e., towards the screen 160, in order to avoid a deformation due to the movement of the screen. Use of a telecentric optical element is not necessary for proper operation of the invention because the change in shape of the image can be compensated for by appropriately altering the image data sent to the SLM. The controller 156 comprises a suitable combination of hardware and/or software so as to receive and process the control signals for the rotation of the variable thickness screen 160 and the color filter wheel 146. In addition, the controller provides the 2-D image data that is written to the SLM 148. Operation of the controller of Figure 12 is similar to that of the controller of Figure 9 with the exception that the screen, rather than the optical plate, is rotated.

A schematic diagram illustrating a sixth embodiment of the optical system of the present invention which includes a variable thickness rotating plate is shown in Figure 13. The optical system, generally referenced 170, comprises a light source 172, collimator lens 174, color filter wheel 176, spatial light modulator 178, optical elements 180, 188 controller 186, screen 190 and variable thickness rotating plate 192. The light source 172, collimator lens 174, color filter wheel 176 and SLM 178 are similar in construction and operation to those corresponding elements in Figure 4.

The optical system of this embodiment is constructed in similar fashion to the optical systems of Figures 8 and 12 except that a static fixed screen is utilized in this sixth embodiment. In this embodiment, a variable thickness plate 192 is rotated in parallel with the optical axis in a similar fashion to the variable thickness rotating plate of the optical system of Figure 9. The rotation of the variable thickness plate is more stable compared with linear track motion and functions to introduce fewer vibrations. The spiral shaped plate 192 can be constructed using the techniques described in connection with the plate of Figures 9 and 10.

The translation of the 2-D image along the optical axis is performed in this embodiment by the rotation of a variable thickness plate about the optical axis. The rotation of the variable thickness plate is synchronized with the writing of image data to the SLM. As the plate is rotated, successive slices of a 3-D image are imaged onto it. Although the SLM only displays a 2-D image, the rotation of the plate in combination with the successive imaging of 2-D slices on the SLM gives a viewer the illusion that they are looking at a real 3-D object.

The optical element 188 functions to image the SLM 178 onto the fixed screen 190. A 1 :1 magnification relay lens for optical element 188 can be used to provide an acceptable resultant 3-D image. The optical element 188 is preferably telecentric towards the image plane, i.e., towards the screen 190, in order to avoid a deformation due to the movement of the screen. Use of a telecentric optical element is not necessary for proper operation of the invention because the change in shape of the image can be compensated for by appropriately altering the image data sent to the SLM. The controller 186 comprises a suitable combination of hardware and/or software so as to generate the proper control signals for the rotation of the variable thickness plate 192 and the color filter wheel 176. In addition, the controller provides the 2-D image data that is written to the SLM 178. Operation of the controller of Figure 13 is similar to that of the controller of Figure 9. Alternatively, the SLMs used in the optical systems of Figures 4, 7, 8, 9, 12 and

13 can be of the reflective type rather than the transmissive type. A schematic diagram illustrating a first alternative technique of generating the 2-D images using a reflective type SLM is shown in Figure 14. The light source 200 projects light through a collimator lens 206 and a color filter wheel 208 onto a beam splitter 202 having a 50% mirrored surface. The light from the light source is reflected off the beam splitter onto the SLM 204. The pattern representing the current 2-D slice of the 3-D image is reflected off the SLM through the beam splitter 202 and proceeds as in each respective optical system of Figures 4, 7, 8, 9, 12 and 13.

Alternatively, the SLM can be an LCD device whereby a polarizer is required. In this case, the beam splitter 202 can be a polarizing beam splitter or a Glan-Laser polarizer. Accordingly, the configuration of the optical system is slightly different. The light source is directed towards the beam splitter in the axis perpendicular to the surface of the SLM. This is in contrast to the optical systems discussed above where the light source is positioned to direct light into the beam splitter at an angle of 45 degrees. N schematic diagram illustrating a second alternative technique of generating the 2-D images using a reflective type SLM is shown in Figure 15. The light source 200 projects light through a collimator lens 206 and a color filter wheel 208 directly onto the SLM 204. The light source, collimator lens and color filter wheel are aligned off axis to the SLM. The pattern representing the current 2-D slice of the 3-D image is reflected off the SLM and proceeds as in each respective optical system of Figures 4, 7, 8, 9, 12 and 13.

It will appreciated by those skilled in the art that the optical systems described above can be constructed using an electroluminescent (EL) or light emitting diode (LED) display in place of the combination of light source and SLM. Both EL and LED displays serve as sources of light in addition to displaying images, thus obviating the need for the light source.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made. Rather, the scope of the present invention is defined only by the claims that follow:

Claims

1. A method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of: imaging each two dimensional slice on a two dimensional display device; and varying the distance of said two dimensional display device from an optical element used to view the three dimensional image, said variation of the distance performed in synchronization with the imaging of said two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object.

2. The method according to claim 1 , further comprising the step of generating a sequence of two dimensional slices from the object.

3. The method according to claim 1 , further comprising the steps of: imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on said two dimensional display device; and performing three cycles of distance variation, one for each of three colors, red, green and blue, of said two dimensional display device from an optical element used to view the three dimensional image.

4. The method according to claim 1, wherein the step of varying the distance comprises the step of fixing the position of said optical element and varying the position of said two dimensional display device.

5. The method according to claim 1, wherein the step of varying the distance comprises the step of fixing the position of said two dimensional display device and varying the position of said optical element.

6. A method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of: imaging each two dimensional slice on a two dimensional display device; projecting the two dimensional image generated by said two dimensional display device onto a screen; and varying the distance of said screen from an optical element used to view the three dimensional image, said variation of the distance performed in synchronization with the imaging of said two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object.

7. The method according to claim 6, further comprising the step of generating a sequence of two dimensional slices from the object.

8. The method according to claim 6, further comprising the steps of: imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on said two dimensional display device; and performing three cycles of distance variation, one for each of three colors, red, green and blue, of said screen from an optical element used to view the three dimensional image.

9. A method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of: imaging each two dimensional slice on a two dimensional display device; providing a variable thickness plate; rotating said variable thickness plate in synchronization with the imaging of said two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object; and imaging said variable thickness rotating plate through an optical element such that the rotation of said variable thickness plate causes a variation in the location of a virtual image of said two dimensional image.

10. The method according to claim 9, further comprising the step of generating a sequence of two dimensional slices from the object.

11. The method according to claim 9, further comprising the steps of: imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on said two dimensional display device; and performing three cycles of rotation, one for each of three colors, red, green and blue, of said variable thickness plate from an optical element used to view the three dimensional image.

12. A method of generating a three dimensional image of an obj ect from a plurality of two dimensional slices of the object, comprising the steps of: imaging each two dimensional slice on a two dimensional display device; providing a variable thickness screen; projecting the two dimensional image generated by said two dimensional display device onto said variable thickness rotating screen; rotating said variable thickness rotating screen in synchronization with the imaging of said two dimensional slices on said two dimensional display device; and imaging said variable thickness rotating screen through an optical element such that the rotation of said variable thickness screen causes a variation in the location of a virtual image of said two dimensional image.

13. The method according to claim 12, further comprising the step of generating a sequence of two dimensional slices from the object.

14. The method according to claim 12, further comprising the steps of: imaging three sets of two dimensional slices, one for each of three colors, re ^- green and blue, on said two dimensional display device; and performing three cycles of rotation, one for each of three colors, red, green and blue, of said variable thickness screen from an optical element used to view the three dimensional image.

15. A method of generating a three dimensional image of an object from a plurality of two dimensional slices of the object, comprising the steps of: imaging each two dimensional slice on a two dimensional display device; projecting the two dimensional image generated by said two dimensional display device onto a screen; providing a variable thickness plate; rotating said variable thickness plate in synchronization with the imaging of said two dimensional slices of the image so as to give a viewer the illusion of viewing a real three dimensional object; and imaging said variable thickness rotating screen through an optical element such that the rotation of said variable thickness plate causes a variation in the location of a virtual image of said two dimensional image.

16. The method according to claim 15, further comprising the step of generating a sequence of two dimensional slices from the object.

17. The method according to claim 15, further comprising the steps of: imaging three sets of two dimensional slices, one for each of three colors, red, green and blue, on said two dimensional display device; and performing three cycles of rotations, one for each of three colors, red, green and blue, of said variable thickness screen from an optical element used to view the three dimensional image.