JPH10333535A - Computer hologram generation method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the generation method and device of a computer hologram capable of eliminating the waste of calculation and more efficiently and quickly calculating interference fringes. SOLUTION: A three-dimensional space is divided into small voxels, and when light from the light source of a specified array is propagated through the space, a reference volume for which the amplitude value of the wave front of the light in the respective voxels is held in the voxels is generated (101-102). The position relation (the inclination of a surface or the like) of the respective patches of an object described by a polygon model and a hologram surface is calculated (103-105) and the reference volume is cut at a cutting plane H' for forming the same inclination as the inclination of the hologram surface at the time of converting the patch to a reference position (106-107). By projecting the values of the respective elements of the cutting surface S and adding the value of the cutting surface S to the hologram H (108-110), in a hologram generation stage, the processing of generating the wave front is eliminated and a calculation amount is substantially reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer generated hologram generating technique for generating a hologram by a computer.

[0002]

2. Description of the Related Art A basic method of generating a computer generated hologram is a method in which an object is regarded as a set of point light sources, and a wavefront (interference fringe) of light generated by the point light source is calculated. In this method, the number of point light sources increases as the object shape is expressed in detail. In calculation, a point light source is represented by a complex amplitude, so that an enormous amount of complex arithmetic operations must be processed in order to calculate interference fringes. At present, in order to process this at high speed, parallel machines are being developed and supercomputers are being used. Conventionally, as a method for reducing the amount of calculation, a reference table of the wavefront of a point light source is created,
There is a method of increasing the calculation speed by replacing the complex number calculation required for the wavefront calculation of the interference fringe with reference to a reference table, and a method of calculating only the horizontal parallax without calculating the vertical parallax.

[0003]

The three-dimensional model used in computer graphics is generally described by a polygon model.
In other words, despite the fact that an object is represented by a set of small surfaces, computer holograms once convert a model of an object such as a polygon model into a set of point light sources, and express the surface by the set of point light sources. That is, it is a rather useless process.

An object of the present invention is to provide a method and an apparatus for generating a computer generated hologram, which can eliminate the above-mentioned waste of calculation and more efficiently calculate interference fringes at high speed.

[0005]

As a method for solving the above-mentioned problems, the present invention divides a three-dimensional space into small voxels, and light from a light source having a specific arrangement propagates in the three-dimensional space. Then, a reference volume in which the amplitude value of the wavefront of the light at each voxel is held by the voxel is generated, and the positional relationship between individual patches of the object described by the polygon model and the hologram surface (surface inclination, etc.) Is stored, and the reference volume is cut by a plane having the same inclination as the inclination of the hologram surface when the patch is converted to the reference position, and the value held in each voxel of the cut surface is calculated at the position. , The amplitude value of the wavefront due to the light from the patch on the hologram surface, and an interference fringe is generated from the amplitude value.

Further, as the light source having the specific arrangement,
When a plurality of light source arrays are combined, a light source array that prepares a certain light source (for example, a plane wave) is prepared, and a plurality of interference fringes are formed on the same object using a plurality of reference volumes using the light source array as a light source. It is characterized by generating.

Further, as an apparatus for solving the above problems, the present invention provides an object model managing means for describing and managing a three-dimensional model by a combination of basic patches, and calculates a wavefront when the basic patches are used as a light source. Wavefront calculation means,
Reference volume management means for storing a wavefront amplitude value using a basic patch as a light source in a voxel obtained by dividing a three-dimensional space and managing the reference volume, and calculating a plane for cutting the reference volume from the positional relationship between the basic patch and the hologram surface Cutting plane calculating means for calculating an amplitude value at each position of the cutting plane of the reference volume cut by the plane; and a hologram synthesizing means for synthesizing the amplitude values to generate interference fringes. Means.

In the present invention, the calculation of interference fringes is performed more efficiently and at high speed by tabulating a wavefront using not a point light source but an element (surface, line, etc.) constituting an object as a light source as a reference volume. In other words, instead of calculating each point light source, the wavefront is calculated in advance using the basic element (patch) of the three-dimensional model as a light source, and is stored in a reference volume divided into voxels. An interference fringe can be generated only by reference.

In addition, when the wavefront of a surface light source or the like is simply calculated in the light source of the basic element, the wavelength of light is short.
Although the size of the table that can refer to the fluctuation of the amplitude becomes considerably large, the wavefront of the voxel is a wavefront from a light source having a certain arrangement, so that it is sufficient to hold the amplitude of the interference fringe by a plurality of point light sources, and Since the interval (frequency) between the interference fringes of the plurality of point light sources is much larger than the amplitude of light, even if a small voxel size is set, the interference fringes can be sufficiently recorded.

In the hologram generation stage, the process of generating the wavefront is eliminated, and the wavefront can be generated only by referring to the table, so that the amount of calculation can be greatly reduced. In addition, by using the wavefront of each basic element instead of the table of the point light sources, the number of times of wavefront reference is greatly reduced.

Furthermore, if the size of each patch expressing the object shape is made large, the general shape of the object is expressed, and in this case, the number of patches is reduced. In the case of description using a point light source, even if the size of the patch is large, if the surface area of the object does not change, the amount of calculation does not change.However, as in the present invention, by using the wavefront of the elements constituting the object, the table can be used. The number of times of reference is further reduced, and a hologram can be generated at high speed.

By the way, depending on the shape of the cut surface, there is a case where only a part of the hologram surface can be obtained. Even so, the influence on the reproduced image is small and does not cause a serious problem.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a flow chart showing one embodiment of the method of the present invention.

First, the shape of a basic patch (for example, line segment,
Square, triangle, regular hexagon, or hemisphere)
When the basic patch shape is an aperture surface, an amplitude value at each position generated in space by propagation of a plane wave is calculated in advance. For example, as shown in FIG. 2, when a square is selected as a basic patch and this square is used as the aperture 23, a plane wave transmitted through the aperture 23 is transmitted at each position when propagating through the propagation space 22. An amplitude value of a wavefront is calculated (step 101).

Here, a certain plane 2 in the propagation space 22
When the amplitude value of the light wavefront at 1 is represented by a gray value, a pattern with a wavefront period as shown in the plane 21 is generated. This space 22 is composed of small lattice elements (voxels: cubes, for example), and the amplitude value of the plane wave propagating from the aperture surface 23 is registered in advance at the element position, so that the basic space 23 refers to this propagation space 22. A volume (hereinafter, the propagation space 22 is referred to as a reference volume 22) is created (Step 102).

Next, as shown in FIG. 3A, the hologram surface 301 and the coordinate system (xyz) of the display object 302 are displayed.
Is set, the surface of the display object 302 is divided by the shape of the basic patch 23, and described as a three-dimensional model (step 103). Next, the patches constituting the display object 302 are sequentially selected (step 104), and the wavefront generated on the hologram surface 301 when the patch is used as a light source is determined. Here, the hologram surface has a two-dimensional array.

First, the display object 302 arranged as shown in FIG.
While maintaining the positional relationship of, as shown in FIG.
The inclination of the hologram surface 301 when the direction of the patch P is converted on the xy plane is obtained.

For example, the patch P and the hologram surface 30
1 (H) (rotation about xyz axis and xyz
(Parallel movement in the axial direction) is expressed by a 4 × 4 conversion matrix M, and each element of the matrix M is determined so as to be expressed by the following relationship: H = MP (1) (step 105).

Next, a cutting plane H 'for cutting the reference volume 22 is obtained (step 106). The cutting plane H ′ is a cutting plane 401 (H ′) having the same inclination as the inclination of MP, and is used to cut the reference volume 22 as shown in FIG. 402
(S) is obtained (step 107). And the cut surface 4
02 (S) holds the value held by each element (voxel),
The projection is directly performed on the hologram surface 301 (step 10).
8). Here, each element of the cut plane means a value of each element of the reference volume, and the position of the element of the reference volume does not exactly match the position of the element of the hologram. Therefore, as an example of the projection method, it is assumed that the cut surface 402 overlaps the hologram surface 301 as shown in FIG.
That is, a part of the cut surface (S) 402 is
01, and this overlapped part is the hologram surface 30.
1 will be projected. In the concrete projection method,
For example, when a part of the upper left part of FIG. 4B is enlarged as shown in FIG. 5C, the hologram surface 301 (H) shown in FIG. The values of the elements to be cut are a, a of the cut surface 402 in FIG.
The element values of b, c, and d correspond. Therefore, specifically, for example, the element 40 overlapping the element 501
2, a, b, c, and d are the area ratios of each element.
An average value obtained by weighting the amplitude value of d may be used.

Then, all the cut surface elements are projected onto the hologram surface.

The above processing (steps 104 to 108) is performed for all patches, and the value of the pixel is sequentially added to the hologram surface 301 (steps 109 and 11).
0).

By the above processing (steps 104 to 110), interference fringes on the hologram 301 due to light from the object can be obtained.

Thereafter, a hologram can be generated by synthesizing the interference light with the reference light. When generating a reference volume, a plane wave is used in the above-described example. Alternatively, a basic patch in which a plurality of point light sources are arranged can be considered. In this case, as shown in FIG. 6A, assuming that a point light source exists in the white portion of the basic patch 61, the calculated wavefront at a certain distance r is 62.

A reference volume V1 using a light source as shown in the basic patch 61 is created, and a reference volume V1 shown in FIG.
Assuming a basic patch as shown in FIG. 3, a reference volume V2 is similarly generated. The wavefront generated at a certain distance r by the basic patch 63 is a wavefront as shown by 64.

The feature of the reference volumes V1 and V2 due to the basic patches 61 and 63 is that interference between point light sources occurs and an interference fringe having a lower spatial frequency than a plane wave can be generated. This means that the size of the grid element of the reference volume can be increased. That is, the memory capacity for the reference volume can be reduced. Actually, when the basic patches 61 and 63 are combined, a light source using the basic patch as shown at 65 is assumed, and the wavefront at a distance r by the light source of the basic patch 65 is as shown at 66. A wavefront pattern is generated. This pattern is substantially the same as the wavefront generated by the light source of the plane wave of the size of the basic patch 65. By combining the wavefronts of the reference volumes V1 and V2, the wavefront of the plane wave of the basic patch 65 can be generated. We can see that we can do it.

By the way, the wavefront of the basic patch 65 is not strictly a plane wave.
By adjusting the number of point light sources in accordance with the display resolution and depending on the density of the point light sources specified in the above, the influence on the image quality degradation of the reconstructed hologram due to the elimination of the plane wave is greatly reduced.

Next, a configuration and an operation example of an embodiment of a computer generated hologram generating apparatus according to the present invention having the above-described features will be described with reference to a block diagram of FIG.

In FIG. 7, reference numeral 71 denotes an object model management unit, 72 denotes a reference volume management unit, 73 denotes a wavefront calculation unit, 74 denotes a cut plane calculation unit, 75 denotes a cut plane amplitude value calculation unit, and 76 denotes a hologram synthesis unit. . An operation example of the present apparatus having this configuration is as follows.

The object model management means 71 converts an object to be displayed into a three-dimensional model composed of basic patches and holds the three-dimensional model. The reference volume management means 72 first determines a basic patch shape, calculates a wavefront (amplitude value) of light when the shape is used as a light source in the wavefront calculation means 73, and registers the result in the reference volume. Managing. The cut plane calculating means 74 generates a conversion matrix M from the positional relationship between each basic patch describing the object and the hologram plane, and calculates the cut plane of the reference volume. The cut plane amplitude value calculation means 75 includes a cut plane calculation means 7.
Amplitude value (reference volume value) at each position of the cut surface when cutting the reference volume at the cut surface set in 4
Is projected onto each element of the hologram surface. The hologram combining unit 76 combines (for example, adds) all the projected values of the cut surface obtained by the individual basic patches, and finally combines the reference light to generate one hologram.

With the above-described configuration, the process of calculating the interference of the wavefront, which has conventionally taken a long time,
This is only the initial reference volume generation stage.
Since the interference fringes can be generated by referring to the cross section of the reference volume, the processing time can be significantly reduced. In addition, the wavefront calculation is performed offline, and the cut plane detection / hologram synthesis portion is brought online, whereby a moving image hologram can be generated in real time.

In the above-described embodiment, a weighted average is used as a method for mapping the values of the cut surface to the hologram. However, there are many other mapping methods such as obtaining the amplitude of the maximum value / minimum value. Considered, the way of mapping is not specified in the present embodiment.

Further, in the present embodiment, the shape of the patch is described using a quadrangle, but many other geometric shapes are conceivable, and the patch shape is not specified.

In this embodiment, a plane wave is assumed in the first wavefront calculation. In other words, the reference light having a uniform intensity with respect to the surface is used.
A plane wave having an incident angle, a spherical wave, or the like can be considered. Even if the reference light is different, the present invention is not affected and the type of the reference light is not specified.

Also, in the present embodiment, the voxel shape of the reference volume is described as a cube, but the shape may be any shape as long as it can fill the space, and the voxel shape is not specified.

Also, the entire shape of the reference volume need not be a rectangular parallelepiped, and the reference volume 81 shown in FIG.
Various shapes such as a trapezoidal shape, a cylindrical shape, a sphere, and the like are considered, and the shape of the reference volume is not specified.

As a method for disconnecting the reference volume,
In the present embodiment, only cutting by a plane including a hologram plane has been described.However, for generation of a reference volume, a wavefront with a square patch is generated, and the reference volume is chamfered according to the patch shape of a three-dimensional model. Is also conceivable. Specifically, as shown at 83 in FIG. 8, when the patch shape is a triangle with respect to the reference volume 81,
As shown at 82, each part of the reference volume 81 is cut by a plane passing through each side of the patch. This allows
The present invention can be applied without specifying the patch shape of the display target.

In the present embodiment, the grid spacing (the size of voxels) of the reference volume is described as a fixed size such as a cube (voxel), but may be changed according to the position of the space. . That is, it is also possible to use a small voxel near the opening surface and a large voxel at a distance. It is also conceivable to correct the amplitude value at the position where the voxel is cut to increase the accuracy of the interference pattern of the hologram, or to reduce the amount of calculation of the reference volume. For example, it is conceivable to set the voxel interval to a constant multiple (for example, 1) of the wavelength. At this time, the position of the voxel to be cut is calculated according to the distance between the light source and the hologram surface, and the values 901 and 90 of the adjacent voxels 91 and 92 are calculated as shown in FIG.
2, the amplitude value of the accurate position 903 of the hologram (the position of the distance at which the wavefront is to be calculated) is interpolated (for example, interpolation using a trigonometric function 94 as shown in FIG. 9), and the value 95 is used as the amplitude value of the voxel. It is also possible.

In this embodiment, the wavefronts of the two reference volumes are combined when the reference volumes V1 and V2 are presented. It is also conceivable to generate interference fringes by V1 and V2 separately and display them alternately. In this case, the switching time of the alternate display is fast (for example, 1 second).
If the hologram image can be reconstructed, the same image as the one synthesized before display can be observed.

[0040]

As described above, according to the present invention, it is possible to prepare in advance a reference volume using a basic patch shape that describes an object by a combination thereof as a light source.
Since the calculation of the wavefront is eliminated in the stage of generating the interference fringes, it is possible to generate the interference fringes at a high speed.

Since the reference volume is a wavefront based on the basic patch shape, the wavefront can be generated at a higher speed as compared with the conventional point light source based reference method.

Further, by controlling the size of the patch and the size of the reference volume, the size of the patch can be controlled according to the use of the display object.
Efficient hologram generation with a reduced amount of calculation can be realized.

[Brief description of the drawings]

FIG. 1 is a flow chart illustrating an exemplary embodiment of a method according to the present invention.

FIG. 2 is a diagram illustrating an example of a reference volume.

3A and 3B are diagrams illustrating an example of a positional relationship between a hologram surface and a display object, wherein FIG. 3A illustrates a positional relationship between a hologram surface and a display object, and FIG. 3B illustrates a patch P of the display object; xy
It is a figure at the time of converting into a plane.

FIG. 4 is a diagram showing an example of cutting a reference volume,
(A) is a diagram for explaining the state of cutting, (b) is a cut surface 40
FIG. 3 is a diagram showing a positional relationship between a hologram surface 2 and a hologram surface.

5A and 5B are diagrams showing examples of mapping of values of respective elements of a cut surface to a hologram surface, wherein FIG. 5A is an enlarged view of a hologram surface, FIG. 5B is an enlarged view of a cut surface, and FIG. FIG. 4 is a diagram showing a mapping state between a plane and a hologram plane.

FIGS. 6A, 6B, and 6C are diagrams illustrating examples in which a basic patch is represented as a set of point light sources.

FIG. 7 is a block diagram showing an embodiment of the apparatus of the present invention.

FIGS. 8A and 8B are diagrams showing another example of a reference volume.

FIG. 9 is a diagram illustrating a method of interpolating voxel values.

[Explanation of symbols]

Reference Signs List 21: One section of reference volume 22: Propagation space of wavefront / reference volume 23: Opening surface / basic patch 301: Hologram surface 302: Display object 401: Cutting plane 402: Cutting surface of reference volume 501: Hologram surface A certain pixel 61, 63, 65... Example of basic patch 62, 64, 66.
Wavefronts generated by 63 and 65 71: Object model management means 72 ... Reference volume management means 73 ... Wavefront calculation means 74 ... Cut plane calculation means 75 ... Cut plane amplitude value calculation means 76 ... Hologram synthesis means 81 ... Reference volume 91, 92: each voxel of the reference volume 94: function curve (trigonometric function) used for interpolation 95: amplitude value of the position based on the interpolation result 901, 902: value registered in the voxel 903: position of the distance at which the wavefront is to be calculated / Position of hologram

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Satoshi Suzuki 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. Assume that a light source is present on the surface of a three-dimensional model of an object, calculate the amplitude value of a wavefront generated by the light from the light source on the hologram plane, and calculate the amplitude value of all light from the three-dimensional model. In a computer generated hologram generation method that generates a hologram by further synthesizing a reference beam with an interference fringe generated by synthesizing the amplitude value of the wavefront at each position on the hologram surface, the three-dimensional space is divided into small voxels. A first step of generating a reference volume in which the voxel holds the amplitude value of the wavefront of the light at each voxel when light from a specific light source row propagates through the three-dimensional space; The positional relationship between each patch of the extracted object and the hologram surface is stored, and the reference is made on a plane having the same inclination as that of the hologram surface when the patch is converted to the reference position. A second step of cutting the volume, and a third step of setting a value held in each voxel of the cut surface of the reference volume to an amplitude value of a wavefront due to light from a patch on the hologram surface at the position. A computer generated hologram generation method, comprising: 2. The method according to claim 1, wherein, in the first step, when the plurality of light source arrays are combined as the specific light source array, the plurality of light source arrays are set to be the specific light source array. The computer generated hologram generation method according to claim 1, wherein a plurality of reference volumes are generated according to the following: In the second step, wavefronts based on the plurality of reference volumes are sequentially used. 3. A computer generated hologram generating apparatus for calculating an amplitude value of a wavefront generated on a hologram surface by light from a three-dimensional model of an object, and generating a hologram by combining reference light with the calculated wavefront. An object model management means for describing and managing a three-dimensional model by a combination of basic patches; a wavefront calculation means for calculating a wavefront when the basic patches are used as a light source; and the calculated basic patches as a light source. Reference volume management means for holding the amplitude value of the wavefront in a voxel obtained by dividing the three-dimensional space and managing it as a reference volume; and a cut plane calculation for calculating a plane for cutting the reference volume from the positional relationship between the basic patch and the hologram plane. Means for calculating an amplitude value at each position of the cut surface of the reference volume cut by the plane; If, computer generated hologram generating apparatus characterized by comprising: a hologram synthesizing means for generating interference fringes by combining the determined amplitude value.