JP7540981B2 - Computer generated hologram generating device, method and program - Google Patents

Description

The present invention relates to a computer-generated hologram generating device, method, and program that generates a "continuous parallax hologram," a type of computer-generated hologram (CGH), quickly and with high quality.

CGH is a technology that uses a computer to perform light wave simulations of the propagation and interference of light waves required to calculate holograms, and outputs interference fringes as electronic data such as an image.

When calculating a CGH from 3D computer graphics as input, it is necessary to calculate a CGH that can display a reconstructed image with hidden surfaces removed according to the viewpoint position so that the reconstructed image is consistent when viewed from various viewpoints.

Non-Patent Document 1 proposes continuous parallax holograms as a calculation method for accurately realizing hidden surface removal according to the viewpoint position. Figure 16 shows the calculation process flow for continuous parallax holograms proposed in Non-Patent Document 1, and the calculation is performed in the following steps.

Step (a): A 3D scene composed of a polygon model is input. Ray tracing is performed on this model, emitting a virtual ray of light from the center of the hologram surface at a specified angle, and the intersection point between the ray and the polygon model is calculated. Next, the color of the intersection point is calculated based on a conventional shading technique (Phong shading), and a 3D point cloud is obtained by assuming that a point light source having the calculated color exists at the intersection point.

Step (b): Ray tracing is again performed from each point light source to each pixel on the hologram surface, and it is determined whether or not there is an obstruction between the light source and the hologram surface.

Step (c): Object light wave propagation calculation is performed only for pixels that are not occluded from the point light source, for example, using the well-known point light source method disclosed in Non-Patent Document 2. After that, interference calculation between the object light wave and the reference light wave is performed to output the CGH.

On the other hand, in Non-Patent Document 1, in step (a) as shown in FIG. 17, a process (hereinafter referred to as backface culling) is performed to determine whether the polygon intersected with the ray is on the front or back side, and to avoid acquiring point light sources that intersected on the back side. The purpose of backface culling is to speed up calculations, and by avoiding the acquisition of point light sources that belong to the back side and are not visible from each viewpoint position in step (a), it is possible to reduce in advance the number of point light sources for which occlusion judgment processing is performed in step (b).

Keita Watanabe, Yuji Sakamoto, "Hidden Surface Removal Method Using Object Point Based Ray Tracing in CGH" International Workshop on Advanced Image Technology 2021 (IWAIT2021), 2B-3, Jan 2021. A. Stein, Z. Wang, and J. Jr, "Computer-generated holograms: A simplified ray-tracing approach," Comput. Phys. 6, 389-392 (1992).

In the backface culling proposed in Non-Patent Document 1, there is a possibility that points for which propagation calculations should be performed are discarded in the backface culling process. As a result, point light sources that should be calculated disappear, causing degradation in the quality of the reconstructed image.

Specific examples include cases such as that shown in Figure 18, where a point light source that is subject to backface culling when ray tracing from the center of the hologram surface may be on the front side when viewed from other pixel positions. In such cases, the point light source should not be discarded.

The object of the present invention is to provide a computer-generated hologram generating device, method, and program that solves the above technical problems and, when using backface culling to reduce the number of point light sources used in light wave propagation calculations, can obtain point light sources for polygons whose visible front and back change depending on the pixel position on the hologram surface, thereby preventing point light sources for which propagation calculations should be performed from being removed by backface culling, thereby preventing degradation of the quality of the reconstructed image.

To achieve the above object, the present invention is a device for generating a computer-generated hologram by calculating the propagation of light waves from a 3D point group on a polygon model to a hologram surface, and is characterized by having the following configuration.

(1) The system includes a means for determining whether each polygon of a polygon model is a partial backface polygon in which there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side of the polygon is visible, a means for acquiring a 3D point cloud by rendering processing from the hologram surface to each polygon, and a selective backface culling means for not discarding point light sources acquired from the back side of the partial backface polygon.

(2) The means for determining whether or not a polygon is a partial backface polygon is configured to determine that a polygon whose virtually extended plane intersects with the hologram surface is a partial backface polygon.

(3) The means for determining whether or not a polygon is a partial backface polygon determines the surface visible from a plurality of representative positions on the hologram surface for each polygon, and determines as a partial backface polygon a polygon in which the surfaces visible from each representative position do not match on either the front or back.

(4) The means for determining whether or not a polygon is a partial backface polygon is configured to determine whether or not each polygon is a partial backface polygon based on the relative angle of each polygon with the hologram surface.

(5) The system further includes a means for determining whether each pixel on the hologram surface is occluded from the 3D point cloud after the selective backface culling, and determines all pixel areas on the hologram surface in which the back side of the partial backface polygon is visible as occluded areas.

(1) In backface culling, which discards point light sources obtained from the back side of a polygon, the system is equipped with a selective backface culling means that does not discard point light sources obtained from the back side of a partial backface polygon, thereby reducing the number of light wave propagation calculations without degrading the quality of the reconstructed image, enabling high-speed, high-quality CGH calculations.

(2) For polygons where a plane that is a virtual extension of each polygon intersects with the hologram surface, there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side is visible, making it possible to quantitatively identify partial backface polygons.

(3) For polygons where the faces visible from each representative position do not match, either the front or back, there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side is visible, making it possible to quantitatively identify partial backface polygons.

(4) Each polygon is judged to be a partial backface polygon or not based on the relative angle with the hologram surface, so a large number of polygons can be identified in a short period of time.

(5) The pixel areas on the hologram surface where the back side of the partial backface polygon is visible are determined to be occluded areas at once, so that occlusion determination for the backface area can be performed quickly, and CGH calculations can be accelerated without degrading the quality of the reconstructed image.

1 is a functional block diagram of a computer-generated hologram generating device according to a first embodiment of the present invention. FIG. 13 is a diagram for explaining a partial backface polygon. 13 is a diagram for explaining a method for determining a backface polygon on the basis of a plane intersection. FIG. FIG. 13 is a diagram for explaining selective backface culling. 13A to 13C are diagrams for explaining a method of calculating color information of a point light source obtained from a partial backface polygon. FIG. 11 is a functional block diagram of a computer-generated hologram generating device according to a second embodiment of the present invention. 13A and 13B are diagrams for explaining a method for determining a backface polygon based on a representative position. FIG. 11 is a functional block diagram of a computer-generated hologram generating device according to a third embodiment of the present invention. FIG. 1 is a diagram (part 1) for explaining a method for identifying backface polygons based on viewing angle. This is the second diagram to explain the method of identifying backface polygons based on the viewing angle. 13 is a diagram showing an example in which a discrepancy occurs between the discrimination result based on the viewing zone angle and the requirements for a partial backface polygon. This is the first diagram to explain why the discrepancy between the results of discrimination based on the viewing angle and the requirements for partial backface polygons does not cause a decrease in quality. This is the second diagram to explain why the discrepancy between the viewing angle-based discrimination results and the requirements for partial backface polygons does not cause a decrease in quality. FIG. 11 is a functional block diagram of a computer-generated hologram generating device according to a fourth embodiment of the present invention. 13A and 13B are diagrams for explaining a method for collectively determining whether or not a backface region of a partial backface polygon is occluded. FIG. 13 is a diagram showing a calculation process flow for a continuous parallax hologram. FIG. 13 is a diagram for explaining back face culling. 1A and 1B are diagrams for explaining why backface culling causes quality degradation in a reconstructed image.

The following describes in detail an embodiment of the present invention with reference to the drawings. FIG. 1 is a functional block diagram of a computer generated hologram generating device 1 according to a first embodiment of the present invention, with the main components being a partial backface polygon discriminator 10, a point cloud acquisition unit 20, an occlusion determination unit 30, an object light wave propagation calculation unit 40, and an interference calculation unit 50, and the point cloud acquisition unit 20 includes a selective backface culling unit 201. In this embodiment, the partial backface polygon discriminator 10 is equipped with a plane intersection based discriminator 101.

Such a computer-generated hologram generating device 1 can be configured by implementing applications (programs) that realize each function on at least one general-purpose computer or server equipped with a CPU, ROM, RAM, bus, interface, etc. Alternatively, it can be configured as a dedicated machine or a single-function machine in which part of the application is implemented as hardware or software.

A 3D polygon model for calculating the CGH is input to the computer generated hologram generating device 1. In this embodiment, each polygon that makes up the polygon model is a triangle or a rectangle, and each polygon is given information in advance that allows it to distinguish between its front and back.

For example, in backface culling in CG rendering, the multiple vertices that make up a polygon are arranged in a counterclockwise order when viewed from the front side. When rendering is performed with each pixel position on the hologram surface as the viewpoint, if the vertices appear to be arranged counterclockwise, it can be determined that the front side is being seen, and if they appear to be arranged clockwise, it can be determined that the back side is being seen. Similarly, in this embodiment, each polygon is assigned information that arranges its vertices in a counterclockwise order when viewed from the front side.

When a 3D polygon model for calculating a CGH is input, the partial backface polygon discrimination unit 10 determines whether each polygon is a partial backface polygon in which both the front and back sides are visible from the hologram surface depending on the pixel position, as shown in Figure 2. Polygons other than partial backface polygons, i.e. polygons in which only one side, the front or back, is visible from any pixel position on the hologram surface, are sometimes referred to as non-partial backface polygons.

In this embodiment, the partial backface polygon discrimination unit 10 includes a plane intersection base discrimination unit 101, and assumes a plane (extended plane) PL that is a virtual extension of each polygon, as shown diagrammatically in FIG. 3. A polygon P1 that intersects with the hologram surface, such as the extended plane PL1, is determined to be a partial backface polygon, and a polygon P2 that does not intersect with the hologram surface, such as the extended plane PL2, is determined to be a non-partial backface polygon.

The point cloud acquisition unit 20 includes a selective backface culling unit 201, and acquires a 3D point cloud by rendering from the hologram surface to a polygon model. In this embodiment, the intersections between each ray and the polygon model are acquired by ray tracing from an arbitrary point (typically the center point) on the hologram surface to the polygon model.

As shown diagrammatically in FIG. 4, the selective backface culling unit 201 performs selective backface culling, which eliminates points obtained from the back side of each polygon as in general backface culling, but if the polygon in question is determined to be a partial backface polygon, it preserves the points obtained from the back side of each polygon without eliminating them.

The point cloud acquisition unit 20 calculates the color of the points that are not eliminated by the selective backface culling process and acquires the position information and color information of each point as a point light source. The color of each point light source can be calculated based on Phong shading, for example, as disclosed in Non-Patent Document 1. As shown in FIG. 5, the back side is visible when rendering from the center of the hologram surface, but since it is a partial backface polygon, color information of the front side instead of the back side may be calculated for the stored points. This is because the visible front side color is recorded when different materials are set for the front and back sides of the polygon, or when the color is calculated using the normal vector of the polygon, and the colors obtained on the front and back sides are different.

The occlusion determination unit 30 inputs the point cloud stored by the point cloud acquisition unit 20 after the selective backface culling process, and performs an occlusion determination as to whether each point light source is visible or invisible from each pixel (x, y) on the hologram surface to obtain occlusion information Si(x, y). In this embodiment, the occlusion information Si(x, y) is registered as "1" for non-occluded pixels and "0" for occluded pixels.

The object light wave propagation calculation unit 40 calculates the propagation of the object light wave from each point light source to the hologram surface using the following equations (1) and (2) based on the point light source method disclosed in Non-Patent Document 2.

Here, ai (x, y) is the distribution of light waves on the hologram surface propagating from each point light source i. Ai is the brightness of point light source i, and ri represents the distance between point light source i and each pixel (x, y) on the hologram surface. k represents the wave number calculated from the wavelength of light.

The interference calculation unit 50 performs an interference calculation between the object light wave a(x, y) on the hologram surface and the reference light wave R(x, y). In this embodiment, parallel light expressed by the following equation (3) is incident, but any reference light can be used. Here, φ is the angle of incidence of the reference light on the hologram surface, and R0 is the intensity of the reference light. In this embodiment, φ=0 (plane wave incident perpendicular to the hologram surface).

Finally, the interference between this reference light wave and the object light wave is calculated using the following equation (4).

Here, I(x, y) is the luminance distribution of the CGH. In this embodiment, I(x, y) is finally normalized to the range of 0-255 and output as an image. This image is then reproduced on a spatial light modulator, and the reproduced image is reproduced and viewed by irradiating it with a reproduction illumination light.

According to this embodiment, in backface culling, which discards points obtained from the back side of a polygon, selective backface culling is performed that does not discard points obtained from the back side of a partial backface polygon, so that the number of light wave propagation calculations can be reduced without degrading the quality of the reconstructed image, enabling high-speed, high-quality CGH calculations.

In addition, according to this embodiment, polygons whose planes, which are virtually extended from each polygon, intersect with the hologram surface are determined to be partial backface polygons, making it possible to quantitatively determine partial backface polygons.

Figure 6 is a functional block diagram showing the configuration of the main parts of a computer-generated hologram generating device 1 according to a second embodiment of the present invention. The same reference numerals as those described above represent the same or equivalent parts, and therefore their explanation will be omitted. This embodiment is characterized in that the partial backface polygon discriminator 10 is equipped with a representative position-based discriminator 102.

Figure 7 is a schematic diagram showing a method for discriminating partial backface polygons by the representative position-based discrimination unit 102. In this embodiment, virtual representative positions A1 to A4 (A3 and A4 are not shown) are set at the four corners of the hologram surface, and the visible surface of each polygon is discriminated for each representative position. As a result, polygons whose surfaces visible from the four representative positions A1 to A4 match on one side (either the front or back side) are discriminated as non-partial backface polygons, and polygons whose surfaces visible from the four representative positions A1 to A4 do not match are discriminated as partial backface polygons.

In this embodiment, a total of four representative positions A1 to A4 are set at the four corners of the hologram surface, but the present invention is not limited to this, and multiple (<4) positions selected from the four corners of the hologram surface may be set as representative positions. Furthermore, the representative positions are not limited to the four corners of the hologram surface, and multiple positions selected from the four sides may be set. In other words, the multiple representative positions can be selected from at least one of the four corners or four sides of the hologram surface. In this case, it is desirable to set the representative positions so that they are farther apart from each other.

According to this embodiment, polygons whose faces visible from each representative position do not match on either the front or back are determined to be partial backface polygons, making it possible to quantitatively determine partial backface polygons.

Figure 8 is a functional block diagram showing the configuration of the main parts of a computer-generated hologram generating device 1 according to a third embodiment of the present invention. The same reference numerals as those described above represent the same or equivalent parts, and therefore their explanation will be omitted.

When determining partial backface polygons by calculating the intersection of planes as in the first embodiment, or by calculating the surfaces visible from a representative position as in the second embodiment, the calculation time increases as the number of polygons increases. In this embodiment, in order to achieve high-speed determination of partial backface polygons, the partial backface polygon determination unit 10 is characterized by having a viewing angle-based determination unit 103, which determines partial backface polygons uniformly based on the viewing angle of the reproduction optical system.

The viewing angle θ of a Fresnel hologram is calculated using the following formula (5). Here, p is the pixel pitch of the hologram surface, and λ is the wavelength of the reference light. Note that the viewing angle θ is a fixed value that depends on the reconstruction optical system, so in this embodiment it is assumed to be calculated in advance.

The viewing zone is the range over which the viewer can move their viewpoint, with its upper and lower bounds of +θ/2 and -θ/2 being the maximum diffraction angles on the hologram surface. Therefore, as shown in Figure 9, the relative angle between a polygon that meets the requirements for being a partial backface polygon and the plane Ax (Ay) perpendicular to the hologram surface falls within the range of -θ/2 to θ/2.

As shown in Figure 10, the viewing zone angle-based discrimination unit 103 focuses on the relative angle between each polygon and two virtual planes that are perpendicular to the hologram surface and mutually orthogonal (plane Ax [Figure 10(a)] perpendicular to the x-axis and plane Ay [Figure 10(b)] perpendicular to the y-axis), and discriminates as partial backface polygons any polygon whose relative angle within the viewing zone is within the range of -θ/2 to θ/2 with respect to any of the virtual planes.

In the example of FIG. 9, the relative angle of polygon Pa is the upper bound of the diffraction angle, +θ/2, and the relative angle of polygon Pb is the lower bound of the diffraction angle, -θ/2. The viewing zone angle-based discrimination unit 103 uniformly discriminates polygons whose relative angles are within the range of θ/2 to +θ/2 within the viewing zone as partial backface polygons, while as shown in FIG. 11, it discriminates polygons Pc that are located outside the viewing zone and polygons Pd that are within the viewing zone but whose relative angles are outside the range of -θ/2 to +θ/2 as other than partial backface polygons.

Note that even if they are located within the viewing zone, polygon Pe located above the top edge of the hologram surface and polygon Pf located below the bottom edge of the hologram surface are identified as partial backface polygons using a uniform discrimination method based on the viewing zone angle because their relative angles are within the range of -θ/2 to +θ/2. However, polygons Pe and Pf do not meet the requirements for a partial backface polygon because the pixel positions at which their front sides are visible do not exist on the hologram surface. Therefore, there is a discrepancy between the discrimination results based on the viewing zone angle and the requirements for a partial backface polygon.

In addition, although polygon Pg is not determined to be a partial backface polygon because its relative angle is outside the range of -θ/2 to +θ/2, it meets the requirements for a partial backface polygon because both the pixel positions from which its front side is visible and the pixel positions from which its back side is visible appear to be on the hologram surface. Therefore, there is a discrepancy between the results of the discrimination based on the viewing zone angle and the requirements for a partial backface polygon.

In this way, discrepancies may occur under certain conditions when using a uniform discrimination method using the viewing zone angle-based discrimination unit 103. However, as described in detail below, discrepancies between the results of discrimination based on the viewing zone angle and the requirements for partial backface polygons do not cause quality degradation, so this embodiment also enables high-speed, high-quality CGH calculation.

That is, for polygons such as polygons Pe and Pf in FIG. 11 that do not meet the requirements for partial backface polygons but that the viewing zone angle-based discrimination unit 103 discriminates as partial backface polygons, a point light source is acquired even though the front side is not visible from the hologram surface. However, in the subsequent occlusion determination unit 30, a point light source whose hologram surface is not visible is determined to be completely occluded, and light wave propagation is not calculated. As a result, no interference fringes are formed, and this does not cause quality degradation.

On the other hand, for polygons such as the polygon Pg that meet the requirements for a partial backface polygon but that the viewing zone angle-based discrimination unit 103 determines are not partial backface polygons, there is a concern that quality degradation may occur because a point light source is not obtained by backface culling.

However, in general, when calculating the light wave propagation from a point light source to the hologram surface to form interference fringes in CGH calculations, only the pixel area that can be seen within the diffraction angle from the point light source is included in the calculation range, as shown in Figure 12, and pixel areas outside the diffraction angle are not included in the calculation range. This is because even if interference fringes are formed by performing light wave propagation calculations for pixel areas outside the diffraction angle, the reconstruction illumination light during reconstruction does not bend more than the diffraction angle, so the light from that pixel area is not imaged at the position of the point light source, which would actually cause a deterioration in quality.

When this is applied to the present embodiment, as shown in FIG. 13, although there is a pixel area on the hologram surface from which the front side of polygon Pg is visible, the pixel area cannot be seen from the front side of polygon Pg within the diffraction angle, so the occlusion determination unit 30 determines that the pixel area is completely occluded. In other words, it is treated the same as if the point light source had been excluded. As a result, the pixel area is excluded from the calculation of light wave propagation in the object light wave propagation calculation unit 40, and is not considered to be a cause of quality degradation.

Thus, in the viewing zone angle-based discrimination method adopted in this embodiment, discrepancies may occur between the discrimination results and the requirements for partial backface polygons, but the discrepancies are compensated for in the subsequent process and do not cause quality degradation, making it possible to discriminate a large number of polygons in a short period of time without degrading quality.

Figure 14 is a functional block diagram showing the configuration of the main parts of a computer-generated hologram generating device 1 according to a fourth embodiment of the present invention. The same reference numerals as those described above represent the same or equivalent parts, and therefore their explanation will be omitted. This embodiment is characterized in that the occlusion determination unit 30 is equipped with a collective determination unit 301.

When the point light source for performing the occlusion determination calculation is obtained from a partial backface polygon, the collective determination unit 301 identifies the pixel region of the hologram surface where the back side of the partial backface polygon is visible as a backface region, as shown in FIG. 15, and determines that the backface region is occluded collectively instead of individually determining on a pixel-by-pixel basis, and performs individual determination on a pixel-by-pixel basis outside the backface region.

As explained above with reference to Figure 3, the back face area can be determined by calculating the points where an extended plane of each polygon intersects with the hologram surface and dividing the area at these points, and determining the side where the back side is visible.

If the partial backface polygon discrimination unit 10 discriminates the partial backface polygon using the plane intersection base discrimination unit 101, the area of the partial backface polygon that intersects with the hologram surface has already been calculated, so the backface area may be determined by referring to the calculation result.

According to this embodiment, occlusion determination for the back face region can be performed quickly, which makes it possible to speed up CGH calculations without degrading the quality of the reconstructed image.

Furthermore, according to each of the above embodiments, high-quality CGH can be generated in a short time and can be provided in real time even via communication infrastructure, making it possible to provide a variety of entertainment to many people regardless of geographic or economic disparities. As a result, it will be possible to contribute to Goal 9 "Build resilient infrastructure and promote inclusive and sustainable industrialization" and Goal 11 "Make cities inclusive, safe, resilient and sustainable" of the Sustainable Development Goals (SDGs) led by the United Nations.

10...Partial backface polygon discrimination unit, 20...Point cloud acquisition unit, 30...Occlusal determination unit, 40...Object light wave propagation calculation unit, 50...Interference calculation unit, 101...Plane intersection based discrimination unit, 102...Representative position based discrimination unit, 103...Viewing zone angle based discrimination unit, 201...Selective backface culling unit, 301...Bulk determination unit

Claims (18)

A device for generating a computer-generated hologram by calculating the propagation of light waves from a 3D point group on a polygon model to a hologram surface,
a means for determining whether or not each polygon of the polygon model is a partial backface polygon in which there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side of the polygon is visible;
A means for acquiring a 3D point cloud by rendering each polygon from a hologram surface;
A computer-generated hologram generating device characterized by comprising: a means for performing selective backface culling that does not discard point light sources obtained from the back side of a partial backface polygon in backface culling that discards point light sources obtained from the back side of a polygon. The computer generated hologram generating device according to claim 1, characterized in that the means for determining whether or not a polygon is a partial backface polygon determines that a polygon whose virtually extended plane intersects with the hologram surface is a partial backface polygon. The computer generated hologram generating device according to claim 1, characterized in that the means for determining whether or not a polygon is a partial backface polygon determines the surface visible from a plurality of representative positions on the hologram surface for each polygon, and determines as a partial backface polygon a polygon whose surface visible from each representative position does not match on either the front or back. The computer-generated hologram generating device according to claim 3, characterized in that the multiple representative positions are the four corners of the hologram surface. The computer-generated hologram generating device according to claim 3, characterized in that the multiple representative positions are multiple positions selected from at least one of the four corners and four sides of the hologram surface. The computer generated hologram generating device according to claim 1, characterized in that the means for determining whether or not a polygon is a partial backface polygon determines whether or not each polygon is a partial backface polygon based on the relative angle of each polygon with the hologram surface. The computer-generated hologram generating device of claim 6, characterized in that the means for determining whether or not a polygon is a partial backface polygon determines as a partial backface polygon a polygon whose relative angle with two imaginary planes that are perpendicular to the hologram surface and mutually orthogonal is within the maximum diffraction angle. The method further includes a means for determining whether each pixel on a hologram surface is occluded from the 3D point cloud after the selective backface culling,
8. The computer-generated hologram generating device according to claim 1, wherein the means for performing the occlusion determination collectively determines pixel areas on the hologram surface through which the back side of the partial backface polygon is visible as occlusion areas. A method for generating a computer-generated hologram by calculating light wave propagation from a 3D point group on a polygon model to a hologram surface by a computer,
determining whether or not each polygon of the polygon model is a partial backface polygon in which there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side of the polygon is visible;
A 3D point cloud is obtained by rendering each polygon from the hologram surface.
A computer-generated hologram generation method characterized by performing selective backface culling in which point light sources obtained from the back side of a partial backface polygon are not discarded in backface culling, which discards point light sources obtained from the back side of a polygon. The computer-generated hologram generating method according to claim 9, characterized in that when determining whether or not a polygon is a partial backface polygon, a polygon in which a plane obtained by virtually extending each polygon intersects with the hologram surface is determined to be a partial backface polygon. The computer-generated hologram generating method according to claim 9, characterized in that when determining whether or not a polygon is a partial backface polygon, the surfaces visible from multiple representative positions on the hologram surface are determined for each polygon, and a polygon in which the surfaces visible from each representative position do not match on either the front or back are determined to be a partial backface polygon. The computer-generated hologram generating method according to claim 9, characterized in that when determining whether each polygon is a partial backface polygon, it is determined whether each polygon is a partial backface polygon based on the relative angle with the hologram surface. The computer-generated hologram generating method according to any one of claims 9 to 12, characterized in that when performing an occlusion determination for each pixel on the hologram surface from the 3D point cloud after the selective backface culling, pixel areas on the hologram surface where the back side of the partial backface polygon is visible are collectively determined to be occluded areas. In this program, a computer calculates the propagation of light waves from a 3D point cloud on a polygon model to a hologram surface to generate a computer-generated hologram.
a step of determining whether or not each polygon of the polygon model is a partial backface polygon in which there are pixel positions on the hologram surface where the front side of the polygon is visible and pixel positions where the back side of the polygon is visible;
A procedure for obtaining a 3D point cloud by rendering each polygon from the hologram surface;
A computer-generated hologram generation program that causes a computer to execute the steps of: performing selective backface culling that does not discard point light sources obtained from the back side of a partial backface polygon in backface culling that discards point light sources obtained from the back side of a polygon; and The computer-generated hologram generation program according to claim 14, characterized in that in the step of determining whether or not a polygon is a partial backface polygon, a polygon in which a plane obtained by virtually extending each polygon intersects with the hologram surface is determined to be a partial backface polygon. The computer-generated hologram generation program according to claim 14, characterized in that in the step of determining whether or not a polygon is a partial backface polygon, the surfaces visible from a plurality of representative positions on the hologram surface are determined for each polygon, and a polygon in which the surfaces visible from each representative position do not match on either the front or back is determined to be a partial backface polygon. The computer generated hologram generation program according to claim 14, characterized in that in the step of determining whether or not a polygon is a partial backface polygon, each polygon is determined to be a partial backface polygon based on its relative angle with the hologram surface. The method further includes a step of determining whether each pixel on a hologram surface is occluded from the 3D point cloud after the selective backface culling,
18. A computer-generated hologram generation program as claimed in any one of claims 14 to 17, characterized in that in the step of making the occlusion determination, pixel areas of the hologram surface through which the back side of the partial backface polygon is visible are collectively determined to be occluded areas.

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