KR100837365B1 - Method for generating and reconstructing computer generated hologram using look-up table and apparatus thereof - Google Patents

Abstract

A method and an apparatus for generating and reproducing a CGH(Computer Generated Hologram) by using a look up table are provided to reduce a calculation time significantly through minimum once multiply and once addition and achieve real time hologram reproduction as using a small capacity of memory. In a method for generating and reproducing a CGH by using a look up table, the method comprises the following steps of: generating one reference element fringe pattern for each point of an object(210) spaced from a reference point of a hologram plane as much as the same distance; recording the reference element fringe pattern in a look up table according to a distance of each point of an object from the reference point; enabling a CGH forming unit(230) to generate CGH information(250) by shifting the reference element fringe pattern with respect to each point of the object located in the same plane as the distance corresponding to the reference element fringe pattern; and enabling a CGH pattern restoring unit(260) to reproduce a three-dimensional image by restoring the CGH information.

Description

Method for generating and reconstructing computer generated hologram using look-up table and Apparatus

The present invention relates to a method for generating and reproducing holograms, and more particularly, to a method and apparatus for generating and reproducing computer-generated holograms using a lookup table.

Recently, researches on 3D image and image reproduction technology are being actively conducted, and it is expected that the next generation display will be developed as a new concept of realistic image media that raises the level of visual information. In addition, the demand for 3D images is increasing because 3D images are more realistic, natural, and closer to the reality that humans feel.

Among the 3D image related technologies, the holography method is a method in which a viewer observes a virtual image of a virtual image while looking at the holography at a certain distance away from the front of the holography.

The holography method is a method of observing holography produced using a laser, and it is possible to feel the same stereoscopic image as the real one without wearing special glasses. Therefore, the holography method is known to be the most ideal way to feel the three-dimensional image without the fatigue and excellent stereoscopic feeling.

Generally, a ray-tracing method that calculates the diffraction of light is mainly used when calculating the hologram pattern. In this case, the target object is regarded as a set of points and the hologram pattern for each point is calculated and added. However, this method has a problem that it is difficult to reproduce in real time due to a large amount of computation.

In order to overcome this problem, a method of calculating a hologram using a look-up table (LUT) has been proposed. This method calculates all the element fringes of all points for the possible area in advance, and then, when calculating the hologram, retrieves and sums the element fringes corresponding to the point of the object to enable real-time processing. However, this method has a problem in that as the size of the object area increases, the number of element fringes required increases, and thus the size of the lookup table becomes too large.

The present invention provides a computer-generated hologram generation and reproduction method and apparatus using a lookup table capable of real-time hologram reproduction.

The present invention also provides a computer-generated hologram generation and reproduction method using a lookup table with a small memory required for hologram reproduction, and an apparatus thereof.

Technical problems other than the present invention will be easily understood through the following description.

According to an aspect of the present invention, in the hologram generation and reproduction method performed by the computer-generated hologram generation and reproduction apparatus using a lookup table, one reference for each point of the target object spaced by the same distance from the reference point of the hologram plane Generating an element fringe pattern; Recording the reference element fringe pattern in a look-up table according to the distance of each point of the object from the reference point; Generating computer-generated hologram information by shifting the reference element fringe pattern with respect to each point of the target object located on the same plane as the distance corresponding to the reference element fringe pattern; And regenerating the computer-generated hologram information and reproducing the 3D image by reproducing the 3D image.

In addition, according to another aspect of the invention, the reference element fringe pattern generation unit for generating one reference element fringe pattern for each point of the target object spaced by the same distance from the reference point of the hologram plane; A look-up table in which the reference element fringe pattern is recorded according to the distance of each point of the object from the reference point; A CGH forming unit generating computer-generated hologram information by shifting the reference element fringe pattern with respect to each point of the target object located on the same plane as a distance corresponding to the reference element fringe pattern; And a lookup table including a CGH pattern reconstruction unit for reconstructing the computer-generated hologram information and reproducing a 3D image.

Here, the reference element fringe pattern may be represented by the following equation.

,

는 공기 중에서의 빛의 파장,

은 기준파와 물체파 사이의 각도,

는 대상 물체의 p번째 점의 물체파의 위상값임. Where T is the reference element fringe pattern, (xp, yp, zp) is the coordinate of the p-th point of the object, rp is the distance between the p-th point of the object and the reference point (x, y, 0),

,

Is the wavelength of light in the air,

Is the angle between the reference and the object wave,

Is the phase value of the object wave at the pth point of the target object.

Here, the computer-generated hologram information can be represented by the following equation.

는 대상 물체의 p번째 점의 물체파의 세기값, N은 대상 물체를 구성하는 전체 점의 개수임. Where I is the computer-generated hologram information,

Is the intensity value of the object wave at the p-th point of the target object, and N is the total number of points constituting the target object.

The computer-generated hologram generating and reproducing method using the lookup table according to the present invention and its apparatus have the effect of real-time hologram reproducing.

In addition, the computer-generated hologram generating and reproducing method using the look-up table according to the present invention and the device have a small memory required for hologram reproduction.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

In addition, in the description with reference to the accompanying drawings, the same components regardless of reference numerals will be given the same reference numerals and duplicate description thereof will be omitted. In the following description of the present invention, if it is determined that the detailed description of the related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, before describing the preferred embodiments of the present invention in detail, a general principle and system for obtaining three-dimensional information using holography techniques will be described.

1 is a diagram illustrating a 3D information acquisition method using a holography technique according to an embodiment of the present invention.

The principle of the hologram is to split the beam from the laser into two, so that one beam shines directly on the screen and the other beam shines on the object. At this time, a light beam that directly shines on the screen is called a reference wave, and a light beam that shines on an object is called an object wave.

The object wave is the light reflected from each surface of the object, so the phase difference is different depending on the distance from the object surface to the screen. In this case, the unmodified reference wave interferes with the object wave, and the generated interference fringe is stored on the screen. Films in which such interference fringes are stored are called holograms.

A computer generated hologram (CGH) pattern is generated by computer calculation by (x, y, z) coordinate values and intensity values (I) of pixels. Computer generated hologram (CGH) is used for 3D hologram image acquisition. Figure 1 shows the geometric calculation model of the hologram. Hereinafter, the description will be made based on the CGH, but the present invention is not limited thereto.

The hologram is located on the x-y plane 130 and the P th point of the object is located at (xp, yp, zp) 110. ap and Φp represent the strength and phase of the points, respectively, and these are calculated by the computer by

The complex amplitude O (x, y) in the hologram can be obtained by the superposition of the object waves as shown in equation (1) below.

(1)

(One)

Where p represents a point constituting an object (object point), and N is the total number of points constituting the object. ap represents the intensity of the object wave and k is a wave vector, defined as k = 2π / λ. λ is the wavelength of light in free space. exp (jωt) is not included in equation (1). rp represents the oblique distance between the pth object point and the point (x, y, 0) in the hologram, and is defined by Equation (2) below.

(2)

(2)

In addition, the complex amplitude R (x, y) of the reference wave, which is a plane wave, is as shown in Equation (3) below.

(3)

(3)

Where aR and θR represent the intensity of the reference wave and the incident angle of the reference wave, respectively. The overall lattice intensity I (x) on the hologram plane is represented by equation (4) as the interference pattern between the object wave O (x, y) and the reference wave R (x, y). * Means the phase is reversed.

(4)

(4)

는 물체파의 세기를 나타내고, 두 번째 부분인

은 기준파의 세기를 나타낸다. 세 번째 부분

은 홀로그램 정보를 부분적으로 포함하고 있는 물체파와 기준파 사이의 간섭 패턴을 의미하며, 물체파의 공간 위치에 따른 위상 정보를 포함하고 있다.The first part of equation (4)

Represents the intensity of the object wave, the second part

Represents the intensity of the reference wave. Third part

Denotes an interference pattern between the object wave and the reference wave partially including the hologram information, and includes phase information according to the spatial position of the object wave.

에만 포함되어 있기 때문에 I(x,y)는 다음과 같이 표현할 수 있다. In equation (5) below, the hologram information is the third part

Because it is included only in, I (x, y) can be expressed as

(5)

(5)

The hologram pattern generated in this way can be arbitrarily divided and reproduced. In the hologram recording process, the object point is recorded in the whole area of the hologram pattern. That is, the object point is recorded at each time point. Therefore, when the divided hologram pattern is reproduced, the entire image is reproduced. This is a multiview image reproduced with horizontal and vertical parallax.

According to an embodiment of the present invention, with respect to a specific point of the target object located at the same distance from the reference point (for example, (x, y, 0) described above) of the hologram plane on which the hologram pattern is formed. Create a reference element fringe pattern. Here, the hologram plane is spaced apart from the target object by a predetermined distance. The reference element fringe pattern forms and records only one pattern at the same depth. Thereafter, the hologram pattern may be generated in real time by shifting the generated reference element fringe pattern with respect to the points of the target object existing at the same depth. The 3D image is reproduced by restoring the generated hologram pattern. Techniques for generating and reproducing holographic patterns are obvious to those of ordinary skill in the art, and thus detailed descriptions thereof will be omitted within the scope of the present invention.

2 is a diagram illustrating a computer-generated hologram generating and reproducing apparatus using a lookup table according to an exemplary embodiment of the present invention. 2, the target object 210, the three-dimensional information extraction unit 220 for extracting the three-dimensional information, the CGH forming unit 230 for forming the CGH, the look-up table 240 for storing the element fringe pattern, The CGH pattern 250 and the CGH pattern restoration unit 260 for restoring the CGH pattern are shown. In FIG. 2, the actions / functions performed by each component are described. Here, the embodiment of the present invention may further include a reference element fringe pattern generation unit for generating the above-described reference element fringe pattern.

Before describing such components, first, an aspect of the embodiment of the present invention will be described as follows. In general, image space is not discrete. However, since the capabilities of the human visual system are limited, the resolution can be selected without degrading the image. At this time, the degree of discretization should be small enough not to be perceived by the human eye so that two consecutive points can be recognized as continuous points without being separated. For example, humans recognize two points with a distance of 3 milliradians as one point. Therefore, if the image is viewed at a distance of 500 mm, a point with an interval of 500 mm × 0.003 = 150 microns or less is recognized as one point. Therefore, in the following, the vertical and horizontal degree of discretization is set to 150 micron.

The 3D information extractor 220 extracts the depth information of the target object 210 by extracting the color image and the depth image.

The reference element fringe pattern generation unit generates one reference element fringe pattern for each point of the target object spaced by the same distance from the reference point of the hologram plane. The reference element fringe pattern is stored in the lookup table 240 according to the distance of each point of the target object from the reference point.

The element fringe pattern of the lookup table 240 can be generated from the above equation (5). That is, the fringe pattern T having a reference intensity is expressed as follows.

(6)

(6)

According to an embodiment of the present invention, when calculating the hologram, a fringe pattern for each point is calculated using a lookup table, which is a set of fringe patterns for each point, instead of calculating the fringe pattern for each point as shown in Equation (5). Do it. Therefore, the information I of the hologram is expressed as follows.

(7)

(7)

Here, N is the total number of points constituting the object.

In the existing lookup table method, the speed is increased by using a pre-calculated fringe pattern. However, the biggest drawback of this method is the memory usage by the amount of pre-calculated fringe patterns. For example, if the image space consists of 100 (vertical) × 100 (horizontal) × 100 (depth) points, and the size of the element fringe pattern for each point is 1 MB, the size of the total lookup table used is 1 MB. × 100 × 100 × 100 = 1 TB.

Thus, according to an embodiment of the present invention, a reduced lookup table is presented that includes only one reference element fringe pattern at each depth (height) in order to reduce the size of the lookup table.

The CGH forming unit 230 shifts the reference element fringe pattern with respect to each point of the target object 210 located on the same plane as the distance corresponding to the reference element fringe pattern to generate computer-generated hologram (CGH) information. Create Here, the generated CGH information is as follows. The CGH information represents the CGH pattern 250.

(8)

(8)

는 대상 물체의 p번째 점(point)의 물체파의 세기값, N은 대상 물체를 구성하는 전체 점의 개수이다. Where I is the computer-generated hologram information,

Is the intensity value of the object wave at the p-th point of the object, and N is the total number of points constituting the object.

The CGH pattern restorer 260 reconstructs the CGH pattern 250 to reproduce the 3D image.

3 is a diagram illustrating a hologram pattern using a shift of a reference element fringe pattern according to an exemplary embodiment of the present invention. Referring to FIG. 3, an input image 310, a composite image 320 of a shifted reference element fringe pattern, and a CGH pattern 330 are illustrated.

의 위치에 있다면 기준 요소 프린지 패턴을 이 점을 중심으로 각각 x, y 방향으로 -xp와 yp만큼 쉬프트를 시킨다. 이러한 절차를 모든 포인트에 대하여 수행한 후, 쉬프트된 요소 프린지 패턴을 합성한다. 이와 같이 쉬프트되어 패턴을 형성한 개략적인 그림이 쉬프트된 기준 요소 프린지 패턴의 합성 영상(320)에 도시된다. 또한, 결과적인 패턴은 CGH 패턴(330)에 도시된다. Two point light sources are shown in the input image 310. One point light source centers around the used point to create a reference element fringe pattern

If at, shift the reference element fringe pattern around this point by -xp and yp in the x and y directions, respectively. After this procedure is performed for all points, a shifted element fringe pattern is synthesized. The schematic illustration of the shifted pattern to form the pattern is shown in the composite image 320 of the shifted reference element fringe pattern. The resulting pattern is also shown in CGH pattern 330.

As described above, in the embodiment of the present invention, the degree of vertical and horizontal discretization was set to 150 micron. Therefore, if the pixel size of the hologram is 10 μm, 15 pixels must be moved to move 150 μm. At this time, if the size of the reference element fringe pattern is too small, the reference element fringe pattern does not fill the size of the predetermined hologram. To avoid this situation, the size of the element fringe pattern should be set to some extent. However, if the size of the reference element fringe pattern becomes too large, the file size eventually increases. Therefore, it is necessary to determine the size of the appropriate element fringe pattern.

Here, if the depth of the image space is composed of 100 × 100 points and the size of the hologram pixel is 10 μm, the reference element fringe pattern is in the x and y directions in order to represent the first point to the last point in the image space. Each 100 × 15 pixels = 1,500 pixels must be moved. That is, if the size of the hologram pattern is 256 × 256, the total size of the reference element fringe pattern is 1,756 (256 + 1,500) × 1,756 (256 + 1,500).

The computer-generated hologram generation and reproduction method using the look-up table and a configuration diagram generally showing the apparatus have been described. Hereinafter, referring to the accompanying drawings, the computer-generated hologram generation and reproduction method using the look-up table according to the present invention is described. And the device will be described with reference to specific embodiments. It is obvious that the present invention is not limited to these examples.

4 is a diagram illustrating an input image and a depth image used in a computer-generated hologram generation and reproduction method using a lookup table according to an exemplary embodiment of the present invention.

In the embodiment of the present invention, the input image 410 used in the experiment is an automobile image. Here, the input image 410 is an image for processing information by inputting a target object to a computer. The depth image 420 is an image of the input image 410 according to the depth information. Each image has a resolution of 100 × 100 and the size of the hologram is 256 × 256. 3D information of the target object is obtained by combining the input image 410 and the depth image 410. Points of the same depth were aligned in the depth direction to calculate one reference element fringe pattern.

5 is a view comparing the hologram pattern according to an embodiment of the present invention with the hologram pattern according to the prior art. Referring to FIG. 5, a hologram pattern 510 generated by a conventional diffraction based method, a hologram pattern 520 generated using a conventional lookup table, and a reduced lookup according to an embodiment of the present invention. The hologram pattern 530 generated using the table is shown.

FIG. 6 is digitally reconstructed images corresponding to FIG. 5. An image 610 reconstructed by a conventional diffraction based method, an image 620 reconstructed by a method using an existing lookup table, and an image reconstructed by a method using a reduced lookup table according to an embodiment of the present invention. 630 is shown. All three images show that the car has been restored cleanly.

The table below compares the generation time of the hologram and the memory size used according to the three methods described above.

Traditional diffraction methods Conventional Lookup Table Method Reduced Lookup Table Method Calculation time per point (ms) 959.4702 11.0539 19.6958 Memory used for lookup tables 64 GB 295 MB

In the embodiment of the present invention, PC and Matlab 6.5 were used. The calculation time shown in the table above represents the average time for calculating the hologram for one point of the object. That is, in the conventional diffraction based method, 959.5 ms is required to calculate the hologram for one point, 11.1 ms is required in the conventional lookup table method, and 19.7 ms in the method according to the embodiment of the present invention. need. Therefore, using the lookup table, the speedup is 86.8 times faster than the existing lookup table.

This speed improvement can be seen by simply calculating with reference to Equations 1 to 5 described above. That is, in the conventional diffraction-based method, to generate a hologram pattern, at least 6 additions, 7 multiplications, one division, one square root, and two trigonometric functions (sine, cosine) must be performed.

In contrast, the proposed reduced lookup table-based approach requires only at least one multiplication and one addition. Therefore, the proposed method is expected to significantly reduce the computation time.

In addition, with respect to the amount of memory used, the conventional lookup table method requires 64 GB of memory space to store the element fringe patterns, but the method according to the embodiment of the present invention requires only 295 MB.

For example, suppose that an image space is composed of 100 (vertical) x 100 (horizontal) x 100 (depth) points, and the size of the hologram is 256 x 256. In the conventional lookup table method, 100 x 100 x 100 = 1,000,000 element fringe patterns are required, and the size of each element fringe pattern is 256 x 256. Therefore, the size of one element fringe pattern is 256 × 256 × 8 bits = 64 KB, and the size of the entire table is 64 KB × 1,000,000 = 64 GB. On the other hand, the size of the reference element fringe pattern according to the embodiment of the present invention is 1,756 × 1,756 as described above. In addition, each size is 1,756 × 1,756 × 8 bits = 2.95 MB, which is larger than the conventional method. However, since only 100 reference element fringe patterns are needed, the overall lookup table has a size of 2.95 MB x 100 = 295 MB.

Therefore, the size of the reference element fringe pattern is 2.95MB, which is 46.1 times larger than the conventional method, but overall, only 1/217 of space is required.

The computer-generated hologram generation and reproduction method using the lookup table according to the embodiment of the present invention described above may be performed in combination with a predetermined device, for example, a mobile communication terminal after being stored in a recording medium. Here, the recording medium may be a magnetic or optical recording medium such as a hard disk, a video tape, a CD, a VCD, a DVD, or a database of a client or server computer built offline or online.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and variations can be made.

1 is a view showing a three-dimensional information acquisition method using a holography technique according to an embodiment of the present invention.

2 is a diagram illustrating a computer-generated hologram generation and reproduction method using a lookup table according to an embodiment of the present invention.

3 is a diagram illustrating a hologram pattern using a shift of a reference element fringe pattern according to an embodiment of the present invention.

4 illustrates an input image and a depth image used in a computer-generated hologram generation and reproduction method using a lookup table according to an exemplary embodiment of the present invention.

5 is a view comparing the hologram pattern according to an embodiment of the present invention with the hologram pattern according to the prior art.

6 is a view comparing an image reproduced according to an embodiment of the present invention with an image reproduced according to the prior art;

Claims (6)

A hologram generation and reproduction method performed by a computer-generated hologram generation and reproduction apparatus using a lookup table, Generating one reference element fringe pattern for each point of the target object spaced the same distance from the reference point of the hologram plane; Recording the reference element fringe pattern in a look-up table according to the distance of each point of the object from the reference point; Generating computer-generated hologram information by shifting the reference element fringe pattern with respect to each point of the target object located on the same plane as the distance corresponding to the reference element fringe pattern; And And generating a 3D image by reconstructing the computer generated hologram information. The method of claim 1, The reference element fringe pattern is a computer-generated hologram generation and reproduction method using a look-up table, characterized in that represented by the following equation.

Here, T is the reference element fringe pattern, (xp, yp, zp) is the coordinate of the p-th point of the target object, rp is the distance between the p-th point of the target object and the reference point (x, y, 0),

,

Is the wavelength of light in the air,

Is the angle between the reference and the object wave,

Is the phase value of the object wave at the p-th point of the target object. The method of claim 2, And the computer-generated hologram information is represented by the following equation.

Where I is the computer-generated hologram information,

Is the intensity value of the object wave at the pth point of the object, and N is the total number of points constituting the object. A reference element fringe pattern generator configured to generate one reference element fringe pattern for each point of the target object spaced by the same distance from the reference point of the hologram plane; A look-up table in which the reference element fringe pattern is recorded according to the distance of each point of the object from the reference point; A CGH forming unit generating computer-generated hologram information by shifting the reference element fringe pattern with respect to each point of the target object located on the same plane as a distance corresponding to the reference element fringe pattern; And And a computer-generated hologram generating and reproducing apparatus using a look-up table including a CGH pattern restoring unit for restoring the computer-generated hologram information to reproduce a 3D image. The method of claim 4, wherein And the reference element fringe pattern is represented by the following equation.

Here, T is the reference element fringe pattern, (xp, yp, zp) is the coordinate of the p-th point of the target object, rp is the distance between the p-th point of the target object and the reference point (x, y, 0),

,

Is the wavelength of light in the air,

Is the angle between the reference and the object wave,

Is the phase value of the object wave at the p-th point of the target object. The method of claim 5, And the computer-generated hologram information is represented by the following equation.

Where I is the computer-generated hologram information,

Is the intensity value of the object wave at the p-th point of the target object, and N is the total number of points constituting the target object.

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