JP4841930B2 - 3D moving image playback apparatus and 3D moving image playback method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device reproducing a three-dimensional dynamic image by holography, the device having a simple system configuration that directly reproduces a high-quality three-dimensional moving image, with a wide-viewing angle by using an in-line hologram recorded by phase shift digital holography and that separates and reproduces a real image from the reference light and the conjugate image. <P>SOLUTION: The device includes a step of converting the interference fringe component of an in-line hologram into an interference fringe component of an off-axis hologram, by using captured image data, wherein the step is carried out, by compositing or combining hologram data in two sheets captured by phase shift digital holography of two sheets which are different by 90&deg; in phase in the reference light. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention includes video technology field, amusement field, entertainment field, internet field, information field, multimedia field, communication field, advertising field, advertising field, medical field, art field, education field, design support field, simulation field, virtual reality. The present invention relates to an apparatus and method for reproducing a three-dimensional moving image using an inline hologram that enables three-dimensional display used in, for example. In particular, it has the advantage of being able to reproduce a three-dimensional moving image from an in-line hologram that can be recorded using an existing image sensor with a large pixel pitch, and is capable of reproducing a three-dimensional moving image having a wide viewing angle with a small amount of data. The present invention relates to a moving image reproducing apparatus and a three-dimensional moving image reproducing method.

  In recording of a three-dimensional image by holography, interference fringes created by object lights are recorded in addition to interference fringes created by reference light and object light. If the interference fringes due to object light can be removed from the recorded interference fringes and only the interference fringes due to the reference light and object light can be extracted, the viewing angle of the recorded image should be increased to the light diffraction angle determined by the pixel pitch of the light receiving element. Can do. Phase shift holography is a technique for extracting only interference fringes due to reference light and object light from recording interference fringes.

  By the way, as a method for recording a three-dimensional image by phase holography, there are an inline method in which the reference light is incident from the same direction as the object light and an off-axis method in which the reference light is incident from a different direction from the object light. Comparing the two, the off-axis method records a spatial carrier-type hologram and narrows the viewing angle of image recording, whereas the in-line method can record an image with a wide viewing angle with less hologram data. However, when an image is reproduced from an inline hologram, the direction of the direct object light overlaps with the directions of the conjugate object light and the direct transmitted light, and a high-quality image cannot be reproduced. This is a major drawback of the in-line method. For this reason, an off-axis method that can separate and reproduce direct object light from conjugate object light and direct transmitted light is employed for recording and reproducing three-dimensional images.

  The in-line hologram has a great advantage that a three-dimensional image having a wide viewing angle can be recorded as compared with the off-axis hologram. However, when a three-dimensional image is reproduced from an in-line hologram, the real image overlaps the reference light and the conjugate image, so that a three-dimensional image that can be clearly observed cannot be reproduced. In order to avoid the overlap between the reference light and the conjugate image, image reproduction by holography is performed using an off-axis hologram. In the off-axis hologram, it is necessary to increase the crossing angle of the reference light and the object light so that the actual image is separated from the reference light and the conjugate image. If the crossing angle between the reference light and the object light is increased, the interval between the interference fringes due to the reference light and the object light becomes narrower, and the pixel pitch of the image sensor and the spatial modulation element needs to be smaller than the distance between the interference fringes. Image sensor and spatial modulation element are required. Normally, in an off-axis hologram formed so that the actual image does not overlap with the reference light and the conjugate image, the distance between the interference fringes is submicron, and it is technically difficult to capture such a small interference fringe as an image. .

  In addition, there is a problem that only a small image far from the hologram surface can be recorded or reproduced due to the spatial frequency limitation of the image sensor and the spatial light modulator. Phase shift holography has been invented as a technique for solving this problem (for example, see Patent Document 1).

  In phase-shift digital holography, the phase of a reference wave is shifted and the phase data of the object wave and the wave of the object wave are converted from the plurality of hologram image data generated by the reference wave and the object wave of each of the reference waves having different phases. It is necessary to calculate the amplitude data.

For example, the phase of the reference light is phase-shifted by π / 2 to generate a plurality of reference lights having different phases, for example, three reference lights, and three hologram images of each reference light and object light having different phase values Generate data. A simultaneous equation is solved among a plurality of hologram image data, and phase data related to the phase of the object light and amplitude data related to the amplitude of the object light are calculated. Object light wavefront data including all information necessary for creating a reproduced image is generated from the phase data of the object light and the amplitude data of the object light obtained by the calculation. The generated object light wavefront data is subjected to predetermined conversion such as Fresnel conversion, and a reproduced image is calculated and obtained.
Japanese Patent No. 3471556

  In this way, in order to solve the problems of the conventional in-line hologram, the phase data and the object relating to the phase of the object wave are obtained by calculation processing from a plurality of hologram image data having different reference light phases recorded by phase shift digital holography. The method for obtaining the amplitude data relating to the amplitude of the wave requires a long time numerical calculation because the number of hologram data is large. In addition, in order to obtain a reproduced image from the phase data of the object light and the amplitude data of the object light obtained by calculation, it is necessary to perform a long-time numerical calculation such as Fresnel transformation on the data of the object light wavefront.

  The present invention relates to an apparatus for reproducing a three-dimensional moving image by holography, and directly reproduces a high-quality three-dimensional moving image having a wide viewing angle using an in-line hologram recorded by phase shift digital holography, and further, a reference beam. It is another object of the present invention to provide an apparatus having a simple system configuration that reproduces an actual image separated from a conjugate image.

  In order to solve the problem, a step of recording an image by in-line holography in which object light and reference light are crossed coaxially or with a small crossing angle, and the reference light is phase-shifted by a spatial modulation element, and the phase shift is performed. Inline phase shift digital holography comprising a step of capturing an interference fringe image by combining the reference light and the object light, and using the captured image data, the interference fringe component of the inline hologram is converted to an off-axis hologram. A step of converting to an interference fringe component, and this step is performed for image reproduction by combining or combining two hologram data captured by two phase-shift digital holography in which the phase of the reference light is different by 90 degrees Spatial light with a pixel pitch less than half of the interference fringe spacing It was an image reproduced using the tone elements.

The conceptual process of combining or combining data according to the present invention will be described in detail below. An image reproducing apparatus is manufactured using a spatial light modulator having a pixel pitch that is half or less of the interference fringe interval, and the reference light is used as an inline hologram. Two tildes I _C and I _S of phase-shifted in-line holograms having phases different by 90 degrees are prepared. Image reproduction is performed by displaying, on the element, an image reproduction hologram obtained by combining or combining tilde I _C and I _S data of two holograms, and irradiating it with reference light. By changing the synthesis or combination of the tilde I _C and I _S data, the position of the reproduced image can be moved in any direction within the field of view determined by the pixel pitch of the light modulation element. It is possible to reproduce the actual image at a position where it does not overlap.

  If only the pixel pitch of the spatial light modulator is sufficiently smaller than the interference fringe interval under a constant hologram data amount, the reproducible field of view can be expanded. Therefore, when a spatial modulation element having a small pixel pitch is used, the actual image can be separated from the reference light and the conjugate image, so that it is easy to block the reference light and the conjugate image, and only the actual image can be reproduced. . In this apparatus, since data of two in-line holograms may be combined or combined and displayed on the spatial light modulation element, no special elements or parts are required, and the system configuration of the apparatus is simplified.

  According to the method and apparatus of the present invention, a reproduction hologram can be easily created only by combining two phase-shifted inline digital holograms, and the influence of the reference beam and the conjugate image can be eliminated by changing the combination as appropriate. A high-quality image with a wide viewing angle can be reproduced from the hologram. In addition, when plane wave reference light is used for inline hologram recording and image reproduction, a reproduction hologram can be created simply by combining hologram data without performing numerical calculations. Furthermore, when a spatial light modulation element with a small pixel pitch is used, it is easy to reproduce only the actual image while blocking the reference light and the conjugate image. In addition, when recording, it is possible to record high-quality three-dimensional images as phase-shifted inline holograms using in-line holography using existing light-receiving elements with a large pixel pitch, so digital holography using current image sensors and spatial light modulators Recording and reproduction of 3D images can be easily realized.

The present invention manufactures an image reproducing device using a spatial light modulation element having a pixel pitch that is half or less of the interference fringe interval, and tilde I of two phase-shifted inline holograms that differ in phase of reference light by 90 degrees as inline holograms. to prepare the _C and I _S. Image reproduction is performed by displaying, on the element, an image reproduction hologram obtained by combining or combining tilde I _C and I _S data of two holograms, and irradiating it with reference light. By changing the synthesis or combination of the tilde I _C and I _S data, the position of the reproduced image can be moved in any direction within the field of view determined by the pixel pitch of the light modulation element. It is possible to reproduce the actual image at a position where it does not overlap. For example, when plane wave reference light is used for hologram recording and image reproduction, inline holograms are displayed in the order of tilde I _C , I _S , tilde -I _C , and -I _S in the X-axis direction on the spatial light modulator. Then, the reproduced image can be moved in the X-axis direction, and the real image can be reproduced in the direction of the negative first-order diffracted light by the diffraction grating when bright, dark, bright, and dark are displayed in the X-axis direction. And the reference light in the direction of the zero-order diffracted light can be separated.

  If only the pixel pitch of the spatial light modulator is sufficiently smaller than the interference fringe spacing under a fixed hologram data amount, the actual image can be separated from the reference beam and the conjugate image, making it easy to block the reference beam and the conjugate image. It becomes possible to reproduce only the actual image. In this apparatus, since data of two in-line holograms may be combined or combined and displayed on the spatial light modulation element, no special elements or parts are required, and the system configuration of the apparatus is simplified.

  The principle of phase shift holography will be described below.

  When the hologram recording surface is irradiated with scattered light (object light) emitted from an object and reference light, interference fringes formed by the object light and the reference light can be recorded as a hologram. The object light O (x, y, t) and the reference light R (x, y, t) on the recording surface with the angular frequency ω are expressed as (Expression 1) and (Expression 2) in a general form.

  The light intensity I (x, y) recorded on the hologram surface is (Equation 3).

(Equation 3) The first term and the second term on the right side correspond to the light intensities of the object light and the reference light on the hologram surface, respectively, and do not include the phases of the object light and the reference light. The third term represents an interference fringe component generated by the object light and the reference light, and this term includes the amplitude O ₀ and the phase φ _O of the object light. The wavefront information of the object light is recorded by the third term on the right side, and the object light wavefront can be reproduced from this term.

As a method of extracting only the interference fringe component formed by the reference light and the object light from the recording hologram, there is a method of recording a plurality of holograms on the same image while shifting the phase of the reference light. Now, if the phase φ _{R of the} reference light is shifted by π to be φ _R + π, the polarity of the third term on the right side of (Equation 3) is inverted. Therefore, if the light intensities I ₀ and Iπ before and after shifting the phase of the reference light are recorded, the tilde of the cosine interference fringe component including the amplitude and phase of the object light is expressed as I _C = (I ₀ −Iπ) / 2. More can be taken out,

It becomes. Next, when the phase of the reference light to record light intensity i [pi] _{/ 2} and I ₃ π _{/ 2} when the φ _R + π / 2 and φ _R + 3π / 2, to obtain a sinusoidal interference fringe component (5) In the same manner .

  A technique for extracting the wavefront information of the object light from the recording hologram by shifting the phase of the reference light is called phase shift holography, and the obtained hologram is called a phase shift hologram.

In the case of recording by the in-line method, when the image is reproduced from the interference fringe component of (Equation 4) or (Equation 5), the direction of the object light directly overlaps the direction of the conjugate object light. The problem that the conjugate object light and the direct object light overlap can be solved by converting the interference fringe component of the in-line hologram into the interference fringe component of the off-axis hologram. The phase is changed by φ _R (x, y) −φ _R ′ (x, y), and the phase of the interference fringe component is φ _O (x, y) −φ _R ′ (x, y). The tilde I _C (x, y) of the cosine interference fringe component expressed by

  By substituting the cosine interference fringe component of (Equation 4) and the sine interference fringe component of (Equation 5) taken out from the recording hologram, (Equation 6) can be rewritten into (Equation 7).

  Eventually, when the extracted cosine interference fringe component and sine interference fringe component are used, the interference fringe component of the in-line hologram can be converted into the interference fringe component generated by the reference beam (Equation 8) and the object beam (Equation 1).

  In order to convert an inline hologram to an off-axis hologram, both the cosine interference fringe component and the sine interference fringe component of the inline hologram are required.

The hologram I ′ (x, y) = I _DC + tilde I _C ′ (x, y) is created by biasing the DC component I _DC to the interference fringe component of (Equation 7), and the reproduction reference beam, (Equation 9) is irradiated to reproduce an image.

  When the transmittance of the hologram is expressed as T (x, y) = KI ′ (x, y) using the constant K, the light immediately after passing through the hologram becomes (Equation 10).

  The first term on the right side represents directly transmitted light, the second term represents direct object light, and the third term represents conjugate object light. Therefore, when the hologram I ′ (x, y) created by converting the in-line hologram is used, the directions of the transmitted light, the direct object light, and the conjugate object light can be separated, and the transmitted light is the direction of the reproduction reference light. In addition, the direct object light is reproduced in the direction of the recording object light, and the conjugate object light is reproduced in the direction conjugate with the direct object light with respect to the reproduction reference light.

  Next, the creation of a reproduction hologram will be specifically described.

The tilde I _C (x, y) of the cosine interference fringe component, the tilde I _S (x, y) of the sine interference fringe component, and the cosine cos (φ _R −φ of the phase difference between the recording reference light and the reproduction reference light) _{If R} ′) and sine sin (φ _R −φ _R ′) are given, an image reproducing hologram can be created from the in-line hologram by simple calculation of only multiplication and addition of (Equation 7). The calculation for creating a hologram is a simple calculation by simply combining a cosine interference fringe component and a sine interference fringe component. However, since the number of hologram data is large, it is short to perform three-dimensional video reproduction in real time. It is required to perform calculations in time. As a method for performing a calculation for creating a hologram in a short time, it is conceivable to perform parallel calculation or optical calculation processing by a computer. By the way, when plane wave reference light is used for hologram recording and image reproduction, a hologram for reproduction can be created by combining only hologram data without performing numerical calculation for hologram synthesis.

  Hereinafter, a three-dimensional moving image reproducing apparatus and method using an inline hologram of the present invention will be described with reference to FIGS.

FIG. 1A is a diagram illustrating the z-x plane, and FIG. 1B is an explanatory diagram illustrating an equiphase surface of the obliquely incident reference light in the zy plane. A plane wave having a wavelength λ is incident perpendicularly to the hologram plane 1 as recording reference light. At this time, the phase φ _R (x, y) of the light on the hologram surface 1 becomes a constant value, and the phase of the light on the hologram surface 1 with respect to the origin becomes zero. On the other hand, when the reproduction reference beam 2 is obliquely incident with the angle θ _x rotated in the _x- axis direction and the angle θ _y rotated in the y-axis direction, the light phase φ _R ′ ( x, y) is given by (Equation 11).

Incidentally, the sampling interval d of the interference fringe data on the xy plane is equal to the pixel pitch of the light receiving element. The values of the incident angles θ _x and θ _y of the reproduction reference beam 2 are determined so as to satisfy the relational expression (Equation 12) with respect to the sampling interval d.

  Here, the integers m and n are 0, 1 or 2. When the incident angle is determined in this way, the phase difference between the recording reference light and the reproduction reference light 2 becomes (Equation 13) at the sampling point (id, jd) on the xy plane.

Accordingly, cos (φ _R −φ _R ′) = 1 and sin (φ _R −φ _R ′) = 0 at the point where the remainder obtained by dividing mi + nj by 4 becomes 0, and the reproduction represented by (Expression 7) The tilde I _C ′ of the cosine interference fringe component of the hologram 1 is equal to the tilde I _C of the cosine interference fringe component of the in-line hologram. Similarly, in that the remainder obtained by dividing the mi + nj 4 is 1 tilde I _C 'and the tilde I _S, tilde I _C is in that the remainder is at the 2' and tilde -I _C is too becomes 3 In point, the tilde I _C 'is equal to the tilde I _S , respectively. Eventually, the tilde I _C , I _S , −I _C , and −I _S of the interference fringe components of the inline hologram are selected as the tilde I _C ′ of the cosine interference fringe component of the reproduction hologram 1 at the sampling point (id, jd). Thus, the reproducing hologram 1 can be created. That is, when an optical plane wave is used as the recording reference light and the reproduction reference light 2, the image can be reproduced using the inline hologram data itself.

FIG. 2 and FIG. 3 show examples in which data of in-line holograms are combined for producing the reproduction hologram 1. FIG. 2 shows a combination of hologram data when m = 0 and n = 0. By this combination, the directly transmitted light can be directly rotated from the object light in the y-axis direction by the angle θ _y = arcsin (λ / 4d). The conjugate object light can be rotated by an angle 2θ _y directly from the object light. FIG. 3 shows a combination of hologram data when m = 2 and n = 1. Direct transmission light is directly reflected from the object light by an angle θ _x = arcsin (λ / 2d) in the x-axis direction and an angle θ _{y in the} y-axis direction. = Arcsin (λ / 4d). The conjugate object light is reproduced in the direction rotated by 2θ _y directly from the object light.

  The results of the image reproduction experiment are shown below.

  In order to demonstrate image reproduction using an in-line hologram, an image reproduction experiment was performed by displaying a computer-generated hologram on a high-definition reflective LCD display panel having a pixel pitch of 8.1 μm.

  Considering a character string having a width of 2 cm placed at a position 50 cm from the hologram surface as an object model, a computer-generated inline hologram was created assuming that object light and planar reference light are incident on the hologram surface from the vertical direction. An actual image reproduced by irradiating the hologram with a green laser having a wavelength of 532 nm is shown in an image reproduced from the computer-generated in-line hologram of FIG. The real image is reproduced at a position 50 cm behind the hologram surface, and the conjugate image is reproduced at a position 50 cm before the hologram surface. The viewing angle of the reproduction character string is 2.3 degrees with respect to the diffraction angle of 3.8 degrees determined from the pixel pitch and the light wavelength, and an image having a wide field of view is reproduced from the in-line hologram. The light around the real image is the reproduced conjugate object light. In the reproduction from the in-line hologram, the direct object light, the conjugate object light, and the direct reflected light are reproduced in the normal direction of the hologram, so that the three lights overlap, and the quality of the reproduced image is low.

FIGS. 5 and 6 show images reproduced from a reproduction hologram created using an inline hologram. FIG. 5 shows an image reproduced from the hologram when m = 0 and n = 1. Since the reference light for reproduction is directly irradiated from the object light from the direction rotated by the angle θ _y = arcsin (λ / 4d) in the _y -axis direction, the directly reflected light moves upward in the reproduced character string. Although the conjugate object light is not shown in the photograph of FIG. 5, it is reproduced directly in a direction rotated by an angle 2θ _y from the object light. FIG. 6 shows an image reproduced from the hologram when m = 2 and n = 1. Since the reference light for reproduction is directly irradiated from the object light from the direction rotated by the angle θ _x = arcsin (λ / 2d) in the x-axis direction and the angle θ _y = arcsin (λ / 4d) in the _y -axis direction, the directly reflected light is It moves to the upper right of the replayed character string. Although the conjugate object light is not shown in the photograph of FIG. 6, it is reproduced directly in the direction rotated by an angle 2θ _y from the object light. As a result of separating the reproduction object light from the direct reflection light and the conjugate object light, a direct image with high image quality is reproduced as shown in FIGS.

  The three-dimensional color image recording / reproducing apparatus according to the present invention includes a video technology field, an amusement field, an entertainment field, an Internet field, an information field, a multimedia field, a communication field, an advertising field, a medical field, an art field, an education field, The present invention can be used as a three-dimensional moving image reproducing apparatus using an in-line hologram that enables three-dimensional display used in the design support field, simulation field, virtual reality field, and the like.

(A) The figure which shows the inside of a zx plane, (b) The explanatory view which shows the equiphase surface of the obliquely incident reference light in a zy plane The figure which shows the combination of the hologram data for producing the hologram for reproduction | regeneration when it is set as m = 0 and n = 1. The figure which shows the combination of the hologram data for producing the hologram for reproduction | regeneration when it is set as m = 2 and n = 1. Diagram showing an image reproduced from a computer-generated inline hologram The figure which shows the image reproduced | regenerated from the hologram for reproduction | regeneration of this invention when it is set as m = 0 and n = 1. The figure which shows the image reproduced | regenerated from the hologram for reproduction | regeneration of this invention when it is set as m = 2 and n = 1.

Explanation of symbols

1 Hologram plane 2 Reproduction reference beam

Claims (2)

A three-dimensional image reproduction device for reproducing an image recorded by in-line holography in which object light and reference light are crossed coaxially or with a small crossing angle,
A phase shift inline hologram generating means for generating two phase shift inline holograms, wherein the phase of the recording reference light is different by 90 degrees by the spatial modulation element;
Reproduction hologram data generation means for generating reproduction hologram data by combining or combining a cosine interference fringe component and a sine interference fringe component, including the amplitude and phase of the object light of the phase shift inline hologram,
The reproduction hologram data generation means sets an incident angle of the reproduction reference light when generating the reproduction hologram data so as to coincide with a diffraction angle by a diffraction grating having an interval twice or four times the pixel pitch. A three-dimensional image reproduction device characterized by the above. A three-dimensional image reproduction method for reproducing an image recorded by in-line holography in which object light and reference light are crossed coaxially or with a small crossing angle,
A phase-shift inline hologram generation step for generating two phase-shift inline holograms, wherein the phase of the recording reference light is different by 90 degrees by the spatial modulation element;
A reproduction hologram data generation step for generating reproduction hologram data by combining or combining a cosine interference fringe component and a sine interference fringe component, including the amplitude and phase of the object light of the phase shift inline hologram,
In the reproduction hologram data generation step , the incident angle of the reproduction reference light when the reproduction hologram data is generated is set so as to coincide with a diffraction angle by a diffraction grating having an interval twice or four times the pixel pitch. A three-dimensional image reproduction method characterized by the above.

Images