Patent Publication Number: US-2015085069-A1

Title: Holographic image generation and reconstruction

Description:
BACKGROUND 
     Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Holography techniques can be used to record holograms representing images of an object and reconstruct the images from the recorded holograms. As an example of conventional holography techniques, transmission-type holography techniques can be used to generate holograms of a two-dimensional or three-dimensional object on a transmitting side, for example, by means of a CCD (charge coupled device) camera. The holograms can be transmitted to a receiving side device (e.g., a holographic television set) in the form of video signals. On the receiving side device, the holograms can be reproduced and displayed on a high-definition liquid crystal display (LCD) panel constituted of pixels having a resolution of the order of the optical diffraction limit, based on fringe patterns contained in the received video signals. In particular, the hologram can be formed by irradiating a reconstruction light that readily causes interference, e.g., irradiating coherent light emitted from a laser light source, on the fringe patterns displayed on one side of the display panel. The irradiation of the reconstruction light on the fringe patterns causes diffraction in the fringe patterns, such that a user can observe the diffracted light as holographic images emitted from the other side of the display panel. 
     To reproduce a color holographic image, the receiving side device may be configured to obtain a color image by reproducing interference fringe patterns of individual colors (e.g., red, green and blue) on a LCD panel in a time-division manner based on the color video signals. Such a device may employ a so-called field sequential color system. In order to obtain a color image in the field sequential color system, the fields of individual colors must be switched at a very high rate corresponding to no more than 1 to 5 milliseconds per field. However, the present disclosure recognizes that the response rate of such a conventional LCD (e.g., using nematic liquid crystal) is typically a few milliseconds, which may not be suitable for performing switching operation at such a high rate as used in the field sequential color system. 
     SUMMARY 
     Technologies are generally described for generating color holographic images and reconstructing the color holographic images. 
     Various example apparatus described herein may be configured to generate a holographic image of an object. An example apparatus may include a plurality of light sources, a shutter, a beam splitter, a mirror unit, an image sensor array, and a video signal generator unit. Each of the light sources may be configured to generate a light beam corresponding to a wavelength in a different range. The shutter may be configured to receive the light beams from the plurality of light sources and selectively pass each of the received light beams in turn to provide a selected light beam. The beam splitter may be configured to split the selected light beam into a first light beam and a second light beam. Also, the beam splitter may be further configured to irradiate the first light beam on the object such that at least part of the first light beam may be scattered by the object to generate an object light beam. The mirror unit may be configured to receive the second light beam from the beam splitter, and reflect at least part of the second light beam to generate a reference light beam. The image sensor array may be configured to receive the reference light beam and the object light beam, and also configured to detect an image of interference caused by the reference light beam and the object light beam. The video signal generator unit may be configured to convert the detected image into an image signal associated with each of the plurality of light sources. 
     In some examples, a holographic image reconstruction apparatus is described such as any example apparatus described herein that may be adapted to reconstruct a holographic image of an object. The apparatus may be adapted to utilize a receiver unit configured to receive an input signal representative of a hologram of the object. The apparatus may be further adapted to utilize a virtual image light source configured to generate a virtual image light beam responsive to the input signal, and a scan mirror configured to receive the virtual image light beam and reflect the virtual image light beam to generate a scan beam to be irradiated on a screen. The screen may be coated with a photochromic material and configured to receive the scan beam from the scan mirror. Also, the screen may include a visible light transmittance characteristic that may be adjusted in response to the scan beam and effective to form the hologram of the object on the screen. The apparatus may be further adapted to utilize a plurality of reconstruction light sources and a shutter. Each of the reconstruction light sources may be configured to generate a reconstruction light beam corresponding to a wavelength in a different range. The shutter may be configured to receive the reconstruction light beams from the plurality of reconstruction light sources, and selectively pass one of the reconstruction light beams through the shutter to irradiate the screen to reconstruct the holographic image of the object. 
     In some examples, methods for generating a holographic image of an object are described. The example methods may include generating, by a plurality of light sources, a plurality of light beams corresponding to a different range of wavelengths. Switching operation may be performed, by a shutter, to selectively pass one of the plurality of light beams through the shutter. The light beam irradiated from the shutter may be split, by a beam splitter, into a first portion and a second portion of the light beam such that the first portion of the light beam is irradiated on the object. The second portion of the light beam may be received and reflected, by a mirror unit, to generate a reference beam. Some methods may further include detecting, by an image sensor array, an interference image caused by interference between the reference beam and the first portion of the light beam scattered by the object. The detected interference image may be converted, by a video signal generator unit, into an image signal. 
     In some examples, methods for reconstructing a holographic image of an object are described. The example methods may include receiving, by a receiver unit, an input signal representative of a hologram of the object. A virtual image light beam may be generated, by a virtual image light source, responsive to the input signal. The virtual image light beam may be received and reflected, by a scan mirror, to generate a scan beam. The scan beam from the scan mirror may be received, by a screen coated with a photochromic material, and the hologram of the object may be formed on the screen as a result of variations in the visible light transmittance characteristic of the screen in response to the scan beam. A reconstruction light beam corresponding to a wavelength in a different range may be generated by each of a plurality of reconstruction light sources. Some methods may further include receiving, by a shutter, the reconstruction light beams from the plurality of reconstruction light sources, and selectively passing one of the reconstruction light beams through the shutter to irradiate the screen to reconstruct the holographic image of the object. 
     In some examples, a computer-readable storage medium is described that may be adapted to store a program for causing a processor to generate a holographic image of an object. The processor may include various features as further described herein. The program may include one or more instructions for generating, by a plurality of light sources, a plurality of light beams corresponding to a different range of wavelengths, performing switching operation, by a shutter, to selectively pass one of the plurality of light beams through the shutter, and splitting, by a beam splitter, the light beam irradiated from the shutter into a first portion and a second portion of the light beam such that the first portion of the light beam is irradiated on an object. The program may further include one or more instructions for receiving and reflecting, by a mirror unit, the second portion of the light beam to generate a reference beam, detecting, by an image sensor array, an interference image caused by interference between the reference beam and the first portion of the light beam scattered by the object, and converting, by a video signal generator unit, the detected interference image into an image signal. 
     In some examples, a computer-readable storage medium is described that may be adapted to store a program for causing a processor to reconstruct a holographic image of an object. The processor may include various features as further described herein. The program may include one or more instructions for receiving, by a receiver unit, an input signal representative of a hologram of the object, generating, by a virtual image light source, a virtual image beam responsive to the input signal, and receiving and reflecting, by a scan mirror, the virtual image light beam to generate a scan beam. The program may further include receiving, by a screen coated with a photochromic material, the scan beam from the scan mirror, and forming the hologram of the object on the screen as a result of variations in the visible light transmittance characteristic of the screen in response to the scan beam. The program may further include generating, by each of a plurality of reconstruction light sources, a reconstruction light beam corresponding to a wavelength in a different range, and receiving, by a shutter, the reconstruction light beams from the plurality of reconstruction light sources, and selectively passing one of the reconstruction light beams through the shutter to irradiate the screen to reconstruct the holographic image of the object. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The foregoing and other features of this disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  schematically shows a block diagram of an illustrative example holographic image generator apparatus; 
         FIG. 2  schematically shows a perspective view of another illustrative example holographic image generator apparatus; 
         FIG. 3  schematically shows a block diagram of an illustrative example holographic imaging system including a holographic image generator apparatus coupled to a holographic image reconstruction apparatus through a network; 
         FIG. 4  schematically shows a block diagram of an illustrative example holographic image reconstruction apparatus; 
         FIG. 5  schematically shows a perspective view of another illustrative example holographic image reconstruction apparatus; 
         FIG. 6  schematically shows a perspective view of an illustrative example scan mirror that may be used in a holographic image reconstruction apparatus; 
         FIG. 7  illustrates an example flow diagram of a method adapted to generate a holographic image of an object; 
         FIG. 8  illustrates an example flow diagram of a method adapted to reconstruct a holographic image of an object; 
         FIG. 9  shows a schematic block diagram illustrating an example computing system that can be configured to perform methods for generating and/or reconstructing a holographic image of an object; 
         FIG. 10  illustrates computer program products that can be utilized to generate a holographic image of an object; and 
         FIG. 11  illustrates computer program products that can be utilized to reconstruct a holographic image of an object, all arranged in accordance with at least some embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     This disclosure is generally drawn, inter alia, to methods, apparatus, systems, devices and computer program products related to generating and reconstructing color holographic images. 
     Briefly stated, technologies are generally related to holographic imaging. In some examples, techniques are described for generating a holographic image of an object using a plurality of light sources, a shutter, and an image sensor array. Each of the light sources is configured to generate a light beam using a respective wavelength in a different range. In various examples, an apparatus as described here may be configured to control the shutter to receive the light beams from the plurality of light sources and selectively pass each of the received light beams to provide a selected light beam. The apparatus may further include a beam splitter and a mirror unit configured to generate an object light beam and a reference light beam from the selected light beam. The apparatus may include an image sensor array configured to detect an image of interference caused by the reference light beam and the object light beam. 
       FIG. 1  schematically shows a block diagram of an illustrative example holographic image generator apparatus, arranged in accordance with at least some embodiments described herein. As depicted, a holographic image generator apparatus  100  may include a light source unit  110  with a plurality of light sources  110   a  to  110   n , each being configured to generate a coherent light beam, such as a visible laser light beam. The coherent light beams of each light source may correspond to a different range of wavelengths, either overlapping in ranges or non-overlapping in ranges. An example light source unit  110  may include a red laser light source, a green laser light source and a blue laser light source, although many other wavelengths and types of light sources are contemplated. 
     In some embodiments, light source unit  110  of holographic image generator apparatus  100  may further include a shutter  112  configured to receive the light beams from the plurality of light sources  110   a  to  110   n  and selectively pass each of the received light beams to provide a selected light beam L 1 . In case where light source unit  110  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, shutter  112  may be configured to selectively pass (e.g., sequentially and/or repeatedly actuating shutter  112 ) one of a red laser light, a green laser light and a blue laser light. Light beam L 1  provided by shutter  112  may be transmitted to a beam splitter  130 . 
     In some embodiments, beam splitter  130  may be configured to collaboratively operate with light source unit  110  and a mirror unit  140 . Beam splitter  130  may be implemented using any suitable materials including an aluminum layer formed on a glass substrate. For example, beam splitter  130  may be configured to split the selected light beam L 1  into a first light beam L 13  and a second light beam L 12 . Beam splitter  130  may also be configured to irradiate an object  150  with first light beam L 13  such that at least part of first light beam L 13  may be scattered by object  150  to generate an object light beam L 3 . Beam splitter  130  may also be configured to irradiate mirror unit  140  with second light beam L 12 . Mirror unit  140  may be configured to reflect at least part of second light beam L 12  to generate a reference light beam L 2 , such that object light beam L 3  and reference light beam L 2  may cause interference patterns to be formed on an image sensor array  160 . 
     When two light beams, such as light beams L 2  and L 3 , reach the surface of image sensor array  160 , the light waves may intersect and interfere with each other. The interference pattern formed by the intersecting light waves may represent the manner in which the scene&#39;s light from object  150  interferes with the original light source from the light source unit  110 . Image sensors in image sensor array  160  may be configured to detect and receive images of the interference patterns. 
     In some embodiments, holographic image generator apparatus  100  may further include a video signal generator unit  180  configured to convert the image detected by image sensor array  160  into an image signal associated with each of the plurality of light sources  110   a  to  110   n.    
     In some embodiments, image sensor array  160  may include a charge coupled device (CCD) array or any other types of imaging sensors. Also, image sensor array  160  may include a sensor array configured in a two dimensional plane or any other shapes. For example, image sensor array may include an array of sensors configured in a shape of a cylinder or a polygonal prism that substantially surrounds object  150 . 
     In some embodiments, holographic image generator apparatus  100  may further include a controller  170  configured to selectively control operation of shutter  112  and video signal generator unit  180 . Controller  170  may be configured to store a control program that may be used by controller  170  in operation of holographic image generator apparatus  100 . Additionally, holographic image generator apparatus  100  may include a video signal recorder unit  190  configured to capture (or record) the image signal from video signal generator unit  180  in a storage unit (not shown). 
     In case where light source unit  110  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, controller  170  may be configured to control operation of holographic image generator apparatus  100  as follows. Shutter  112  may be configured to selectively pass (e.g., via switching operations) a red laser light L 1  from the red laser light source. The red laser light L 1  may be split into two light beams L 12  and L 13  by beam splitter  130 , where one split light beam L 13  may be irradiated on object  150  and may be scattered from object  150  to generate object light beam L 3 , which may be made incident on image sensor array  160 . The other split light beam L 12  may be reflected by mirror unit  140  to generate reference light beam L 2 , which may also be incident on image sensor array  160 . Then, at least a portion of a hologram of object  150  can be generated by interference between object light beam L 3  and reference light beam L 2  (hereinafter referred to as a red hologram) may be formed on image sensor array  160 . Further, video signal generator unit  180  may generate at least a portion of a holographic video signal based on the red hologram formed on image sensor array  160  (hereinafter referred to as a red holographic video signal). Video signal recorder unit  190  may record the red holographic video signal. 
     Further, shutter  112  may be selectively pass (e.g. via actuation or switched operation) a green laser light from the green laser light source. A green hologram of object  150  may be formed on image sensor array  160  in the same manner as described above. Then, video signal generator unit  180  may generate a green holographic video signal based on the green hologram formed on image sensor array  160 . Video signal recorder unit  190  may record (or capture) the green holographic video signal. Similarly, shutter  112  may be selectively pass (e.g., via actuation or switched operation) a blue laser light from the blue laser light source, and a blue holographic video signal may be generated by video signal generator unit  180  based on a blue hologram formed on image sensor array  160 . Video signal recorder unit  190  may be configured to record the blue holographic video signal. 
     In some embodiments, the above-described operations for generating each of the three-color holographic video signals may be executed in a range from about 1 to 5 milliseconds. Further, these operations may be repeatedly performed until holographic image generation apparatus  100  is turned off. In the above embodiments, since shutter  112  can be controlled to selectively pass one of the plurality of light sources  110   a  to  110   n  at a high speed, holographic image generation apparatus  100  can be effectively utilized to generate a color stereoscopic holographic image, e.g., in a field sequential color system. 
     In  FIG. 1 , one light source unit  110  and corresponding beam splitter  130  and mirror unit  140  are illustrated for the sake of explanation. However, the number of light sources, beam splitters and mirror units may not be limited thereto. In some examples, two or more pairs of light sources and beam splitters (and mirror units) may be arranged depending on the desired implementation. In one example, light beam L 1  from the light source unit  110  may be reflected by at least one additional mirror (not shown), effective to irradiate the beam splitter  130  through an indirect path. In another example, light beam L 13  from beam splitter  130  can be reflected by at least one additional mirror (not shown) to irradiate object  150  with light beam L 13  from an indirect path. In still another example, mirror  140  may be eliminated and light beam L 12  can be directly incident on image sensor array  160 . In still further examples, light beam L 3  can be indirectly received from the image sensor array  160  from at least one additional mirror (not shown). Additional examples of direct and indirect light paths using optical devices such as beam splitters, mirrors, lenses, and the like are contemplated and considered within the scope of the present disclosure. 
       FIG. 2  schematically shows a perspective view of another illustrative example holographic image generator apparatus, arranged in accordance with at least some embodiments described herein. A holographic image generator apparatus  200  has a similar configuration to holographic image generator apparatus  100  as shown in  FIG. 1 , except for that an image sensor array  260  is arranged in a shape of a rectangular prism. As depicted, image sensor array  260  may have a rectangular prism-shaped inner surface where an array of imaging sensors (e.g., CCD sensor devices) may be arranged. In an alternative embodiment, image sensor array  260  may have any other suitable shape of the inner surface, such as a cylindroid or other polygonal prism. 
     Similar to holographic image generator apparatus  100  shown in  FIG. 1 , apparatus  200  may include a light source unit  110  including a plurality of light sources, each being configured to generate a coherent light beam, such as a visible laser light beam, each corresponding to a wavelength in a different range, either overlapping or non-overlapping in ranges with the wavelength of the other light sources. In some embodiments, light source unit  110  may include a red laser light source, a green laser light source and a blue laser light source. 
     In some embodiments, holographic image generator apparatus  200  may further include a shutter in light source unit  110  configured to receive the light beams from the plurality of light sources and selectively pass each of the received light beams in turn to provide a selected light beam L 1 . The light beam L 1  provided by the shutter in the light source unit  110  may be transmitted to a beam splitter  130 . 
     In some embodiments, beam splitter  130  may be configured to collaboratively operate with light source unit  110  and a mirror unit  140 . Beam splitter  130  may be implemented using any suitable materials including an aluminum layer formed on a glass substrate. For example, beam splitter  130  may be configured to split light beam L 1  into a first light beam L 13  and a second light beam L 12 . Beam splitter  130  may also be configured to irradiate an object  150  with first light beam L 13  such that at least part of first light beam L 13  may be scattered by object  150  to generate an object light beam L 3 . Beam splitter  130  may also be configured to irradiate mirror unit  140  with second light beam L 12 . Mirror unit  140  may be configured to reflect at least part of second light beam L 12  to generate a reference light beam L 2 , such that object light beam L 3  and reference light beam L 2  may cause interference patterns to be formed on image sensor array  260 . 
     In some embodiments, holographic image generator apparatus  200  may further include a video signal generator unit (not shown) configured to convert the image detected by image sensor array  260  into an image signal associated with each of the plurality of light sources in light source unit  110 . Additionally, holographic image generator apparatus  200  may include a video signal recorder unit (not shown) configured to record the image signal from video signal generator unit in a storage unit. 
     In some embodiments, operations for generating multiple color holographic video signals (e.g., red, green and blue holographic video signals) may be executed by holographic image generator apparatus  200  in a similar manner as described above with reference to  FIG. 1 . Such operations for generating each of the color holographic video signals may be performed in a range from about 1 to 5 milliseconds and may be repeatedly performed until holographic image generation apparatus  200  is turned off. In the above embodiments, since the shutter can be controlled to selectively pass one of the plurality of light sources at a high speed, holographic image generation apparatus  200  can be effectively utilized to generate a color stereoscopic holographic image, e.g., in a field sequential color system. 
     In  FIG. 2 , one light source unit  110  and corresponding beam splitter  130  and mirror unit  140  are illustrated for the sake of explanation. However, the number of light sources, beam splitters and mirror units may not be limited thereto. In some examples, four pairs of light sources and beam splitters (and mirror units) may be arranged in correspondence with four inner surfaces in rectangular prism shaped image sensor array  260 . 
     In some embodiments, the image signals generated by holographic image generator apparatus  100  or  200  according to the above embodiments may be recorded in a local storage unit and/or transmitted to a holographic image reconstruction apparatus.  FIG. 3  schematically shows a block diagram of an illustrative example holographic imaging system including a holographic image generator apparatus coupled to a holographic image reconstruction apparatus through a network, in accordance with at least some embodiments described herein. As depicted, a holographic imaging system  300  may include a holographic image generator apparatus  310 , which may be coupled to a recorder unit  320  and a transmitter unit  330 . Transmitter unit  330  may be coupled to receiver unit  340  through one or more networks  360 . Receiver unit  340  may be coupled to a holographic image reconstruction apparatus  350 . 
     In some embodiments, holographic image generator apparatus  310  may have a similar configuration to holographic image generator apparatus  100  or  200  as shown in  FIGS. 1 and 2 . Holographic image generator apparatus  310  may be configured to generate image signals in a similar manner as described above with reference to  FIGS. 1 and 2 . Thus generated digital image signals may be transmitted and recorded in recorder unit  320 . The image signals recorded in recorder unit  320  may be read by transmitter unit  330  and sent to a remote device, such as a receiver unit  340  or a holographic image reconstruction apparatus  350 , through a network  360 . 
     Receiver unit  340  may be configured to receive the image signals from transmitter unit  330  and transmit the image signals to holographic image reconstruction apparatus  350 . 
     In some embodiments, holographic image reconstruction apparatus  350  may be configured to reconstruct images of object  150  based on the received image signals.  FIG. 4  schematically shows a block diagram of an illustrative example holographic image reconstruction apparatus, arranged in accordance with at least some embodiments described herein. 
     As shown in  FIG. 4 , a holographic image reconstruction apparatus  400  may include a virtual image light source  420  configured to generate a virtual image light beam L 41 , such as an ultraviolet laser beam or an electron beam, based on a holographic image signal S 41 . In some embodiments, the holographic image signal S 41  may be provided from a receiver unit  450  or a holographic image generator apparatus such as holographic image generator apparatus  100 ,  200  or  310  in  FIGS. 1 to 3 . Thus generated virtual image light beam L 41  may have intensities which may vary based on the levels of the holographic image signal S 41 . Virtual image light source  420  may be configured to irradiate the generated virtual image light beam L 41  onto a scan mirror  430 . Scan mirror  430  may be configured to reflect the virtual image light beam and generate a scan beam L 42  that is irradiated on a screen  460 . 
     In some embodiments, screen  460  may be coated with a photochromic material and configured to form a hologram of an object, such as object  150 , using a visible light transmittance characteristic that is adjusted in response to the scan beam L 42  from scan mirror  430 . For example, screen  460  may include a photochromic material formed on a transparent layer. The transparent layer may be formed of at least one of a quartz glass material, a borosilicate glass material, a transparent plastic material and PET (polyethylene terephthalate). The photochromic material may include at least one of KTaO 3  doped with an impurity and SrTiO 3  doped with an impurity. The impurity doped into the photochromic material may include nickel (Ni) and/or iron (Fe). Additionally or alternatively, the photochromic material may include an organic photochromic material such as HABI (hexaarylbiimidazole). 
     In some embodiments, when screen  460  coated with a photochromic material such as KTaO 3  doped with Ni and Fe is irradiated with the scan beam L 42 , electrons in the photochromic material may be excited by the scan beam L 42  and trapped in complex defects formed by the impurity Ni and oxygen vacancies. Specifically, one or two electrons may be trapped by a complex defect of an Ni ion with an oxygen vacancy VO at the center (Ni 3+ —VO), whereby the complex defect (Ni 3+ —VO) becomes (Ni 3+ —VO-2e) or (Ni 3+ —VO-e). Complex defects having trapped electrons may exhibit sufficiently wide absorption characteristics for light with visible spectrum. In particular, (Ni 3+ —VO-2e) has a light absorption peak at the wavelength of 630 nm and has a wide absorption band. On the other hand, an iron ion (Fe 3+ ) traps holes to beam Fe 4+ , and the center of the impurity has an absorption band having a peak at about 440 nm. Thus, KTaO 3  doped with both Ni and Fe, when irradiated with the scan beam L 42  such as ultraviolet light beam or electron beam, exhibits a wide absorption band over the entire visible spectrum including red, green and blue color spectrum. 
     On screen  460  coated with the photochromic material having the above-described characteristics, holograms may be formed by changing a visible light transmittance of the photochromic material in response to the varying intensities of the virtual image light beams such as scan beams L 42 . That is, images of an object corresponding to the holographic image signals may be formed on screen  460  in the form of images representing varying visible light transmittance. 
     In some embodiments, holographic image reconstruction apparatus  400  may further include a reconstruction light source unit  410 , which may include a plurality of reconstruction light sources  410   a  to  410   n . Each of reconstruction light sources  410   a  to  410   n  may be configured to irradiate a reconstruction light beam corresponding to a wavelength in a different range, such as a visible laser beam, towards screen  460 . For example, the plurality of reconstruction light sources  410   a  to  410   n  may include a red laser light source, a green laser light source, and a blue laser light source. 
     In some embodiments, reconstruction light source unit  410  of holographic image generator apparatus  400  may further include a shutter  412  configured to receive the reconstruction light beams from the plurality of reconstruction light sources  410   a  to  410   n  and selectively pass (e.g., via actuated or switched operation) each of the received light beams in turn to provide a selected light beam L 43 . In case where reconstruction light source unit  410  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, shutter  412  may be sequentially switched to pass one of a red laser light, a green laser light and a blue laser light. Light beam L 43  provided by shutter  412  may be transmitted to screen  460 . When the holograms formed on screen  460  are irradiated with reconstruction light beam L 43 , an image of the object may be reconstructed. 
     In some embodiments, holographic image reconstruction apparatus  400  may further include a controller  440  configured to control operation of one or more of shutter  412 , virtual image light source  420  and/or scan mirror  430 . Controller  440  may be configured to store a control program that may be used by controller  170  in operation of holographic image reconstruction apparatus  400 . Additionally, holographic image reconstruction apparatus  400  may include receiver unit  450  configured to receive an input signal S 42  representative of a hologram of the object from an external device such as holographic image generator apparatus  100 ,  200  or  310 . 
     In case where light source unit  410  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, controller  440  may be configured to control operation of holographic image reconstruction apparatus  400  as follows. Shutter  412  may be configured to selectively pass (e.g., via switching operations) a red laser light L 43  from the red laser light source. The red laser light L 43  may be made incident on the holograms formed on screen  460 , and thus, a red-color image of the object may be reconstructed. Further, shutter  412  may be configured to selectively pass a green laser light L 43  from the green laser light source. A green-color image of the object may be reconstructed on screen  460  in the same manner as described above. Similarly, shutter  412  may be configured to selectively pass a blue laser light L 43  from the blue laser light source, and a blue-color image of the object may be reconstructed on screen  460 . 
     In some embodiments, the above-described operations for reconstructing each of three color holographic images may be executed in a range from about 1 to 5 milliseconds. Further, these operations may be repeatedly performed until holographic image reconstruction apparatus  400  is turned off. In the above embodiments, since shutter  412  can be controlled to selectively pass one of the plurality of reconstruction light sources  410   a  to  410   n  at a high speed, holographic image reconstruction apparatus  400  can be effectively utilized to reconstruct a color stereoscopic holographic image, e.g., in a field sequential color system. 
     In  FIG. 4 , one virtual image light source  420  and corresponding scan mirror  430  are illustrated for the sake of explanation. However, the number of virtual image light sources and scan mirrors may not be limited thereto. In some examples, two or more pairs of virtual image light sources and scan mirrors may be arranged depending on the desired implementation. 
       FIG. 5  schematically shows a perspective view of another illustrative example holographic image reconstruction apparatus, arranged in accordance with at least some embodiments described herein. A holographic image reconstruction apparatus  500  has a similar configuration to holographic image reconstruction apparatus  400  as shown in  FIG. 4  except for that a screen  560  is arranged in a shape of a rectangular prism. As depicted, screen  560  may have a rectangular prism-shaped inner surface that may be coated with a photochromic material. In an alternative embodiment, screen  560  may have any other suitable shape of the inner surface, such as a cylindroid or other polygonal prism. 
     In some embodiments, screen  560  may be configured to form a hologram of an object, such as object  150 , using a visible light transmittance characteristic that can be adjusted in response to the scan beam L 42  from scan mirror  430 . For example, screen  560  may include a photochromic material formed on a transparent layer. The transparent layer may be formed of at least one of a quartz glass material, a borosilicate glass material, a transparent plastic material and PET (polyethylene terephthalate). The photochromic material may include at least one of KTaO 3  doped with an impurity and SrTiO 3  doped with an impurity. The impurity doped into the photochromic material may include nickel (Ni) and/or iron (Fe). Additionally or alternatively, the photochromic material may include an organic photochromic material such as HABI (hexaarylbiimidazole). 
     Similar to holographic image reconstruction apparatus  400  shown in  FIG. 4 , apparatus  500  may include a virtual image light source  420  configured to generate a virtual image light beam L 41 , such as an ultraviolet laser beam or an electron beam, based on a holographic image signal. In some embodiments, the holographic image signal may be provided from a holographic image generator apparatus such as holographic image generator apparatus  100 ,  200  or  310  in  FIGS. 1 to 3 . Thus generated virtual image light beam L 41  may have intensities which may vary based on the level of the holographic image signal, e.g., based on a value of a color component represented by the holographic image signal. Virtual image light source  420  may be configured to irradiate the generated virtual image light beam L 41  onto a scan mirror  430 . Scan mirror  430  may be configured to reflect the virtual image light beam and generate a scan beam L 42  that is irradiated on screen  560 . 
     In some embodiments, holographic image reconstruction apparatus  500  may further include a reconstruction light source unit  410 , which may include a plurality of reconstruction light sources (not shown) such as reconstruction light sources  410   a  to  410   n . Each of the reconstruction light sources may be configured to irradiate a reconstruction light beam corresponding to a wavelength in a different range, such as a visible laser beam, on screen  560 . For example, the plurality of reconstruction light sources may include a red laser light source, a green laser light source, and a blue laser light source. 
     In some embodiments, reconstruction light source unit  410  of holographic image generator apparatus  500  may further include a shutter (not shown), such as shutter  412 , configured to receive the reconstruction light beams from the plurality of reconstruction light sources and selectively pass each of the received light beams to provide a selected light beam L 43 . When the hologram formed on screen  560  is irradiated with the reconstruction light beam L 43 , an image of the object may be reconstructed. 
     In some embodiments, holographic image reconstruction apparatus  500  may further include a controller (not shown) configured to control operation of one or more of the shutter, virtual image light source  420  and/or scan mirror  430 . Controller  440  may be configured to store a control program to control operation of holographic image reconstruction apparatus  500 . Additionally, holographic image reconstruction apparatus  500  may include a receiver unit (not shown) configured to receive an input signal representative of a hologram of the object from an external device such as holographic image generator apparatus  100 ,  200  or  310 . 
     In some embodiments, operations for reconstructing multiple color holographic images (e.g., red, green and blue holographic images) may be executed by holographic image generator apparatus  500  in a similar manner as described above with reference to  FIG. 4 . Such operations for reconstructing each of the color holographic images may be performed in a range from about 1 to 5 milliseconds and may be repeatedly performed until holographic image reconstruction apparatus  500  is turned off or otherwise disabled in operation. In the above embodiments, since the shutter can be controlled to selectively pass one of the plurality of reconstruction light sources at a high speed, holographic image generation apparatus  500  can be effectively utilized to reconstruct a color stereoscopic holographic image, e.g., in a field sequential color system. 
     In  FIG. 5 , one virtual image light source  420  and corresponding scan mirror  430  are illustrated for the sake of explanation. However, the number of virtual image light sources and scan mirrors may not be limited thereto. In some examples, four pairs of virtual image light sources and scan mirrors may be arranged in correspondence with four inner surfaces in rectangular prism shaped screen  560 . 
     As illustrated in  FIG. 5 , screen  560  may be arranged in a shape of a polygonal prism such as a rectangular prism. Alternatively, screen  560  may be arranged in a shape of a cylinder or any other shapes such as a cylindroid. Also, scan mirror  420  may be actuated by any variety of mechanisms such as magnetic actuation, electrical actuation, or electromagnetic actuation, wherein the actuation of the scan mirror  420  is effective to steer the scan beam (e.g., actuation may facilitate a change the direction of virtual image light beams reflected on surfaces of scan mirror  420 ). 
       FIG. 6  schematically shows a perspective view of an illustrative example scan mirror that may be used in a holographic image reconstruction apparatus, in accordance with at least some embodiments described herein. As depicted, a scan mirror  600  may include vertical axis  612 ,  614 ,  616  and  618 , along which mirror portions  630  and  640  may be actuated to rotate in a horizontal direction. Further, scan mirror  600  may include horizontal axis  622 ,  624 ,  626  and  628 , along which mirror portions  630  and  640  may be actuated to rotate in a vertical direction. 
     In some embodiments, the rotational actuation of mirror portions  630  and  640  may be driven by electric, magnetic, or electromagnetic forces, which may be again generated based on electric control signals provided from a holographic image reconstruction apparatus such as holographic image reconstruction apparatus  500  in  FIG. 5 . In some examples, scan mirror  600  may be implemented using MEMS (micro-electro-mechanical systems) technologies, in which mirror portions  630  and  640  may be actuated by piezoelectric force, which may be again generated based on electric control signals provided from the holographic image reconstruction apparatus. 
       FIG. 7  illustrates an example flow diagram of a method adapted to generate a holographic image of an object, arranged in accordance with at least some embodiments described herein. An example method  700  in  FIG. 7  may be implemented using, for example, a computing device including a processor adapted to generate holographic images. 
     Method  700  may include one or more operations, actions, or functions as illustrated by one or more of blocks S 710 , S 720 , S 730 , S 740 , S 750  and/or S 760 . Although illustrated as discrete blocks, various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation. In some further examples, the various described blocks may be implemented as a parallel process instead of a sequential process, or as a combination thereof. Method  700  may begin at block S 710 , “GENERATE, BY A PLURALITY OF LIGHT SOURCES, A PLURALITY OF LIGHT BEAMS CORRESPONDING TO A DIFFERENT RANGE OF WAVELENGTHS.” 
     At block S 710 , a plurality of light beams may be generated by a plurality of light sources, where each of the plurality of light sources is operable to generate light corresponding to a wavelength in a different range. As depicted in  FIGS. 1 and 2 , each of a plurality of light sources  110   a  to  110   n  may be configured to generate a coherent light beam, such as a visible laser light beam, corresponding to a wavelength in a different range. In some embodiments, light sources  110   a  to  110   n  may include a red laser light source, a green laser light source and a blue laser light source. Block S 710  may be followed by block S 720 , “SELECTIVELY PASSING ONE OF THE PLURALITY OF LIGHT BEAMS THROUGH A SHUTTER.” 
     At block S 720 , a switching operation may be performed by a shutter (e.g., dynamic actuation of the shutter) to selectively pass one of the plurality of light beams through the shutter. As illustrated in  FIGS. 1 and 2 , a shutter  112  may receive the light beams from the plurality of light sources  110   a  to  110   n  and selectively pass each of the received light beams to provide a selected light beam L 1 . In cases where the plurality of light sources  110   a  to  110   n  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, shutter  112  may selectively pass one of a red laser light, a green laser light and a blue laser light. Block S 720  may be followed by block S 730 , “SPLIT, BY A BEAM SPLITTER, THE LIGHT BEAM IRRADIATED FROM THE SHUTTER INTO A FIRST PORTION AND A SECOND PORTION OF THE LIGHT BEAM.” 
     At block S 730 , the light beam irradiated from the shutter may be split, by a beam splitter, into a first portion and a second portion of the light beam. The first portion of the light beam is then transmitted towards the object. As illustrated in  FIGS. 1 and 2 , a beam splitter  130  may be configured to split the selected light beam L 1  into a first light beam L 13  and a second light beam L 12 . The first light beam L 13  may be irradiated on an object  150  such that at least part of the first light beam L 13  may be scattered by object  150  to generate an object light beam L 3 . Block S 730  may be followed by block S 740 , “RECEIVE AND REFLECT, BY A MIRROR UNIT, THE SECOND PORTION OF THE LIGHT BEAM TO GENERATE A REFERENCE BEAM.” 
     At block S 740 , the second portion of the light beam may be received and reflected, by a mirror unit, to generate a reference beam. As depicted in  FIGS. 1 and 2 , a mirror unit  140  may be configured to reflect at least part of second light beam L 12  to generate a reference light beam L 2 , such that object light beam L 3  and reference light beam L 2  may cause interference patterns to be formed on an image sensor array  160 . Block S 740  may be followed by block S 750 , “DETECT, BY AN IMAGE SENSOR ARRAY, THE INTERFERENCE IMAGE.” 
     At block S 750 , an interference image caused by interference between the reference beam and the first portion of the light beam scattered by the object may be detected by an image sensor array. For example, as shown in  FIGS. 1 and 2 , when two light beams L 2  and L 3  reach the surface of image sensor array  160 , the light waves may intersect and interfere with each other effective to form an interference pattern. The interference pattern formed by the intersecting light waves may represent the manner in which the scene&#39;s light from object  150  interferes with the original light source. Image sensors (e.g., from an image sensor array  160 ) may be configured to detect and receive images of the interference patterns. Block S 750  may be followed by block S 760 , “CONVERT, BY A VIDEO SIGNAL GENERATOR UNIT, THE DETECTED INTERFERENCE PATTERN INTO AN IMAGE SIGNAL.” 
     At block S 760 , the detected interference pattern may be converted, by a video signal generator unit, into an image signal. As depicted in  FIGS. 1 and 2 , a video signal generator unit  180  may convert the image detected by image sensor array  160  into an image signal associated with each of the plurality of light sources  110   a  to  110   n.    
     In some embodiments, method  700  may be repeatedly performed for each light beam selectively generated from the plurality of light sources. For example, in case where the plurality of light sources  110   a  to  110   n  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, method  700  may be repeatedly performed to sequentially generate red, green and blue holographic image signals. Also, method  700  including the above-described operations for generating each of the three-color holographic video signals may be executed in a range from about 1 to 5 milliseconds. 
       FIG. 8  illustrates an example flow diagram of a method adapted to reconstruct a holographic image of an object, arranged in accordance with at least some embodiments described herein. An example method  800  in  FIG. 8  may be implemented using, for example, a computing device including a processor adapted to reconstruct holographic images. 
     Method  800  may include one or more operations, actions, or functions as illustrated by one or more of blocks S 810 , S 820 , S 830 , S 840 , S 850  and/or S 860 . Although illustrated as discrete blocks, various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation. In some further examples, the various described blocks may be implemented as a parallel process instead of a sequential process, or as a combination thereof. Method  800  may begin at block S 810 , “RECEIVE, BY A RECEIVER UNIT, AN INPUT SIGNAL REPRESENTATIVE OF A HOLOGRAM OF THE OBJECT.” 
     At block S 810 , an input signal representative of a hologram of the object may be received by a receiver unit. For example, as depicted in  FIGS. 4 and 5 , receiver unit  450  may receive an input signal representative of a hologram of the object or at least portion of the hologram, e.g., from a holographic image generator apparatus through one or more networks. Block S 810  may be followed by block S 820 , “GENERATE, BY A VIRTUAL IMAGE LIGHT SOURCE, A VIRTUAL IMAGE LIGHT BEAM RESPONSIVE TO THE INPUT SIGNAL.” 
     At block S 820 , a virtual image light beam responsive to the input signal may be generated by a virtual image light source. As illustrated in  FIGS. 4 and 5 , a virtual image light source  420  may be configured to generate a virtual image light beam L 41 , such as an ultraviolet laser beam or an electron beam, based on holographic image signals. In some embodiments, the holographic image signals may be provided from a holographic image generator apparatus such as holographic image generator apparatus  100 ,  200  or  310  in  FIGS. 1 to 3 . Thus generated virtual image light beams L 41  may have intensities which may vary based on the levels of the holographic image signals. Virtual image light source  420  may be configured to irradiate the generated virtual image light beams L 41  onto a scan mirror  430 . Block S 820  may be followed by block S 830 , “RECEIVE AND REFLECT, BY A SCAN MIRROR, THE VIRTUAL IMAGE LIGHT BEAM TO GENERATE A SCAN BEAM.” 
     At block S 830 , the virtual image light beam may be received and reflected, by a scan mirror, to generate a scan beam. As depicted in  FIGS. 4 and 5 , scan mirror  430  may be configured to receive and reflect the virtual image light beams and generate a scan beam L 42  that is irradiated on a screen  460 . Block S 830  may be followed by block S 840 , “RECEIVE, BY A SCREEN COATED WITH A PHOTOCHROMIC MATERIAL, THE SCAN BEAM FROM THE SCAN MIRROR, AND FORM THE HOLOGRAM OF THE OBJECT ON THE SCREEN.” 
     At block S 840 , the scan beam from the scan mirror may be received, by a screen coated with a photochromic material, and the hologram of the object on the screen may be formed as a result of variations in the visible light transmittance characteristic of the screen in response to the scan beam. For example, as shown in  FIGS. 4 and 5 , on screen  460  coated with a photochromic material, holograms may be formed by changing a visible light transmittance of the photochromic material in response to the varying intensities of the virtual image light beams such as scan beams L 42 . That is, images of an object corresponding to the holographic image signals may be formed on screen  460  in the form of images representing varying visible light transmittance. Block S 840  may be followed by block S 850 , “GENERATE, BY A PLURALITY OF RECONSTRUCTION LIGHT SOURCES, RECONSTRUCTION LIGHT BEAMS CORRESPONDING TO A DIFFERENT RANGE OF WAVELENGTHS.” 
     At block S 850 , reconstruction light beams corresponding to a different range of wavelengths may be generated by a plurality of reconstruction light sources. As shown in  FIGS. 4 and 5 , each of reconstruction light sources  410   a  to  410   n  may be configured to irradiate a reconstruction light beam corresponding to a wavelength in a different range, such as a visible laser beam, on screen  460 . For example, the plurality of reconstruction light sources  410   a  to  410   n  may include a red laser light source, a green laser light source, and a blue laser light source. Block S 850  may be followed by block S 860 , “SELECTIVELY PASS, BY A SHUTTER, ONE OF THE RECONSTRUCTION LIGHT BEAMS FROM THE PLURALITY OF RECONSTRUCTION LIGHT SOURCES TO IRRADIATE THE SCREEN.” 
     At block S 860 , the reconstruction light beams may be received from the plurality of reconstruction light sources by a shutter, and one of the reconstruction light beams may be selectively passed through the shutter to irradiate the screen to reconstruct the holographic image of the object. For example, as illustrated in  FIGS. 4 and 5 , a shutter  412  may be configured to receive the reconstruction light beams from the plurality of reconstruction light sources  410   a  to  410   n  and selectively pass each of the received light beams in turn to provide a selected light beam L 43 . In case where light source unit  410  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, shutter  412  may be sequentially switched to pass one of a red laser light, a green laser light and a blue laser light. Light beam L 43  provided by shutter  412  may be transmitted to screen  460 . When the holograms formed on screen  460  are irradiated with the reconstruction light beams L 43 , images of the object may be reconstructed. 
     In some embodiments, method  800  may be repeatedly performed for each reconstruction light beam selectively generated from the plurality of reconstruction light sources. For example, in case where the plurality of reconstruction light sources  410   a  to  410   n  includes three color light sources, e.g., a red laser light source, a green laser light source, and a blue laser light source, method  800  may be repeatedly performed to sequentially reconstruct red, green and blue holographic images. Also, the above-described operations of method  800  may be executed in a range from about 1 to 5 milliseconds. 
     One skilled in the art will appreciate that, for this and other methods disclosed herein, the functions performed in the methods may be implemented in differing order. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations without detracting from the essence of the disclosed embodiments. 
       FIG. 9  shows a schematic block diagram illustrating an example computing system that can be configured to perform methods for generating and/or reconstructing a holographic image of an object, arranged in accordance with at least some embodiments described herein. As depicted in  FIG. 9 , a computer  900  may include a processor  910 , a memory  920  and one or more drives  930 . Computer  900  may be implemented as a conventional computer system, an embedded control computer, a laptop, or a server computer, a mobile device, a set-top box, a kiosk, a vehicular information system, a mobile telephone, a customized machine, or other hardware platform. 
     Drives  930  and their associated computer storage media may provide storage of computer readable instructions, data structures, program modules and other data for computer  900 . Drives  930  may include a holographic imaging system  940 , an operating system (OS)  950 , and application programs  960 . Holographic imaging system  940  may be adapted to control a holographic image generator apparatus  100 ,  200  or  310  and/or a holographic image reconstruction apparatus  350 ,  400  or  500  in such a manner as described above with respect to  FIGS. 1 to 8 . 
     Computer  900  may further include user input devices  980  through which a user may enter commands and data. Input devices can include an electronic digitizer, a camera, a microphone, a keyboard and pointing device, commonly referred to as a mouse, trackball or touch pad. Other input devices may include a joystick, game pad, satellite dish, scanner, or the like. 
     These and other input devices can be coupled to processor  910  through a user input interface that is coupled to a system bus, but may be coupled by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). Computers such as computer  900  may also include other peripheral output devices such as display devices, which may be coupled through an output peripheral interface  985  or the like. 
     Computer  900  may operate in a networked environment using logical connections to one or more computers, such as a remote computer coupled to a network interface  990 . The remote computer may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and can include many or all of the elements described above relative to computer  900 . 
     Networking environments are commonplace in offices, enterprise-wide area networks (WAN), local area networks (LAN), intranets, and the Internet. When used in a LAN or WLAN networking environment, computer  900  may be coupled to the LAN through network interface  990  or an adapter. When used in a WAN networking environment, computer  900  typically includes a modem or other means for establishing communications over the WAN, such as the Internet or a network  995 . The WAN may include the Internet, the illustrated network  995 , various other networks, or any combination thereof. It will be appreciated that other mechanisms of establishing a communications link, ring, mesh, bus, cloud, or network between the computers may be used. 
     In some embodiments, computer  900  may be coupled to a networking environment. Computer  900  may include one or more instances of a physical computer-readable storage medium or media associated with drives  930  or other storage devices. The system bus may enable processor  910  to read code and/or data to/from the computer-readable storage media. The media may represent an apparatus in the form of storage elements that are implemented using any suitable technology, including but not limited to semiconductors, magnetic materials, optical media, electrical storage, electrochemical storage, or any other such storage technology. The media may represent components associated with memory  1020 , whether characterized as RAM, ROM, flash, or other types of volatile or nonvolatile memory technology. The media may also represent secondary storage, whether implemented as storage drives  930  or otherwise. Hard drive implementations may be characterized as solid state, or may include rotating media storing magnetically encoded information. 
     Processor  910  may be constructed from any number of transistors or other circuit elements, which may individually or collectively assume any number of states. More specifically, processor  910  may operate as a state machine or finite-state machine. Such a machine may be transformed to a second machine, or specific machine by loading executable instructions. These computer-executable instructions may transform processor  910  by specifying how processor  910  transitions between states, thereby transforming the transistors or other circuit elements constituting processor  910  from a first machine to a second machine. The states of either machine may also be transformed by receiving input from user input devices  980 , network interface  990 , other peripherals, other interfaces, or one or more users or other actors. Either machine may also transform states, or various physical characteristics of various output devices such as printers, speakers, video displays, or otherwise. 
       FIG. 10  illustrates computer program products that can be utilized to generate a holographic image of an object, arranged in accordance with at least some embodiments described herein. Program product  1000  may include a signal bearing medium  1002 . Signal bearing medium  1002  may include one or more instructions  1004  that, when executed by, for example, a processor, may provide the functionality described above with respect to  FIGS. 1 to 8 . By way of example, instructions  1004  may include: one or more instructions for generating, by a plurality of light sources, a plurality of light beams corresponding to a different range of wavelengths; one or more instructions for performing switching operation, by a shutter, to selectively pass one of the plurality of light beams through the shutter, one or more instructions for splitting, by a beam splitter, the light beam irradiated from the shutter into a first portion and a second portion of the light beam such that the first portion of the light beam is irradiated on an object; one or more instructions for receiving and reflecting, by a mirror unit, the second portion of the light beam to generate a reference beam; one or more instructions for detecting, by an image sensor array, an interference image caused by interference between the reference beam and the first portion of the light beam scattered by the object; or one or more instructions for converting, by a video signal generator unit, the detected interference image into an image signal. Thus, for example, referring to  FIGS. 1 and 2 , holographic image generator apparatus  100  or  200  may undertake one or more of the blocks shown in  FIG. 7  in response to instructions  1004 . 
       FIG. 11  illustrates computer program products that can be utilized to reconstruct a holographic image of an object, arranged in accordance with at least some embodiments described herein. Program product  1100  may include a signal bearing medium  1102 . Signal bearing medium  1102  may include one or more instructions  1104  that, when executed by, for example, a processor, may provide the functionality described above with respect to  FIGS. 1 to 8 . By way of example, instructions  1104  may include at least one of: one or more instructions for receiving, by a receiver unit, an input signal representative of a hologram of the object; one or more instructions for generating, by a virtual image light source, a virtual image beam responsive to the input signal; one or more instructions for receiving and reflecting, by a scan mirror, the virtual image light beam to generate a scan beam; one or more instructions for receiving, by a screen coated with a photochromic material, the scan beam from the scan mirror, and forming the hologram of the object on the screen as a result of variations in the visible light transmittance characteristic of the screen in response to the scan beam; one or more instructions for generating, by a plurality of reconstruction light sources, reconstruction light beams corresponding to a different range of wavelengths; or one or more instructions for receiving, by a shutter, the reconstruction light beams from the plurality of reconstruction light sources, and selectively passing one of the reconstruction light beams through the shutter to irradiate the screen to reconstruct the holographic image of the object. Thus, for example, referring to  FIGS. 4 and 5 , holographic image reconstruction apparatus  400  or  500  may undertake one or more of the blocks shown in  FIG. 8  in response to instructions  1104 . 
     In some implementations, signal bearing medium  1002  or  1102  may encompass a computer-readable medium  1006  or  1106 , such as, but not limited to, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, memory, etc. In some implementations, signal bearing medium  1002  or  1102  may encompass a recordable medium  1008  or  1108 , such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations, signal bearing medium  1002  or  1102  may encompass a communications medium  1010  or  1110 , such as, but not limited to, a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). Thus, for example, program product  1000  or  1100  may be conveyed to one or more modules of holographic image generator apparatus  100  or  200  or holographic image reconstruction apparatus  400  or  500  by an RF signal bearing medium  1002  or  1102 , where the signal bearing medium  1002  or  1102  is conveyed by a wireless communications medium  1010  or  1110  (e.g., a wireless communications medium conforming with the IEEE 802.11 standard). 
     The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. 
     The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. 
     As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.