Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/04—Processes or apparatus for producing holograms
  • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
  • G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
  • G03H1/2294—Addressing the hologram to an active spatial light modulator
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/32—Systems for obtaining speckle elimination
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
  • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
  • G03H1/2294—Addressing the hologram to an active spatial light modulator
  • G03H2001/2297—Addressing the hologram to an active spatial light modulator using frame sequential, e.g. for reducing speckle noise
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2210/00—Object characteristics
  • G03H2210/40—Synthetic representation, i.e. digital or optical object decomposition
  • G03H2210/45—Representation of the decomposed object
  • G03H2210/452—Representation of the decomposed object into points
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2222/00—Light sources or light beam properties
  • G03H2222/34—Multiple light sources
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2225/00—Active addressable light modulator
  • G03H2225/30—Modulation
  • G03H2225/31—Amplitude only
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2225/00—Active addressable light modulator
  • G03H2225/30—Modulation
  • G03H2225/32—Phase only
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2225/00—Active addressable light modulator
  • G03H2225/30—Modulation
  • G03H2225/33—Complex modulation
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2226/00—Electro-optic or electronic components relating to digital holography
  • G03H2226/05—Means for tracking the observer
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2240/00—Hologram nature or properties
  • G03H2240/20—Details of physical variations exhibited in the hologram
  • G03H2240/40—Dynamic of the variations
  • G03H2240/41—Binary
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
  • G03H2240/00—Hologram nature or properties
  • G03H2240/20—Details of physical variations exhibited in the hologram
  • G03H2240/40—Dynamic of the variations
  • G03H2240/42—Discrete level

Definitions

• the invention relates to a method for reconstructing a three-dimensional scene in a holographic display, in which the three-dimensional scene (SD scene) is decomposed into individual object points, which are coded as sub-holograms in a spatial light modulator means.
• Light sources of an illumination system illuminate the light modulation means sufficiently coherent.
• Holographic partial reconstructions of the 3D scene are generated by the sequentially modulated wavefronts in a reconstruction space according to the method of the invention and are seen at an eye position within a range of visibility.
• the invention also relates to a device for carrying out the method and a holographic display for using methods and device.
• the invention is applicable in areas where a detailed and realistic spatial representation of 3D scenes can be improved by holographic displays.
• the present invention can be implemented both in a direct view display and in a projection display, which always have a visibility region which lies in the back transformation plane of the encoded hologram within a periodicity interval of the transformation used and is also referred to as a viewer window.
• the holographic reconstruction of the 3D scene is preferably carried out by illuminating a light modulation means with sufficiently coherent light in cooperation with a reconstruction optics in a reconstruction space, which is spanned by the visibility region and the light modulation means.
• Each object point of the encoded 3D scene contributes with a wavefront to a resulting superimposed lightwave front, which is seen from the visibility area as the reconstruction of the 3D scene.
• the visibility range may be approximately equal in size to the size of an eye pupil. For Each viewer eye can be created a separate visibility area. In the case of a movement of the observer, tracking of the visibility region or zones is effected by appropriate means.
• the viewer can look at a light modulation means in which the hologram of the 3D scene is directly encoded and serves as a screen. This is referred to in this document as a direct view setup.
• the viewer may look at a screen onto which either an image or a transform of the hologram values encoded in the carrier medium is projected. This is called projection construction in this document.
• the eye positions are determined in a known manner by a position finder.
• the principle of such displays is known from earlier documents by the Applicant, e.g. from (1) EP 1 563 346 A2, (2) DE 10 2004 063 838 A1 or (3) DE 10 2005 023 743 A1.
• the 3D scene to be reconstructed for the calculation of the hologram values is split by program means parallel to a reference plane in sectional planes and in these planes by a grid into individual points, the points in this document are object points.
• Each object point is coded in a light modulation means in a separate area of the coding surface, which reconstructs this object point.
• This area contains the sub-hologram of this object point.
• the sub-hologram corresponds approximately to a holographically coded lens function that reconstructs this one object point at its focal point.
• FIG. 1a An exemplary illustration of this is contained in FIG. 1a, in which of three object points OP1; OP2 and OP3 from three different cutting planes (not represented) of the 3D scene in each case two-dimensional sub-holograms S1; S2 and S3 are coded into the controllable elements of a light modulation means L.
• the sub-holograms S1 to S3 here have a certain extent in the horizontal and vertical directions and are all in the same modulator plane. For a better understanding of the overlap S2 is shown but with a distance to the modulator plane.
• Each sub-hologram reconstructs only one object point from the 3D scene, which can be seen from a visibility area SB in an eye position AP.
• the corresponding sub-hologram S3 is coded in another area of the light modulation means L and does not overlap.
• the totality of all sub-holograms generally results in the reconstruction of the entire 3D scene.
• the complex values of the overlapping sub-holograms must be added together in the hologram calculation and thus take up additional computation time and storage space.
• the complex values are generally represented by the transparency values of a hologram.
• the term transparency value is used here in the general sense. It may also include reflectivity in reflective light modulators or phase values.
• each object point of a reconstruction is reconstructed from the entire hologram.
• the information of all object points of the reconstruction is superimposed.
• the complex values in the modulator pixels must therefore be added for all object points.
• each pixel of the hologram contributes to the reconstruction of all object points.
• a light modulation means which modulates light in amplitude and / or phase
• a limited number of amplitude and / or phase steps can be realized.
• 256 gray levels can be displayed in a typical amplitude modulator, which corresponds to a resolution of 8 bits, ie 2 to 8 gray levels, and identifies the gray scale range or the bit depth of a light modulation means.
• quantization errors The larger the dynamic range of a hologram and the smaller the bit depth of a light modulation means, the more errors occur when coding the Hologram values, hereafter called quantization errors.
• Light modulator means If holograms are used e.g. encoded in an amplitude modulator so that the maximum occurring amplitude is also represented by the gray value with maximum transmission of the modulator, so leads to a large
• a hologram calculated according to (1) and (2) has a lower dynamic range than a Fourier hologram for comparable objects, since only sub-holograms of a small part of all object points have to overlap and have to be added up.
• hologram representation also known as binary light modulating means are known.
• binary light modulating means are known.
• An example of a binary light modulation means is a ferroelectric liquid crystal modulator (FLC).
• FLC ferroelectric liquid crystal modulator
• PWM Pulse Width Modulation
• this method is not readily holographic Rendering device transferable, since it requires sufficient coherent light for a reconstruction. If, for example, amplitudes of a hologram with a high dynamic range were simulated by a PWM on a binary light modulator, a chronological sequence of incoherent partial reconstructions would result instead of a coherent reconstruction, which would make visible averaged reconstruction deviating from the 3D scene to be reconstructed. On a binary light modulator, therefore, binary holograms can usually only be reproduced while tolerating considerable quantization errors. To reduce the quantization errors in binary holograms, iterative calculation methods are known. But they require a lot of computational effort to reduce reconstruction errors, but they can not fully compensate.
• binary holograms are real-valued, which implies that only symmetrical reconstructions are possible. This represents a considerable restriction on the reconstruction. Even binary holograms, which represent values other than (O 1 ⁇ ) or (0, 1), have in principle these properties.
• Documents (1) and (2) describe the reconstruction of individual object points by a respective sub-hologram, which represents a lens function.
• a respective sub-hologram which represents a lens function.
• Fresnel ' s zone plate can be with a binary
• structure can not be between a lens of focal length + f and a lens of
• Focal length -f can be distinguished.
• Zone plate would each see an object point in front of the display and always an associated equally bright object point behind the display. With a binary modulator 3D scenes can be reconstructed, but one would always see a reflection of the 3D scene in front of the display behind the display. This only changes when you implement at least three different phase levels in a phase modulator.
• a coding method adapted to the individual modulators is required. For example, encoding a complex number by several amplitude values is known, but has the disadvantage of low diffraction efficiency. If, on the other hand, a complex number is encoded by several phase values, two-phase encoding is used in particular. However, since it causes reconstruction errors and the addition of different sub-holograms results in a distribution of more than two phase values, ie a higher dynamic range, it must additionally be combined with iterative calculation methods.
• the object of the invention is to obviate or at least reduce the cited disadvantages of the prior art in coding a hologram of a 3D scene and in holographic reconstruction of the 3D scene in a real-time holographic display device, wherein the encoding of holograms on the Based on complex transparency values using a low dynamic range.
• the method should be designed so that the use of at least one spatial light modulator with low bit depth and fast switching time and the reduction of the computational effort for the hologram calculation is possible and a good reconstruction quality is achieved.
• the basis of the method according to the invention is a 3D scene to be reconstructed which, according to the description in document (2), is decomposed into a number of sectional planes, each with one grid, whereby a number of object points can be determined, from each of which a sub-hologram is calculated and put into one Light modulator is encoded.
• the light modulation means may be a pixelated light modulator having a discrete array of controllable elements (pixels) or a light modulator having a continuous, non-pixelated coding surface which is formally divided into discrete regions by the information to be displayed. A discrete area is then to be equated to one pixel each. As coherent light passes through the light modulator, the controllable elements change the amplitude and / or phase of the light to reconstruct the object points of the SD scene.
• the method is further based on an illumination system having at least one sufficiently coherently emitting light source and at least one optical imaging means that illuminates a spatial light modulation means. From the with the information of the object points modulated wavefronts, the 3D scene is reconstructed within a reconstruction space spanned by a light modulation means and / or screen and a visibility area. The reconstruction is seen by an observer within the visibility range in an eye position determined by a position finder.
• the method further uses a processor with processor elements for calculating and encoding the 3D scene and is characterized in its method steps according to the invention in that
• PE 1 in the light modulation means (L) a displaceable two-dimensional grid
• a second processor element controls the illumination system in synchronism with the shift of the grid in the light modulation means (L), so that from the plurality of sequentially encoded holograms in rapid time sequence in coherent, but mutually incoherent partial reconstructions of the object point groups (OPGm) generated and sequentially superimposed in the visibility area (SB).
• the partial reconstructions of the 3D scene are thus seen from the eye position as a single time-averaged reconstruction.
• all object points of the 3D scene can be precisely assigned to the regularly arranged two-dimensional grid cells in the light modulation means, and specific object points can be selected for forming object point groups on the basis of a criterion.
• the formation of object point groups advantageously simplifies the coding and reconstructing of the 3D scene and significantly reduces the computing time compared to an object-by-point coding and reconstruction of the 3D scene.
• the first processor element for selecting object points defines a depth range bounded by two planes in the reconstruction space, which contains all object points contributing to the reconstruction of the 3D scene and determines the area of its sub-holograms in the light modulation means by projections from the visibility region.
• the sub-holograms do not overlap.
• the maximum area of a single sub-hologram is given by the axial distance between one of the levels of the defined depth range and the level of the visibility area.
• one of the planes is the foremost viewer-facing plane of the defined depth region in the reconstruction space.
• the rearmost level of the defined depth range determines the maximum area of the sub-hologram when the reconstruction is done behind the screen. For a 3D scene that is partially reconstructed both in front of and behind the light modulation means, the larger of both faces of the sub-hologram is to be used.
• the first processor element defines the area size of a grid cell of the grid to correspond to the largest sub-hologram. This definition guarantees that a single sub-hologram does not exceed the size of a grid cell.
• the depth range is limited to a maximum axial distance before and optionally behind the light modulation means, so that the reconstruction of the entire 3D scene is always generated within the reconstruction space.
• the object points are selected as a function of their spatial position relative to a grid cell of the generated grid and combined to form an object point group.
• the criterion for selecting the object points is the centric position of an object point in the depth range defined on a grid cell of the generated grid at a given time. Centric position here means that an imaginary line from the center of the observer window through the object point also passes through the center of a grid cell. Object points that satisfy this criterion form an object point group.
• the formation of a further object point group from object points of the 3D scene is carried out by shifting the grid by at least one pixel of the light modulation means programmatically by the first processor element.
• the shift is only carried out horizontally for a one-dimensionally acting hologram or horizontally and vertically for a two-dimensionally acting hologram.
• the formation of prikou ⁇ is completed when the grid has been moved horizontally and / or vertically in increments of at least one pixel, so that a total shift to a full grid cell is achieved.
• all different positions of all object points of the 3D scene are recorded in the defined depth range.
• a further method step is characterized in that the determined sub-holograms of the 3D scene, since they do not overlap, are coded horizontally and vertically simultaneously in the light modulation means.
• the coding of a sub-hologram can take place one-dimensionally or two-dimensionally in adjacent pixels of a raster cell.
• * D is calculated ⁇ / p x, y 2 (1), where z is the axial distance between an object point and said light modulation means or a screen, D is the distance the region of visibility by the light modulation means and the screen, ⁇ is the wavelength of light of a used Light source of the illumination system and p ⁇ , y are the width (p x ) and the height (p y ) of a macropixel.
• a macropixel is either a single pixel or a group of neighboring pixels in which a complex value is written.
• a processor-controlled position controller adjusts the propagation direction of the modulated wavefronts of the common holograms to the current eye position of a viewer's eye determined by a position finder in order to continue to represent the viewer in the event of a change in position in front of the screen.
• the light modulation means may be formed according to the embodiment examples optionally transmissive, transflexive or reflective.
• light modulating agents can be used individually for carrying out the method or as a combination of at least one phase modulator and one amplitude modulator.
• the amplitude modulator preferably generates a frame around a single sub-hologram.
• the frame width depends on the intensity and axial distance of an object point to the screen and limits the area of the sub-hologram in the screen cell, the frame representing the area of non-transparency of the screen cell.
• the light modulation means in which the holograms are coded serve directly as a screen.
• the screen is an optical element onto which a hologram coded in the light modulation means or a wavefront of the 3D scene coded in the light modulation means is imaged.
• the amplitude modulator generates a frame in each case preferably around a single sub-hologram.
• Another embodiment of the method provides that an intensity of object points which is visible in the temporal mean is set by reconstructing the object points sufficiently coherently for time intervals of different lengths, exemplarily defined as T2.
• the task is further complemented by a device for reconstructing the 3D
• Solved scene comprising a lighting system with at least one sufficiently coherently radiating light source to illuminate at least one spatial light modulating means, which is associated with at least one optical imaging means,
• Reconstruction means for reconstructing the decomposed into individual object points
• Visibility area spanned reconstruction space, wherein the reconstruction can be seen from an eye position within the visibility area, and a processor with processor elements for calculating and encoding of
• a first processor element for generating a displaceable two-dimensional grid with regularly arranged grid cells in the light modulation means, for defining a depth range in the reconstruction space, for generating object point groups from object points of the 3D scene, for calculating a plurality of sub-holograms of the object points of a respectively generated object point group and for simultaneous Coding the sub-holograms is provided in each case a separate grid cell as a common hologram of the respective object point group, wherein the common holograms of all object point groups are sequentially encoded, and
• a second processor element is provided to control the illumination system in synchronism with the shift of the raster in the light modulating means, so that out of the plurality of sequentially encoded common holograms in one temporal sequence in which coherent, but mutually incoherent partial reconstructions of the object point groups are generated and superimposed sequentially in the visibility area.
• the partial reconstructions of the 3D scene are visible from the eye position as a single time-averaged reconstruction for a viewer's eye.
• the device is preferably a holographic display, which is designed as a direct-view display or a projection display.
• the device includes a light modulation means designed as a screen.
• the screen is an optical element onto which a hologram coded in the light modulation means or a wavefront of the 3D scene coded in the light modulation means is imaged.
• the grid consists of regularly arranged grid cells, the area of the largest possible sub-hologram determining the size of the area of the grid cells.
• a raster cell has several pixels horizontally and vertically adjacent.
• An expedient embodiment of the light modulation means may be a phase modulator.
• a sub-hologram can be represented, for example, in the phase modulator in a raster cell as a lens function, and the intensity of a reconstructed object point can be adjusted by displaying this lens function as a sub-hologram for a different time interval T2 in the raster cell. Outside the sub-hologram, for the time interval T2 in which no lens function is present, a linear phase function is then displayed in the screen cell, by which the light is deflected to a position outside the visibility range. With this feature of the invention it is achieved that an object point is displayed with its real intensity.
• the phase modulator can be a binary modulator.
• the phase modulator is a modulator which is adjustable in a few, but at least three phase stages.
• the light modulating means may also consist of a combination of a phase modulator and an amplitude modulator.
• the amplitude modulator is advantageously used to inscribe in a raster cell a frame delimiting the extent of a sub-hologram between the sub-hologram and the edge of the raster cell, which has a minimum transmission.
• Both the phase and the amplitude modulator can be designed as binary modulators in this example.
• the phase modulator is adjustable in a few but at least three phase stages.
• the intensity of a reconstructed object point, which is visible in the time average, is set by the fact that the amplitude modulator is connected transmissively for a different time interval T2 in the region of a sub-hologram.
• the device is designed such that the illumination system has at least one light source to illuminate at least one grid cell of the light modulation means, wherein the intensity of the light source is controllable in order to vary the visible in the temporal average intensity of the reconstruction of individual object points can.
• the grid is shifted in the program by at least one pixel of the light modulation means and by a maximum of one grid cell for forming new object point groups and for generating other common holograms.
• a partial reconstruction of the 3D scene is generated from a coded object point group.
• the displacement of the grid takes place both horizontally and vertically by a maximum of one grid cell.
• the invention further relates to a holographic display for reconstructing a three-dimensional scene with an illumination system for sufficiently coherently illuminating a spatial light modulation means whose light is modulated with holographic information of the encoded three-dimensional scene (3D scene) and passed through an imaging system to an eye position within a visibility region , from which the reconstruction of the 3D scene can be seen in a frustum of a reconstruction space spanned by the light modulator means and the visibility area for at least one observer eye whose position is determined by a position finder connected to a processor for calculating and coding holograms of the 3D scene.
• an illumination system for sufficiently coherently illuminating a spatial light modulation means whose light is modulated with holographic information of the encoded three-dimensional scene (3D scene) and passed through an imaging system to an eye position within a visibility region , from which the reconstruction of the 3D scene can be seen in a frustum of a reconstruction space spanned by the light modulator means and the visibility
• the display uses a selection method for coding the decomposed into object points 3D scene according to the method claims, which is characterized in that one together with the Light modulator controlled first processor element is provided to generate in the light modulation means a displaceable two-dimensional grid with regularly arranged raster cells, in each of which common holograms of the 3D scene are encoded, which consist of the selection method calculated, horizontally and / or vertically simultaneously to be coded sub-holograms and partial reconstructions of the 3D scene, wherein a sub-hologram is in each case encoded in a raster cell, and - a second processor element controlling the illumination system in synchronism with the displacement of the raster in the light modulator means is provided to perform other partial reconstructions of the 3D raster resulting from the displacement of the raster.
• Fig. 1 a in plan view object points of a 3D scene and their coded
• FIG. 1 c shows a one-dimensional HPO image coded in a light modulation means.
• 3a is a plan view of a defined depth range with object points that form an object point group
• FIG. 3b is a plan view of a defined depth range with object points that form another object point group
• FIG. 4 is a raster with coded sub-holograms in a hologram for a partial reconstruction, superimposed therein a displacement of the grid
• FIG. 5 schematically illustrated examples of coded holograms in one
• Fig. 6 schematically illustrated examples of coded holograms in a single light modulator
• T1 intensity control of a light source over a time interval
• Fig. 7b shows two sub-holograms for two object points that are different
• the device for carrying out the method according to the invention-the holographic reproduction of 3D scenes- has illumination, modulation, and reconstruction means as well as processor and control means for program execution of the corresponding method steps up to the reconstruction of the 3D scene.
• the assigned, coded sub-holograms S1; S2 and S3 are represented as one-dimensionally acting HPO coding (Horizontal Parallax OnIy), as seen from an observer's eye position.
• HPO coding Horizontal Parallax OnIy
• a sub-hologram always lies centric to the respective object point, whereby only the object point OP3 has been designated here by way of example in more detail.
• a viewer whose eye pupil is located centrally in the center of the observer window sees the object point in the center in relation to the surface of the corresponding sub-hologram.
• the sub-holograms S1 to S3 vertically only have the extension of a single line in the light modulation means L. Since they are coded on different lines because of their position in the 3D scene, they do not overlap. Only sub-holograms within the same line can overlap on HPO coding. In overlapping sub-holograms, the intensities or information usually overlap in adjacent pixels of a modulator region.
• FIGS. 3 a and 3 b show how certain object points OPn for displaying an object point group OPGm in a hologram are selected according to the method of the invention.
• FIG. 3a shows a plan view of a spatial depth region TB, in which the 3D scene is to be reconstructed and which is defined between two planes Z1 and Z2.
• a sub-hologram S may become large if the associated object point OP is very close to the visibility area SB.
• the depth range TB is defined accordingly.
• the plane Z1 delimits the part of the 3D scene furthest to the screen and the plane Z2 the part of the 3D scene lying farthest behind the screen.
• the depth area TB contains a multiplicity of object points OPn 1, one of which is marked OP1.
• the object point OP1 has a distance z OP1 to the light modulation means L, which lies at a distance D to the visibility region SB.
• the depth range TB is within a reconstruction space, which is normally from the visibility area SB to the light modulation means L as Frustrum is spanned. However, the 3D scene to be reconstructed, which is decomposed into the object points OPn, extends beyond the light modulation means L.
• the light modulation means L is associated with a displaceable grid MR with regularly arranged two-dimensional grid cells. Auxiliary beams emanating from the center of the visibility area SB serve to associate the object points OPn with grid cells of the grid MR. Only the object points forming an object point group are marked as black dots.
• Fig. 3b was a shift of the grid MR by at least one pixel.
• the object points OPn which are now to be reconstructed in the depth region TB are shown in a grid position shifted relative to FIG. 3a.
• By moving another object point group OPG is formed with other object points OPn, which are also marked black again.
• An unillustrated first processor element PE1 generates a screen MR for the screen and summarizes all object points OPn in the depth range TB, which lie axially on an auxiliary beam and centric to a grid cell at a certain time, to form an object point group OPGm.
• the depth range TB is set axially such that a maximum possible area of a sub-hologram S does not exceed the area of a grid cell.
• a grid cell therefore has a grid width and grid height that corresponds to the maximum width and height of the largest sub-hologram S of the object point group.
• the raster cell contains horizontally and vertically adjacent or in a later following third embodiment of an HPO coding only horizontally adjacent several pixels of the light modulation means L.
• the centric position of each object point OP in the depth region TB is defined as a raster cell of the generated raster MR.
• the centric position is determined by auxiliary beams which extend from the center of the visibility region SB to the light modulation means L and there through the center of the raster cells or their projections. All object points OPn lying on such a beam form an object point group OPG.
• object points OPn for generating object point groups OPGm as described in document (2), for example, according to their index in the dot grid, which is defined when cutting the 3D scene in section planes, assigned. In this case, the grouping can take place such that the index of any object point OP in the dot matrix of the respective cutting plane coincides with the pixel index in the center of a screen cell on the light modulation means L.
• a sub-hologram S is calculated and separated into one
• Raster cell coded Since the coding takes place simultaneously, represent the
• OPG object point groups
• a light modulation means L is used, which has a sufficiently fast switching time for the sequential display of the holograms.
• FIG. 4 schematically shows the area of a light modulation means L with the grid MR for simultaneous two-dimensionally acting FP coding (English: fill parallax) of a plurality of non-overlapping sub-holograms Sn in a direct-view display.
• the grid MR is programmatically generated by a first processor element PE1.
• the term programmatically means that a given program is executed by a computer.
• a screen is located at the location of the light modulation means L, for example as a mirror element onto which the information of the holograms of the individual object point groups OPGm is sequentially displayed.
• some sub-holograms are Sn in different Sizes entered.
• the sub-holograms Sn are each centered within a raster cell MR analogous to the centric position of the object points OPn in the sub-holograms.
• the sub-hologram S is either smaller or at most the same size as the grid cell.
• Individual grid cells or areas with grid cells of the grid MR also remain empty if the 3D scene to be reconstructed has no object points OPn at the corresponding location in the depth area TB.
• the generated raster MR is program-technically by at least one pixel of the light modulation means L or, adapted to the resolution of the 3D scene, also in steps moved by several pixels. Then, in a very short time, different subholograms Sn, which do not overlap one another, can be calculated and displayed in the light modulation means L.
• the displacement of the grid MR is illustrated by dotted lines.
• a second processor element PE2 controls at least one light source of the illumination system in synchronism with the displacement of the grid MR in the light modulation means L.
• the light modulated with the respectively coded hologram generates a corresponding partial reconstruction of the 3D scene From the plurality of sequentially coded common holograms coherent, but mutually incoherent partial reconstructions are generated in rapid time sequence and overlaid sequentially in the visibility area SB The viewer sees then at the eye position AP temporally averaged a single reconstruction the 3D scene
• D is the distance of the visibility region SB by the light modulator means L or from the screen
• ⁇ is the wavelength of the light of the light source used
• np x is the number of macro-pixels in width and for np y the number of macro-pixels in height for a sub-hologram S
• a macro-pixel is either a single pixel or a group of neighboring pixels into which a complex value is written
• a maximum sub-hologram size is obtained from the maximum of the two values np xy (Z1) and np xy (Z2).
• different object points OPn in this raster width can be displayed simultaneously on the light modulation means L without their sub-holograms Sn overlapping
• the dynamic range of the amplitudes already mentioned above must be taken into account. It results from the fact that the intensities of the object points OPn to be reconstructed differ and from the different axial distances of the individual object points OPn to the visibility area. Both lead to different amplitudes in the sub-holograms Sn.
• the different intensities of individual object points OPn to be reconstructed and also the different amplitudes of the sub-holograms Sn can be represented more accurately by an intensity control of the light sources of the illumination system.
• the individual object point OP is program-technically reconstructed by the processor element PE2 for a different length of time. The observer eye averages over the time in which the reconstruction of this object point OP can be seen.
• This approach is possible because the sub-holograms Sn of the object points OPn do not overlap and therefore each sub-hologram S can be separately displayed for a different length of time compared to the other sub-holograms Sn. This results in the advantage that light modulators with a low bit depth can be used in the method without the quality of the reconstruction of the 3D scene deteriorating. In the description of FIG. 7 will be discussed as an example.
• each individual modulator row contains independent values, such that a
• Raster MR can be used with a grid width whose maximum is np x (Z1) or np *
• Line of the light modulation means L As a result, many object points OPn can be displayed simultaneously. Less time-sequential holograms have to be coded for the representation of the 3D scene. The requirements on the display speed or switching speed of the light modulation means L to be used are reduced.
• the method according to the invention is realized in a combination of an amplitude modulator and a phase modulator into which the complex hologram values are written.
• the amplitude and phase modulator can advantageously each be a binary modulator. As a phase modulator but also a modulator can be used, which is adjustable in at least 3 phase levels.
• At least the amplitude modulator is a binary modulator, then it generally limits the size of a sub-hologram S. This means that the areas between the edge of the grid cell and the edge of the sub-hologram S do not transmit light and are displayed in black.
• FIG. 5 a This is illustrated in FIG. 5 a for a sub-hologram S, as a result of which the sub-hologram S has a black frame RA.
• the representation of the entire grid cell takes place for a specific time interval T1, in the time interval T2, the sub-hologram S is displayed.
• the frame RA of the sub-hologram S is more or less wide and blocks the light more or less, while the central region of the screen cell is switched to transmission.
• the entire area of the screen cell may be black, as shown in Fig. 5b. This means that there is no object point OP of the 3D scene in the grid at this time,
• the phase modulator can also be a binary modulator in one embodiment of the invention.
• the phase function of a lens can be represented as a binary phase curve in the form of a Fresnel zone plate.
• Fig. 5c shows an example of a phase response as displayed on the phase modulator for representing an object point OP as a lens function.
• the Lens function must be displayed at least for the time interval T2, but can also be displayed for the entire time interval T1 without any disadvantages. In any case, the lens function must be displayed in the central area of the screen cell, which is on transmission on the amplitude modulator in Fig. 5a.
• phase modulators which are adjustable in a few, but at least three phase stages are used to encode a plurality of phase values.
• the lens function can also be encoded directly on the amplitude modulator.
• a 3D video displayed in a holographic display device consists of a large number of 3D scenes (individual images).
• a 3D scene is reconstructed within a time interval TO, wherein the time should optimally be at least 1/25 seconds.
• TO time interval
• Sn sub-holograms
• T1 is approximately equal to T0 / n.
• the phase modulator displays the phase characteristic of the corresponding sub-hologram S simultaneously over the time interval T1.
• the time interval T2 is different for each individual sub-hologram S within the grid MR, since it depends on the intensity and the distance of each object point OP to be reconstructed from the grid MR.
• Adjusting the amplitude to the phase modulator need not be performed as accurately as in the known methods with a combination of two light modulators to represent complex values. There, the modulators must be adjusted exactly to each other to fractions of a pixel size. Any offset between the pixels results in the display of incorrect complex values and the reduction of the quality of the reconstruction. In contrast, in the embodiment according to the invention, a slight lateral misalignment about parts of a pixel only leads to a wrong sub-hologram aperture. The position of the sub-hologram S is then shifted in the range of less percent, but this does not adversely affect, as it affects all sub-holograms Sn alike.
• a single phase modulator is used to write the hologram values.
• at least two pixels are used on the phase modulator to display a hologram value.
• FIG. 6a shows the object point OP as a lens function for the time interval T2, limited to the size of the sub-hologram S in a raster cell.
• a linear phase characteristic is written into adjacent pixels for a time interval T1, for example alternately the phase values 0 and pi, which causes light from these pixels to be directed out of the visibility region SB.
• the sub-hologram S is displayed correctly in its size and intensity.
• FIG. 6b shows, for the time period T1-T2, a linear phase curve applied over the entire grid cell MR.
• the entire light does not reach the visibility area SB 1 for this grid cell but is directed to the outside.
• the object point OP is reconstructed by the illumination system, wherein the illumination system is controlled by the second processor element PE2.
• the phase hologram S is again coded into the sub-hologram S as described above, which deflects the light of these pixels out of the visibility region SB, so that no reconstruction takes place in this time period T1-T2.
• object points OPn are properly reconstructed as long as the phase of the sub-holograms Sn is correctly displayed.
• the object point OP is then respectively correctly reconstructed each time its sub-hologram S is displayed. At the times when the sub-hologram S is not displayed, there is no reconstruction.
• a single sub-hologram S contains a lens function with an over the extension of the Subhologram S approximately constant amount.
• the sub-hologram S can therefore be encoded directly as a phase function without error.
• Another advantage is the ability to use only a single light modulator in the holographic display, which must contain only a larger number of pixels because of the phase encoding than in the first embodiment.
• the switching speed requirements of the phase modulator are higher, but realizable.
• the intensity of the illumination system can additionally be variably controlled in addition to a normal PWM.
• the lighting system may include multiple light sources.
• T1 indicates the course of a time interval in which the intensity of at least one light source illuminating the light modifying means L is additionally changed, while at the same time individual object points OPn are reconstructed in the period T2 (see FIG. 7b).
• IL (T) is the intensity of the light source as a function of the time T in FIG. 7a and Sh (T) OPI and Sh (T) OP2 in FIG. 7a
• this means that for a given switching speed of the light modulator means L, normally the period T1 can be decomposed into M fixed sections. With a constant intensity of the light source IL (T) const, only M different intensity levels can be realized in the reconstruction. However, if the light source IL (T) is varied during the time period T1, the same can be achieved with the same switching speed of the light modulation means L. represent greater number of different intensity levels.
• FIG. 7b shows the reconstruction of the object point OP1 from the sub-hologram S1 during the time periods 1 to 3 and the reconstruction of the other object point OP2 during the time segments 1 and 4.
• the relative intensity then results for the object point OP1 proportional to 1 * 1 + 1 * 2 + 1 * 4 + 0 * 8 and for the object point OP2 to 1 * 1 + 0 * 2 + 0 * 4 + 1 * 8.
• the time interval T1 can be e.g. also divide in k equal sections and the intensity of the light source in the first section by a factor of 2 high (k-1), in the second section by a factor of 2 high (k-2) and in the k-th section by a factor of 2 high 0 , ie 1, relative to a reference value. Then 2 high k different intensity levels can be displayed in k time segments.
• Both embodiments are combinable with the HPO and FP coding.
• the raster cells of the MR array are detected only in a single hologram line.
• the 3D scene can be divided into a smaller number of larger object point groups OPGm and a viewer sees a time-averaged reconstruction over a few partial reconstructions.
• the grid MR only has to be moved line by line.
• this embodiment has the advantage that it has the least amount of computation at a comparable with the previous embodiments reconstruction result and at the same time makes the least demands on the switching speed of the light modulators to be used.
• the raster cells are generally shifted to encode the sub-holograms Sn of the object points OPn in steps of one macropixel each.
• the 3D scene is thus divided into 32 groups of object points OPn and from these 32 holograms are calculated, coded and time-sequential! is displayed so that a viewer sees their reconstructions averaged over time from the visibility area.
• all 32 holograms must be displayed within 40 ms, so a single hologram in a time of approximately 1.25 ms.
• phase modulator In a combination of an amplitude and a phase modulator, the phase modulator would have to have this or a smaller refresh rate.
• the amplitude modulator for PWM of intensities could have an 8X faster frame rate, say, about 150 microseconds. Suitable for this are e.g. Ferrolectric liquid crystal displays with switching times of 40 microseconds.
• pixels of overlapping sub-holograms contribute with their intensity to the reconstruction of several object points during a reconstruction. It is also possible to use light modulation means which have few intensity or phase stages, for example 3, 4 or 8, for the method.
• the maximum size of a sub-hologram of an object point is limited.
• the sub-holograms of all object points do not have to be calculated and displayed one after the other, but a certain number of sub-holograms can be displayed at the same distance as the maximum size of a sub-hologram.
• holograms can be coded with a low dynamic range. Quantization errors and other disadvantages that arise from the overlapping of many sub-holograms of object points of a 3D scene are avoided here.
• a holographic display one may optionally use a combination of several light modulators without the mentioned drawback of strict adjustment effort or a single light modulator, preferably a phase modulator, without the disadvantage of an iterative calculation to encode the log values.

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• 2007
  • 2007-05-16 DE DE102007023738A patent/DE102007023738A1/de not_active Ceased
• 2008
  • 2008-05-09 WO PCT/EP2008/055746 patent/WO2008138885A2/de not_active Ceased
  • 2008-05-09 JP JP2010507890A patent/JP5529725B2/ja not_active Expired - Fee Related
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