ITRM20110402A1 - METHOD OF DISPLAYING SELF-STEREOUSCOPIC HOLOGRAPHIC IMAGES AND ITS OLOVISOR DEVICE. - Google Patents

Description

Method of visualization of autostereoscopic holographic images and related holovisor device

The present invention relates to a method for displaying autostereoscopic holographic images and related holovisor device.

More precisely, the present invention relates to a holovisor method and device capable of displaying holograms in an auto-stereoscopic way starting from a computer generated hologram.

Currently there are different types of 3D displays, some make use of various types of glasses (stereoscopic systems), others use special output lenses (lenticular screens) to display different points of view of the image to be displayed (autostereoscopic systems).

It is known that the only true 3D visualization of an image is given by holography, which exactly reproduces the wave fronts reflected by the objects. Various attempts have been made to view holograms in real time (MIT, NHK) but all of them have so far displayed very small holograms (about 15 cm).

Holographic video display has several problems on:

- display size;

- large horizontal viewing angle (60 °);

- real-time projection of a moving hologram;

- sequential visualization of elementary holograms;

- combined amplitude and phase modulation of the laser beam;

- generation of binary holograms from stereo pairs of video images.

The object of the present invention is to provide a 3D visualization method which solves the problems and overcomes the drawbacks of the prior art.

A further specific object of the present invention is to provide a holovisor device which solves the problems and overcomes the drawbacks of the prior art.

The object of the present invention is a method for displaying autostereoscopic holographic images, characterized by using an optical system comprising a digital display placed on the image plane, and an optics for projection of the images displayed by said display on a holographic diffuser, and by carrying out the following steps:

A. generate a digital holographic image;

B. subdividing said digital holographic image into a number N, with a positive integer N greater than 1, of parallel elementary holographic lines;

and by the fact that, in sequence for each elementary holographic line of said N elementary holographic lines, the following further steps are carried out: C. modify the dimensions of said elementary holographic line adapting them to the dimensions of said digital display, obtaining a corresponding modified elementary hologram ;

D. displaying said modified elementary hologram on said digital display;

E. modify the dimensions of said elementary hologram modified and displayed on said digital display, adapting them to the dimensions of a linear portion of said holographic diffuser having a width equal to 1 / N-m or of the total width of said holographic diffuser, by means of said projection optics, obtaining a corresponding elementary ololine;

F. projecting, through said projection optics, said elementary hololine in a telecentric way on said holographic diffuser,

obtaining on said holographic diffuser the sequential visualization of N parallel lines corresponding to said N elementary holographic lines and then the visualization of an auto-stereoscopic holographic image corresponding to said one digital holographic image.

The essential point of the invention is the decomposition of the digitized holographic image into vertical "elementary" holograms (or more generally parallel to a predefined direction). In the prior art the decomposition is instead carried out in pixels, and since billions of pixels are thus obtained, it is not possible to project them except on very small screens (a few inches).

Preferably according to the invention, the steps from A to F are repeated for the maintenance over time of said an auto-stereoscopic image on said holographic diffuser.

Preferably according to the invention, several digital holographic images are generated and for each digital holographic image steps A to F are repeated, displaying a video sequence on said holographic diffuser.

Preferably according to the invention, each of said elementary holographic lines is broken down into eight bit planes displayed sequentially on said digital display and on said holographic diffuser.

Preferably according to the invention, said digital display is illuminated by a laser beam which is modulated in amplitude through an opto-acoustic modulator modulating its supply voltage in eight different levels corresponding to the eight bit planes, realizing a modulation sequence such as to display 8 bit planes on the digital display and at the same time apply a differentiated voltage to the opto-acoustic modulator, obtaining 8 consecutive levels of modulated bits in 255 amplitude levels.

A further specific object of the present invention is a holovisor device (1000), characterized in that it includes:

- an electronic control unit suitable for:

o decompose a digital holographic image into a number N, with a positive integer N greater than 1 of parallel elementary holographic lines,

o modify the dimensions of each of said digital holographic lines obtaining corresponding modified elementary holograms suitable for viewing on: - a digital display placed on the image plane and able to individually display each of said modified elementary holograms,

- a projection optics able to project in a telecentric way each of said modified elementary holograms displayed on said digital display, again at the same time adapting their dimensions, on

- a holographic diffuser,

and by the fact that:

- said projection optics is adapted to project each of said modified elementary holograms onto parallel and successive linear portions of said holographic diffuser having a width equal to 1 / N-m or of the total width of said diffuser, obtaining corresponding N elementary lines, - said a unit control electronics is adapted to synchronize the sequential display on said digital display and the sequential projection on said holographic diffuser of said N elementary holograms modified in such a way as to obtain on said holographic diffuser a holographic image corresponding to said digital holographic image, said image holographic being by autostereoscopic construction.

Preferably according to the invention, said digital display is a device and a DMD, illuminated by a laser beam coming out of a laser source and adapted in size by an optical projection unit.

Preferably according to the invention, said optical projection assembly comprises an optoacoustic modulator adapted to modify the dimensions of said laser beam.

Preferably according to the invention, said laser beam is modulated in amplitude through the opto-acoustic modulator, modulating its supply voltage in eight different levels corresponding to the eight bit planes, realizing a modulation sequence such as to sequentially display 8 planes of bit on the digital display and at the same time applying a differentiated voltage to the opto-acoustic modulator, thus obtaining 8 consecutive levels of modulated bits in 255 levels of amplitude.

Preferably according to the invention, said projection optics comprises a galvanometric system adapted to perform a linear scan, projecting the light coming from said display onto said holographic diffuser.

Preferably according to the invention, a Fresnel lens is arranged between said galvanometric system and said holographic diffuser.

Preferably according to the invention, that said projection optics comprises an anamorphic optical group.

The invention will now be described for illustrative but not limitative purposes, with particular reference to the drawings of the attached figures, in which:

Figure 1 shows a general diagram of the system according to the invention, according to a perspective view;

Figure 2 shows a lateral schematic view of the telencentric assembly of the system according to the invention;

Figure 3 shows an embodiment of the light beam deflection system used in the device according to the invention; Figure 4 shows the composition of the optical deflection unit in an embodiment of the system according to the invention; figure 5 shows an example of visualization of a line on the device according to the invention;

Figure 6 shows in (a) an example of a computer-generated hologram, in (b) its digitization and in (c) its compression into a hololine, through the device according to the invention;

figure 7 shows (a) a perspective view and (b) a top view of the system according to the invention at the end of the scan;

Figure 8 shows a block diagram of the control electronics of an embodiment of the device according to the invention.

The main purpose of the research that led to the present invention was the realization of a large display (50 inches) by developing an original vertical scanning system, together with a control electronics that makes it possible to view large holograms in time. real.

The at least partial resolution of the aforesaid problems of the prior art is obtained according to the invention by simultaneously using different systems:

1) decomposition of a general hologram into many elementary linear holograms (vertical or horizontal);

2) combined use of an optical device (preferably opto-acoustic) and a display (e.g. DMD) to generate the elementary hologram modulated in phase and in amplitude;

3) fast synchronized loading of the elementary hologram on the display;

4) optical system for modifying the dimensions of the elementary hologram;

5) linear scanning system for the sequential visualization of elementary holograms;

6) synchronization of the modulation, scanning and deflection system;

7) telecentric optical display unit.

Detailed description

Figure 1 shows the device according to the invention comprising a laser source 10, an opto-acoustic modulator 20 for the amplitude modulation of the laser source, a beam expander 30 (with a spatial filter inside) , to uniformly illuminate the microscopic mirror device or "Digital Micromirror Device" (DMD) 40, an anamorphic optical group 50, a galvanometric mirror 60, a vertical holographic diffuser 70, a telecentric Fresnel lens 80, a total reflection prism ( "Total Internai Reflection prism", TIR prism) 90 to separate direct and reflected light, a reproduced image 100, a control electronics 110.

We now describe in more detail the composition of the device according to the invention.

With reference to Figure 4, after the source 10 there is an opto-acoustic modulator 20 and immediately after the beam-expander 30 composed of the lenses 31 and 32. This is followed by the prism 90 which deflects the light onto the DMD 40 , the mirror 120 and the optical system of anamorphic lenses 57, 58, 59 which operates in such a way that the light reflected by the DMD 40 is compressed horizontally and expanded vertically. Naturally, the person skilled in the art can realize an anamorphic optical unit optimized according to the needs and capable of having the effect just mentioned.

Finally, before the Fresnel lens 80 there is the galvanometric mirror 111 and its controller 110.

Referring also to Figure 3, a galvanometric mirror 62 or a rotating polygonal mirror 61 is inserted in the nodal point, a focus common to the vertical 58 and horizontal lenses 57,59 of the anamorphic system and the reflected light is thus sent to an optical output unit .

This optical output assembly is also illustrated with reference to Figure 2, and is composed of a telecentric lens 80 and a vertical diffuser for the display 70. The scanning beam 66 projected by the galvanometric mirror 60 affects the Fresnel lens 80 and is transmitted horizontally to the vertical diffuser 70 and from this the ray 78 goes towards the observer. The galvanometric system therefore acts as a horizontal scanner, projecting the light coming from the DMD onto the Fresnel lens 80 in order to generate vertical lines 83, as illustrated in figure 5.

With this device according to the invention, computer-generated holograms can be projected. Figure 7 shows a generic computer generated hologram. A hologram 1000 mm wide and 700 mm high has a resolution of at least 1000 lines per millimeter, so the data to be stored considering one byte per data are:

1000lpm x 1000mm x 10001pm x768mm = 768GB.

If you remove the vertical parallax, you reduce by a factor of 1000 the amount of data that requires 768MB of data per hologram, with a screen that should have a resolution of horizontal IMpixel and 768 vertical lines. Starting from an image projected by the DMD (1024x768), which originally has a size of 2cm x 1.5cm and through an optical system, is compressed horizontally by 20 times and vertically expanded by 40 times, we obtain strips of size Imm x 768 mm. By sequentially displaying 1000 of these images by means of the galvanometric scanner according to the invention, a screen with a resolution of 1M pixel x 768 lines is obtained.

The original hologram is then decomposed into 1000 strips (hololine) each with a definition of 1024 pixels x 768 lines, displayed on the DMD as on the image plane, modified in size by the anamorphic optics and projected on the output screen.

An observer in front of the screen will receive two different images on his eyes depending on the distance from the screen and the viewing angle.

These images are produced by the diffraction of light produced by elementary holograms projected on the screen. The optical output system must be of the telecentric type, in order to project the lines parallel to the observer and all of the same size, as illustrated further in figure 7.

For this purpose, an optical system is used consisting of a Fresnel-type lens 80 with a vertical holographic display diffuser 70.

Referring to Figure 8, the control electronics 110 is formed by three main parts, the opto-acoustic controller 111, the deflection controller 112 and the DMD controller 113.

According to a preferred embodiment, the opto-acoustic modulator 20 consists of a tellurium oxide crystal (Te02) which varies its refractive index as a function of the frequency and amplitude of an acoustic wave generated by an applied piezoelectric transducer on the crystal. This acoustic wave is modulated in amplitude by a direct voltage applied to the modulator. The first order of diffraction is used.

The modulation is temporal. Considering that the amplitude of the output beam is proportional to the voltage applied to the modulator, and this voltage varies from 0 to 5 V, this voltage is divided by the number of levels of the image 255, which gives a value of about 20mV per step, for which the modulation sequence consists in visualizing bit planes on the display and at the same time applying a voltage that is equal to the initial step multiplied by the displayed bit order, for which we have:

1st bit 40 mV Minimum intensity of the modulated beam 2nd bit 80 mV

3rd bit 160 mV

4th bit 320 mV

5th bit 640 mV

6th bit 1280 mV

7th bit 2560 mV

8th bit 5120 mV Maximum intensity of the modulated beam In this way the 8 consecutive frames (bits) are modulated in 255 levels of amplitude, the video signal displayed and the conversion is done by the persistence of the image on the retina of the eye. The method allows you to modulate the entire color range of 255 gray levels with just eight DMD loading sequences (one for each bit).

The counter ("bitplane counter") is incremented with each loaded bit plane and loads the laser amplitude modulation value from a lookup table.

At the end of a color sequence consisting of 8 R, 8 G, and 8 B levels, the position counter is increased by one step to move the galvanometer or to control the "stepper motor" that drives the polygon mirror. Considering that the DMD is loaded in 10 microseconds, this means that to load 24 bit planes it takes 240 microseconds. To get a refresh rate of at least 30HZ (33 milliseconds), you can do about 130 uploads which correspond to 130 points of view, enough to get smooth motion.

The deflection is then obtained, in the case of a galvanometric mirror, using a 10-bit DAC converter, in the case of a polygon mirror, using a stepping motor.

The phase modulation is given instead by the lighting sequence of each mirror of the DMD.

The phase of each mirror is ± 71; a mirror matrix determines the modulation level of the plane wave arriving on the DMD (usually a 4x4 mirror matrix is chosen). Due to the fact that the response of each mirror is "on / off", the plane wave is interrupted and a phase modulation is created which is used to create a focus, as if it would be obtained with a special lens. This is not the classic use of DMD, because according to the invention coherent light is used.

Thus an image is focused in space.

This technique is innovative in combination with a DMD (or in general a MEMS device) because in the prior art a white light is used for the DMD and this white light cannot be controlled. According to the present invention, instead, a laser source is used, modulated in amplitude and therefore controllable.

In the foregoing, the preferred embodiments have been described and variants of the present invention have been suggested, but it is to be understood that those skilled in the art will be able to make modifications and changes without thereby departing from the relative scope of protection, as defined by the claims attached.

Claims (12)

CLAIMS 1) Method for viewing auto-stereoscopic holographic images, characterized by using an optical system comprising a digital display (40) placed on the image plane, and a projection lens (50,60,80) of the images displayed by said display (40) on a holographic diffuser (70), and by carrying out the following steps: A. generate a digital holographic image; B. subdividing said digital holographic image into a number N, with a positive integer N greater than 1, of parallel elementary holographic lines; and by the fact that, in sequence for each elementary holographic line of said N elementary holographic lines, the following further steps are carried out: C. modify the dimensions of said elementary holographic line adapting them to the dimensions of said digital display (40), obtaining a corresponding modified elementary hologram; D. displaying said modified elementary hologram on said digital display (40); E. modify the dimensions of said elementary hologram modified and displayed on said digital display (40), adapting them to the dimensions of a linear portion of said holographic diffuser (70) having a width equal to 1 / N-m or of the total width of said holographic diffuser, by means of said projection optics (50,60,80), obtaining a corresponding elementary ololinea; F. projecting, through said projection optics (50,60,80), said elementary hololine in a telecentric way on said holographic diffuser (70), obtaining on said holographic diffuser (70) the sequential display of N parallel lines corresponding to said N elementary holographic lines and then the visualization of an auto-stereoscopic holographic image (100) corresponding to said digital holographic image. 2) Method according to claim 1, characterized in that steps A to F are repeated for the maintenance over time of said an auto-stereoscopic image on said holographic diffuser (70). 3) Method according to claim 1, characterized by the fact of generating several digital holographic images and for each digital holographic image the steps from A to F are repeated, displaying a video sequence on said holographic diffuser (70). 4) Method according to any one of claims 1 to 3, characterized in that each of said elementary holographic lines is broken down into eight bit planes displayed sequentially on said digital display (40) and on said holographic diffuser (70). 5) Method according to claim 4, characterized in that said digital display (40) is illuminated by a laser beam which is modulated (20) in amplitude through an opto-acoustic modulator (20) modulating its supply voltage in eight levels corresponding to the eight bit planes, creating a modulation sequence such as to display 8 bit planes on the digital display (40) and at the same time apply a differentiated voltage to the opto-acoustic modulator (40) obtaining 8 consecutive levels of modulated bits in 255 levels of amplitude. 6) Holovisor device (1000), characterized by the fact of including: - an electronic control unit suitable for: o decompose a digital holographic image into a number N, with a positive integer N greater than 1, of parallel elementary holographic lines, o modify the dimensions of each of said digital holographic lines obtaining corresponding modified elementary holograms suitable for viewing on: - a digital display (40) placed on the image plane and able to individually display each of said modified elementary holograms, - a projection optics (50, 60, 80) capable of telecentric projecting each of said modified elementary holograms displayed on said digital display (40), again at the same time adapting their dimensions, on - a holographic diffuser (70), and by the fact that: - said projection optics (50,60,80) is adapted to project each of said modified elementary holograms onto parallel and successive linear portions <1> or <1> of said holographic diffuser (70) having a width equal to 1 / N-mo of the total width of said diffuser, obtaining corresponding elementary N ollines, - said an electronic control unit is adapted to synchronize the sequential display on said digital display (40) and the sequential projection on said holographic diffuser (70) of said N elementary holograms modified in such a way as to obtain on said holographic diffuser (70) a holographic image (100) corresponding to said digital holographic image, said holographic image (100) being auto-stereoscopic by construction. 7) Device according to claim 6, characterized by the fact that said digital display is a device (40) and is a DMD, illuminated by a laser beam coming out of a laser source (10) and adapted in size by an optical projection group (20 , 30). 8) Device according to claim 7, characterized in that said optical projection group (20,30) comprises an optoacoustic modulator (20) adapted to modify the dimensions of said laser beam. 9) Device according to claim 8, characterized by the fact that said laser beam is modulated in amplitude through the optoacoustic modulator (20), modulating its supply voltage in eight different levels corresponding to the eight bit planes, realizing a modulation sequence such as to sequentially display 8 bit planes on the digital display (40) and at the same time applying a differentiated voltage to the opto-acoustic modulator (40), thus obtaining 8 consecutive levels of bits modulated in 255 levels of amplitude. 10) Device according to any one of claims 6 to 9, characterized in that said projection optics (50, 60, 80) comprises a galvanometric system (60) capable of performing a linear scan, projecting the light coming from said display ( 40) on said holographic diffuser (70). 11) Device according to claim 10, characterized in that a Fresnel lens (80) is arranged between said galvanometric system and said holographic diffuser (70). 12. Device according to any one of claims 6 to 11, characterized in that said projection optics (50,60,80) comprises an anamorphic optical group (50).