JP2011112764A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning image display device using a laser beam which eliminates troubles caused when displaying an image using a conventional Gaussian beam, enables clear image display with a high resolution feeling, and enables high-quality image display. <P>SOLUTION: The image display device includes a light source 10 that shoots a Hermitian Gaussian beam L of a higher order, and a scanning optical system 20 that scans the Hermitian Gaussian beam L emitted from the light source in a 2-dimensional direction on a projection surface 50 and draws an image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image display device.

  2. Description of the Related Art Conventionally, a scanning projector is known as one of image display apparatuses capable of displaying a large screen (for example, Patent Document 1). A scanning projector displays an image by raster-scanning modulated laser light on a projection surface such as a screen.

  Laser light has characteristics such as high color purity because it is a single wavelength, and easy beam shaping because of its high coherence. Therefore, in an image display device that displays an image with laser light, the contrast, color reproducibility, resolution, and the like can be significantly improved.

  Further, in a scanning projector, gradation adjustment can be performed by a modulation circuit instead of a liquid crystal light valve or the like. Therefore, complete black can be expressed by downsizing the projector or stopping the supply of laser light. Therefore, the light utilization efficiency can be increased by making the device much smaller and eliminating the light loss in the projection lens.

JP-A-1-245780

  However, the laser light source normally used in the scanning projector has room for improvement for the following reasons from the viewpoint of improving the image quality.

  First, as a laser beam used for image display, a Gaussian beam having a circular cross section in a plane perpendicular to the optical axis is usually used. Therefore, the laser beam irradiated on the projection surface shows a circular or elliptical spot shape. On the other hand, since the image data of the display image is generally expressed by rectangular pixels, the shape of the laser beam does not correspond to the pixel shape of the image data. Therefore, since the image display is always performed by superimposing a part of the adjacent beam spots, useless color mixing occurs between the pixels, causing the display image to deteriorate.

  In the scanning projector, the spot diameter of the laser light on the projection surface corresponds to the pixel size of the projected image, and the smaller the spot diameter, the higher resolution image display is possible. However, laser light generally used in scanning projectors has a large spot diameter, and has not been satisfactory for market demands for high-resolution display images.

  In addition, when displaying on a projector using a laser light source, there is a phenomenon called so-called speckle, in which light spots and dark spots are distributed in a striped pattern or a spotted pattern due to light interference caused by a scatterer such as a screen. May occur. Speckle can cause glare to the viewer and cause adverse effects such as discomfort when viewing images. Therefore, it is important to use speckle removal technology for scanning projectors that use laser light. It is becoming.

  The present invention has been made in view of such circumstances, and in a scanning image display apparatus using laser light, eliminates the problems that occur when performing image display using a conventional Gaussian beam, and is clear. An object of the present invention is to provide an image display device capable of displaying a high-quality image.

In order to solve the above problems, an image display device of the present invention includes a light source unit that emits a higher-order Hermitian Gaussian beam, and the Hermitian Gaussian beam emitted from the light source unit in a two-dimensional direction on a projection surface. Scanning means for drawing an image by scanning.
Here, the “higher order Hermitian Gaussian beam” refers to a Hermitian Gaussian mode laser beam excluding the zeroth order. The Hermitian Gaussian beam irradiates a substantially rectangular area as compared with the Gaussian beam (0th-order Hermitian Gaussian beam) as a whole, so that it is possible to irradiate an area corresponding to the pixel shape of the display image, and is unnecessary between pixels. Therefore, it is possible to obtain an image display apparatus that is capable of displaying high-quality images with less likely color mixing.

In the present invention, the Hermitian Gaussian beam includes a plurality of sub-beams arranged in at least one direction within one beam and having different spatial phases, and the light source unit includes a plurality of sub-beams having different arrangement directions of the sub-beams. It is desirable that the Hermitian Gaussian beam can be emitted.
According to this configuration, it is possible to display an image by emitting a Hermitian Gaussian beam having a desired sub-beam arrangement direction.

In the present invention, the light source unit is configured to detect a contour of a symbol included in the image, and based on a detection result by the detection unit, the sub beam so that an area of a portion protruding from the symbol is minimized. It is desirable to have selection means for selecting the arrangement direction.
Here, the “contour of the symbol” is a concept including not only the contour that borders the outer periphery of the symbol but also the boundary of the color within the symbol. According to this configuration, the contour of an image to be displayed can be detected, and a Hermitian Gaussian beam having an appropriate arrangement direction can be emitted according to the position of the contour and the extending direction of the contour. Therefore, it can be set as the image display apparatus which can raise the resolution feeling in an outline.

In the present invention, the light source unit converts a first light source that emits a Gaussian beam and the Gaussian beam emitted from the first light source into the Hermitian Gaussian beam in which the arrangement direction of the sub beams is a first direction. The Hermitian Gaussian beam in which the arrangement direction of the sub beam of the first phase modulation means, the second light source emitting a Gaussian beam, and the Gaussian beam emitted from the second light source is a second direction different from the first direction It is desirable to have a second phase modulation means for converting to
According to this configuration, each phase modulation means provided for each light source is configured to convert into Hermitian Gaussian beams having different sub-beam arrangement directions. Therefore, by setting the Hermitian Gaussian beam necessary for displaying the outline of the pattern well and setting the light source unit with the required number of sets of light sources and phase modulation means, the arrangement of sub-beams A suitable light source can be selected according to the direction, and good image display can be performed.

In the present invention, the light source unit includes a light source that emits a Gaussian beam, and a phase modulation unit that converts the Gaussian beam into the Hermitian Gaussian beam, and the phase modulation unit includes an incident surface of the Gaussian beam. And controlling the spatial phase of the Gaussian beam incident on each pixel in each pixel, thereby controlling the sub-beam arrangement direction in a plurality of directions. It is desirable to do.
According to this configuration, it is possible to emit a Hermitian Gaussian beam having an arbitrary sub-beam arrangement direction by controlling the phase modulation means. Therefore, the configuration of the light source unit can be simplified and the apparatus can be downsized.

In the present invention, the phase modulation means is preferably a liquid crystal device having a plurality of liquid crystal elements corresponding to the plurality of pixels.
According to this configuration, a phase difference is provided in the light emitted through the liquid crystal device due to a difference in refractive index caused by switching ON / OFF of the liquid crystal element, and a Gaussian beam is favorably converted into a Hermitian Gaussian beam. be able to.

In the present invention, it is desirable that the phase modulation means includes a plurality of reflecting mirrors corresponding to the plurality of pixels and a moving device that individually changes the position of the reflecting mirror in the normal direction of the reflecting mirror.
According to this configuration, since the position of the reflecting mirror differs in the normal direction, a phase difference occurs in the reflected light, and the Gaussian beam can be converted into a Hermitian Gaussian beam. By using a member having a high response speed for the moving device, the position control of the reflecting mirror can be performed quickly, and phase modulation means capable of phase modulation following the display speed can be obtained.

In the present invention, it is preferable that the light source unit changes the arrangement direction of the sub beams within one frame or between frames of the image projected by the scanning unit.
According to this configuration, it is possible to display an image by changing the arrangement direction of the sub-beams between adjacent Hermitian Gaussian beams within one frame. Further, it is possible to display an image by superimposing Hermitian Gaussian beams having different sub-beam arrangement directions between frames at the same position on the projection surface. In this way, different interference fringes (speckle patterns) are generated within one frame or between frames on the projection surface, and different speckle patterns are superimposed in the form of the viewer's retina, resulting in image distortion (speckle). Is reduced. Therefore, an image display device with reduced speckles can be obtained.

1 is a schematic diagram of a projector according to a first embodiment of the invention. It is explanatory drawing explaining an HG beam. It is the schematic of the phase modulator which the projector of 1st Embodiment has. It is explanatory drawing which shows the mode of the image display by the projector of 1st Embodiment. It is the schematic of the projector which concerns on 2nd Embodiment of this invention. It is the schematic of the phase modulator which the projector of 2nd Embodiment has. It is explanatory drawing which shows the mode of the image display by the projector of 2nd Embodiment.

[First Embodiment]
The image display apparatus according to the first embodiment of the present invention will be described below with reference to FIGS. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is a schematic diagram showing a projector (image display device) 1 according to this embodiment. As shown in the figure, the projector 1 scans a laser beam on a light source unit 10A (light source unit 10) that emits an HG beam L, which is a Hermitian Gaussian beam (hereinafter referred to as HG beam), and a screen (projected surface) 50, thereby scanning an image. And a scanning optical system (scanning means) 20 for drawing.

  When an electrical signal corresponding to the input image is supplied from a signal source 40 such as a PC, the electrical signal is processed by the control device 30 and output to the light source unit 10 and the scanning optical system 20. The light source unit 10 emits an HG beam L whose gradation changes with time in accordance with an electric signal, and is emitted toward the screen 50 by the scanning optical system 20.

  Although the detailed structure of the light source unit 10A is not illustrated, the laser light source 11 that is a semiconductor laser element that emits a Gaussian mode laser beam La and the laser beam La that is incident on itself are converted into an HG beam L that is an HG beam. And a phase modulator (phase modulation means) 12.

  In the light source unit 10A of the present embodiment, laser beams La emitted from two laser light sources 11 that emit laser beams of the same color are incident on the two phase modulators 12a and 12b, respectively, and converted into HG beams L. And is configured to be injected. In the figure, the projector 1 is configured to include only one light source unit 10A, but may include, for example, three light source units 10 that emit red, green, and blue laser beams.

  FIG. 2 is an explanatory diagram showing an example of the HG beam L formed by the phase modulator 12 shown in FIG. 1, and shows a beam spot in a plane perpendicular to the optical axis.

  Here, assuming that the propagation method of the HG beam L is the z-axis, the Helmholtz equation of Equation 1 is obtained for the electric field of light from the Maxwell equation. The solution of this equation can be expressed as shown in Equation 2 using Hermite polynomials, and Equations 3 to 5 corresponding to 0th-order to second-order solutions of Hermite polynomials are obtained from Equation 2.

  A conventional laser scan display uses a 0th-order mode called a Gaussian beam among the solutions. 2A shows a Gaussian beam (zero-order HG beam), and FIGS. 2B to 2F show a high-order HG beam L. FIG.

  The Gaussian beam shown in FIG. 2A has a substantially circular cross-sectional shape, whereas the (1,0) mode HG beam shown in FIG. Are arranged. In addition, the dimensions W1 and W2 are equal in the Gaussian beam, whereas in the (1,0) mode HG beam, the dimension W3 in the beam spot arrangement direction is 0.6 times the dimension W1 or W2. The dimension W4 in the direction orthogonal to the spot arrangement direction is reduced to 0.9 times the dimension W1 or W2.

  The mode of the HG beam L formed by the phase modulator 12 may be any of FIG. 2B to FIG. As shown in the figure, the high-order HG beam L has a plurality of sub-beams and is divided into a plurality of beam spots and irradiated, but the entire HG beam is irradiated to a rectangular region compared to a Gaussian beam. It becomes. Therefore, when the HG beam is used, it becomes easy to irradiate a region corresponding to the pixel shape of the display image, and unnecessary color mixing between pixels can be prevented.

  FIG. 3 is a schematic diagram illustrating an example of the phase modulator 12 of the present embodiment. The phase modulator 12 shown in the figure is configured to convert the laser light La, which is a Gaussian beam, into the (1, 0) mode HG beam L shown in FIG.

  The phase modulator 12 is a phase difference plate having two adjacent incident areas AR1 and AR2. The incident areas AR1 and AR2 have thicknesses d1 and d2 (d1 <d2) in the optical axis direction, respectively. The laser light La incident on each of the incident areas AR1 and AR2 has a phase difference according to the thickness of the phase modulator 12 and the refractive index of the phase modulator 12 in the incident area, and has an opposite phase to each other. Are emitted as two sub-beams L1 and L2.

  In the two phase modulators 12a and 12b shown in FIG. 1, the arrangement directions of the incident areas AR1 and AR2 are orthogonal to each other. Therefore, the HG beams L emitted from the phase modulators 12a and 12b are different types of HG beams in which the sub beam arrangement directions are orthogonal to each other. In the projector 1, an image is displayed by alternatively using the different types of HG beams.

  The scanning optical system 20 includes a first scanning mirror 21, a second scanning mirror 22, and a mirror driving unit 25. The first scanning mirror 21 is disposed at a position where the HG beam L emitted from the light source unit 10 is incident, and the second scanning mirror 22 is disposed at a position where the HG beam L reflected by the first scanning mirror 21 is incident. Has been placed. The mirror driving unit 25 drives the first scanning mirror 21 and the second scanning mirror 22 based on the drive signal.

  The first scanning mirror 21 is composed of, for example, a micromechanical mirror formed by MEMS technology or the like, and is supported by a torsion spring or the like. The first scanning mirror 21 receives an electrostatic force generated by the voltage supplied from the mirror driving unit 25 and is vibrated (rotated) in the forward and reverse directions around the first shaft 21a. As the first scanning mirror 21 rotates, the incident angle of the HG beam L incident on the first scanning mirror 21 changes, and the optical axis of the HG beam L reflected by the first scanning mirror 21 changes.

  The second scanning mirror 22 is composed of, for example, a galvanometer mirror. The second scanning mirror 22 is rotated around the second axis 22a by the mirror driving unit 25 based on the driving signal. In the present embodiment, the second scanning mirror 22 is arranged so that the second shaft 22 a is substantially parallel to the screen 50 when the projector 1 is installed in a predetermined direction.

  The incident position of the HG beam L in the second scanning mirror 22 changes as the first scanning mirror 21 rotates. As the second scanning mirror 22 rotates, the incident angle of the HG beam L incident on the second scanning mirror 22 changes, and the optical axis of the HG beam L reflected by the second scanning mirror 22 changes.

  Due to the movement of the scanning optical system 20, the optical axis of the light emitted from the projector 1 is changed in the main scanning direction by the rotation of the first scanning mirror 21, and the sub-scanning is performed by the rotation of the second scanning mirror 22. Change direction.

  The control device 30A includes a timing generation circuit 31, an image signal processing circuit 32, a buffer 33, a determination circuit (detection means) 34, a selection circuit (selection means) 35, a timing correction circuit 36, laser drivers 37a and 37b, and a mirror drive circuit. 39 is included.

  The electrical signal input from the signal source 40 includes an image signal that includes gradation data for each pixel of the input image, and a synchronization signal that includes data such as the number of pixels and the refresh rate of the input image. Yes. The input electrical signal is separated into an image signal and a synchronization signal by an interface (not shown), and the synchronization signal is sent to the timing generation circuit 31 and the image signal is sent to the image signal processing circuit 32.

  The timing generation circuit 31 generates a timing signal indicating the display timing for each pixel according to the number of pixels of the input image, the refresh rate, the scanning method, and the like. With the timing signal, the image signal can be converted into a format that matches the scanning method of the projector 1. The timing signal is output to the timing correction circuit 36.

  The image signal processing circuit 32 performs various image processing such as gamma processing on the image signal. Further, the image signal processing circuit 32 adjusts the image signal based on the timing signal so that the gradation data included in the image signal is output in time sequential manner matched with the scanning method. The adjusted image signal is stored in the buffer 33.

  The determination circuit 34 uses the image signal stored in the buffer 33 to detect the boundary of the color of the symbol and the contour of the symbol included in the image to be drawn from now on using the HG beam L, and detects the detected boundary and contour. The type of HG beam suitable for drawing is determined.

  For example, when a circular pattern P as shown in FIG. 4A is to be displayed, an HG beam in which the beam spot BS of the HG beam is arranged in a direction orthogonal to the tangent line of the contour is determined in the contour portion. To do. In addition, when a diagram D as shown in FIG. 4B is to be displayed, the HG beam in which the beam spots BS are arranged is determined so that the area of the portion protruding from the diagram D is reduced.

  The selection circuit 35 selects which of the two phase modulators 12a and 12b to use the HG beam based on the determination result of the determination circuit 34, and uses the result of the selection as a timing correction circuit 36 and a laser driver. 37a and 37b, and output to the mirror drive circuit 39.

  The timing correction circuit 36 corrects the timing signal generated by the timing generation circuit 31 according to the type of HG beam selected by the selection circuit 35 and the image data to be displayed. For example, if a circular broken line indicated by reference numeral BX in FIG. 4A is a beam spot displayed in a normal display using a Gaussian beam, for example, a half of the beam spot protruding from the circular pattern P is reduced. The timing signal is corrected so as to irradiate the HG beam by delaying the pixel timing. The corrected timing signal is output to the laser drivers 37a and 37b and the mirror drive circuit 39.

  The laser drivers 37a and 37b are alternatively selected according to the type of the HG beam selected by the selection circuit 35, and the light quantity of the HG beam L emitted from the light source unit 10 corresponds to the gradation for each pixel. The output of the light source unit 10 is adjusted based on the image signal so as to change.

  The mirror drive circuit 39 generates a drive signal for driving the scanning optical system 20 based on the timing signal, and outputs the drive signal to the scanning optical system 20. In the projector 1, two types of HG beams L emitted from different phase modulators 12 a and 12 b are incident on the scanning optical system 20 at different angles. For this reason, it is preferable to individually prepare a drive signal for scanning the scanning optical system 20 according to the type of the HG beam L to be used, and to use the drive signal according to the type of the HG beam selected by the selection circuit 35.

  According to the projector 1 having the above-described configuration, it is possible to irradiate a region corresponding to the pixel shape of the display image by using the HG beam irradiated to the substantially rectangular region. Color mixing can be prevented and high-quality image display can be realized. Further, by changing the arrangement direction of the sub-beams (the arrangement direction of the beam spots), it is possible to display an image by emitting an HG beam having a sub-beam arrangement direction suitable for the design of the image. Therefore, the projector 1 can display a high-quality image.

  In the present embodiment, the light source unit 10A having the two phase modulators 12a and 12b is used to change the arrangement direction of the sub-beams of the HG beam to be emitted as appropriate, but only one phase modulator 12 is used. It is also possible to use a projector that uses an HG beam in which the arrangement direction of the sub beams is limited. Even in this case, since the shape of the irradiation region is close to a rectangle as compared with the Gaussian beam, it is possible to obtain an effect of preventing unnecessary color mixing between pixels and realizing high-quality image display.

[Second Embodiment]
5 to 7 are explanatory diagrams of the projector 2 according to the second embodiment of the invention. The projector 2 of the present embodiment is partially in common with the projector 1 of the first embodiment. The difference is that in the phase modulator of the first embodiment, the incident region for performing phase modulation is fixed, whereas in the phase modulator of this embodiment, the incident region for performing phase modulation can be arbitrarily changed. That is. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  As shown in FIG. 5, the projector 2 according to the present embodiment includes a light source unit 10 </ b> B including a laser light source 11 and a phase modulator (phase modulation unit) 13 in which an incident region for performing phase modulation is variable. The control unit 30 </ b> B has a phase modulator driver 38 that operates the phase modulator 13 based on the determination result of the determination circuit 34.

  FIG. 6 is an explanatory diagram of the phase modulator 13, FIG. 6A is a schematic perspective view of the phase modulator 13, and FIG. 6B is a schematic cross-sectional view of the phase modulator 13.

  As shown in FIG. 6A, the phase modulator 13 includes a plurality of reflecting mirrors 13a arranged in a two-dimensional matrix on the surface, and is configured to reflect the incident laser light La. In the phase modulator 13, the laser light La incident on the incident area AR1 is reflected and converted into the sub-beam L1, and the laser light La incident on the incident area AR2 is reflected and converted into the sub-beam L2. The laser beam La is converted into an HG beam L.

  As shown in FIG. 6B, each reflecting mirror 13 a is disposed on the substrate 15 via the extendable part 14. The expansion / contraction part 14 is formed of, for example, a piezo element, and can input an electric signal to cause a certain expansion / contraction. When a height difference of height d is generated between the incident area AR1 and the incident area AR2 due to the expansion / contraction of the expansion / contraction part 14, the laser beam La incident at the incident angle θ and reflected by the reflecting mirror 13a has a position of 2d / cos θ. A phase difference will occur. In the phase modulator 13, the incident region where the phase modulation is performed is made variable by arbitrarily setting the region that causes the phase difference by controlling the expansion / contraction part 14.

  According to the projector 2 having the above-described configuration, the same effect as that of the projector 1 shown in the first embodiment can be obtained. In addition, the light source unit 10B including a set of laser light sources and a phase modulator can convert the HG beam. Therefore, the light source unit 10B can be simplified, and the projector 2 can be downsized.

  Further, according to the projector 2, as shown in FIG. 7A, the pattern P is displayed while changing the arrangement direction of the beam spots BS at the irradiated portions of the adjacent HG beams, so that the projected portion The generated interference fringes (speckle pattern) can be made different to reduce speckle.

  Further, as shown in FIG. 7B, different speckle patterns can be observed by changing the arrangement direction of the sub-beams of the HG beam irradiated to the same portion between the frames as indicated by reference symbols BS1 and BS2. Can be superimposed on a person's retina, and speckle can be reduced. The display as shown in FIG. 7B is also possible in the projector 1 of the first embodiment.

  In addition, although the phase modulator 13 of the present embodiment is configured to include a plurality of reflecting mirrors, the present invention is not limited thereto, and may be a liquid crystal device including a plurality of liquid crystal elements corresponding to the reflecting mirrors. In this case, a phase difference is provided in the light emitted through the liquid crystal device due to a difference in refractive index caused by switching ON / OFF of the liquid crystal element, and the Gaussian beam can be converted into an HG beam satisfactorily. it can. As the liquid crystal device, both a reflection type and a transmission type can be used.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  DESCRIPTION OF SYMBOLS 1, 2 ... Projector (image display apparatus) 10, 10A, 10B ... Light source part, 11 ... Laser light source (light source) 12, 12a, 12b, 13 ... Phase modulator (phase modulation means), 13a ... Reflector, DESCRIPTION OF SYMBOLS 14 ... Telescopic part (moving device), 20 ... Scanning optical system (scanning means), 30, 30A, 30B ... Control device, 34 ... Determination circuit (detection means), 35 ... Selection circuit (selection means), 50 ... Screen ( Projection surface), L ... Hermitian Gaussian beam, La ... laser beam,

Claims (8)

A light source that emits a higher order Hermitian Gaussian beam;
An image display device comprising: a scanning unit that draws an image by scanning the Hermitian Gaussian beam emitted from the light source unit on a projection surface in a two-dimensional direction. The Hermitian Gaussian beam has a plurality of sub-beams arranged in at least one direction within one beam and having different spatial phases.
The image display device according to claim 1, wherein the light source unit is configured to be capable of emitting a plurality of the Hermitian Gaussian beams having different arrangement directions of the sub beams. The light source unit includes a detecting unit that detects a contour of a pattern included in the image;
3. The image display according to claim 2, further comprising a selection unit that selects an arrangement direction of the sub-beams so that an area of a portion protruding from the design is minimized based on a detection result by the detection unit. apparatus.   The light source unit includes a first light source that emits a Gaussian beam, and a first phase modulation unit that converts the Gaussian beam emitted from the first light source into the Hermitian Gaussian beam in which the arrangement direction of the sub beams is a first direction. A second light source that emits a Gaussian beam, and a second light source that converts the Gaussian beam emitted from the second light source into the Hermitian Gaussian beam in which the sub beam arrangement direction is a second direction different from the first direction. The image display device according to claim 1, further comprising: a phase modulation unit. The light source unit includes a light source that emits a Gaussian beam, and phase modulation means that converts the Gaussian beam into the Hermitian Gaussian beam,
The phase modulation means has a plurality of pixels arranged in a two-dimensional matrix on the incident surface of the Gaussian beam, and controls the spatial phase of the Gaussian beam incident across each pixel for each pixel. 4. The image display device according to claim 1, wherein the arrangement direction of the sub-beams is controlled in a plurality of directions. 5.   The image display device according to claim 5, wherein the phase modulation unit is a liquid crystal device having a plurality of liquid crystal elements corresponding to the plurality of pixels.   6. The phase modulation means includes a plurality of reflecting mirrors corresponding to the plurality of pixels, and a moving device that individually changes the positions of the reflecting mirrors in the normal direction thereof. The image display device described.   8. The image display according to claim 2, wherein the light source unit changes the arrangement direction of the sub-beams within one frame or between frames of the image projected by the scanning unit. 9. apparatus.