Patent Publication Number: US-2009225071-A1

Title: Image display system with light source controlled by non-binary data

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of a pending U.S. patent application Ser. No. 11/823,942 filed on Jun. 29, 2007. The application Ser. No. 11/823,942 is a Continuation in Part (CIP) Application of a U.S. patent application Ser. No. 11/121,543 filed on May 4, 2005, now issued into U.S. Pat. No. 7,268,932. The application Ser. No. 11/121,543 is a Continuation in Part (CIP) Application of three previously filed Applications. These three Applications are Ser. No. 10/698,620 filed on Nov. 1, 2003; Ser. No. 10/699,140 filed on Nov. 1, 2003 and issued into U.S. Pat. No. 6,862,127; and Ser. No. 10/699,143 filed on Nov. 1, 2003 and issued into U.S. Pat. No. 6,903,860 by one of the Applicant of this Patent Applications. The disclosures made in these Patent Applications are hereby incorporated by reference in this Patent Application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates generally to image display device. More particularly, this invention relates to an image display device implemented with an adjustable light source controlled by non-binary data. 
     2. Description of the Related Art 
     Even though there have been significant advances made in recent years in the technology of implementing electromechanical micromirror devices as spatial light modulators (SLM), there are still limitations and difficulties when these are employed to display high quality images. Specifically, when the display images are digitally controlled, the quality of the images is adversely affected because the images are not displayed with a sufficient number of gray scale gradations. 
     Electromechanical mirror devices are drawing a considerable amount of interest as spatial light modulators (SLM). The electromechanical mirror device consists of a mirror array arranging a large number of mirror elements. In general, the number of mirror elements range from 60,000 to several millions and are arranged on the surface of a substrate in an electromechanical mirror device. 
     Refer to  FIG. 1A  for a digital video system  1  as disclosed in relevant U.S. Pat. No. 5,214,420, which includes a display screen  2 . A light source  10  is used to generate light energy to illuminate display screen  2 . Light  9  is further concentrated and directed toward lens  12  by mirror  11 . Lens  12 ,  13 , and  14  serve a combined function as a beam columnator to direct light  9  into a column of light  8 . A spatial light modulator  15  is controlled by a computer through data transmitted over data cable  18  to selectively redirect a portion of the light from path  7  toward lens  5  to display on screen  2 . The SLM  15  has a surface  16  that includes switchable reflective elements, e.g., micro-mirror devices  32  with elements  17 ,  27 ,  37 , and  47  as reflective elements attached to a hinge  30 , as shown in  FIG. 1B . When element  17  is in one position, a portion of the light from path  7  is redirected along path  6  to lens  5  where it is enlarged or spread along path  4  to impinge the display screen  2  so as to form an illuminated pixel  3 . When element  17  is in another position, light is not redirected toward display screen  2  and hence pixel  3  would be dark. 
     Most of the conventional image display devices, such as the devices disclosed in U.S. Pat. No. 5,214,420, are implemented with a dual-state mirror control that controls the mirrors to operate in either an ON or OFF state. The quality of an image display is limited due to the limited number of gray scale gradations. Specifically, in a conventional control circuit that applies a PWM (Pulse Width Modulation), the quality of the image is limited by the LSB (least significant bit) or the least pulse width, since the control is related to either the ON or OFF state. Since the mirror is controlled to operate in either an ON or OFF state, the conventional image display apparatuses have no way of providing a pulse width to control the mirror that is shorter than the LSB. The lowest intensity of light, which determines the smallest gradation to which brightness can be adjusted when adjusting the gray scale, is the light reflected during the period corresponding to the smallest pulse width. The limited gray scale gradation due to the LSB limitation leads to a degradation of the quality of the display image. 
     In  FIG. 1C , a circuit diagram of a control circuit for a micro-mirror according to U.S. Pat. No. 5,285,407 is presented. The control circuit includes memory cell  32 . Various transistors are referred to as “M*” where * designates a transistor number and each transistor is an insulated gate field effect transistor. Transistors M 5 , and M 7  are p-channel transistors; transistors, M 6 , M 8 , and M 9  are n-channel transistors. The capacitances, C 1  and C 2 , represent the capacitive loads presented to memory cell  32 . Memory cell  32  includes an access switch transistor M 9  and a latch  32   a,  which is the basis of the Static Random Access switch Memory (SRAM) design. All access transistors M 9  in a row receive a DATA signal from a different bit-line  31   a.  The particular memory cell  32  to be written is accessed by turning on the appropriate row select transistor M 9 , using the ROW signal functioning as a word-line. Latch  32   a  is formed from two cross-coupled inverters, M 5 /M 6  and M 7 /M 8 , which permit two stable states. State 1 is Node A high and Node B low and state 2 is Node A low and Node B high. 
     The dual-state switching, as illustrated by the control circuit, controls the micromirrors to position either at an ON or an OFF orientation, as that shown in  FIG. 1A . The brightness, i.e., the gray scales of display for a digitally control image system, is determined by the length of time the micromirror stays at an ON position. The length of time a micromirror is controlled at an ON position is in turned controlled by a multiple bit word. For simplicity of illustration,  FIG. 1D  shows the “binary time intervals” when controlled by a four-bit word. As shown in  FIG. 1D , the time durations have relative values of 1, 2, 4, 8 that in turn define the relative brightness for each of the four bits, where 1 is for the least significant bit and 8 is for the most significant bit. According to the control mechanism as shown, the minimum controllable differences between gray scales is a brightness represented by a “least significant bit” that maintains the micromirror at an ON position. 
     When adjacent image pixels are shown with a great degree of difference in the gray scales, due to a very coarse scale of controllable gray scale, artifacts are shown between these adjacent image pixels. That leads to image degradations. The image degradations are especially pronounced in the bright areas of display, where there are “bigger gaps” between gray scales of adjacent image pixels. For example, it can be observed in an image of a female model that there are artifacts shown on the forehead, the sides of the nose and the upper arm. The artifacts are generated by technical limitations in that the digitally controlled display does not provide sufficient gray scales. Thus, in the bright areas of the display, the adjacent pixels are displayed with visible gaps of light intensities. 
     As the micromirrors are controlled to have a fully on and fully off position, the light intensity is determined by the length of time the micromirror is at the fully on position. 
     In order to increase the number of gray scale gradations of a display, the switching speed of the micromirror must be increased such that the digital control signals can be increased to a higher number of bits. However, when the switching speed of the micromirrors is increased, a stronger hinge is necessary for the micromirror to sustain the required number of operational cycles for a designated lifetime of operation. In order to drive the micromirrors supported on a further strengthened hinge, a higher voltage is required. In this case, the higher voltage may exceed twenty volts and may even be as high as thirty volts. A micromirror manufacturing process applying the CMOS (Complementary Metal Oxide Semiconductor) technologies would probably produce micromirrors that would not be suitable for operation at this higher range of voltages, and therefore, DMOS (Double diffused Metal Oxide Semiconductor) micromirror devices may be required in this situation. In order to achieve a higher degree of gray scale control, a more complicated manufacturing process and larger device areas are necessary when a DMOS micromirror is implemented. Conventional modes of micromirror control are therefore facing a technical challenge in that gray scale accuracy has to be sacrificed for the benefit of a smaller and more cost effective micromirror display, due to the operational voltage limitations. 
     There are many patents related to light intensity control. These Patents include U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227, 6,648,476, and 6,819,064. There are further patents and patent applications related to different shapes of light sources. These Patents includes U.S. Pat. Nos. 5,442,414, 6,036,318 and Application 20030147052. The U.S. Pat. No. 6,746,123 discloses special polarized light sources for preventing light loss. However, these patents and patent application do not provide an effective solution to overcome the limitations caused by insufficient gray scales in the digitally controlled image display systems. 
     Furthermore, there are many patents related to spatial light modulation that includes U.S. Pat. Nos. 20,25,143, 2,682,010, 2,681,423, 4,087,810, 4,292,732, 4,405,209, 4,454,541, 4,592,628, 4,615,595, 4,728,185, 4,767,192, 4,842,396, 4,907,862, 5,214,420, 5,287,096, 5,506,597, 5,489,952, 6,064,366, 6,535,319, and 6,880,936. However, these inventions have not addressed and provided direct resolutions for a person of ordinary skill in the art to overcome the above-discussed limitations and difficulties. 
     Therefore, a need still exists in the art of image display systems applying digital control of a micromirror array as a spatial light modulator to provide new and improved systems such that the above-discussed difficulties can be resolved. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a color display device implemented with a spatial light modulator and an adjustable light source. A controller is employed to control the light source and the spatial light modulator by applying non-binary data generated by converting the input image signal. The control processes apply the non-binary data to simultaneously control the light source and the spatial light modulator thus achieving increased gray scale resolutions for improving the quality of the display images. 
     The first exemplary embodiment of the present invention is an image display system for displaying an image according to an input image signal, and comprises a light source for emitting an illumination light; a data converting circuit for receiving and converting the input image signal into non-binary data; a spatial light modulator for receiving and applying the non-binary data for modulating the illumination light; a light source control circuit for applying the non-binary data in coordination with the spatial light modulator for controlling the light source. 
     The second exemplary embodiment of the present invention is an image display system for displaying an image according to an input image signal, and comprises a light source for emitting an illumination light; a data conversion circuit for receiving and converting several bits of input image data into an output data; a spatial light modulator for modulating the illumination light; a control circuit for receiving and applying the output signal for controlling the light source and the spatial light modulator. 
     The third exemplary embodiment of the present invention is an image display system for displaying an image according to an input image signal, and comprises a light source for emitting an illumination light; a data conversion circuit for receiving and converting an input image data into non-binary data; a spatial light modulator for receiving and applying the non-binary data for modulating the illumination light; a control circuit for receiving and applying the non-binary data to control the spatial light modulator; and a light source control circuit receives and applies a clock signal synchronous with a reference clock signal used for converting the input image data for controlling the light source. 
     A fourth exemplary embodiment of the present invention is an image display device for displaying images according to inputted image signals. The image display device comprises a light source for supplying illuminating light, a spatial light modulator(SLM) comprises a plurality of deflective light modulation elements for deflecting the illuminating light according to a deflection state, a data converting circuit for converting at least N consecutive bits (N is a positive integer) of the image signal to non-binary data and a light source control circuit receives and applies the non-binary data to control the light source to emit the illuminating light. 
     These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The present invention is described in detail below with reference to the following Figures. 
         FIG. 1A  is a functional block diagram for showing the configuration of a projection apparatus according to a conventional technique; 
         FIG. 1B  is a top view for showing the configuration of a mirror element of the projection apparatus according to a conventional technique; 
         FIG. 1C  is a circuit diagram for showing the configuration of the drive circuit of a mirror element of the projection apparatus according to a conventional technique; 
         FIG. 1D  is a timing diagram for showing the format of image data used in the projection apparatus according to a conventional technique; 
         FIG. 2A  shows a bit structural diagram implemented by a control process according to a prior art scheme and  FIGS. 2B and 2C  shows modified bit structures for a control process to operate a mirror device with an intermediate state control of this invention. 
         FIG. 3A  shows a control system using non-binary data. 
         FIG. 3B  is a cross-sectional view showing a deflective modulation element arranged in an SLM in the form of an array. 
         FIG. 4A  shows a bit structure mapped into a timing diagram for implementing a control process of a prior art scheme and  FIGS. 4B and 4C  show the improved bit structure mapped into timing diagram for implementing a PWM control system using non-binary data of this invention. 
         FIG. 5  shows a functional block diagram for illustrating a method of controlling the illumination of this invention. 
         FIG. 6A  shows a functional block diagram of an SLM, and  FIG. 6B  shows a control circuit diagram that executes a Digital Signal Control scheme. 
         FIGS. 7A and 7B  show the data and corresponding display states of another preferred embodiment, with the N bits as the difference between the number of bits of incoming image signal and the number of bits to display in gray scale. 
         FIG. 8A  shows a pulse width diagram of a control signal for an SLM, with corresponding light intensity in a frame period; 
         FIG. 8B  shows a control circuit diagram that implements an illuminating light from a semiconductor laser source or LED light source. 
         FIGS. 9 to 12  show the circuit diagrams of different control circuit diagrams for carrying out different gray scale control schemes as embodiments of this invention. 
         FIG. 13  shows an optical configuration example of a single-panel image display device according to a preferred embodiment of the present invention. 
         FIGS. 14A ,  14 B, and  14 C show an optical configuration example of a two-panel image display device according to a preferred embodiment of the present invention. 
         FIG. 15  shows an optical configuration example of a three-panel image display device according to a preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2A  shows a prior art scheme with input data of five bits as binary data of either zero or one, with the least significant bit having a weighting factor of one and the most significant bit (MSB) having a weighting factor of 16, to control the frame period. In contrast,  FIGS. 2B and 2C  are diagrams for showing embodiments of this invention that include a data converter, as that shown in  FIG. 3A  below, to convert a binary input data into non-binary data to control the oscillation or positioning of the mirrors in an SLM, to further increase the gray scales of an image display device. The non-binary data is applied, as shown in  FIG. 2B , to control the mirrors to have an intermediate position. In  FIG. 2C , the non-binary data is applied to control the mirrors to have an intermediate state of oscillation. As will be further discussed below, the image display device therefore includes a controller to receive non-binary data to carry out an oscillation control or a positioning control. 
     An image display device according to a preferred embodiment of the present invention is an image display device using a spatial light modulator (SLM), and comprises: illuminating light incident to a deflective modulation element provided in the SLM; the deflective modulation element for deflecting the illuminating light, depending on the deflection state of the element itself; binary data according to an image signal; a data converting unit for converting at least N consecutive bits of the binary data into non-binary data; and a controlling unit for controlling the deflective modulation element with the non-binary data. 
     With the image display device having such a configuration, a weaker projected light, than that obtained from a stationary deflection state in a fully ON direction, may be obtained by using an oscillating state or a stationary intermediate state as the deflection state of the deflective modulation element. Additionally, the oscillating state can be controlled by the application of non-binary data. As a result, a display of higher gray scales can be achieved. 
       FIG. 2A  shows a control example of projected light in one frame period in a conventional image display device using an SLM having a deflective modulation element for deflecting illuminating light in a fully ON or a fully OFF stationary deflection direction. As shown in  FIG. 2A , with the conventional image display device, projected light in one frame period is controlled by controlling the deflection direction of the deflective modulation element according to the values of bits from LSB to MSB in binary data, and weighting factors respectively pre-assigned to the bits from LSB to MSB. Projected light is conventionally controlled by using binary data, which is the unchanged input data. 
       FIG. 2B  shows projected light in one frame period in an image display device according to a preferred embodiment of the present invention, which uses an SLM having a deflective modulation element for defecting illuminating light in a fully ON, a fully OFF, or an intermediate stationary deflection direction. The intermediate direction is a stationary direction between the fully ON direction and the fully OFF direction. The state of the intermediate stationary deflection direction is also referred to as an intermediate state. 
     As shown in  FIG. 2B , with the image display device according to this preferred embodiment, at least N consecutive bits of binary data, which is inputted data, is converted into non-binary data, and the remaining bits are left unchanged as binary data. In the example shown in  FIG. 2B , the lowest-order 3 bits of binary data, are converted into non-binary data, and the remaining highest-order 2 bits are left unchanged as binary data. The state of the deflection direction of the deflective modulation element is controlled to be fully ON or fully OFF, according to the values of the bits left unchanged as the binary data and the weighting factors pre-assigned to these bits, and controlled to be in the intermediate stationary deflection direction, according to the converted non-binary data. Specifically, in this preferred embodiment, projected light is controlled by converting part of the inputted data, binary data, into non-binary data and by using the non-binary data and the remaining binary data. 
       FIG. 2C  shows projected light in one frame period in an image display device according to a preferred embodiment of the present invention, which uses an SLM having a deflective modulation element for deflecting illuminating light in a fully ON direction, a fully OFF direction, or an oscillating state. The oscillating state is a state where the deflection direction temporally varies between the fully ON direction and the fully OFF direction. The oscillating state is also referred to as an intermediate state. 
     As shown in  FIG. 2C , in the image display device according to this preferred embodiment, the entire imputed binary data is converted into non-binary data. Then, the deflection direction of the deflective modulation element is controlled to be fully ON, fully OFF direction, or in the oscillating state, according to the converted non-binary data. More specifically, the deflection direction of the deflective modulation element is controlled to be continually fully ON or fully OFF by using non-binary data converted from consecutive binary data, and controlled to be continually in the oscillating state by using non-binary data converted from the remaining consecutive binary data. In this preferred embodiment, projected light is controlled by converting inputted binary data into non-binary data and by using the non-binary data. 
     In the control example shown in  FIG. 2B , the control of the intermediate state can be replaced with the control of the oscillating state shown in  FIG. 2C . Or, in the control example shown in  FIG. 2C , the control of the intermediate state can be replaced with the control of the state of the intermediate direction shown in  FIG. 2B . 
       FIG. 3A  is a functional block diagram illustrating a control system. The image signal  101  is received into the controller as digital data and stored into a memory  102 . The digital image data is then read into a data converter  103  to convert a part of or all of the digital image data into non-binary data for inputting to a spatial light modulator (SLM)  104  with drivers to receive the signal to control the deflective micromirrors. The controller further includes a controlling processor  105  for controlling the data converter  103  and the SLM  104 . 
     The above-described image display device according to the preferred embodiment of the present invention further comprises a light source to project a light which is deflected by the deflective modulation element. The light reflected by the deflective modulation element has a cross-section of a non-uniform intensity distribution, wherein a gray scale display can be made by using the deflection state of the deflective modulation element. 
     With the image display device implement the system configuration and control process, the projected light has a cross-section of a non-uniform intensity distribution is further used, wherein the amount of output light with less intensity can be extracted for controlling and projecting images with a higher level of gray scales. 
     In  FIG. 3A , a data converter  103  converts at least N consecutive bits of binary data into non-binary data under the control of a processor  105 . An SLM  104  drives a deflective modulation element under the control of the processor  105  according to non-binary data, converted from part of the binary data by the data converter  103 , and the remaining binary data, or according to non-binary data converted from entirety of the binary data, as described above. In this way, the SLM  104  can perform, the controls shown in  FIG. 2B  or  FIG. 2C . 
       FIG. 3B  is a cross-sectional view showing an example of a deflective modulation element arranged in the SLM  104  in the form of a two-dimensional array. In  FIG. 3B , a mirror element, which is a deflective modulation element, comprises a deflectable mirror  113  supported on a hinge  112  on a substrate  111 . The mirror  113  is protected by a cover glass  114 . On the substrate  111 , an OFF electrode  115 , an OFF stopper  115   a,  an ON electrode  116 , and an ON stopper  116   a  are arranged symmetrically about the hinge  112 . 
     By the application of a predetermined potential, the OFF electrode  115  tilts the mirror  113  to a position in which the mirror  113  contacts the OFF stopper  115   a  with a Coulomb force between the OFF electrode  115  and the mirror  113 . Consequently, incident light  117  is reflected by the mirror  113  towards the light path  118  of the OFF position, is not aligned with the optical axis of the projection optical system. The deflection state of the mirror element in this position is referred to as a fully OFF state or simply as an OFF state. 
     Similarly, with the application of a predetermined potential, a Coulomb force is generated, and the ON electrode  116  tilts the mirror  113  to a position in which the mirror  113  contacts the ON stopper  116   a.  Consequently, incident light  117  is reflected by the mirror  113  towards the light path  119  of the ON position, which is aligned with the optical axis of the projection optical system. The deflection state of the mirror element in this position is referred to as a fully ON state or merely as an ON state. 
     Stopping the application of the predetermined potential to the OFF electrode  115  or the ON electrode  116  causes the mirror  113  to start a free oscillation with the elasticity of the hinge  112 . As a result, the incident light  117  is reflected by the mirror  113  towards a light path (for example, a light path  120 ), which varies, with time, between the OFF light path  118  and the ON light path  119 . The deflection state of the mirror element in this case is referred to as an oscillating state. 
     By applying a first potential and a second potential, lower than the first potential, to the OFF electrode  115  and the ON electrode  116 , respectively, the OFF the mirror  113  is tilted with Coulomb force into a position on the side of the OFF electrode  115  but just before contacting the OFF stopper  115   a.  Since Coulomb force is exerted also between the mirror  113  and the ON electrode  116  at this time, the mirror  113  stops in a position before contacting the OFF stopper  115   a.  As a result, the incident light  117  is reflected by the mirror  113  towards a stationary light path (for example, the light path  120 ) between the OFF light path  118  and the ON light path  119 . The deflection state of the mirror element in this position is referred to as a state of an intermediate direction. 
       FIG. 4A  shows a prior art scheme for a PWM control using binary data, and  FIGS. 4B and 4C  show PWM control systems using non-binary data. 
     If PWM control is performed by using non-binary data, an image display device according to a preferred embodiment of the present invention can be also configured as follows. Specifically, the image display device using a spatial light modulator (SLM) comprises: illuminating light incident to a deflective modulation element provided in the SLM; a deflective modulation element for deflecting the illuminating light, depending on at least two deflection states of the element itself; binary data according to an image signal; a data converting unit for converting at least N consecutive bits of the binary data into non-binary data; and a controlling unit for controlling the deflective modulation element with the non-binary data, wherein the controlling unit controls the deflective modulation element so that the deflection state of the deflective modulation element is maintained continuously. 
     With the image display device having such a configuration, the following effects can also be expected when non-binary data is applied to a stationary deflection direction of the deflective modulation element: 
     1) An image display can be made by using sub-frames having the same display time, whereby the control unit can process the sub-frame data with a uniform throughput requirement (see  FIGS. 4B and 4C ). 
     2) A desired gray scale can be achieved in one or more continuing deflection states of the deflective modulation element, whereby the number of times the deflection states are switched, which can cause an error of a gray scale display, can be reduced or made uniform. Accordingly, the accuracy of gray scale display can be improved (see  FIGS. 4B and 4C ). 
       FIG. 4A  shows an example of PWM control performed with binary data in one frame period in a conventional image display device, using an SLM having a deflective modulation element for deflecting illuminating light in a fully ON direction or a fully OFF direction, and also shows an example of controlling the projected light shown in  FIG. 2A . As shown in  FIG. 4A , with the conventional image display device, one frame period is divided into a plurality of sub-frame periods having different times according to weighting factors pre-assigned to the bits from the LSB to MSB of inputted binary data, and the deflective modulation element is controlled to be in the fully ON direction or the fully OFF direction, according to the value of a corresponding bit in each of the sub-frame periods. With such a control, the deflection state switches six times (from the fully OFF direction to the fully ON direction, or vice versa), if the inputted binary data is “10101” of 5 bits shown in  FIG. 4A  (see Transition points of  FIG. 4A ). 
     In contrast,  FIG. 4B  shows an example of PWM control performed with non-binary data in one frame period in an image display device according to a preferred embodiment of the present invention, which uses an SLM having a deflective modulation element for deflecting illuminating light in a fully ON direction or a fully OFF direction, and also shows an example of controlling the projected light. With the image display device according to this preferred embodiment, the inputted binary data is converted into non-binary data. More specifically, data of the highest-order 2 bits in 5-bit binary data is converted into a bit string of 6 bits, all of which have a weighting factor of 4, and data of the remaining lowest-order 3 bits in the 5-bit binary data is converted into a bit string of 7 bits, all of which have a weighting factor of 1. Data obtained by converting the inputted binary data into data with one or more bit strings, where the weighting factors of bits are equal, is referred to as non-binary data. 
     Then, one frame period is divided into 13 sub-frame periods, composed of 6 sub-frame periods having a time t 1 , which corresponds to the weighting factor of 4, and 7 sub-frame periods having a time t 2 , which corresponds to the weighting factor of 1, according to the weighting factors of the bits of the non-binary data. The deflective modulation element is then controlled to continuously be in a fully ON direction or fully OFF direction, according to the value of the corresponding bit in the non-binary data in each of the sub-frame periods. With such a control, the deflection state is switched 4 times in the image display device according to this preferred embodiment, which is less than in the conventional image display device shown in  FIG. 4A . 
       FIG. 4C  shows another example of PWM control performed with non-binary data in one frame period in an image display device according to a preferred embodiment of the present invention, which uses an SLM having deflective modulation elements for deflecting illuminating light in a fully ON direction or the fully OFF direction, and also shows another example of controlling the projected light. Similar to the example show in  FIG. 4B , the inputted binary data is converted into non-binary data. More specifically, the inputted binary data of 5 consecutive bits is converted into a bit string where the weighting factors of all of bits are equal (not shown). For example, the binary data is converted into a bit string where the weighting factors of all of bits are 1. Then, one frame period is divided into a plurality of sub-frame periods according to the weighting factors of the bits of the non-binary data, and the deflective modulation element is controlled to continuously be in a fully ON direction or fully OFF direction, according to the value of the corresponding bit in the non-binary data in each of the sub-frame periods. With such a control, the deflection state is switched twice (see Transition points of  FIG. 4C ), which is less than in the conventional image display device shown in  FIG. 4A . 
       FIG. 5  is a control block diagram for illustrating a method to control illumination. 
     The above described image display device, according to the preferred embodiment of the present invention, can be also configured to further comprise a light source controlling unit for controlling the light intensity, the light emission cycle, or the light emission state, such as the intensity distribution, etc. of the illuminating light. 
     With the image display device having such a configuration, the intensity of projected light can be decreased when the deflective modulation element is in the oscillating state or in the state of the intermediate direction, thereby implementing a higher gray scale. 
       FIG. 5  shows a system configuration example of the image display device having such a configuration. The system configuration example shown in  FIG. 5  is a configuration implemented by adding a light source controlling circuit  130 , and a light source/optical system  131  to the system configuration example shown in  FIG. 3A . The light source controlling circuit  130  controls the light intensity, the light emission cycle, or the light emission state, such as the intensity distribution, etc. of illuminating light irradiated from the light source. 
       FIG. 6A  is a functional block diagram of an SLM, and  FIG. 6B  is a control circuit diagram that executes a Digital Signal Control scheme. 
     In the above described image display device, according to the preferred embodiment of the present invention, the controlling unit can be also configured to control the deflective modulation element with a digital control signal. 
     With the image display device having such a configuration, the oscillating state can be controlled by using non-binary data as a digital signal, without converting the digital signal into an analog signal with a D/A converter, etc. Performing the control by using non-binary data as a digital signal in this way is preferable in that it is not practical to configure the device with D/A converters, the number of which is equal to the number of bit lines (see  FIG. 6B ), when the pixel size of the deflective modulation element is increased. 
       FIG. 6A  shows a layout example of the internal configuration of the SLM comprising the image display device having such a configuration. In  FIG. 6A , the SLM (for example, the SLM  104 ) comprises a mirror element array  141 , which is a deflective modulation element array, column drivers  142 , row drivers  143 , a timing controller  144 , and a parallel/serial interface  145 . The timing controller  144  controls the row drivers  143  based on a digital control signal (from, for example, the processor  105 ). The parallel/serial interface  145  inputs a digital signal (from, for example, the data converter  103 ), incoming as a parallel signal, into a serial signal and feeds the signal to the column drivers  142 . In the mirror element array  141 , a plurality of mirror elements are arranged in positions where a bit line  146 , which extends from the column driver  142  in a vertical direction, intersects with a word line  147 , which extends from the row driver  143  in the horizontal direction. 
       FIG. 6B  is a conceptual diagram showing a configuration example of one of the mirror elements arrayed in the SLM. In  FIG. 6B , an OFF capacitor  151   b  is connected to an OFF electrode  151  (corresponding, to the OFF electrode  115  of  FIG. 3B ) and also connected to a bit line  146 - 1  and a word line  147  via a gate transistor  151   c.  Additionally, an ON capacitor  152   b  is connected to an ON electrode  152  (corresponding to the ON electrode  116  of  FIG. 3B ) and also connected to a bit line  146 - 2  and the word line  147  via a gate transistor  152   c.  The opening/closing of the gate transistors  151   c  and  152   c  is controlled by the word line  147 . Specifically, consecutive mirror elements in a row in an arbitrary word line  147  are simultaneously selected, and the charge/discharge of the OFF capacitor  151   b  and the ON capacitor  152   b  is controlled by the bit lines  146 - 1  and  146 - 2 , and the ON/OFF states of the mirror  153  in each of the mirror elements in the row is individually controlled. 
     In the above described image display device, according to the preferred embodiment of the present invention, non-binary data is also configured to be decimal data. Additionally, in the above described image display device, the weighting factor of the least significant bit of binary data of at least N consecutive bits, which is converted into non-binary data, can be configured to be equal to the weighting factor of the smallest bit of the non-binary data, specifically, to make the display period of the least significant bit of the binary data of N bits equal to the smallest display period of the non-binary data. This is shown in the control example of  FIG. 4B . 
       FIGS. 7A and 7B  show another preferred embodiment, where the N bits represent the difference between the number of bits of incoming image signal and the number of bits to display in gray scale. 
     If the number of input bits of an image signal is different from that of display gray scales, the above described image display device can be also configured to implement at least N consecutive bits of binary data, which is converted into non-binary data used when the deflective modulation element is controlled to be in the oscillating state, as the number of bits of the difference between the number of input bits of the image signal and the number of bits of the display gray scales, or configured to include the number of bits of the difference. 
       FIG. 7A  shows an example of controlling the projected light in one frame period in the image display device having such a configuration. Assuming that the number of input bits of an image signal and the number of bits of display gray scales are 10 and 7, respectively, the difference between them is 3 bits. In this case, at least 3 consecutive bits of the inputted binary data are converted into non-binary data, used when the deflective modulation element is controlled to be in the oscillating state. Additionally, the remaining bits of the inputted binary data are left unchanged as the binary data. 
     In the example shown in  FIG. 7A , the lowest-order 3 bits of the inputted binary data are converted into non-binary data and the remaining 7 bits are left unchanged as the binary data. Then, the deflective modulation element is controlled to be in the fully ON direction or the fully OFF direction, according to the values of the bits left unchanged as the binary data and the weighting factors pre-assigned to these bits, or controlled to be in the oscillating state, according to the converted non-binary data. In this way, projected light in one frame period is controlled. Here, the non-binary data can be also implemented, for example, as decimal data. 
       FIG. 7B  shows another example of control in a case where the difference between the number of input bits of an image signal and the number of bits of display gray scales is 3, similar to the example shown in  FIG. 7A . In this control example, the entirety of the inputted binary data is converted into non-binary data to control the deflection state of the deflective modulation element. Note that the deflective modulation element is controlled to be fully ON, according to the non-binary data converted from the highest-order 7 bits of the inputted binary data and controlled to be in the oscillating state, according to non-binary data converted from the lowest-order 3 bits of the inputted binary data. Here, the non-binary data can be also implemented, for example, as decimal data. 
     In the above described image display device according to the preferred embodiment of the present invention, the intensity distribution of illuminating light can be also made non-uniform. Furthermore, the above described image display device can be also configured to change the light intensity or the intensity distribution of the illuminating light, when a control according to non-binary data is performed. 
       FIG. 8A  is a pulse width diagram of a control signal for an SLM, with corresponding light intensity in a frame period, and  FIG. 8B  is a control circuit diagram that implements illumination light from a semiconductor laser source or LED light source. 
     The above described image display device, according to the preferred embodiment of the present invention, can be also configured to implement the illumination light as light from a semiconductor laser light source, or light from an LED light source. 
       FIG. 8A  shows an example of controlling the projected light in one frame period in the image display device having such a configuration. In  FIG. 8A , the operations of the mirror element, is shown in the top section, and examples of two different patterns of light emission made by a semiconductor laser light source are shown in the middle and bottom sections. In the image display device, according to this preferred embodiment, part of the inputted binary data is converted into non-binary data, and the remaining binary data is left unchanged as the binary data. As shown in the top section of  FIG. 8A , the deflection state of the mirror element is controlled to be in the fully ON direction (+X o ) or the fully OFF direction (−X o ) according to the remaining binary data, and controlled to be the oscillating state (+X o ˜−X o ) according to the non-binary data. Additionally, as shown in the middle and bottom sections of  FIG. 8A , the intensity of output light and the light emission time of the semiconductor laser light source are controlled simultaneously with the deflection state of the mirror element. Note that in the example of the light emission pattern shown in the bottom section of  FIG. 8A , the intensity of output light when the mirror element is controlled in the oscillating state is less than that in the light emission pattern shown in the middle section. 
     The system configuration example shown in  FIG. 8B  is a configuration implemented by adding a light source controlling circuit  160 , a light source driving circuit  161 , and a semiconductor laser light source  162  or an LED light source  163  to the system configuration example shown in  FIG. 3A . The light source controlling circuit  160  controls the light source driving circuit  161  under the control of the processor  105 . The light source driving circuit  161  drives the semiconductor laser light source  162  or the LED light source  163 , which serves as the source of the illumination light, under the control of the light source controlling circuit  160 . With such a configuration, the control of the mirror element and the light emission patterns shown in  FIG. 8A  can be performed. 
       FIG. 9  is a digital circuit diagram to carry out a function of non-binary data conversion process. In the above described image display device, according to the preferred embodiment of the present invention, the data converting unit can be configured with a digital circuit. 
     The system configuration example shown in  FIG. 9  is a configuration implemented by adding a counter  171  to the above described system configuration example shown in  FIG. 3A , and by making the data converter  103  comprise a bit comparator  103   a  and a digital computing circuit  103   b,  as digital circuits. The counter  171  performs a count operation under the control of the processor  105 . The bit comparator  103   a  makes a comparison between the inputted binary data and the count value of the counter  171 , and outputs the result of the comparison to the digital computing circuit  103   b  as a digital signal of “H(1)” or “L(0)”. The digital computing circuit  103   b  generates non-binary data from the result of the comparison made by the bit comparator  103   a  with a digital computation process and outputs the generated data. 
     In the above described image display device, the data converting unit can also be configured to have a correction function on an image signal and to convert the image signal into non-binary data, on which a correction made by the correction function is reflected. Here, the correction function is, for example, a function to make a γ removal or a γ correction of the image signal. Or, the correction function may correct the intensity or the intensity distribution of light modulated by the deflective modulation element. Alternately, the correction function may also make visual corrections of an image signal, such as a quantization error in image signal processing, an error of opto-electric conversion made by the deflective modulation element, a uniformity error and the false contour of illuminating light, dithering, IP conversion (Interlace Progressive conversion), scaling, a dynamic range change, etc. 
       FIG. 10  shows a system configuration example of the image display device having such a configuration. The system configuration example shown in  FIG. 10  is a configuration implemented by further comprising the data converter  103  with a correction circuit  181  in the system configuration example shown in  FIG. 9 . The correction circuit  181  makes the above described corrections to the inputted binary data under the control of the processor  105 , and outputs the corrected binary data to the bit comparator  103   a  in the next step. 
     In the above described image display device, the data converting unit can also be configured to have a gray scale conversion function to improve the gray scale of binary data. Here, the gray scale conversion function is, for example, a function to convert 8-bit binary data into 10-bit binary data. 
     In the above described image display device, non-binary data, which is converted by the data converting unit, can also be configured to be directly transferred to the SLM, or transferred to the SLM via a memory. If the non-binary data is transferred via a memory, it is preferable that the memory has a capacity equivalent to or greater than the number of deflective modulation elements of the SLM. 
       FIG. 11  shows a system configuration example of an image display device configured to transfer non-binary data via a memory. In  FIG. 11 , the system configuration example shown in  FIG. 9  is further comprised of a buffer memory  191  between the data converter  103  and the SLM  104 . With this configuration, non-binary data converted by the data converter  103  is transferred to the SLM  104  via the buffer memory  191 . It is preferable that the buffer memory  191  has a capacity equivalent to or greater than the number of deflective modulation elements which are comprised in the SLM  104 . The capacity of the buffer memory  191  can be reduced according to the processing speed of the data converter  103  and the display rate of the SLM  104 . 
     In the above described image display device, according to the preferred embodiment of the present invention, the controlling unit can also be configured to feed a mode signal, for determining the deflection state of the deflective modulation element, to the SLM. 
       FIG. 12  shows a system configuration example of the image display device having such a configuration. In  FIG. 12 , the system configuration example shown in  FIG. 9  is further configured by causing the processor  105  to feed the mode signal to the SLM  104 . With this configuration, the deflection states of the deflective modulation elements in the SLM  104  are controlled according to the mode signal and non-binary data converted by the data converter  103 . As a result, data to be transferred to the ON capacitor  152   b  and/or the OFF capacitor  151   b  of each mirror element in the SLM  104  is fed from the data converter  103  to the SLM  104 , whereby the deflection state of the deflective modulation element can be controlled, and the amount of fed data can be reduced. 
     The above described image display device according to the preferred embodiment of the present invention can be also configured as a single-panel image display device comprising one SLM, or a multi-panel image display device comprising a plurality of SLMs. 
       FIG. 13  shows an optical configuration example of a single-panel image display device according to a preferred embodiment of the present invention. In  FIG. 13 , the single-panel image display device comprises one SLM  104 , a processor  105 , a TIR (Total Internal Reflection) prism  203 , a projection optical system  204 , and a light source optical system  205 . The SLM  104  and the TIR prism  203  are arranged on the optical axis of the projection optical system  204 , and the light source optical system  205  is arranged so that its optical axis is orthogonal to that of the projection optical system  204 . 
     The TIR prism  203  directs the illumination light  206 , which is incident from the light source optical system  205 , to the SLM  104  at a predetermined tilt angle as incident light  207 . The TIR prism  203  further directs the reflection light  208 , reflected by the SLM  104 , towards the projection optical system  204 . The projection optical system  204  projects the reflection light  208 , incoming via the SLM  104  and the TIR prism  203 , onto a screen  210  as projected light  209 . 
     The light source optical system  205  includes a variable light source  211  for generating the illumination light  206 , a condenser lens  212 , for concentrating the illumination light  206 , a rod integrator  213 , and a condenser lens  214 . The variable light source  211 , the condenser lens  212 , the rod integrator  213 , and the condenser lens  214  are arranged on the optical axis of the illumination light  206 , which is emitted from the variable light source  211  and incident to the side of the TIR prism  203 . 
     In the optical configuration example shown in  FIG. 13 , a color display on the screen  210  can be projected with a color sequential method by using one SLM  104 . In this case, the variable light source  211  is configured with a red laser light source, a green laser light source, and a blue laser light source, the light emission states of which can be independently controlled. One frame of display data is divided into a plurality of sub-fields (3 sub-fields respectively corresponding to R (Red), G (Green), and B (Blue) in this case), and the red, green, and blue laser light sources sequentially emit light for durations corresponding to the sub-fields of each color. 
       FIGS. 14A ,  14 B, and  14 C show an optical configuration example of a two-panel image display device according to a preferred embodiment of the present invention.  FIG. 14A  is the side view;  FIG. 14B  is the front view; and  FIG. 14C  is the rear view. In  FIGS. 14A ,  14 B, and  14 C, the same constituent elements as those shown in  FIG. 13  are denoted with the same reference numerals. However, the variable light source  211  is depicted independently of the light source optical system  205  in this example. 
     The optical configuration example shown in  FIGS. 14A ,  14 B, and  14 C includes a device package  104 A, where two SLMs  104  are mounted together, a color synthesis optical system  221 , a light source optical system  205 , and a variable light source  211 . The two SLMs mounted in the device package  104 A are fixed so that their rectangular outlines tilt almost at 45 degrees on a horizontal plane with reference to each side of the rectangular device package  104 A. 
     Above the device package  104 A, the color synthesis optical system  221  is arranged. The color synthesis optical system  221  is composed of prisms  221   b  and  221   c,  right-angled triangular columns, which are joined to form a triangle in which the two hypotenuses are equal, and an optical guide block  221   a,  in the form of a right-angled triangle joined on its hypotenuse to the hypotenuses of the prisms  221   b  and  221   c.  In the prisms  221   b  and  221   c,  a light absorber  222  is provided on the side opposite the side on which the optical guide block  221   a  is joined. On the bottom of the optical guide block  221   a,  a light source optical system  205  of a green laser light source  211   a  and a light source optical system  205  of a red laser light source  211   b  and a blue laser light source  211   c  are provided with their optical axes vertical to the bottom of the optical guide block  221   a.    
     Illumination light emitted from the green laser light source  211   a  is incident, as incident light  207 , to one of the SLMs  104 , which is positioned immediately below the prism  221   b,  via the optical guide block  221   a  and the prism  221   b.  Illumination lights emitted from the red laser light source  221   b  and the blue laser light source  211   c  are incident, as incident lights  207 , to the other SLM  104 , which is positioned immediately below the prism  221   c,  via the optical guide block  221   a  and the prism  221   c.    
     When the deflective modulation element is in the fully ON state, the red and the blue incident lights  207 , incident to the SLM  104 , are reflected within the prism  221   c  vertically upward as reflection light  208 , further reflected on the outer side of the prism  221   c  and the joining face, are incident to the projection optical system  204 , and result in projected light  209 . When the deflective modulation element is in the fully ON state, the green incident light  207 , incident to the SLM  104 , is reflected within the prism  221   b  vertically upward as reflection light  208 , further reflected on the outer side of the prism  221   b,  and is incident to the projection optical system  204  with the same optical path as the green and the blue reflection light  208 , resulting in the projection light  209 . 
     As described above, in the optical configuration example shown in  FIGS. 14A ,  14 B, and  14 C, the incident light  207  from the green laser light source  211   a  is irradiated onto one of the SLMs  104  included in the device package  104 A. The incident light  207  from either or both of the red laser light source  211   b  and the blue laser slight source  211   c  is irradiated onto the other SLM  104 . The lights respectively modulated by the two SLMs  104  are concentrated within the color synthesis optical system  221 , enlarged by the projection optical system  204 , and projected onto a screen as projected light  209 , as described above. 
       FIG. 15  shows an optical configuration example of a three-panel image display device according to a preferred embodiment of the present invention. Also in  FIG. 15 , the same constituent elements as those shown in  FIG. 13  are denoted with the same reference numerals. The three-panel image display device according to this preferred embodiment comprises three SLMs  104 , and a light separation/synthesis optical system  231  is arranged between the projection optical system  204  and each of the three SLMs  104 . 
     The light separation/synthesis optical system  231  is composed of three TIR prisms  231   a,    231   b,  and  231   c.  The TIR prism  231   a  guides the illumination light  206 , which is incident from the side face of the optical axis of the projection optical system  204 , to the side of the SLM  104  as incident light  207 . The TIR prism  231   b  separates red (R) light from the incident light  207 , incoming via the TIR prism  231   a,  and directs the red reflection light  208  to the TIR prism  231  a. Similarly, the TIR prism  231   c  separates blue (B) and green (G) lights from the incident light  207 , incoming via the TIR prism  213   a,  and directs their reflection lights  208  to the TIR prism  231   a.  Accordingly, spatial light modulations for the three colors R, G, and B are simultaneously modulated, and the reflection lights  208 , resultant from the modulations, become projected light  209  via the projection optical system  204  and are projected onto the screen  210  as a color display. 
     Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosures are not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.