Patent Publication Number: US-8994764-B2

Title: Image display apparatus and image display method

Description:
This application claims priority to Japanese Patent Application No. 2010-070283, filed on Mar. 25, 2010, the entirety of which is hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image display apparatus and an image display method. 
     2. Related Art 
     In a projection-type image display apparatus of such as a projector, in the case where the image display apparatus includes light modulation devices such as liquid crystal light valves, the resolution of an image projected on a screen is typically equal to the resolution of the light modulation devices (the number of horizontal pixels, the number of vertical pixels). In the following explanation, “resolution of image projected on screen” will be referred to as “display resolution”. Here, as a method of improving the display resolution without changing the resolution of the light modulation devices, there is a method of increasing the number of light modulation devices and performing projection while shifting the positions of the images of the respective pixels formed by the respective light modulation devices on the screen. However, according to the method, it is necessary to increase the number of light modulation devices, and there is a problem that significant increase in costs is caused. 
     As a method of solving the problem, a method of shifting the positions of the images of the respective pixels not spatially but along the temporal axis has been proposed (for example, see Patent Documents 1, 2 (JP-A-11-298829, JP-A-2005-91519)). According to the method, it is unnecessary to increase the number of light modulation devices. In Patent Document 1, as a specific example, a configuration in which a parallel plate is inserted between the light modulation devices and a projection lens at a tilt relative to the normal line of the optical axis, the optical axis is shifted with respect to each field by changing the tilt angle of the parallel plate, and the positions of the pixels are temporally shifted has been proposed. As another specific example, a configuration in which a rotating plate having two regions different in refractive index or amount of refraction is obliquely inserted between the light modulation devices and the projection lens, the optical axis is shifted by rotating the rotating plate, and the positions of the images of the pixels are temporally shifted has been proposed. 
     Note that, in the following explanation, temporal (temporal axis) shift of the positions of the images of the respective pixels on a projection surface may be referred to as “temporal axis pixel shift” for convenience. 
     However, as in Patent Documents 1, 2, the image display apparatus in related art of employing the temporal axis pixel shift technology constantly performs display while shifting the positions of the images of the respective pixels along the temporal axis regardless of contents of externally input images. The temporal axis pixel shift technology is to improve the display resolution by displaying images for one frame in the shifted positions using two frames for pixel shift, for example. In other words, the temporal axis pixel shift technology is a technology of improving the spatial resolution at the expense of the temporal resolution. Therefore, the technology is suitable for still images having no temporal frequency components, but not suitable for moving images having temporal frequency components. For example, deterioration of image quality such that images moving at a high speed blur may be caused. 
     Further, in the apparatus of Patent Document 2, as means for reducing blur of the images, a technology of inserting a frame for black representation between plural frames for image display has been disclosed. However, in the case of using the technology, there is a problem that the brightness of display is deteriorated by the insertion of the black representation. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide an image display apparatus and an image display method that can improve display resolution of still images while preventing image quality deterioration of moving images such that the moving images blur or become darker. 
     An image display apparatus according to an aspect of the invention includes a light source that outputs light, a light modulation device that has plural pixels arranged in a matrix and modulates the light from the light source, a projection system that projects the light modulated by the light modulation device onto a projection surface, a pixel image shift unit that can shift positions of images of the pixels of the light modulation device projected on the projection surface, and a control unit that controls the light modulation device and the pixel image shift unit, wherein the control unit can switch whether the pixel image shift unit temporally shifts the positions of the images of the pixels or not. 
     Further, it is desirable that the control unit controls the pixel image shift unit to temporally shift the positions of the images of the pixels on the projection surface if images to be displayed are still images and not to temporally shift the positions of the images of the pixels on the projection surface if the images to be displayed are moving images. 
     The image display apparatus according to the aspect of the invention switches use or nonuse of the temporal axis pixel shift technology according to whether the images to be displayed are still images or moving images. That is, according to the image display apparatus of the aspect of the invention, the control unit can switch whether the pixel image shift unit temporally shifts the positions of the images of the pixels or not. More specifically, the control unit controls the pixel image shift unit to temporally shift the positions of the images of the pixels on the projection surface if the images to be displayed are still images, and display resolution of the still images may be improved. On the other hand, the unit controls the pixel image shift unit not to temporally shift the positions of the images of the pixels on the projection surface if the images to be displayed are moving images, and image deterioration of blur of the moving images or the like may be suppressed and smooth moving images may be represented. Further, the smooth moving images may be represented without insertion of frames of black representation, and thus, the display does not become darker. 
     In the image display apparatus according to the aspect of the invention, a configuration in which the control unit controls the pixel image shift unit to temporally shift the positions of the images of the pixels on the projection surface constantly unless images to be displayed are determined to be moving images may be employed. 
     According to the configuration, the temporal axis pixel shift function is basically performed and the temporal axis pixel shift function is stopped only when the control unit determines that the images are moving images, and therefore, the temporal axis pixel shift function may be exerted at the maximum and the display resolution may sufficiently be improved. 
     In the image display apparatus according to the aspect of the invention, the control unit may include an image determination part that compares respective image data input in plural frames and determines whether images to be displayed are still images or moving images, and the image determination part may output a control signal to the pixel image shift unit based on a determination result of itself. 
     According to the configuration, the image determination part may determine the use or nonuse of the temporal axis pixel shift function using normal image data. It is not necessary to prepare special image data. 
     Alternatively, in the image display apparatus according to the aspect of the invention, the control unit may include an image determination part that acquires still image/moving image information previously contained in input image data, and determines whether images to be displayed are still images or moving images from the still image/moving image information, and the image determination part may output a control signal to the pixel image shift unit based on a determination result of itself. 
     According to the configuration, it is necessary to prepare image data previously containing the still image/moving image information, however, means for comparing image data of plural frames and determining whether the images are still images or moving images (for example, a frame memory and a computation part) are not necessary, and the load on the apparatus may be reduced and the configuration of the control unit may be simplified. 
     In the image display apparatus according to the aspect of the invention, the control unit controls the pixel image shift unit to temporally shift the positions of the images of the pixels on the projection surface if resolution of images to be displayed is higher than resolution of the light modulation device and not to temporally shift the positions of the images of the pixels on the projection surface if the resolution of the images to be displayed is equal to or lower than the resolution of the light modulation device. 
     According to the configuration, the resolution of the images to be displayed and the resolution of the light modulation device may be compared, and the temporal axis pixel shift function may be determined to be effective and the function may be performed only if the resolution of the images to be displayed is higher than the resolution of the light modulation device. 
     An image display method according to another aspect of the invention is an image display method using an image display apparatus including a light source that outputs light, a light modulation device that has plural pixels arranged in a matrix and modulates the light from the light source, a projection system that projects the light modulated by the light modulation device onto a projection surface, and a pixel image shift unit that shifts positions of images of the pixels of the light modulation device projected on the projection surface, and the method includes controlling the pixel image shift unit to temporally shift the positions of the images of the pixels on the projection surface if images to be displayed are still images and not to temporally shift the positions of the images of the pixels on the projection surface if the images to be displayed are moving images. 
     According to the image display method of the aspect of the invention, the positions of the images of the pixels on the projection surface are temporally shifted if the images to be displayed are still images, and display resolution of the still images may be improved. On the other hand, the positions of the images of the pixels on the projection surface are not temporally shifted if the images to be displayed are moving images, and image deterioration of blur of the moving images or the like may be suppressed and smooth moving images may be represented. Further, it is not necessary to insert frame of black representation, and thus, the display does not become darker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic configuration diagram of a projector of a first embodiment of the invention. 
         FIG. 2  shows a state of optical axis shift when a light transmissive plate is driven. 
         FIG. 3  is a conceptual diagram of shifted positions of pixel images. 
         FIG. 4  is a block diagram showing a schematic configuration of a control unit of the projector of the embodiment. 
         FIG. 5  is a block diagram showing a schematic configuration of a determination part within the control unit of the embodiment. 
         FIG. 6  is a flowchart showing a flow of processing of the control unit of the embodiment. 
         FIG. 7  is a block diagram showing a schematic configuration of a determination part within a control unit of a projector of a second embodiment of the invention. 
         FIG. 8  is a flowchart showing a flow of processing of the control unit of the embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
     Hereinafter, the first embodiment of the invention will be explained using  FIGS. 1 to 6 . 
     An image display apparatus of the embodiment is a configuration example of the so-called 3LCD projector having three liquid crystal light valves. 
       FIG. 1  is a schematic configuration diagram of the projector of the embodiment.  FIG. 2  shows a state of optical axis shift when a light transmissive plate is driven.  FIG. 3  is a conceptual diagram of shifted positions of pixel images.  FIG. 4  is a block diagram showing a schematic configuration of a control unit.  FIG. 5  is a block diagram showing a schematic configuration of a determination part within the control unit.  FIG. 6  is a flowchart showing a flow of processing of the control unit. 
     Note that, in the respective following drawings, the ratios and scales of dimensions may be differed depending on component elements for facilitating visualization of the component elements. 
     The projector  1  (image display apparatus) of the embodiment includes an illumination system  2 , liquid crystal light valves  3 R,  3 G,  3 B (light modulation devices), a cross dichroic prism  4  (light combining system), a projection lens (projection system), etc. as shown in  FIG. 1 . The illumination system  2  of the embodiment includes a light source  7 , a pair of fly-eye lens arrays  8  sequentially arranged at the downstream of the light source  7 , a polarization conversion element  9 , dichroic mirrors  10 ,  11 , etc. The light source  7  includes a white lamp  12  such as a high-pressure mercury lamp or a metal halide lamp, and a reflector  13  that reflects light of the white lamp  12  and outputs it forward. Accordingly, from the white lamp  12 , white light containing red light (R-light), green light (G-light), blue light (B-light), i.e., plural color lights of different colors is output. 
     The pair of fly-eye lens arrays  8  homogenize the distribution of light intensity of light output from the light source  7 . Thereby, the illuminance distribution of light radiated on the liquid crystal light valves  3 R,  3 G,  3 B as illuminated areas are homogenized. 
     The polarization conversion element  9  includes a polarization beam splitter array (PBS array) and a half wave plate array though its detailed structure is not shown. Of the lights entering the PBS array from the fly-eye lens arrays  8 , a linearly-polarized light in a first polarization direction is transmitted through a polarization separation layer (PBS layer) within the PBS array and a linearly-polarized light in a second polarization direction is reflected by the PBS layer within the PBS array. The reflected polarized light is output with its polarization direction changed in the first polarization direction by the half wave plate array. As described above, the polarization conversion element  9  is formed so that the polarization directions of the light source lights may be aligned in one direction without loss of the amount of the light source lights. 
     The dichroic mirrors  10 ,  11  are formed by stacking dielectric multilayer films on glass surfaces, for example. Thereby, the color lights in a predetermined wavelength band are selectively reflected and the color lights in other wavelength bands are transmitted. Specifically, of the light source lights output from the light source  7 , the red light LR is transmitted through the dichroic mirror  10 , and the green light LG and the blue light LB are reflected by the dichroic mirror  10 . Further, of the green light LG and the blue light LB reflected by the dichroic mirror  10 , the blue light LB is transmitted through the dichroic mirror  11  and the green light LG is reflected by the dichroic mirror  11 . 
     The red light LR transmitted through the dichroic mirror  10  is reflected by a reflection mirror  15  and enters the liquid crystal light valve  3 R for red light through a parallelizing lens  16 . The green light LG reflected by the dichroic mirror  11  enters the liquid crystal light valve  3 G for green light through a parallelizing lens  16 . The blue light LB transmitted through the dichroic mirror  11  enters the liquid crystal light valve  3 B for blue light through a relay system  17 . The relay system  17  includes a relay lens  18 , a reflection mirror  19 , a relay lens  20 , a reflection mirror  21 , a relay lens  22 , etc. sequentially arranged from the dichroic mirror  11  side. The relay lens  22  also functions as a parallelizing lens. In the case of the blue light, the optical path from the light source  7  to the liquid crystal light valve  3 B is longer than those of the other color lights, and the relay system  17  is provided to prevent light loss due to the longer optical path. 
     Each of the liquid crystal light valves  3 R,  3 G,  3 B includes a transmissive liquid crystal cell  24  and polarizers  25 ,  26  respectively provided at the light incident side and the light exit side thereof. The transmissive liquid crystal cell  24  is of active matrix type, for example, and has a liquid crystal layer sandwiched between a pair of electrodes. Further, the liquid crystal light valves  3 R,  3 G,  3 B are electrically connected to a signal source that supplies image signals. When image signals are supplied from the signal source, voltages are applied between the electrodes of the transmissive liquid crystal cells  24  and orientation directions of liquid crystal molecules are controlled in response to the applied voltages. Thereby, lights can be modulated. The red light LR, the green light LG, and the blue light LB modulated by the respective liquid crystal light valves  3 R,  3 G,  3 B enter the cross dichroic prism  4 . 
     The cross dichroic prism  4  has a structure formed by bonding triangular prisms to have a selective reflection surface by which the red light LR is reflected and the green light LG and the blue light LB are transmitted and a selective reflection surface by which the blue light LB is reflected and the red light LR and the green light LG are transmitted orthogonal to each other on the inner surfaces. The red light LR and the blue light LB are selectively reflected by these selective reflection surfaces, the green light LG is selectively transmitted through the selective reflection surfaces, and the three color lights are output to the same side. Thereby, the three color lights are superimposed to form a combined light L. 
     The combined light L output from the cross dichroic prism  4  is enlarged and projected onto a screen  28  (projection surface) by the projection lens  5  containing plural lens groups. Further, in the embodiment, a wobbling device  29  (pixel image shift unit) is provided between the cross dichroic prism  4  and the projection lens  5 . The wobbling device  29  temporally shifts the positions of the images of the respective pixels of the liquid crystal light valves  3 R,  3 G,  3 B projected on the screen  28 . In the embodiment, as an example of the wobbling device  29 , a light transmissive plate  30  is used. 
     The light transmissive plate  30  produces refraction inside when the light is transmitted and shifts the optical axis of the transmitted light, and includes a parallel plate formed from a material having light transmissivity such as glass, for example. Further, a drive unit  31  that drives the light transmissive plate  30  to change the tilt of the light transmissive plate  30  in a direction of an arrow A is provided. The drive unit  31  drives the light transmissive plate  30  so that the angle formed by the light-incident surface of the light transmissive plate  30  and a surface perpendicular to the optical axis of the projection lens  5  may temporally change. Specifically, the drive unit  31  is adapted to switch the angle formed by the light-incident surface of the light transmissive plate  30  and the surface perpendicular to the optical axis of the projection lens  5  between a first angle θ 1  and a second angle θ 2  at 120 Hz. For the drive unit  31 , for example, a piezoelectric device may be used. Further, a control unit  32  that controls the respective liquid crystal light valves  3 R,  3 G,  3 B and the drive unit  31  is provided. 
     An action when the tilt of the light transmissive plate  30  changes is shown in  FIG. 2 . Note that, in  FIG. 2 , for simplicity of the drawing, the projection lens  5  is shown as one lens. First, if a light-incident surface  30   a  of the light transmissive plate  30  is perpendicular to the optical axis G of the projection lens  5  as shown by solid lines, the light L output from the cross dichroic prism  4  perpendicularly enters the light-incident surface  30   a  of the light transmissive plate  30  and is perpendicularly output from a light-exiting surface  30   b , and the light L is not refracted by the light transmissive plate  30  and the position of the optical axis of the transmitted light does not shift between the upstream and the downstream of the light transmissive plate  30 . Then, when the light-incident surface  30   a  of the light transmissive plate  30  is tilted relative to the optical axis of the projection lens  5  as shown by chain double-dashed lines, the light output from the cross dichroic prism  4  enters the light-incident surface  30   a  of the light transmissive plate  30  at an angle other than a right angle, refraction is produced, and further, the light enters the light-exiting surface  30   b  at an angle other than a right angle, and is refracted and output. Accordingly, the position of the optical axis of the transmitted light shifts by a distance ΔX in response to the tilt angle between the upstream and the downstream of the light transmissive plate  30 . 
       FIG. 3  shows a state in which images of pixels projected on the screen  28  shift. In the embodiment, the images includes images of one frame rewritten at 60 Hz (i.e., one frame = 1/60 seconds), and the light transmissive plate  30  is switched between the above described first angle θ 1  and second angle θ 2  at 120 Hz. In this regard, as shown in  FIG. 3 , the lattice including plural pixel images located in solid lines at arbitrary 1/120 seconds (this is referred to as the first field) shifts to the position shown by broken lines at the next 1/120 seconds (this is referred to as the second field). The plural pixel images are arranged in the horizontal direction and the vertical direction of the screen  28 , and it is desirable that the shift direction is oblique relative to the arrangement direction of the pixel images. Further, it is desirable that the shift distance ΔX 1  is set to a half of the length of the diagonal line of one lattice. In this manner, the images located in the first field are rewritten at 60 Hz, and the images located in the position of the second field, which is shifted from the position of the first field, are also rewritten at 60 Hz. In this regard, the eyes of an observer fail to recognize the slight position change of the pixel images at 120 Hz, and thus, the observer may obtain feeling of improvement of the display resolution. 
     As below, a configuration of the control unit  32  will be explained. 
     As shown in  FIG. 4 , the control unit  32  has a temporal axis pixel shift on-off function determination part  33  (hereinafter, simply referred to as “determination part”, an image determination part), a first display image data generation part  34 , and a second display image data generation part  35 . The determination part  33  determines whether images to be displayed are still images or moving images based on input image signals. Further, the determination part  33  outputs a control signal that allows one of the first display image data generation part  34  and the second display image data generation part  35 , which will be described later, to generate image data (signals for modulation) based on a determination result of itself. The control unit  32  controls the drive unit  31  of the wobbling device  29  to constantly perform temporal axis pixel shift unless the images to be displayed are determined to be moving images. 
     Note that, in the block diagram of  FIG. 4 , for simplicity of the drawing, the part of the optical system from the light source  7  to the cross dichroic prism  4  in  FIG. 1  is collectively shown as a light valve unit  36  (L/V unit). 
     The first display image data generation part  34  generates image data, i.e., signals for modulation when display is performed without the temporal axis pixel shift. Therefore, the first display image data generation part  34  generates signals for modulation to be supplied to the respective liquid crystal light valves  3 R,  3 G,  3 B based on the input image signals like a display image data generation part that an existing projector without the pixel shift function has. 
     The second display image data generation part  35  generates image data, i.e., signals for modulation when display is performed with the temporal axis pixel shift. The second display image data generation part  35  has a timing generation circuit and an image processing circuit (not shown). The timing generation circuit generates timing signals indicating the start time of the first field and the start time of the second field, and output them to the drive unit  31  and the image processing circuit. The image processing circuit generates signals for first modulation for the first field and signals for second modulation for the second field based on the image signals. The image processing circuit supplies the signals for first modulation to the respective liquid crystal light valves  3 R,  3 G,  3 B in synchronization with the display timing of the images of the first field determined by the timing signal and supplies the signals for second modulation to the respective liquid crystal light valves  3 R,  3 G,  3 B in synchronization with the display timing of the images of the second field determined by the timing signal. 
     As shown in  FIG. 5 , the determination part  33  of the embodiment has a display image size acquisition part  38 , a temporal axis pixel shift on-off function first determination computation part  39  (hereinafter, simply referred to as “first determination computation part”), a plural frame securement part  40 , and a temporal axis pixel shift on-off function second determination computation part  41  (hereinafter, simply referred to as “second determination computation part”). The display image size acquisition part  38  acquires sizes of the images to be displayed based on the input image signals. The first determination computation part  39  computes a difference between the predetermined resolution of the liquid crystal light valves  3 R,  3 G,  3 B and the resolution of the input image signals and compares them. The plural frame securement part  40  includes a frame memory etc., for example, and secures image signals of plural frames. The second determination computation part  41  computes a color difference between image signals of temporally adjacent two frames secured by the plural frame securement part  40 . 
     Here, a flow of the processing of the control unit  32  will be explained with reference to  FIG. 6 . 
     First, the display image size acquisition part  38  acquires the sizes of the images to be displayed based on the input image signals, and outputs the acquisition result of the image size to the first determination computation part  39  (step S 1  in  FIG. 6 ). 
     Then, the first determination computation part  39  computes a difference between the image size input from the display image size acquisition part  38 , i.e., the resolution of the images and the resolution of the liquid crystal light valves  3 R,  3 G,  3 B stored in advance and compares them (step S 2  in  FIG. 6 ). 
     As a result of comparison between the resolution of the images and the resolution of the liquid crystal light valves, if the resolution of the images is equal to or less than the resolution of the liquid crystal light valves  3 R,  3 G,  3 B, the temporal axis pixel shift function is determined to be stopped, and the first display image data generation part  34  generates signals for modulation when display is performed without the temporal axis pixel shift (step S 9  in  FIG. 6 ). 
     Further, the first display image data generation part  34  generates a halt command signal for halting the operation of the wobbling device  29 , and outputs the halt command signal to the drive unit  31  of the wobbling device  29  (step S 10  in  FIG. 6 ). 
     On the other hand, as a result of comparison between the resolution of the images and the resolution of the liquid crystal light valves, if the resolution of the images is more than the resolution of the liquid crystal light valves  3 R,  3 G,  3 B, the plural frame securement part  40  secures image signals of plural frames (step S 3  in  FIG. 6 ). 
     Then, the second determination computation part  41  computes the color difference between the image signals of temporally adjacent two frames obtained by the plural frame securement part  40  (step S 4  in  FIG. 6 ). 
     Further, in the second determination computation part  41 , a threshold value of the color difference for determination as to whether the images are still images or moving images is set in advance, and the second determination computation part  41  compares the computed value to the threshold value of the color difference (step S 5  in  FIG. 6 ). 
     As a result of the comparison between the computed value and the threshold value of the color difference, if the computed value is equal to or less than the threshold value, the second determination computation part  41  determines continuation of the temporal axis pixel shift on the grounds that the display images are still images, and the second display image data generation part  35  respectively generates the signals for first modulation for the first field and the signals for second modulation for the second field when display is performed with the temporal axis pixel shift (step S 6  in  FIG. 6 ). 
     Then, the respective liquid crystal light valves  3 R,  3 G,  3 B perform modulation of incident lights based on the signals for first modulation and the signals for second modulation input from the second display image data generation part  35  and form images (step S 7  in  FIG. 6 ). 
     Further, in the wobbling device  29  at the downstream of the liquid crystal light valves  3 R,  3 G,  3 B, the transmitted light axis is shifted by the driving of the light transmissive plate  30 , and the temporal axis pixel shift is performed while the positions of the pixel images on the screen  28  shift (step S 8  in  FIG. 6 ). 
     On the other hand, as a result of the comparison between the computed value and the threshold value of the color difference, if the computed value is more than the threshold value, the second determination computation part  41  determines stop of the temporal axis pixel shift on the grounds that the display images are moving images, and the first display image data generation part  34  generates signals for modulation when display is performed without the temporal axis pixel shift (step S 9  in  FIG. 6 ). 
     Further, the first display image data generation part  34  generates a halt command signal for halting the operation of the wobbling device  29 , and outputs the halt command signal to the drive unit  31  of the wobbling device  29  (step S 10  in  FIG. 6 ). 
     According to the projector  1  of the embodiment, the control unit  32  is basically set to constantly execute the temporal axis pixel shift, continues the temporal axis pixel shift if the images to be displayed are determined to be still images, and thereby, the display resolution of the still images may be improved. On the other hand, the control unit  32  controls the drive unit  31  of the wobbling device  29  to stop the temporal axis pixel shift if the images to be displayed are determined to be moving images, and thereby, image deterioration of blur or the like of the moving image may be suppressed and the smooth moving image may be represented. Further, the smooth moving image may be represented without insertion of frames of black representation, and thus, the display does not become darker. Using the projector  1  of the embodiment, both the improvement of display resolution in the still images and the smoothness and brightness of display in the moving images may be realized. 
     Further, because of the configuration in which the control unit  32  compares the image signals in the plural frames, determines whether the images to be displayed are still images or moving images, and controls the drive unit  31  of the wobbling device  29 , whether the use or nonuse of the temporal axis pixel shift function using normal image data may be determined. Thereby, it is not necessary to prepare special image data. Further, since the determination as to whether the images are still images or moving images is made with reference to the threshold value, the switching level between the use and nonuse of the temporal axis pixel shift function may be adjusted by appropriately changing the threshold value. For example, in the case where the threshold value is set higher, for some moving images, the temporal axis pixel shift is executed for improvement of the display resolution. Contrary, in the case where the threshold value is set lower, even for the still images that slightly move, the temporal axis pixel shift may be stopped and the smooth motion may be represented. 
     Second Embodiment 
     As below, the second embodiment of the embodiment will be explained using  FIGS. 7 and 8 . 
     An image display apparatus according to the invention is also a configuration example of the 3LCD projector and its basic configuration is the same as that of the first embodiment, and the explanation of the basic configuration of the projector will be omitted and only the configuration of the control unit will be explained. 
       FIG. 7  is a block diagram showing a configuration of a determination part within a control unit of the projector of the embodiment.  FIG. 8  is a flowchart showing a flow of processing of the control unit. 
     The first embodiment has the configuration in which the control unit automatically determines the use or nonuse of the temporal axis pixel shift based on the difference computation of the image signals of the temporally adjacent two frames. On the other hand, the embodiment employs a configuration in which information for determination of use or nonuse of the temporal axis pixel shift is added in advance to the image signals to be input and the control unit reads the information and determines the use or nonuse of the temporal axis pixel shift. 
     As shown in  FIG. 7 , the determination part  43  of the embodiment has a temporal axis pixel shift on-off information acquisition part  44  (hereinafter, simply referred to as “information acquisition part”) and a temporal axis pixel shift on-off function determination part  45  (hereinafter, simply referred to as “function determination part”). The information acquisition part  44  acquires still image/moving image information previously contained in the input image signals. The still image/moving image information refers to information indicating whether the image signals themselves are still images or moving images, that is, whether the temporal axis pixel shift is executed or stopped. The determination part  43  generates a stop command signal for stopping the temporal axis pixel shift if the images are moving images based on the still image/moving image information obtained by the information acquisition part  44 . 
     Next, a flow of the processing of the control unit will be explained with reference to  FIG. 8 . 
     First, the information acquisition part  44  acquires still image/moving image information from the input image signals (step S 101  in  FIG. 8 ). 
     Then, the function determination part  45  reads the still image/moving image information input from the information acquisition part  44  and determines whether the images are moving images or not, that is, whether information for stopping the temporal axis pixel shift is contained or not (step S 102  in  FIG. 8 ). 
     Here, if the images are still images, that is, the information for stopping the temporal axis pixel shift is not contained, the function determination part  45  determines continuation of the temporal axis pixel shift on the grounds that the display images are still images, and the second display image data generation part  35  respectively generates the signals for first modulation for the first field and the signals for second modulation for the second field when display is performed with the temporal axis pixel shift (step S 103  in  FIG. 8 ). 
     Then, the respective liquid crystal light valves  3 R,  3 G,  3 B perform modulation of incident lights based on the signals for first modulation and the signals for second modulation input from the second display image data generation part  35  and form images (step S 104  in  FIG. 8 ). 
     Further, in the wobbling device  29  at the downstream of the liquid crystal light valves  3 R,  3 G,  3 B, the transmitted light axis is shifted by the driving of the light transmissive plate  30 , and the temporal axis pixel shift is performed while the positions of the pixel images on the screen  28  shift (step S 105  in  FIG. 8 ). 
     On the other hand, if the images are moving images, that is, the information for stopping the temporal axis pixel shift is contained, the function determination part  45  determines stop of the temporal axis pixel shift on the grounds that the display images are moving images, and the first display image data generation part  34  generates signals for modulation when display is performed without the temporal axis pixel shift (step S 106  in  FIG. 8 ). 
     Further, the first display image data generation part  34  generates a halt command signal for halting the operation of the wobbling device  29 , and outputs the halt command signal to the drive unit  31  of the wobbling device  29  (step S 107  in  FIG. 8 ). 
     Also, in the projector of the embodiment, the same advantage that both the improvement of display resolution in the still images and the smoothness and brightness of display in the moving images may be realized as that of the first embodiment may be obtained. Further, in the case of the embodiment, it is necessary to prepare image signals previously containing the still image/moving image information, however, means for comparing image data of plural frames and determining whether the images are still images or moving images (for example, the plural frame securement part, the second determination computation part, etc. of the first embodiment) are not necessary, and the load on the apparatus may be reduced and the configuration of the control unit may be simplified. The embodiment is preferable for the case of application of display of digital signage and presentation materials for which image contents to be displayed are determined in advance. 
     Note that the technological range of the invention is not limited to the above described embodiments, and various changes may be made without departing from the scope of the invention. For example, two configurations of the configuration in which the control unit automatically determines use or nonuse of the temporal axis pixel shift in the first embodiment and the configuration in which information for determination of use or nonuse of the temporal axis pixel shift is added in advance to the image signals to be input and the control unit reads the information have been exemplified. In addition to these configurations, a configuration in which a user of the projector appropriately determines use or nonuse of the temporal axis pixel shift in response to image contents and manually operates a switch or the like provided in the projector to switch between them, for example. 
     Further, the example in which the pixel images are shifted to two positions of the first field and the second field has been exemplified, however, a configuration in which the pixel images are shifted to three or more positions may be employed. Further, the example in which the transmissive liquid crystal light valves are used as the light modulation devices has been exemplified, however, reflective liquid crystal light valves, Digital Micromirror Devices (DMD, registered trade mark), or the like may be used. In the case of using DMD, use or nonuse of the temporal axis pixel shift may be switched not for the entire screen, but for the partial screen, and, for example, the case where moving images are partially incorporated into still images or the like may be accommodated. Further, the specific configurations of the respective parts of the projectors described in the embodiments may appropriately be changed.