Patent Publication Number: US-2017374328-A1

Title: Display device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of PCT application No. PCT/JP2016/000076 filed Jan. 8, 2016, which claims the benefit of priority from Japanese Patent Application No. 2015-047096 filed on Mar. 10, 2015 and Japanese Patent Application No. 2015-235420 filed on Dec. 2, 2015, and incorporates all the disclosures herein. 
    
    
     BACKGROUND 
     The present invention relates to a display device. 
     In recent years, there has been demanded a display device that displays a high dynamic range (HDR) picture. Dynamic range is defined as the brightness ratio between the brightest spot and the darkest spot. Regarding such a display device, for example, Japanese Unexamined Patent Application Publication No. 2007-310045 discloses a picture display device that displays a high contrast picture. 
     The picture display device described in Japanese Unexamined Patent Application Publication No. 2007-310045 provides a high contrast display, using an RGB projection display device that outputs light based on three primary color signals, and a Y projection display device that modulates the light from the RGB projection display device based on a luminance signal. 
     SUMMARY 
     As described above, in the technology described in Japanese Unexamined Patent Application Publication No. 2007-310045, the Y projection display device modulates the luminance of the light including RGB components. Therefore, in the RGB projection display device, the dynamic range decreases, due to the influence of light that has leaked from an R modulation element, a G modulation element, or a B modulation element. To facilitate understanding of this phenomenon, a case of displaying only the R color will be described as an example. For example, in the case of displaying only the R color, leaked light from the G modulation element and leaked light from the B modulation element enter the Y projection display device, in addition to the R light from the R modulation element. As a result, the dynamic range becomes narrow. 
     A display device according to an embodiment includes: a projection unit configured to emit light modulated depending on a first picture signal, the first picture signal including three primary color signals; a display unit configured to include a transmissive liquid crystal panel, a polarizing plate, and a first screen, the transmissive liquid crystal panel modulating each of three primary color lights emitted from the projection unit, depending on a second picture signal, and then emitting the light, the second picture signal including three primary color signals, the polarizing plate emitting light that is included in the incident light and that has a predetermined polarizing direction; and a display control unit configured to generate the first picture signal for driving the projection unit and the second picture signal for driving the transmissive liquid crystal panel, from an input picture signal, and generate a synchronization signal for synchronizing the first picture signal and the second picture signal, the input picture signal including three primary color signals, in which the display unit is configured such that the transmissive liquid crystal panel, the polarizing plate, and the first screen are arrayed in this order with respect to an advancing direction of the light that is emitted from the projection unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the external appearance of a display device according to Embodiment 1; 
         FIG. 2  is a configuration diagram showing an example of the internal configuration of the display device according to Embodiment 1; 
         FIG. 3A  is a diagram schematically showing a polarization state in the display device according to Embodiment 1, and shows the polarization state of light that enters a retardation plate; 
         FIG. 3B  is a diagram schematically showing a polarization state in the display device according to Embodiment 1, and shows the polarization state of light that is emitted from the retardation plate; 
         FIG. 3C  is a diagram schematically showing a polarization state in the display device according to Embodiment 1, and shows the polarization state of light that is emitted from a display unit; 
         FIG. 4A  is a diagram schematically showing a polarization state in the configuration of a comparative example, and shows the polarization state of light that enters a retardation plate; 
         FIG. 4B  is a diagram schematically showing a polarization state in the configuration of the comparative example, and shows the polarization state of light that is emitted from the retardation plate; 
         FIG. 4C  is a diagram schematically showing a polarization state in the configuration of the comparative example, and shows the polarization state of light that is emitted from a display unit; 
         FIG. 5  is a block diagram showing the configuration of the display device according to Embodiment 1; 
         FIG. 6  is a block diagram showing the configuration of a signal processing unit according to Embodiment 1; 
         FIG. 7A  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of an input picture signal; 
         FIG. 7B  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of a transmissive liquid crystal panel; 
         FIG. 7C  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the projection unit; 
         FIG. 8A  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the input picture signal; 
         FIG. 8B  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the transmissive liquid crystal panel; 
         FIG. 8C  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the projection unit; 
         FIG. 9A  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the input picture signal; 
         FIG. 9B  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the transmissive liquid crystal panel; 
         FIG. 9C  is a graph showing an example of the gamma characteristic of the display device according to Embodiment 1, and shows the gamma characteristic of the projection unit; 
         FIG. 10  is a configuration diagram showing an example of the internal configuration of a display device according to Embodiment 2; 
         FIG. 11  is a table summarizing features of liquid crystal panels with a TN scheme, a VA scheme, and an IPS scheme; 
         FIG. 12  is a table summarizing configuration examples in the case where the display device is configured by a projection unit that emits linearly polarized light; 
         FIG. 13  is a table summarizing configuration examples in the case where the display device is configured by a projection unit that emits circularly polarized light; and 
         FIG. 14  is a table summarizing configuration examples in the case where the display device is configured by a projection unit that emits unpolarized light. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 1 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  is a perspective view showing the external appearance of a display device  1 . The display device  1  is a rear-projection type projector (rear projector), and a display unit  30  is provided on a front surface of a housing  10 . More specifically, the display device  1  is a rear projector configured using an LCOS (Liquid Crystal on Silicon) that is a reflective liquid crystal display element.  FIG. 2  is a configuration diagram showing an example of the internal configuration in the housing  10  of the display device  1 . 
     As shown in  FIG. 2 , the display device  1  includes a projection unit  20 , a display unit  30 , a mirror  40 , and a display control unit  50 . The mirror  40  reflects the light emitted from the projection unit  20 , in the direction of the display unit  30 . 
     The projection unit  20  generates projection light based on a picture signal, for projecting a picture on the display unit  30 . More specifically, the projection unit  20  emits linearly polarized light depending on a later-described first picture signal including three primary color signals. In the following, the configuration of the projection unit  20  will be described. 
     The projection unit  20  includes a light source  201 . The light source  201  is a lamp, for example. The light radiated from the light source  201  enters a dichroic mirror  203 , through an integrator  202  that emits the light radiated from the light source  201  while rendering uniform the illuminance distribution on a plane perpendicular to the optical axis. The dichroic mirror  203  splits the entering light into R light as a red-color band component, G light as a green-color band component, and B light as a blue-color band component. The R light and G light after the splitting by the dichroic mirror  203  enter a mirror  204 . The B light after the splitting by the dichroic mirror  203  enters a mirror  205 . 
     The R light and G light after the splitting by the dichroic mirror  203  are reflected by the mirror  204 , and enter a dichroic mirror  206 . The dichroic mirror  206  splits the entering R light and G light. The R light after the splitting by the dichroic mirror  206  enters, through an R field lens  207 R, an R polarization control element  208 R that is inclined at 45°. 
     The R polarization control element  208 R, which is, for example, a wire-grid type polarization beam splitter, transmits P-polarized light and reflects S-polarized light. The P-polarized R light transmitted by the R polarization control element  208 R enters an R display element  209 R. The R display element  209 R, which is configured by an LCOS, modulates the R light based on a picture signal that is output from the display control unit  50  described later. The R light after entering the R display element  209 R is reflected by the R display element  209 R, and returns to the R polarization control element  208 R. At this time, the component modulated to the S-polarized light by the R display element  209 R is reflected by the R polarization control element  208 R, in the direction of a dichroic prism  210 . The R light reflected in the direction of the dichroic prism  210  enters a first surface of the dichroic prism  210 . On the other hand, the component not modulated by the R display element  209 R is transmitted by the R polarization control element  208 R, and returns in the direction of the R field lens  207 R. 
     The G light after the splitting by the dichroic mirror  206  enters, through a G field lens  207 G, a G polarization control element  208 G that is inclined at 45°. The G polarization control element  208 G, which is, for example, a wire-grid type polarization beam splitter, transmits P-polarized light and reflects S-polarized light. The P-polarized G light transmitted by the G polarization control element  208 G enters a G display element  209 G. The G display element  209 G, which is configured by an LCOS, modulates the G light based on a picture signal that is output from the display control unit  50 . The G light after entering the G display element  209 G is reflected by the G display element  209 G, and returns to the G polarization control element  208 G. At this time, the component modulated to the S-polarized light by the G display element  209 G is reflected by the G polarization control element  208 G, in the direction of a dichroic prism  210 . The G light reflected in the direction of the dichroic prism  210  enters a second surface of the dichroic prism  210 . On the other hand, the component not modulated by the G display element  209 G is transmitted by the G polarization control element  208 G, and returns in the direction of the G field lens  207 G. 
     The B light after the splitting by the dichroic mirror  203  is reflected by the mirror  205 , and enters, through a B field lens  207 B, a B polarization control element  208 B that is inclined at 45°. The B polarization control element  208 B, which is, for example, a wire-grid type polarization beam splitter, transmits P-polarized light and reflects S-polarized light. The P-polarized B light transmitted by the B polarization control element  208 B enters a B display element  209 B. The B display element  209 B, which is configured by an LCOS, modulates the B light based on a picture signal that is output from the display control unit  50 . The B light after entering the B display element  209 B is reflected by the B display element  209 B, and returns to the B polarization control element  208 B. At this time, the component modulated to the S-polarized light by the B display element  209 B is reflected by the B polarization control element  208 B, in the direction of the dichroic prism  210 . The B light reflected in the direction of the dichroic prism  210  enters a third surface of the dichroic prism  210 . On the other hand, the component not modulated by the B display element  209 B is transmitted by the B polarization control element  208 B, and returns in the direction of the B field lens  207 B. In the following description, the R display element  209 R, the G display element  209 G, and the B display element  209 B are collectively referred to as the display element  209 , in some cases. 
     The dichroic prism  210  emits the S-polarized component of each of the R light, G light, and B light emitted from the three directions, toward a projection lens  212 . Accordingly, linearly polarized light is emitted to the projection lens  212 . The light emitted from the dichroic prism  210  enters the projection lens  212  through a retardation plate  211 . The retardation plate  211  sets the polarizing direction of the emission light from the projection unit  20 , to a polarizing direction required for the incident light of the display unit  30 . For example, the polarizing direction required for the incident light of the display unit  30  is a direction resulting from rotating by 90° a polarizing direction in which the light is transmitted by a later-described polarizing plate  302  of the display unit  30 . The projection lens  212  projects the entering light to the display unit  30  through the mirror  40 , and forms an image. Thus, the light emitted from the projection unit  20  is linearly polarized light. As described above, in the embodiment, the linearly polarized light emitted from the projection unit  20  enters a transmissive liquid crystal panel  301  through the retardation plate  211 . However, in the case where the polarizing direction of the emission light from the projection unit  20  has already been set to the polarizing direction required for the incident light of the display unit  30  without using the retardation plate  211 , the retardation plate  211  does not need to be provided. For example, the retardation plate  211  may be excluded, and the polarizing direction of the emission light from the projection unit  20  may be set to the polarizing direction required for the incident light of the display unit  30 , by arbitrarily adjusting the polarizing direction while rotating the projection unit  20  around an axis in the advancing direction of the light that is emitted from the projection unit  20 . 
     Next, the display unit  30  will be described. As shown in  FIG. 2 , the display unit  30  includes the transmissive liquid crystal panel  301  having a previously determined resolution, the polarizing plate  302  having a size corresponding to the size of a display surface of the transmissive liquid crystal panel  301 , and a screen  303  having a size corresponding to the size of the transmissive liquid crystal panel  301 . 
     In the display unit  30 , the transmissive liquid crystal panel  301 , the polarizing plate  302  and the screen  303  are integrally disposed so as to be arrayed in the order of the transmissive liquid crystal panel  301 , the polarizing plate  302  and the screen  303  with respect to the advancing direction of the light that is emitted from the projection unit  20 . Here, as shown in  FIG. 2 , in the transmissive liquid crystal panel  301 , it is not always necessary to provide a polarizing plate on the incident side for the light from the projection unit  20 . This is because the light emitted from the projection unit  20  is linearly polarized light as described above and therefore it is not necessary to arrange polarization planes on a single plane at a stage before the light enters the transmissive liquid crystal panel  301 . 
     The transmissive liquid crystal panel  301  includes a liquid crystal layer and a glass substrate, which are not illustrated, and modulates each of the three primary color lights from the projection unit  20  and changes the polarizing direction, depending on a later-described second picture signal including three primary color signals. The light having passed through the transmissive liquid crystal panel  301  enters the polarizing plate  302 . The polarizing plate  302  transmits light polarized in a predetermined direction. By such a configuration, the display unit  30  performs a display, by controlling, for each pixel, the respective transmission amounts of the R light, G light, and B light emitted from the projection unit  20 , based on the second picture signal. Here, the resolution of the display unit  30  corresponds to the resolution of the projection unit  20 , and the pixels of the projection unit  20  correspond to the pixels of the transmissive liquid crystal panel  301 , on a one-to-one basis. Accordingly, each of the R light modulated by the R display element  209 R, the G light modulated by the G display element  209 G, and the B light modulated by the B display element  209 B, corresponding to one pixel of the projection unit  20 , is modulated in the display unit  30 , in accordance with the second picture signal. Here, it is necessary to perform the alignment between the dot of the light to be projected by the projection unit  20  and the pixel of the transmissive liquid crystal panel  301  such that the two correspond to each other. 
     Here, polarization states in the display device  1  will be described.  FIG. 3A  to  FIG. 3C  are diagrams schematically showing polarization states in the display device  1 .  FIG. 4A  to  FIG. 4C  are diagrams schematically showing polarization states in the configuration of a comparative example. Here, suppose that the comparative example has a configuration in which the configuration of the projection unit  20  is replaced with a DLP (Digital Light Processing). That is, in the configuration according to the comparative example, the configuration of the former stage of the retardation plate  211  in the projection unit  20  is implemented by the DLP.  FIG. 3A  and  FIG. 4A  show polarization states of lights that enter the retardation plate  211 ,  FIG. 3B  and  FIG. 4B  show polarization states of lights that are emitted from the retardation plate  211 , and  FIG. 3C  and  FIG. 4C  show polarization states of lights that are emitted from the display unit  30 . Here, more specifically,  FIG. 4B  shows a polarization state after the light emitted from the retardation plate  211  is transmitted by an added polarizing plate. 
     As described above, in the embodiment, the light that enters the retardation plate  211  is linearly polarized light (see  FIG. 3A ). In the embodiment, the polarizing direction is adjusted by the retardation plate  211  (see  FIG. 3B ). On the other hand, in the case of the configuration according to the comparative example, the light that enters the retardation plate  211  is in an unpolarized state (see  FIG. 4A ). Therefore, in the case of the configuration according to the comparative example, it is necessary to provide a polarizing plate at the former stage of the transmissive liquid crystal panel  301 . By providing the polarizing plate at the former stage of the transmissive liquid crystal panel  301  in this way, a polarization required for the incident light of the transmissive liquid crystal panel  301  is achieved (see  FIG. 4B ). However, in the case of providing the polarizing plate at the former stage of the transmissive liquid crystal panel  301  in this way, light quantity is lost by the polarizing plate. Further, costs rise in connection with provision of a polarizing plate corresponding to the size of the transmissive liquid crystal panel  301 . The polarization state of the light emitted from the display unit  30  varies depending on the characteristic of the screen  303 . That is, in the case where the screen  303  has a characteristic for maintaining the polarization of the entering light, the polarization of the light entering the screen  303  is maintained, but in the case where the screen  303  has no characteristic for maintaining the polarization, the polarization is lost by the screen  303 . In the configuration shown in the comparative example, the retardation plate  211  may be excluded. 
       FIG. 5  is a block diagram showing the configuration of the display device  1 . As shown in  FIG. 5 , the display control unit  50  includes a signal processing unit  500 , a first synchronization unit  511 , and a second synchronization unit  512 . Each constituent of the display control unit  50  may be implemented by software with a program, or may be implemented by any combination of hardware, firmware, and software, or the like. In the case of implementation by a program, an unillustrated CPU (Central Processing Unit) of the display control unit  50  executes the program stored in, for example, an unillustrated memory of the display control unit  50 . 
     The program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line, such as electric wires and optical fibers, or a wireless communication line. 
     To the signal processing unit  500 , an input picture signal and a synchronization signal are input. The input picture signal to be input to the signal processing unit  500 , for example, may be a signal transferred from another device to the display device  1 , or may be a signal stored in an unillustrated storage device of the display device  1 . As the synchronization signal, for example, a synchronization signal generated by an unillustrated synchronization signal generation circuit is input to the signal processing unit  500 . 
     The input picture signal is a picture signal including three primary color signals for RGB. The input picture signal, for example, is a picture signal having a higher bit level than an 8-bit picture signal, which is typical for picture signals. That is, for example, the input picture signal is configured by a 16-bit input picture signal for the R color, a 16-bit input picture signal for the G color, and a 16-bit input picture signal for the B color. The input picture signal is a picture signal in which a gamma correction to a predetermined gamma value has been performed. By way of example, the gamma value of the gamma characteristic of the input picture signal is 2.2. 
     From the input picture signal, the signal processing unit  500  generates a first picture signal for performing the display control of the projection unit  20 , and a second picture signal for performing the display control of the display unit  30 . That is, the signal processing unit  500  generates the first picture signal and the second picture signal from the input picture signal, controls the projection unit  20  based on the first picture signal, and controls the transmissive liquid crystal panel  301  based on the second picture signal. The generation of the first picture signal and the second picture signal by the signal processing unit  500  will be described later. The signal processing unit  500  performs processing, in synchronization with the input synchronization signal. 
     The signal processing unit  500  outputs the generated first picture signal to the first synchronization unit  511 . Further, the signal processing unit  500  outputs the generated second picture signal to the second synchronization unit  512 . In addition, the synchronization signal is output to the first synchronization unit  511  and the second synchronization unit  512 . 
     The first picture signal is supplied to a device drive unit  250  of the projection unit  20 , through the first synchronization unit  511 . The second picture signal is supplied to a panel drive unit  350  of the display unit  30 , through the second synchronization unit  512 . 
     In the projection unit  20  and the transmissive liquid crystal panel  301 , various signal processes (drive and the like) are performed after the input of the picture signal and before the image output. Therefore, it takes a certain amount of time before the image output. Here, the time required for the image output in the projection unit  20  and the time required for the image output in the transmissive liquid crystal panel  301  are different. Therefore, it is necessary to perform synchronization for matching the image output timings of the two. Accordingly, the first synchronization unit  511  and the second synchronization unit  512  perform delay processes of adding optimal delays to the first picture signal and the second picture signal, respectively. It may be the case that the delay process is performed in one of the first synchronization unit  511  and the second synchronization unit  512 . The first synchronization unit  511  and the second synchronization unit  512  perform the delay processes based on the synchronization signal. Then, the first synchronization unit  511  outputs the first picture signal to the device drive unit  250  of the projection unit  20 . The second synchronization unit  512  outputs the second picture signal to the panel drive unit  350  of the display unit  30 . 
     The device drive unit  250  generates a drive signal for driving the display element  209 , in accordance with the first picture signal, and drives the display element  209  through the drive signal. The panel drive unit  350  generates a drive signal for driving the transmissive liquid crystal panel  301 , in accordance with the second picture signal, and drives the transmissive liquid crystal panel  301  through the drive signal. 
       FIG. 6  is a block diagram showing the configuration of the signal processing unit  500 . As shown in  FIG. 6 , the signal processing unit  500  includes a first LUT (Lookup table) unit  501 , and a second LUT unit  502 . The first LUT unit  501  and the second LUT unit  502  are implemented, for example, by a storage device such as an unillustrated memory of the display control unit  50 . 
     The first LUT unit  501  is a lookup table for adjusting the projection unit  20  to a first output characteristic. The second LUT unit  502  is a lookup table for adjusting the transmissive liquid crystal panel  301  to a second output characteristic. The sum of the gamma value of the first output characteristic and the gamma value of the second output characteristic is equal to the gamma value of the input picture signal. Here, the description will be provided assuming that the gamma value of the input picture signal is 2.2. In this case, the input picture signal is properly displayed when the gamma value of the output characteristic is 2.2. Accordingly, it is necessary to realize a display device in which the gamma value of the output characteristic is 2.2 as the whole of the output by the projection unit  20  and the output by the display unit  30 . Hence, for example, the first LUT unit  501  is configured as a table in which the output characteristic of the projection unit  20  has been adjusted such that the gamma is 1.1. Further, the second LUT unit  502  is configured as a table in which the output characteristic of the display unit  30  has been adjusted such that the gamma is 1.1. Such a table can be created, for example, by actually performing the output in the projection unit  20  or the display unit  30  and measuring the illuminance at that time with an illuminance meter. As a result, the display device  1  can have an output characteristic with a gamma value of 2.2 (=1.1+1.1). 
     The signal processing unit  500  gives the input picture signal as the inputs of the first LUT unit  501  and the second LUT unit  502 . Then, the signal processing unit  500  adopts the output of the first LUT unit  501  with respect to the input picture signal, as the first picture signal, and adopts the output of the second LUT unit  502  with respect to the input picture signal, as the second picture signal. At this time, the first picture signal and the second picture signal are generated for each of the RGB signals of the input picture signal. That is, the first picture signal for R and the second picture signal for R are generated from the input picture signal for R. The first picture signal for G and the second picture signal for G are generated from the input picture signal for G. The first picture signal for B and the second picture signal for B are generated from the input picture signal for B. Here, in the generation of the first picture signal and the second picture signal, as described above, each of RGB only has to be independently processed by the LUTs, and arbitrary bit numbers can be adopted as the bit numbers of the first picture signal and the second picture signal. For example, in the case where the input picture signal has 16 bits, the first picture signal and the second picture signal may be 16-bit picture signals. Alternatively, a signal of the upper 8 bits on the MSB (most significant bit) side may be supplied as the first picture signal, and a signal of the lower 8 bits on the LSB (least significant bit) side may be supplied as the second picture signal. 
     Here, the gamma value that is realized by the LUTs will be further described. In the embodiment, as described above, the gamma characteristic of the input picture signal is divided into two, and therefore, the first output characteristic and the second output characteristic are close to a linear characteristic. Therefore, the reproducibility of the dark-part gradation is enhanced. For example, in the case where the gamma value of the gamma characteristic of the input picture signal is specified as 2.2, the first output characteristic and the second output characteristic are 1.1 in the simple division described above. In the case where the gamma value is 2.2, a value of 1 in the 8-bit input corresponds to a brightness of about 0.000005 with respect to white (a value of 255 in the 8-bit input). Therefore, unless the contrast on the display surface can be displayed at 2000000:1, it is not possible to reproduce a brightness that is indicated by a value of 1 (8 bits) in a theoretical gamma curve. On the other hand, in the case where the gamma value is 1.1, a value of 1 in the 8-bit input corresponds to a brightness of about 0.0023 with respect to white (a value of 255 in the 8-bit input), and it is only necessary that the contrast on the display surface can be displayed at 440:1. Therefore, it is possible to reduce the contrast performance that is required in the transmissive liquid crystal panel  301 . That is, it is possible to achieve an ideal gamma characteristic by a combination of a relatively easily obtainable transmissive liquid crystal panel  301  and the projection unit  20 . 
     Further, when the first picture signal and the second picture signal are generated from the input picture signal, the gamma adjustment is easily achieved because of the independence of RGB as described above. For example, in the case where the luminance is modulated as described in Japanese Unexamined Patent Application Publication No. 2007-310045, the Y (luminance) signal is generated from an input picture signal for RGB, and therefore it is not easy to maintain gradation property in an RGB-mixed color. This is because one dimension is added for the generation of the Y signal and the three dimensions of RGB need to be converted into the four dimensions of RGBY. On the other hand, in the embodiment, the RGB signals of the input picture signal are divided into the RGB signals of the first picture signal and the RGB signals of the second picture signal. Therefore, each color is processed independently, and the gradation property is easily maintained. Further, because of the conversion from the three dimensions of RGB to the three dimensions of RGB, the generation of the first picture signal and the second picture signal is achieved relatively easily. 
     Furthermore, according to the display device  1  in the embodiment, it is possible to display an input picture signal having a great gamma value of 2.2-th power or greater as the gamma characteristic. The reason is shown as follows. For example, in the case where the gamma characteristic is 2.2, the luminance (brightness) has a value specified by the 2.2-th power of the input picture signal. For example, a value of  1  in the 8-bit signal is 1/255=0.003921 . . . , and the luminance (brightness) is (1/255)̂2.2=0.000005077 . . . . Therefore, in the case where the gamma characteristic is set to a value greater than 2.2-th power, the luminance has a value less than that in the case of 2.2-th power (namely, is darker), even when the input picture signal is the same. Therefore, in a display device in the related art, as the gamma characteristic of the input picture signal becomes greater than 2.2-th power, the display at the specified luminance becomes more difficult. On the other hand, in the embodiment, the multiplication product of the output values of the projection unit  20  and the transmissive liquid crystal panel  301  is the final output value, and therefore, the display at the specified luminance is relatively easy. Thus, according to the display device  1 , it is possible to display an input picture signal having a great gamma value of 2.2-th power or greater as the gamma characteristic. Since the dark-part gradation property is kept more suitably as the gamma value of the gamma characteristic of the input picture signal becomes greater, the display device  1  according to the embodiment also contributes to reduction in the quantization error of the dark-part gradation, by processing the error in image data quantization as the image data in the floating-point format. 
     In the above description, by way of example, the gamma value of the first output characteristic (that is, the gamma value of the output characteristic of the projection unit  20 ) is 1.1, and the gamma value of the second output characteristic (that is, the gamma value of the output characteristic of the display unit  30 ) is 1.1. However, the present embodiment is not limited to these values. That is, it is only necessary that the sum of the gamma value of the first output characteristic and the gamma value of the second output characteristic is equal to the gamma value of the input picture signal.  FIG. 7A  to  FIG. 7C ,  FIG. 8A  to  FIG. 8C , and  FIG. 9A  to  FIG. 9C  are graphs showing examples of the relation (gamma characteristic) between the input value that is the input picture signal or the picture signal, and the light output, in the display device  1  according to the embodiment.  FIG. 7A ,  FIG. 8A , and  FIG. 9A  show the gamma characteristics of the input picture signal,  FIG. 7B ,  FIG. 8B , and  FIG. 9B  show the gamma characteristics of the transmissive liquid crystal panel  301 , and  FIG. 7C ,  FIG. 8C , and  FIG. 9C  show the gamma characteristics of the projection unit  20 . In each of  FIG. 7A  to  FIG. 7C ,  FIG. 8A  to  FIG. 8C , and  FIG. 9A  to  FIG. 9C , the x-axis indicates the input value that is the input picture signal or the picture signal, and the y-axis indicates the light output value. That is, in  FIG. 7B ,  FIG. 8B , and  FIG. 9B , the x-axis indicates the input value that is the second picture signal to be output from the second LUT unit  502 , and the y-axis indicates the light output value of the transmissive liquid crystal panel  301 . In  FIG. 7C ,  FIG. 8C , and  FIG. 9C , the x-axis indicates the input value that is the first picture signal to be output from the first LUT unit  501 , and the y-axis indicates the light output value of the projection unit  20 . 
       FIG. 7A  to  FIG. 7C  show the above-described example in which the gamma values of the first output characteristic (the output characteristic of the projection unit  20 ) and the second output characteristic (the output characteristic of the transmissive liquid crystal panel  301 ) are 1.1 in the case where the gamma value of the gamma characteristic of the input picture signal is specified as 2.2. 
       FIG. 8A  to  FIG. 8C  show an example in which the gamma value of the first output characteristic (the output characteristic of the projection unit  20 ) is 2.2 and the gamma value of the second output characteristic (the output characteristic of the transmissive liquid crystal panel  301 ) is 1 in the case where the gamma value of the gamma characteristic of the input picture signal is specified as 3.2. Here, it is assumed that the projection unit  20  has a higher contrast than the transmissive liquid crystal panel  301 . In this way, the gamma value of the output characteristic of one of the projection unit  20  and the transmissive liquid crystal panel  301  that has a higher contrast may be adjusted so as to be greater than the gamma value of the output characteristic of one of the projection unit  20  and the transmissive liquid crystal panel  301  that has a lower contrast. Thereby, it is possible to enhance the contrast of the whole of the display device  1 . 
       FIG. 9A  to  FIG. 9C  show an example in which the modulation of the transmissive liquid crystal panel  301  is performed in a predetermined limited range on the dark-part side. The example shown in  FIG. 9A  to  FIG. 9C  is an example in which the gamma value of the first output characteristic (the output characteristic of the projection unit  20 ) is 2.2 (here, the gamma value is 1.2 in the case where the input is 0.25 or less) and the gamma value of the second output characteristic (the output characteristic of the transmissive liquid crystal panel  301 ) is 1 in the case where the gamma value of the gamma characteristic of the input picture signal is specified as 2.2. In the second output characteristic, in the case where the input value is 0.25 or greater, the light output quantity is maximized in the same manner. In this way, in the case where the input value is equal to or greater than a previously determined value, the output may be fixed at the maximum in the output characteristic of the transmissive liquid crystal panel  301 . Thereby, there is an advantage that it is possible to assign all gradations of the transmissive liquid crystal panel  301  in a gamma region in which the input value is 0.25 or less and to express gradations on the dark-part side as minute gradations. 
     The display device  1  according to the embodiment has been described above. In the display device  1 , as described above, the light modulated for each of RGB by the projection unit  20  is output, and each of the RGB lights emitted from the projection unit  20  is further modulated in the transmissive liquid crystal panel  301 . Thereby, it is possible to suppress the influence of leaked light, and to enhance contrast. Here, by way of example, a case of displaying only the R color will be described with a comparative example. For example, in the case of assuming a liquid crystal display in which the first modulation is performed by the control of a backlight and the like and the second modulation is performed to the light of the backlight as a comparative example, leaked lights of the G light and the B light in a device for the second modulation causes the decrease in contrast. Further, by the influence of the leaked lights of the G light and the B light, a color shifted from the original color; that is, a color shifted to a point in the white color direction in a chromaticity diagram is displayed. Further, as a comparative example, for example, in the case where the luminance is modulated by a device for the second modulation as described in Japanese Unexamined Patent Application Publication No. 2007-310045, the same problem occurs despite being improved compared to the comparative example of the above liquid crystal display. On the other hand, in the display device  1  according to the embodiment, since each of the R light, the G light, and the B light is doubly modulated, it is possible to suppress leaked light. Therefore, it is possible to suppress the contrast decrease and the color shift, and particularly, even for a chromatic color, it is possible to expand the dynamic range. That is, according to the embodiment, it is possible to provide a display device that can provide a display in a high dynamic range. 
     Embodiment 2 
     Next, Embodiment 2 of the present invention will be described. As described above, in the display device  1  according to Embodiment 1 and a display device  2  according to the present embodiment, it is necessary to perform the alignment between the dot of the light to be projected by the projection unit  20  and the pixel of the transmissive liquid crystal panel  301  such that the two correspond to each other. Here, if the projection light from the projection unit  20  exactly focuses on the transmissive liquid crystal panel  301 , there is a concern that a moire pattern appears due to the dot of the projection light from the projection unit  20  and the pixel structure of the transmissive liquid crystal panel  301 . Hence, the present embodiment suppresses the appearance of the moire pattern, by diffusing the projection light from the projection unit  20  that enters the transmissive liquid crystal panel  301 , immediately before the incidence. 
       FIG. 10  is a configuration diagram showing an example of the internal configuration of the display device  2  according to Embodiment 2. In the following description, identical reference characters are assigned to elements identical to the above-described elements, and repetitive descriptions are omitted. As shown in  FIG. 10 , the display device  2  is different from the display device  1  in that the display unit  30  is replaced with a display unit  31 . 
     The display unit  31  includes a screen  304  having a size corresponding to the size of the transmissive liquid crystal panel  301 , the transmissive liquid crystal panel  301 , the polarizing plate  302 , and the screen  303 . In the display unit  31 , the screen  304 , the transmissive liquid crystal panel  301 , the polarizing plate  302 , and the screen  303  are integrally disposed so as to be arrayed in the order of the screen  304 , the transmissive liquid crystal panel  301 , the polarizing plate  302 , and the screen  303  with respect to the advancing direction of the light that is emitted from the projection unit  20 . The screen  304  is a screen that has a characteristic for maintaining the polarization of the entering light. As the screen that has a characteristic for maintaining the polarization, for example, Blue Ocean Screen manufactured by Nitto Jushi Kogyo Co., Ltd. can be used. 
     By such a configuration, in the present embodiment, the light emitted from the projection unit  20  is diffused by the screen  304 , and then enters the transmissive liquid crystal panel  301 . Therefore, the projection light does not directly focus on the transmissive liquid crystal panel  301 , and thereby, the appearance of the moire pattern can be reduced. Accordingly, it is not necessary to perform the position adjustment for reducing the moire pattern, and therefore, the alignment between the projection unit  20  and the transmissive liquid crystal panel  301  becomes easy. Further, for example, since the transmissive liquid crystal panel  301  has a certain thickness, there can be a problem in that two images of an image projected on the screen  303  and an image displayed by the transmissive liquid crystal panel  301  are visually recognized with a slight mismatch due to parallax when the position of the viewing point deviates from the front face of the display unit  30 . However, since the screen  304  is disposed, there is an advantage that the visual recognition of the two images with the mismatch is moderated. 
     The present invention is not limited to the above embodiment, and modifications can be appropriately made without departing from the spirit. For example, in the above embodiment, the input picture signal, the first picture signal, and the second picture signal have been described as RGB signals, but may be signals indicated in another color space. For example, signals indicated by a luminance signal and two color difference signals, as exemplified by YPbPr signals may be used. 
     The above embodiment adopts a configuration in which the projection unit  20  emits the linearly polarized light, but the projection unit  20  may be replaced with a projection unit to emit light that is modulated depending on the above-described first picture signal and that is other than the linearly polarized light. That is, for example, there may be used a projection unit to emit circularly polarized light that is modulated depending on the above-described first picture signal, or a projection unit to emit unpolarized light that is modulated depending on the above-described first picture signal. As the drive scheme for the transmissive liquid crystal panel  301 , an arbitrary scheme can be adopted. For example, the transmissive liquid crystal panel  301  may be a liquid crystal panel with a TN (Twisted Nematic) scheme, a liquid crystal panel with a VA (Vertical Alignment) scheme, or a liquid crystal panel with an IPS (In-Place-Switching) scheme. 
     Here will be described liquid crystal panels with the TN scheme, the VA scheme, and the IPS scheme that control the polarizing direction of the incident light by the voltage to be applied to liquid crystal.  FIG. 11  is a table summarizing features of the liquid crystal panels with the TN scheme, the VA scheme, and the IPS scheme. Here, as an example of the TN scheme, there is shown a type in which light is blocked and the display on the screen becomes black when the voltage to be applied to the liquid crystal panel is maximized and the display on the screen becomes white when the voltage is not applied to the liquid crystal panel. Meanwhile, as an example of the VA scheme and the IPS scheme, there is shown a type in which light is blocked and the display on the screen become black when the voltage is not applied to the liquid crystal panel and the display on the screen becomes white when the voltage to be applied to the liquid crystal panel is maximized. 
     In comparison of contrast among the schemes, the VA scheme exhibits the greatest contrast, and the TN scheme exhibits the second greatest contrast. Therefore, among the three schemes, the IPS scheme is the worst in contrast performance. In comparison of viewing angle among the schemes, the IPS scheme exhibits the greatest viewing angle, and the VA scheme exhibits the second greatest viewing angle. Therefore, among the three schemes, the TN scheme is the worst in viewing angle performance. In  FIG. 11 , as for the numerals in the sections for the contrast and the viewing angle, a smaller value means a better performance. 
     In the following, there will specifically be described configuration examples of the display device in the case where transmissive liquid crystal panels with the above-described schemes are used as the transmissive liquid crystal panel  301 . 
     Here, the reference is set to the polarizing direction of the polarizing plate  302  on the light emission side of the liquid crystal panel; that is, the transmission axis of the polarizing plate  302 . In the case of using a type of TN-scheme liquid crystal panel in which the phase of light changes by 1/2λ in a state where the voltage is not applied to the liquid crystal panel, the polarizing direction of the light transmitted by the liquid crystal panel is orthogonal to the polarizing direction of the light entering the liquid crystal panel. Accordingly, in the case of using this type of TN-scheme liquid crystal panel, the polarizing direction of the light entering the liquid crystal panel is required to be rotated by 90° with respect to the reference. 
     In the case of a type of VA scheme or IPS scheme in which the phase of light changes by 1/2λ in a state where the maximum voltage is applied to the liquid crystal panel, the polarizing direction of the light entering the liquid crystal panel is required to be rotated by 90° with respect to the reference. On the other hand, in a state where the voltage is not applied to the liquid crystal panel, the polarization state does not change. 
     Accordingly, even when any of the above TN scheme, VA scheme, and IPS scheme is used for the liquid crystal panel, the polarizing direction of the light emitted by the projection unit  20  only has to be a direction orthogonal to the reference. 
       FIG. 12  is a table summarizing configuration examples in the case where the display device is configured by the projection unit  20  that emits the linearly polarized light as shown in the above embodiment. As described above, the polarizing direction of the light entering the liquid crystal panel is required to be rotated by 90° with respect to the reference. Therefore, as shown in Configuration Examples 1 and 4 in  FIG. 12 , in the case where the polarizing direction of the emission light of the projection unit  20  is the same as the direction of the reference, a 1/2λ plate that is a retardation plate in which a retarded phase axis or an advanced phase axis is disposed at an orientation angle of 90° on the polarization plane for the incident light is inserted between the projection unit  20  and the transmissive liquid crystal panel  301 , so that the polarizing direction becomes orthogonal to the reference. The above retardation plate  211  corresponds to such a retardation plate. In the case where the polarizing direction of the emission light of the projection unit  20  is orthogonal to the reference as shown in Configuration Examples 2 and 3 in  FIG. 12 , it is not necessary to change the polarizing direction of the emission light of the projection unit  20 , and therefore, the insertion of the retardation plate is unnecessary. 
       FIG. 13  is a table summarizing configuration examples in the case where the display device is configured by a projection unit that emits circularly polarized light. In the case where the above-described display device is configured using a projection unit in which the emission light is circularly polarized light instead of the projection unit  20  that emits the linearly polarized light, as shown in Configuration Examples 5 and 6 in  FIG. 13 , a 1/4λ plate that is a retardation plate in which a retarded phase axis or an advanced phase axis is disposed at an orientation angle of 45° with respect to the reference is inserted between the projection unit  20  and the transmissive liquid crystal panel  301 , so that the polarizing direction becomes orthogonal to the reference. In  FIG. 13 , Configuration Example 5 shows a configuration example in which the projection unit emits clockwise or counterclockwise circularly polarized light in the case where the transmission axis of the polarizing plate is in the vertical direction. Configuration Example 6 shows a configuration example in which the projection unit emits clockwise or counterclockwise circularly polarized light in the case where the transmission axis of the polarizing plate is in the horizontal direction. In both configuration examples, it is possible to make the polarizing direction of the light entering the liquid crystal panel orthogonal to the reference, by rotating and adjusting the optical axis of the retardation plate depending on the rotation direction of the circularly polarized light. 
       FIG. 14  is a table summarizing configuration examples in the case where the display device is configured by a projection unit that emits unpolarized light. In the case where the above-described display device is configured using a projection unit in which the emission light is unpolarized light instead of the projection unit  20  that emits the linearly polarized light, as shown in Configuration Examples 7 and 8 in  FIG. 14 , the display device is configured as follows. That is, in the display device, a polarizing plate having a transmission axis orthogonal to the transmission axis of the polarizing plate  302  on the light emission side of the liquid crystal panel is inserted between the projection unit  20  and the transmissive liquid crystal panel  301 , so that the polarizing direction of the light entering the transmissive liquid crystal panel  301  becomes orthogonal to the reference. In the display device, the retardation plate is not always necessary. 
     As described above, various types of projection units can be employed.  FIG. 12  to  FIG. 14  show, by way of example, only the case where the polarizing direction of the polarizing plate  302  on the light emission side of the liquid crystal panel is the horizontal direction or the vertical direction, but needless to say, the display device can be appropriately configured even by rotation to another direction. 
     As described above, panels with various schemes including the TN scheme, the VA scheme, and the IPS scheme can be employed as the scheme of the transmissive liquid crystal panel. In the case where the object to be seen by a person who views pictures on the display device; that is, the user, is a liquid crystal panel, it is preferable to use the IPS scheme, which has a better viewing angle than the TN scheme and the VA scheme. However, in the above embodiment, the object to be seen by the user is the screen  303 , and therefore, the contrast performance is more important than the viewing angle performance, which depends on the scheme of the liquid crystal panel. Accordingly, it is preferable to use the liquid crystal panel with the VA scheme, as the transmissive liquid crystal panel  301 . 
     The liquid crystal panel having a configuration in which the liquid crystal transmits light when the polarizing direction is rotated by 90° has been described. For example, in the case of using a liquid crystal panel having a configuration in which the liquid crystal blocks light when the polarizing direction is rotated by 90°, the polarizing direction of the emission light of the projection unit may coincide with the above reference. Thus, the display device only has to be configured such that the light having the polarizing direction required for the incident light of the liquid crystal panel enters the liquid crystal panel.