Patent Publication Number: US-2021191237-A1

Title: Display device, and method of controlling display device

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-231180, filed Dec. 23, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a display device and a method of controlling a display device. 
     2. Related Art 
     In the past, there has been known a display device which makes the transition to a standby state of temporarily stopping the operation of a light source and so on, and then returns from the standby state in accordance with signal input or the like from an external device (see, e.g., JP-A-2014-041364 (Document 1)). The projector described in Document 1 puts the light source on, and then displays an image for standby when returning from the standby state. 
     In general, the display device stores in advance data of an image to be displayed in accordance with the operation of the display device. The data of this kind is stored in the nonvolatile storage device so that the memory is kept during the period in which the energization is stopped in the standby state. However, it takes time to retrieve data from the nonvolatile storage device compared to a volatile storage device. Therefore, there is a problem that it takes time until it becomes possible to display an image when returning from the standby state. 
     SUMMARY 
     An aspect for solving the problem described above is directed to a display device including a display section, a processor configured to control the display section, a first memory which is a volatile memory to be reset when the display device makes a transition to a standby state, and a second memory which is a volatile memory configured to keep data in the standby state of the display device, wherein the processor stores data of a display object in the second memory when the display device makes the transition to the standby state, and the data of the display object is displayed in the display section when returning from the standby state to a normal operation state. 
     Another aspect for solving the problem described above is directed to a method of controlling a display device equipped with a display section, the method including the steps of controlling storage of data in a first memory which is a volatile memory to be reset when the display device makes a transition to a standby state, and a second memory which is a volatile memory configured to keep data in the standby state of the display device, and storing data of a display object in the second memory when the display device makes the transition to the standby state, wherein the data of the display object is displayed in the display section when returning from the standby state to a normal operation state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a projector. 
         FIG. 2  is a diagram showing a display example when returning from the standby state. 
         FIG. 3  is a flowchart showing an operation of the projector. 
         FIG. 4  is a flowchart showing an operation of the projector. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. Configuration of Projector 
       FIG. 1  is a block diagram of a projector  1  according to an embodiment implementing the present disclosure. 
     The projector  1  projects image light PL to a screen SC based on the image data supplied from an image supply device not shown to be externally connected, or the image data stored by a nonvolatile memory  15  to form the image on the screen SC. The projector  1  corresponds to an example of a display device, and the operation of the projector  1  forming the image on the screen SC corresponds to display. 
     An installation state of the projector  1  and an object to which the projector  1  projects the image light PL are arbitrary, and in the present embodiment, the description will be presented citing a configuration of projecting the image light PL to the screen SC as an example. It is possible for the projector  1  to project a still image based on still image data, or to project a moving image based on video data. Further, the image to be projected by the projector  1  can be a two-dimensional image, or can also be a three-dimensional image. Including these images, the image to be projected by the projector  1  is called a projection image. 
     The processor  1  has a control section which executes a program to control each section of the projector  1 . This control section is provided with a processor for executing the program, and realizes the control function due to cooperation between hardware and software. In the present embodiment, there is shown an example provided with a CPU  10  as the processor. 
     To the CPU  10 , there are connected a first memory  11 , a second memory  12 , and the nonvolatile memory  15 . The first memory  11  and the second memory  12  are each a volatile storage device formed of a DRAM or the like, and therefore, require supply of the power for keeping the memory state, and are reset by the CPU  10  when the power supply is stopped. For example, when making the transition to the standby state described later, the power supply to the first memory  11  is stopped, and thus, the first memory  11  is reset. The first memory  11  and the second memory  12  form the work area when the CPU  10  executes the program. Further, a part of the storage area of the first memory  11  functions as a frame memory for a GPU  20  described later to develop the image data. 
     The nonvolatile memory  15  is a nonvolatile storage device such as a flash ROM or an EEPROM. The nonvolatile memory  15  stores the program to be executed by the CPU  10  and data to be processed by the CPU  10  or the like in a nonvolatile manner. For example, the nonvolatile memory  15  stores a control program  16  to be executed by the CPU  10 , and OSD data  17  to be processed by the CPU  10  and the GPU  20 . The nonvolatile memory  15  corresponds to an example of a nonvolatile storage section. 
     The control program  16  is a program for the CPU  10  to control each section of the projector  1 , and constitutes an operation system of the projector  1 . 
     The OSD data  17  is the data for the GPU  20  to display display objects  65 ,  66  shown in  FIG. 2 , and includes, for example, the image data of the display object  65  and the display data of the display object  66 . These display objects  65 ,  66  are projected by a projection section  30  due to the GPU  20  executing an OSD processing function. The string of OSD is an abbreviation for On-Screen Display. 
     To the CPU  10 , there is connected the GPU  20 . The GPU  20  is an image processing device for processing the image data to be projected by the projector  1 , and performs the processing of developing the image data in the frame memory provided to the first memory  11 . 
     In the above description, the string of CPU is an abbreviation for Central Processing Unit, and the string of GPU is an abbreviation for Graphical Processing Unit. The CPU  10  and the GPU  20  can each be formed of a single processor, or can each be constituted by a plurality of processors. Further, the CPU  10  and the GPU  20  can each be formed of an SoC integrated with a peripheral circuit such as a memory, or can each be formed of an ASIC. It is possible to combine the CPU  10  and the GPU  20  with a DSP for executing predetermined arithmetic processing. Further, it is also possible to adopt a configuration in which a part of the CPU  10  and all or a part of the GPU  20  are implemented in the hardware, or it is also possible to configure a part of the CPU  10  and all or a part of the GPU  20  using a programmable device such as FPGA. The string of SoC is an abbreviation for System on Chip, and the string of DSP is an abbreviation for Digital Signal Processor. The string of ASIC is an abbreviation for Application Specific Integrated Circuit, and the string of FPGA is an abbreviation for Field-Programmable Gate Array. The string of DRAM is an abbreviation for Dynamic Random Access Memory. The string of ROM is an abbreviation for Read Only Memory. The string of EEPROM is an abbreviation for Electrically Erasable Programmable ROM. 
     The projector  1  is provided with a projection processing section  3  and the projection section  30  as a processing section for performing processing for projecting an image. The projection processing section  3  includes the GPU  20 , a light source drive circuit  21 , and a light modulation device drive section  22 . The projection section  30  is provided with a light source  31 , a light modulation device  32 , and an optical unit  33 . To the projection section  30 , there are connected the light source drive circuit  21  and the light modulation device drive section  22  operating in accordance with the control by the CPU  10 . The projection section  30  corresponds to an example of a display section. 
     The light source  31  is formed of a solid-state light source such as an LED or a laser source. The string of LED is an abbreviation for Light Emitting Diode. To the light source  31 , there is connected the light source drive circuit  21 . The light source drive circuit  21  supplies the light source  31  with power in accordance with the control by the CPU  10  to make the light source  31  emit light. The light source drive circuit  21  executes, for example, PWM control to adjust the luminance of the light source  31 . The string of PWM is an abbreviation for Pulse Wave Modulation. 
     The light modulation device  32  modulates the light emitted by the light source  31  to generate the image light PL, and then irradiates the optical unit  33  with the image light PL. The light modulation device  32  is provided with a light modulation element such as a transmissive liquid crystal light valve, a reflective liquid crystal light valve, or a digital mirror device. The light modulation element of the light modulation device  32  is connected to the light modulation device drive section  22 . The light modulation device drive section  22  drives the light modulation element of the light modulation device  32  to form the image frame by frame. It is also possible for the light modulation device  32  to be provided with a drive circuit for driving the light modulation element. For example, when the light modulation device  32  is formed of a liquid crystal light valve, it is also possible to provide a liquid crystal driver circuit as the drive circuit. 
     The GPU  20  obtains the image data to be projected by the projection section  30  in accordance with the control by the CPU  10  to develop the image forming one frame in the frame memory in the first memory  11 . The GPU  20  executes image processing on the image developed in the first memory  11 . The image processing to be executed by the GPU  20  includes, for example, a geometric correction process for compensating a keystone distortion of the projection image in the screen SC, an adjustment process including a luminance adjustment and corrections of the color tone of the projection image, and an OSD processing for combining the OSD image. It is also possible for the GPU  20  to execute image processing such as a resolution conversion process for adjusting the aspect ratio and the resolution of the image data in accordance with the light modulation device  32  or a frame rate conversion. 
     The GPU  20  outputs a display signal for displaying the image developed in the first memory  11  to the light modulation device  32  to drive the light modulation element of the light modulation device  32  to draw the image. 
     For example, in the OSD processing, the GPU  20  superimposes an image based on the OSD data  17  described above, an OSD menu image, or the like on a background image data set in advance or the image data input from the image source  48 , and then makes the projection section  30  project the result. For example, defining the input data input from the image source  48  as a first layer, and the OSD menu image as a second layer, the superimposing process is performed by superimposing the first layer and the second layer on one other. 
     The optical unit  33  is provided with an optical element such as a lens, a mirror, or a prism, and projects the image light PL toward the screen SC. The optical unit  33  can be provided with an adjustment mechanism for moving the optical element to thereby adjust the zoom or the focus, or can also be a configuration in which the adjustment mechanism operates under the control by the CPU  10 . 
     The projector  1  is provided with a sound processing section  23 , a communication section  25 , an interface  26 , an operation reception section  27 , and a power control section  28 . The interface is hereinafter abbreviated as I/F. 
     The sound processing section  23  is connected to a microphone  41  and a speaker  42 . The sound processing section  23  is provided with, for example, a conversion circuit for converting a vibration of the microphone  41  into a sound signal, and an A/D converter for converting an analog sound signal into a digital sound data. The sound processing section  23  collects the sound with the microphone  41  to generate the digital sound data, and then outputs the digital sound data to the CPU  10 . 
     The sound processing section  23  has, for example, a D/A converter for generating the analog sound signal based on the digital sound data, and an amplifier for amplifying the analog sound signal. The sound processing section  23  outputs the sound signal to the speaker  42  in accordance with sound data and control data input from the CPU  10  to make the speaker  42  output the sound. The microphone  41  and the speaker  42  can be incorporated in the projector  1 , or can also be installed outside the projector  1 . 
     The communication section  25  is a communication module for performing data communication with equipment outside the projector  1  in accordance with the control by the CPU  10 . The communication section  25  is provided with, for example, connectors to which communication cables compliant with a variety of standards such as Ethernet are connected, and a communication interface circuit for transmitting/receiving data via the communication cables. Further, the communication section  25  can be a wireless communication module for performing wireless communication with equipment outside the projector  1 . Ethernet is a registered trademark. 
     The I/F  26  is an interface to which the image data is input. The I/F  26  is provided with, for example, a connector to which a transmission cable not shown is connected, and an interface circuit for receiving the image data via the transmission cable. To the I/F  26 , there can be connected the image source  48  as a device for supplying the image data. As the image source  48 , there can be used, for example, a PC, a tablet terminal, or a smartphone, or it is possible for the image source  48  to be a DVD player, a hard disk recorder, a television tuner system, a video game machine, or the like. The image data to be input to the I/F  26  can be moving image data or still image data, and any data format can be adopted. It is possible for the I/F  26  and the image source  48  to be connected to each other via a wireless communication line. In the present embodiment, there is shown an example in which the I/F  26  and the image source  48  are connected to each other with a cable. The type of the cable is not limited, but it is possible to a variety of types of cable such as a composite video cable, a USB cable, or an HDMI cable. The string of USB is an abbreviation for Universal Serial Bus. HDMI is a registered trademark, and an abbreviation for High Definition Multimedia Interface. The string of PC is an abbreviation for Personal Computer, the string of PDA is an abbreviation for Personal Digital Assistants, and the string of DVD is an abbreviation for digital versatile disk. 
     The communication section  25  and the I/F  26  correspond to an example of a connecting section. 
     The operation reception section  27  receives input to the projector  1 . The operation reception section  27  is connected to a remote control light receiving section  45  for receiving an infrared signal transmitted by a remote controller not shown, and an operation panel  46  provided to a main body of the projector  1 . The operation reception section  27  decodes the signal received by the remote control light receiving section  45  to detect an operation by the remote controller. The operation reception section  27  detects an operation on the operation panel  46 . The operation reception section  27  outputs data representing the operation content to the CPU  10 . 
     The I/F  26  has a function of detecting the fact that the image source  48  is newly connected, and a function of detecting the fact that the image data, the control data, or another signal is newly input from the image source  48 . The I/F  26  generates an interrupt to the CPU  10  when, for example, connecting of the image source  48 , or input of the data or a signal has been detected in the standby state of the projector  1 . 
     The operation reception section  27  generates an interrupt to the CPU  10  when, for example, an operation by the remote control light receiving section  45  or the operation panel  46  has been detected in the standby state of the projector  1 . 
     The power control section  28  supplies each section of the projector  1  with the power in accordance with the control by the CPU  10  based on the power supplied from the commercial AC power supply or an AC adapter not shown. The power control section  28  is provided with, for example, a converter for converting the commercial AC power into DC power, a voltage converter circuit, and a rectifier circuit. When the power is applied to the projector  1 , the power control section  28  starts the power supply to each section of the projector  1 . Further, the power control section  28  starts and stops the power supply to each section of the projector  1  in accordance with the control by the CPU  10 . 
     2. Transition of Operation State of Projector 
     The operation state of the projector  1  makes the transition to a halt state in which the power is turned off, the transition to the standby state, and the transition to a normal operation state. 
     When the projector  1  has detected the operation of turning the power on with the operation reception section  27  in the halt state, the projector  1  starts the power supply to each section of the projector  1  with the power control section  28 . Further, each section of the projector  1  is initialized due to the control by the CPU  10 , and the transition to the normal operation state is made. 
     In the normal operation state, the power is supplied to each section of the projector  1 , and the projection of the image by the projection section  30  is possible. In particular, the power is supplied to the CPU  10 , the first memory  11 , the second memory  12 , the nonvolatile memory  15 , the sound processing section  23 , the communication section  25 , the I/F  26 , the operation reception section  27 , the power control section  28 , the projection processing section  3 , and the projection section  30 . Further, the power is supplied to the remote control light receiving section  45  and the operation panel  46  as needed so that the operation reception section  27  can detect the operation. Since the microphone  41  and the speaker  42  can operate in the normal operation state, the power is supplied to the microphone  41  and the speaker  42  as needed. 
     When the projection section  30  is not projecting the image in the normal operation state, the power is supplied to the projection processing section  3  and the projection section  30  by the power control section  28 , and the light source  31  is put off due to the control by the light source drive circuit  21 . 
     When the projector  1  has detected the operation of turning the power off with the operation reception section  27  in the normal operation state, the power control section  28  sequentially stops the power supply to each section of the projector  1  in accordance with the control by the CPU  10 . Thus, the projector  1  makes the transition to the halt state. 
     When the transition condition of making the transition to the standby state is fulfilled in the normal operation state, the projector  1  makes the transition to the standby state. 
     The standby state is the state in which the projector  1  does not project an image to the screen SC, and in which the power supply to a part of the projector  1  is stopped. In particular, in the standby state, the power supply to the projection processing section  3  and the projection section  30  is stopped. Further, in the present embodiment, the power supply to the nonvolatile memory  15  and the sound processing section  23  is stopped in the standby state. 
     In the standby state, the power supply to each section included in a standby energization device  2  is continued. The standby energization device  2  includes at least the second memory  12  and the power control section  28 . In the present embodiment, the standby energization device  2  further includes the communication section  25 , the I/F  26 , and the operation reception section  27 . In the standby state, the operation reception section  27  keeps the state in which the operation by the remote control light receiving section  45  and the operation panel  46  can be detected. Therefore, the remote control light receiving section  45  and the operation panel  46  are supplied with the power as needed in the standby state, and can therefore be said to be included in the standby energization device  2  together with the operation reception section  27 . The second memory  12  is energized also in the standby state. It is preferable that the storage capacity of the second memory  12  is as small as possible since the power consumption in the standby state can be suppressed. Therefore, for example, the storage capacity of the second memory  12  is small in capacity compared to the storage capacity of the first memory  11 . 
     The communication section  25  can receive data from external equipment in the standby state. When the communication section  25  has received the data from the external equipment in the standby state, the communication section  25  generates an interrupt to the CPU  10 . In the standby state, the communication section  25  can be set in a power saving state so that the power consumption of the communication section  25  becomes lower than in the normal operation state. It is possible for the communication section  25  to make, for example, the transmission period of packets or beacons for keeping the communication state through the communication cable longer in the power saving state than in the normal operation state. Further, for example, it is possible for the communication section  25  to make the period of trials of receiving the data or packets longer in the power saving state than in the normal operation state. Further, when the communication section  25  is the wireless communication module, it is possible to make the transmission output of the wireless signal lower in the power saving state than in the normal operation state. 
     The I/F  26  can detect the connection of the image source  48  and the input of the signal or the data from the image source  48  in the standby state. When the I/F  26  has detected the connection of the image source  48  or the input of the data or the like, the I/F  26  generates an interrupt to the CPU  10 . 
     In the standby state, the I/F  26  can be set in a power saving state so that the power consumption of the I/F  26  becomes lower than in the normal operation state. For example, it is possible for the I/F  26  to make the period of determinations on presence or absence of the connection of the image source  48  longer in the power saving state than in the normal operation state. Further, for example, it is possible for the I/F  26  to make the period of determinations on presence or absence of the input of the signal or the data longer in the power saving state than in the normal operation state. Further, for example, it is possible for the I/F  26  to make the transmission period of the data transmitted/received to/from the image source  48  for checking the connection state longer in the power saving state than in the normal operation state. 
     The operation reception section  27  can detect the operation with the remote control light receiving section  45  and the operation panel  46  in the standby state as described above. When the operation reception section  27  has detected the operation, the operation reception section  27  generates an interrupt to the CPU  10 . In the standby state, the operation reception section  27  can be set in a power saving state so that the power consumption of the operation reception section  27  becomes lower than in the normal operation state. For example, it is possible for the operation reception section  27  to make the period of detecting the infrared signal by the remote control light receiving section  45  longer in the power saving state than in the normal operation state. Further, for example, it is possible for the operation reception  27  to make the period of determinations on presence or absence of the operation of the operation panel  46  longer in the power saving state than in the normal operation state. 
     In the standby state, the CPU  10  determines whether or not the return condition from the standby state to the normal operation state has been fulfilled. When the CPU  10  has determined that the return condition to the normal operation state has been fulfilled, the CPU  10  controls the power control section  28  to start the power supply to each section except the standby energization device  2 . Further, the CPU  10  resets each section except the standby energization device  2  to make the transition of the whole of the projector  1  to the normal operation state. 
     The return condition is, for example, the generation of the interrupt from the communication section  25 , the I/F  26 , or the operation reception section  27 . Further, for example, it is possible for the CPU  10  to have a timing function for timing the current time, and determine that the return condition has fulfilled when the time set in advance has been reached. 
     In the standby state, the CPU  10  can be set in a power saving state so that the power consumption of the CPU  10  becomes lower than in the normal operation state. It is possible for the CPU  10  to operate with, for example, the clock lower in frequency in the power saving state than in the normal operation state. This configuration can be realized by, for example, switching the frequency of the clock signal to be supplied from the clock signal supply circuit not shown to each section of the standby energization device  2  including the CPU  10  to a lower frequency. 
     The power control section  28  perform the power supply to each section of the standby energization device  2  in the standby state. The communication section  25 , the I/F  26 , and the operation reception section  27  are each supplied with the power necessary to continue the operation of generating the interrupt to the CPU  10 . The CPU  10  is supplied with the power necessary to execute the function of determining whether or not the return condition is fulfilled. 
     The second memory  12  is the volatile memory as described above. Therefore, the power supply is necessary to keep the data stored by the second memory  12  in the state of being readable by the CPU  10 . The power control section  28  supplies the second memory  12  with sufficient power to keep the data so that the data in the second memory  12  can also be kept in the standby state. 
     In contrast, the power supply to the first memory  11  is stopped in the standby state. The CPU  10  resets to stop the first memory  11  when making the transition from the normal operation state to the standby state. Therefore, the data stored by the first memory  11  in the normal operation state is lost in the process of making the transition to the standby state. 
     When the CPU  10  has determined that the return condition from the standby state to the normal operation state has been fulfilled, the CPU  10  starts the operation of the projection processing section  3  to start the projection by the projection section  30 . Here, the GPU  20  displays a notice that the return from the standby state is in operation. 
       FIG. 2  is a diagram showing a display example when the projector  1  returns from the standby state, and shows an example of a returning screen  60  and a returning screen  61  to be displayed as the transition from the returning screen  60 . 
     The returning screen  60  is a screen in which a display object  65  including characters for giving the notice that the processing of returning from the standby state is in operation is disposed. When displaying the returning screen  60 , the GPU  20  obtains the OSD data  17  for displaying the display object  65 . The GPU  20  develops the image data of the whole of the projection image in the frame memory based on the data of the background image set in advance, then combines the OSD data  17  with the image data in the frame memory in a superimposed manner to generate the data corresponding to one frame of the returning screen  60 . 
     The OSD data  17  can be the image data of the display object  65 , or can also be data for generating the image data of the display object  65 . For example, the OSD data  17  can be the data obtained by compressing the image data of the display object  65 , and it is possible for the GPU  20  to develop the OSD data  17  in the first memory  11 , and then the image data thus developed is combined in the frame memory. Further, the OSD data  17  can be the data for generating the image data of the whole of the returning screen  60 , but is assumed as the data of the display object  65  in the description of the present embodiment. 
     It is possible for the CPU  10  to make the projection processing section  3  display the returning screen  61  while executing the process of returning from the standby state. The returning screen  61  is a screen in which a display object  66  including characters for giving the notice of the type of the display source  48  connected to the projector  1  is disposed. For example, when the projector  1  is capable of projecting the image data input from a plurality of types of image sources  48 , the display object  66  gives the notice of the type of the image source  48  currently selected. The display object  66  represents the type of the image source  48  which is inputting the image data to the projector  1 , or the type of the image source  48  currently selected from the plurality of selectable image sources  48 . 
     It is possible for the CPU  10  to project the returning screen  61  instead of the returning screen  60 . For example, when the CPU  10  makes the transition from the standby state to the normal operation state in accordance with the interrupt from the I/F  26 , it is possible to project the returning screen  61  representing information related to the image source  48  connected to the I/F  26 . Further, it is possible for the CPU  10  to make the transition of the projection image from the returning screen  60  to the returning screen  61 . 
     The OSD data  17  can be the image data of the display object  66 , or can also be data for generating the image data of the display object  66 . For example, the OSD data  17  can be data obtained by compressing the image data of the display object  66 . Further, the OSD data  17  can be the data for generating the image data of the whole of the returning screen  61 , but is assumed as the data of the display object  66  in the description of the present embodiment. 
     It is preferable for the CPU  10  to selectively use a plurality of types of display objects  66  in accordance with the type of the display source  48 . Therefore, it is preferable for the CPU  10  to display the corresponding number of display objects  66  to the number of the types of the selectable image sources  48  in the projector  1  while switching between the display objects  66 . In this case, the OSD data  17  includes the data of the plurality of display objects  66 . Further, the OSD data  17  can be data including both of the data of the display object  65  and the data of the display object  66 . Further, it is possible for the nonvolatile memory  15  to individually store the OSD data  17  including the data of the display object  65  and the OSD data  17  including the data of the display object  66 . 
     When displaying the returning screen  60  or the returning screen  61 , it is necessary for the GPU  20  to obtain the OSD data  17 . In the data reading speed and the data writing speed, the nonvolatile memory  15  formed of the flash ROM or the EEPROM is remarkably lower compared to the first memory  11  and the second memory  12  formed of the DRAM or the like. Therefore, when the OSD data  17  is retrieved from the nonvolatile memory  15  before the GPU  20  displays the returning screen  60  or the returning screen  61 , namely before the GPU  20  processes the OSD data  17 , the processing of the GPU  20  obtaining the OSD data  17  can be made faster. The first memory  11  has a temporary storage area for temporarily storing data and a program in addition to the frame memory. For example, when the CPU  10  retrieves the OSD data  17  from the nonvolatile memory  15  and then stores the OSD data  17  in the temporary storage area of the first memory  11 , it is possible for the GPU  20  to obtain the OSD data  17  in a short time. 
     However, when the projector  1  makes the transition to the standby state, the power supply to the first memory  11  is stopped, and thus, the first memory  11  is reset. Therefore, even when the OSD data  17  related to the display object  65  and the display object  66  to be displayed when returning from the standby state is stored in the first memory  11  in advance, the OSD data  17  thus stored in the first memory  11  cannot be used. 
     The projector  1  according to the present embodiment stores the OSD data  17  related to the display objects  65 ,  66  to be displayed when returning from the standby state in the second memory  12  in advance to thereby achieve the increase in speed of the processing of the GPU  20  obtaining the OSD data  17 . 
     3. Operation of Projector 
       FIG. 3  and  FIG. 4  are each a flowchart showing the operation of the projector.  FIG. 3  shows the operation of making the transition of the projector  1  to the standby state, and  FIG. 4  shows the operation of the projector  1  returning from the standby state to the normal operation state. 
     In the normal operation state, when the transition condition to the standby state is fulfilled, the CPU  10  starts (step ST 11 ) a transition procedure to the standby state. As the transition condition, there can be cited, for example, the condition that the operation reception section  27  has detected the operationofinstructing the transition to the standby state, the condition that the state in which no input to the I/F  26  exists lasts for a predetermined period of time, and the condition that the state in which the image source  48  does not exist lasts for a predetermined period of time. 
     In the transition procedure, the CPU  10  retrieves (step ST 12 ) the OSD data  17  from the nonvolatile memory  15 , and then stores (step ST 13 ) the OSD data  17  in the second memory  12 . The CPU  10  resets (step ST 14 ) the first memory  11 , and then sequentially stops (step ST 15 ) the operation of each section to which the power supply is stopped in the standby state. The CPU  10  controls the power control section  28  to stop (step ST 16 ) the power supply to each section to be stopped in the standby state, and thus, the projector  1  makes (step ST 17 ) the transition to the standby state. 
     It is preferable for the OSD data  17  to be the data related to the display of the display object  65  and the display object  66 , for example, the image data of the display objects  65 ,  66  and the data obtained by compressing such image data. In this case, the data amount of the OSD data  17  is obviously smaller compared to the data of the whole of the returning screen  60  and the returning screen  61 . Therefore, only a small storage area in the second memory  12  is required for storing the OSD data  17 . Therefore, it is possible to suppress the capacity of the second memory  12  to be energized in the standby state, and it is possible to suppress the power consumption of the projector  1  in the standby state. Further, it is possible to execute the method of storing the OSD data  17  in the second memory  12  without taking a measure such as an increase in the capacity of the second memory  12 . 
     In the standby state, when the return condition described above is fulfilled, the CPU  10  starts (step ST 21  in  FIG. 4 ) a return procedure from the standby state to the normal operation state. 
     The CPU  10  controls the power control section  28  to stop (step ST 22 ) the power supply to each section to which the power supply has been stopped in the standby state, and then, initialize (step ST 23 ) each section to which the power supply is resumed. 
     The CPU  10  determines (step ST 24 ) whether or not the OSD data  17  is stored in the second memory  12 . When the OSD data  17  is stored in the second memory  12  (YES in the step ST 24 ), the CPU  10  retrieves the OSD data  17  from the second memory  12 , and then stores (step ST 25 ) the OSD data  17  in the first memory  11 . 
     The GPU  20  develops (step ST 26 ) the image of the returning screen  60  in the frame memory using the OSD data  17  stored in the first memory  11  in accordance with the control by the CPU  10 . The GPU  20  makes (step ST 27 ) the light modulation device  32  form the returning screen  60  developed in the frame memory. Here, the light source drive circuit  21  puts (step ST 28 ) the light source  31  on in accordance with the control by the CPU  10 , and the projector  1  makes (step ST 29 ) the transition to the normal operation state. The processing in the step ST 27  and the processing in the step ST 28  can be executed in the reverse order, or can also be executed at the same time in parallel to each other. 
     In contrast, when the OSD data  17  is not stored in the second memory  12  (NO in the step ST 24 ), the CPU  10  retrieves the OSD data  17  from the nonvolatile memory  15 , and then stores (step ST 30 ) the OSD data  17  in the first memory  11 , and then makes the transition to the step ST 26 . 
     As described hereinabove, the projector  1  according to the embodiment implementing the present disclosure is the display device provided with the projection section  30  as the display section. The projector  1  is provided with the CPU  10  for controlling the projection section  30 . The projector  1  is provided with the first memory  11  which is the volatile memory to be reset when the projector  1  makes the transition to the standby state, and the second memory  12  which is the volatile memory capable of keeping the data in the standby state of the projector  1 . The CPU  10  stores the OSD data  17  in the second memory  12  when the projector  1  makes the transition to the standby state. The OSD data  17  includes the data of the object  65 , the object  66 , or the objects  65 ,  66  to be displayed by the projection section  30  when returning from the standby state to the normal operation state. 
     The method of controlling the projector  1  controls the storage of the data in the first memory  11  which is the volatile memory to be reset when the projector  1  makes the transition to the standby state, and the second memory  12  which is the volatile memory capable of keeping the data in the standby state of the projector  1 . In this control method, the OSD data  17  is stored in the second memory  12  when the projector  1  makes the transition to the standby state. 
     According to the projector  1  implementing the display device and the method of controlling the display device according to the present disclosure, it is possible to retrieve the OSD data  17  from the second memory  12  and then project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  when returning from the standby state. Since the second memory  12  is the volatile memory capable of performing the data readout at high speed, it is possible to promptly project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  when returning from the standby state. 
     The CPU  10  retrieves the OSD data  17  stored in the second memory  12  and then makes the projection section  30  project the OSD data  17  when the projector  1  returns from the standby state to the normal operation state. Therefore, it is possible to promptly project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  when the projector  1  returns from the standby state to the normal operation state. For example, as shown in  FIG. 2 , it is possible to display the returning screen  60  by disposing the display object  65  based on the OSD data  17  stored in the second memory  12 . The same applies to the returning screen  61 . 
     In the standby state, the CPU  10 , the second memory  12 , and at least one of the communication section  25  and the I/F  26  to be connected to the external equipment can operate. In the standby state, the first memory  11  and the projection section  30  stop the operations, and in the normal operation state, the first memory  11 , the nonvolatile memory  15 , and the projection section  30  can operate. Therefore, when returning from the standby state in which the first memory  11 , the nonvolatile memory  15 , and the projection section  30  stop, it is possible to promptly project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  using the second memory  12 . 
     The projector  1  is provided with the nonvolatile memory  15  for storing the OSD data  17 . The CPU  10  retrieves the OSD data  17  from the nonvolatile memory  15 , and then stores the OSD data  17  in the second memory  12  when the projector  1  makes the transition to the standby state. Therefore, it is possible to keep the OSD data  17  in a nonvolatile manner using the nonvolatile memory  15 . When returning from the standby state, it is possible to promptly project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  using the second memory  12  from which the OSD data  17  can be retrieved at higher speed than from the nonvolatile memory  15 . 
     The projector  1  is a projector provided with the projection section  30  for projecting the image light PL based on the light emitted by the light source  31  as the solid-state light source. In the standby state, the light source  31  stops the light emission, and when returning from the standby state to the normal operation state, the light source  31  starts the light emission, and the projection section  30  projects the image based on the data of the display objects  65 ,  66  retrieved from the second memory  12 . According to this configuration, due to the characteristics of the solid-state light source, when the light source  31  is energized when retuning from the standby state to the normal operation state, the light source  31  promptly emits light at high luminance. Therefore, by the projection processing section  3  promptly generating the frame image, it is possible to project the returning screen  60 , the returning screen  61 , or the returning screens  60 ,  61  in an extremely short time when the return condition from the standby state has been fulfilled. Further, when it takes time for the projection processing section  3  to perform the processing of generating the data of the projection image, unmodulated light is projected to the screen SC. However, the projector  1  can avoid such a situation. Further, there is no need to perform control such as delaying the lighting of the light source  31  in order to prevent the unmodulated light from being projected to the screen SC. 
     4. Other Embodiments 
     The embodiment described above shows a specific example to which the present disclosure is applied, and the present disclosure is not limited to the embodiment. 
     For example, in the embodiment described above, there is presented the description illustrating the configuration in which the CPU  10  and the GPU  20  are connected to the first memory  11 , but the present disclosure is not limited thereto. For example, it is possible to provide the frame memory separately from the first memory  11 . 
     Further, specific specifications of the first memory  11 , the second memory  12 , and the nonvolatile memory  15  are arbitrary. For example, it is possible for the first memory  11  and the second memory  12  to use an SDRAM or a DDR SDRAM. The string of SDRAM is an abbreviation for Synchronous DRAM, and the string of DDR SDRAM is an abbreviation for Double-Data-Rate SDRAM. 
     Further, in the embodiment described above, there is described the example in which the CPU  10  stores the OSD data  17  in the second memory  12  in the step ST 13  when making the transition from the normal operation state to the standby state. The present disclosure is not limited to this example, and for example, it is possible for the CPU  10  to store only the OSD data  17  related to the display object  65  to be displayed first when returning from the standby state to the normal operation state in the second memory  12  in the step ST 13 . In particular, when returning from the standby state to the normal operation state, the returning screen  60  is displayed, and then, it takes time for the GPU  20  to execute the processing of obtaining the display object  66  when subsequently displaying the returning screen  61 , which does not pose a significant problem. In this case, the CPU  10  retrieves the OSD data  17  related to the display object  65  out of the OSD data  17  stored in the nonvolatile memory  15 , and then stores the OSD data  17  related to the display object  65  in the second memory  12  in the step ST 13 . In the step ST 26 , the GPU  20  obtains the OSD data  17  related to the display object  65  to draw the image of the returning screen  60 , and then makes the projection section  30  project the image of the returning screen  60  thus drawn. In this case, there is an advantage that only the small amount of data is required to be stored in the second memory  12 . For example, it is possible to promptly project the returning screen  60  using the second memory  12  provided to the projector  1  in order to keep the operating system. Further, when the OSD data  17  includes the data related to both of the display object  65  and the display object  66 , it is possible for the CPU  10  to extract a part of the OSD data  17  to store the result in the second memory  12  in the step ST 13 . 
     Further, in the embodiment described above, there is described the example in which the CPU  10  stores the OSD data  17  stored in the nonvolatile memory  15  in the second memory  12  in the step ST 13  when the projector  1  makes the transition from the normal operation state to the standby state. The present disclosure is not limited to this example, but it is possible for the CPU  10  to, for example, retrieve the OSD data  17  which represents the OSD image developed in the first memory  11  in the superimposing process and located in the second layer from the first memory  11  and then store the OSD data  17  thus retrieved in the second memory  12  in the step ST 13  when making the transition from the normal operation state to the standby state. Then, in the step ST 26 , the GPU  20  obtains the OSD data  17  in the second memory  12  to draw the image of the returning screen  60 , and then makes the projection section  30  project the image of the returning screen  60  thus drawn when returning from the standby state to the normal operation state. In this case, there is an advantage that the OSD image which has been displayed in the normal operation state immediately before making the transition to the standby state can be displayed after returning from the standby state. 
     The operation states of the projector  1  are not limited to the three states, namely the halt state, the standby state, and the normal operation state. For example, it is possible to be able to execute an AV standby state in which the sound input/output by the sound processing section  23  is possible. The AV standby state is a state in which it is possible for the sound processing section  23  to perform the collection of the sound with the microphone  41 , and the sound output with the speaker  42 , and in which the projection by the projection section  30  is not performed. In the AV standby state, the power supply to at least the projection processing section  3  and the projection section  30  is stopped, and the power supply to the first memory  11  is also stopped. The AV standby state is used, for example, for the purpose of using the projector  1  as a loudspeaker by outputting the sound collected by the sound processing section  23  from the speaker  42 , or for the purpose of outputting the data of the sound collected to the external equipment with the communication section  25 . In this case, it is possible for the CPU  10  to execute the operation shown in  FIG. 3  when making the transition from the normal operation state to the AV standby state similarly to the transition from the normal operation state to the standby state. Further, similarly to the operation shown in  FIG. 4 , it is possible to return to the normal operation state when the return condition has been fulfilled in the AV standby state. In other words, as long as the projector  1  can execute the state in which the power supply to the projection processing section  3  and the projection section  30  is stopped and the first memory  11  is stopped, and stores the OSD data  17  in the second memory  12  when making the transition to this state, it is possible to obtain the advantage derived from the present disclosure. 
     The display device according to the present disclosure is not limited to the projector  1 , but it is also possible to adopt a liquid crystal monitor or a liquid crystal television set for displaying an image on a liquid crystal display panel as the display device. A display device provided with a plasma display panel or an organic EL display panel can also be used. In this case, the display panel corresponds to the display section in the present disclosure. 
     The specific mounting configuration of the functional sections shown in  FIG. 1  is not limited to the configuration shown in  FIG. 1 , and it is not necessarily required to install the hardware individually corresponding to each of the functional sections. A part of the function realized by the software in the embodiment described above can also be realized by hardware, or a part of the function realized by the hardware can also be realized by software. Besides the above, the specific detailed configuration of each of other sections constituting the projector  1  can arbitrarily be modified within the scope or the spirit of the present disclosure.