JP4059281B2 - Liquid crystal display device and electronic camera - Google Patents

Description

  The present invention relates to a liquid crystal display device and an electronic camera, and more particularly to a liquid crystal display device and an electronic camera applied to an electronic camera such as a digital camera.

  Conventionally, when taking a picture with a digital camera or the like and displaying the shot still picture on a liquid crystal monitor, signal processing is performed while reading out the image data once stored in the picture memory from the picture memory to obtain a standard video signal or liquid crystal. The video signal is converted into a video signal suitable for a monitor, and the video signal is output to a liquid crystal monitor to display a still image.

At this time, since the image memory is continuously accessed at a constant frame rate via the memory bus, the image memory is used for purposes other than display, such as image data compression processing or recording processing to an external memory. In order to access the image data in the memory, the display is temporarily stopped or accessed during the horizontal / vertical blanking period.
JP-A-63-243922 Japanese Patent Laid-Open No. 09-093470 Japanese Patent Laid-Open No. 05-056316

  However, in the former case, there is a problem that the display cannot be confirmed because the display once disappears.

In the latter case, since only a short time can be used as the processing time, there is a problem that the entire signal processing time becomes long. For example, in the case of displaying an image of 640 × 480 pixels with an NTSC video signal, for example,
1 frame period = 1/30 = 33.3 (msec)
Vertical blanking period = 1 frame period * (525-480) / 525
= (1/30) * (45) / 525
≒ 2.86 (msec)
If only the vertical blanking period is used, only 2.86 (msec) can be used for signal processing in the 1V period (vertical synchronization period), and even if the horizontal blanking period is used, the increase is slight. .

  In addition, there is an electronic camera that can display a moving image on a liquid crystal monitor and use the liquid crystal monitor as an electronic viewfinder. However, there is a problem that power consumption increases while the liquid crystal monitor is used.

  The objective of this invention is providing the liquid crystal display device and electronic camera which can reduce the power consumption at the time of displaying an image on a liquid crystal display.

  Another object of the present invention is to provide an electronic camera capable of executing signal processing other than display at high speed while displaying an image on a liquid crystal display.

  In order to achieve the above object, a liquid crystal display device according to the present invention includes an image acquisition unit that acquires image data, an image memory that temporarily stores the image data acquired by the image acquisition unit, a liquid crystal display, Selection means for selecting whether to output video data stored in the image memory to an external device or to the liquid crystal display; and video output of the image data stored in the image memory to the external device A first timing signal for generating a video signal is generated, and when outputting the image data stored in the image memory to the liquid crystal display, a second lower frequency than the first timing signal is generated. A timing signal generating means for generating a timing signal, and a video signal output from the image memory stored in the image memory to the external device; Reading out image data from an image memory using the first timing signal and outputting a video signal to the external device; and outputting image data stored in the image memory to the liquid crystal display And a liquid crystal driving means for reading image data from the image memory using the second timing signal and outputting a driving signal corresponding to the video signal to the liquid crystal display together with a video signal for liquid crystal display. It is characterized by that.

  In order to achieve the above object, an electronic camera according to a first aspect of the present invention temporarily captures image data obtained by driving an imaging device and acquiring image data indicating a subject, and image data acquired by the imaging unit. An image memory to be stored, a liquid crystal display, selection means for selecting whether to output video data stored in the image memory to an external device or to the liquid crystal display, and storage in the image memory When outputting the image data to the external device as a video, a first timing signal for generating a video signal is generated, and when outputting the image data stored in the image memory to the liquid crystal display, the first timing signal is generated. Timing signal generating means for generating a second timing signal having a frequency lower than that of the timing signal; and image data stored in the image memory When outputting video to a device, the image data is read from the image memory using the first timing signal, and a video output means for outputting a video signal to the external device; and image data stored in the image memory When the image data is output to the liquid crystal display, the second timing signal is used to read image data from the image memory, and a driving pulse corresponding to the video signal is output together with the video signal for liquid crystal display. And a liquid crystal driving means for outputting to the display.

  In addition, an electronic camera according to a second aspect of the present invention includes an imaging unit that drives an imaging device to acquire image data indicating a subject, a liquid crystal display, and image data acquired by the imaging unit. A selection means for selecting whether to output video to a device or to the liquid crystal display, and a first timing for generating a video signal when the image data acquired by the imaging means is output to the external device as a video A timing signal generating means for generating a second timing signal having a frequency lower than that of the first timing signal when generating a signal and outputting the image data acquired by the imaging means to the liquid crystal display; When the image data acquired by the imaging unit is video-output to the external device, the driving of the imaging element is controlled by the first timing signal. The video output means for outputting a video signal to the external device, and when the image data acquired by the imaging means is output to the liquid crystal display, the image sensor is driven by the second timing signal. And a liquid crystal driving means for outputting a driving pulse corresponding to the video signal to the liquid crystal display together with a video signal for liquid crystal display.

  That is, when outputting a video signal to an external device, it is necessary to output a standard video signal such as NTSC system or PAL system from the video output terminal, which is suitable for generating a standard video signal. In accordance with the first timing signal, the image sensor is driven and image data is read from the image memory. On the other hand, when an image is displayed on the liquid crystal display, the standard video signal is not limited. Therefore, the driving of the image sensor and the reading of the image data from the image memory are performed at a frequency higher than that of the first timing signal. The second timing signal is low, and a driving pulse corresponding to the video signal is output together with the video signal for liquid crystal display. The power consumption is proportional to the frequency of driving the image sensor and reading the image data from the image memory, so that the power consumption when displaying an image on the liquid crystal display can be reduced.

  As described above, according to the present invention, when an image is displayed on the liquid crystal display, the video signal is intermittently supplied, and when the video signal is not input, the output of the pulse necessary for the liquid crystal display is stopped. The current image displayed on the display can be held, which can drive the image sensor, read the image data from the image memory, and stop the signal processing circuit, greatly reducing power consumption. can do. Even if the liquid crystal display is stopped, there is no problem when displaying a still image on the liquid crystal display, and when a moving image is displayed on the liquid crystal display, the display is smoother due to intermittent display. Although the movement is sacrificed, it is sufficiently practical as an electronic viewfinder for framing a subject.

  In addition, since it is not necessary to always read out image data from the image memory or the like, the image memory is accessed during the reading stop period of the liquid crystal display while displaying the image on the liquid crystal display, and other signal processing is performed. A sufficient amount of time (for example, compression processing of image data, recording processing to an external memory, etc.) can be secured, and other signal processing can be executed at high speed.

  Further, according to the present invention, when a video signal is output to an external device, the first timing signal suitable for generating a standard video signal such as NTSC system or PAL system from the video output terminal is used. When driving the image sensor or reading the image data from the image memory and displaying the image on the liquid crystal display, there is no restriction on the standard video signal, so the image sensor is driven and the image is read from the image memory. Since the data is read by the second timing signal having a frequency lower than that of the first timing signal, power consumption when displaying an image on the liquid crystal display can be reduced.

  Hereinafter, preferred embodiments of a liquid crystal display device and an electronic camera according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an electronic camera according to the present invention.

  This electronic camera is a digital camera that records a still image on an external memory card or the like by operating a release button (not shown), and is provided with a liquid crystal display (LCD panel) 30. The LCD panel 30 can display a captured still image or a reproduced still image, and can also display a moving image and can be used as an electronic viewfinder.

  The subject image is formed on the light receiving surface of the solid-state image sensor (CCD) 12 via the taking lens 10. The CCD 12 converts the image light imaged on the light receiving surface into a signal charge in an amount corresponding to the light amount. The signal charges thus converted are sequentially read out as voltage signals (image signals) corresponding to the signal charges based on the CCD drive pulse applied from the CCD drive circuit 13 and added to the CDS circuit 16.

  The CDS circuit 16 includes a CDS clamp, a gain control amplifier, an A / D converter, and the like. The image signal read from the CCD 12 is sampled and held for each pixel by the CDS clamp and amplified by the gain control amplifier. After that, it is converted into R, G, B digital signals by the A / D converter and applied to the signal processing circuit 18. The timing signal generation circuit 14 outputs appropriate timing signals to the CCD drive circuit 13, the CDS circuit 16, and the signal processing circuit 18 in accordance with commands from the microcomputer 20, and synchronizes the circuits. Details of the timing signal will be described later.

  The signal processing circuit 18 includes a YC signal creation circuit, a compression / decompression circuit, etc., and converts the R, G, B digital signals into YC signals (luminance signal Y and chroma signal C) by a command from the microcomputer 20, This YC signal is stored in the memory 22. Further, the signal processing circuit 18 reads the YC signal from the memory 22 continuously or intermittently by a command from the microcomputer 20 and outputs it to the video output circuit 24.

  The video output circuit 24 includes a D / A converter, an encoder, and the like. After the input YC signal is converted into an analog signal by the D / A converter, the encoder generates, for example, an NTSC video signal, which is output to the video output terminal. 26 and the liquid crystal drive circuit 28.

  The liquid crystal drive circuit 28 generates R, G, B signals and pulses necessary for liquid crystal display based on the input video signal, outputs the LCD panel 30, and causes the LCD panel 30 to display an image.

  Reference numeral 32 denotes an external interface for exchanging data with a memory card or an external device. The signal processing circuit 18 accesses the memory 22 by a command from the microcomputer 20 when recording image data, and stores the YC on the memory 22. The signal is compressed, and the compressed image data is recorded on the memory card via the external interface 32. Reference numeral 34 denotes a detector that mechanically or electrically detects whether a cable or a television is connected to the video output terminal 26.

  Next, a case where a still image is recorded on a memory card by operating the release button in the electronic camera having the above configuration will be described.

  In this case, the image data acquired by operating the release button is temporarily stored in the memory 22. The signal processing circuit 18 intermittently reads out image data stored in the memory 22 in units of one screen (one field or one frame) in order to display stillness on the LCD panel 30 in response to a command from the microcomputer 20. A reading stop period of a certain period (for example, one field or one frame) is provided between the previous reading of one screen and the next reading of one screen.

The image data read intermittently in this way is converted into a video signal suitable for liquid crystal display via the video output circuit 24 and applied to the liquid crystal drive circuit 28. As shown in FIG. 2, the liquid crystal driving circuit 28 is a circuit (not shown) for generating R, G, B signals, a synchronizing signal, and a driving control signal based on an input video signal, a driver circuit 28A, and a driving pulse generating circuit. The R, G, and B signals are output to the driver 28A, and the synchronization signal and the drive control signal are output to the drive pulse generation circuit 28B. Note that the drive control signal is a signal indicating whether or not a video signal is input. As shown in FIG. 3B, the period during which the video signal is supplied is T ₁ , and the period during which the video signal supply is stopped. When the the T _2, the drive control signal is a signal that becomes a low level and a high level in synchronization with the period T ₁ and period T _2.

  The driver circuit 28A inverts the polarities of the R, G, and B signals for each horizontal line and outputs them to the horizontal gate switch unit 30A of the LCD panel 30 so that a constant voltage is not applied to the liquid crystal element for a long time.

  The drive pulse generation circuit 28B generates a horizontal pulse and a vertical pulse for driving the LCD panel 30 based on a vertical synchronization signal and a horizontal synchronization signal that are synchronously separated from the video signal. As shown in FIG. The generation of the horizontal pulse and the vertical pulse is stopped during a period in which the control signal is at a high level (that is, a period in which no video signal is input).

  As shown in FIG. 2, the LCD panel 30 includes a horizontal gate switch unit 30A, a horizontal shift register 30B, a vertical shift register 30C, and a display unit 30D in which liquid crystal elements including a capacitive element LC are arranged in a matrix. The gate switch unit 30A receives R, G, B signals from the driver circuit, and the horizontal shift register 30B and the vertical shift register 30C receive horizontal pulses and vertical pulses from the drive pulse generation circuit 28B, respectively. It has become.

  The R, G, and B signals applied to the horizontal gate switch unit 30A are taken in by a horizontal shift register 30B driven by a horizontal pulse, and a predetermined value of the display unit 30D by a vertical shift register 30C driven based on a vertical pulse. Applied to the liquid crystal element of the line. Each liquid crystal element of the display unit 30D modulates transmitted light or reflected light according to the applied voltage, thereby displaying an image.

  The drive pulse generation circuit 28B stops the generation of the horizontal pulse and the vertical pulse in accordance with the non-input period of the video signal. In this case, the charge corresponding to the image data is stored in the capacitor element LC of each liquid crystal element. The voltage corresponding to the image data is held and applied between the liquid crystal electrodes. Thereby, even if the horizontal pulse and the vertical pulse are stopped, the LCD panel 30 continues to display the currently displayed image, and the image display is not interrupted. During this time, the image cannot be updated, but in the case of a digital camera, there is no problem because the captured still image is displayed.

  Although it is not preferable in terms of device characteristics to keep applying a constant voltage to the liquid crystal element for a long time, it is possible to avoid characteristic deterioration by driving the LCD panel 30 intermittently and repeatedly as shown in FIG. it can. Further, flicker and the like can be suppressed to a level with no problem.

  On the other hand, during the stop period in which reading of image data for liquid crystal display from the memory 22 is stopped, the memory bus is released and access to the memory 22 becomes free. Therefore, the signal processing circuit 18 accesses the memory 22 during the stop period, compresses the YC signal on the memory 22, and records the compressed image data on the memory card via the external interface 32.

  As described above, since image data is not always read from the memory 22 for liquid crystal display, it is possible to secure a sufficient time for recording the image data in the memory 22 on the memory card. That is, the recording process can be executed at high speed without interrupting the image display on the LCD panel 30, and the next photographing opportunity can be prevented from being missed.

  In the above embodiment, image data is read and the LCD panel 30 is driven intermittently in units of one screen (one field or one frame). However, the present invention is not limited to this, and lines (1H or several H; Image data may be read and the LCD panel 30 may be driven intermittently in units of H (horizontal scanning period).

Further, the stop period _{T 2} shown in FIG. 3 (B), the period _{T 1} and equal to or greater than (e.g., integer multiples) may be used.

  Next, another embodiment of the present invention will be described.

  In the above embodiment, the case where a still image is displayed on the LCD panel 30 based on the image data once stored in the memory 22 has been described. However, the image data captured via the CCD 12 and the CDS circuit 16 is subjected to signal processing, and the memory A case in which an image is directly displayed on the LCD panel 30 without going through 22 will be described.

  In this case, an image signal for one field is read from the CCD 12. This image signal is converted into R, G, B digital signals by the CDS circuit 16, processed by the signal processing circuit 18, and then output to the liquid crystal driving circuit 28 as a video signal via the video output circuit 24. . The liquid crystal drive circuit 28 supplies pulses necessary for liquid crystal display to the LCD panel 30 together with the R, G, and B signals based on the video signal, and causes the LCD panel 30 to display an image.

  Thereafter, the reading of the image signal from the CCD 12 is stopped, and all or a part of the pulses necessary for the liquid crystal display are stopped to stop the driving of the LCD panel 30. Note that the liquid crystal image on the LCD panel 30 is retained even when the driving is stopped. After stopping for a predetermined period, reading of the image signal from the CCD 12 and driving of the LCD panel 30 are resumed to update the display image.

  The microcomputer 20 can significantly reduce power consumption by stopping the operations of the CCD 12, the CCD drive circuit 13, the CDS circuit 16, and the signal processing circuit 18 during the stop period. For example, with respect to the CCD 12 read out at 1/60 sec, image signals are read out and the LCD panel 30 is driven intermittently at 1/30 sec (1/2 decimation) and 1/15 sec (1/4 decimation). Is displayed. In this case, the smooth movement of the moving image is sacrificed by the intermittent display, but it is sufficiently practical as an electronic viewfinder for framing the subject, for example.

  On the other hand, it is necessary to output a standard video signal (non-intermittent video signal) such as the NTSC system from the video output terminal 26. Therefore, when a cable or a television is connected to the video output terminal 26, the intermittent video signal output from the video output circuit 24 is stopped and a continuous video signal is output.

  That is, when the microcomputer 20 receives a signal indicating that a cable or a television is connected to the video output terminal 26 from the detector 34, the microcomputer 12 intermittently operates the CCD 12, the CCD drive circuit 13, the CDS circuit 16, and the signal processing circuit 18. Thus, a standard video signal is output from the video output circuit 24 so that a television or the like can operate normally.

  Next, still another embodiment of the present invention will be described.

  In the embodiment described above, image signals are read out intermittently or continuously from the CCD 12 or the memory 22, and the LCD panel 30 is also driven intermittently or continuously in accordance with this, and an image is displayed on the LCD panel 30. However, in this embodiment, image signals are read from the CCD 12 or the memory 22 using at least two types of timing signals.

  The first timing signal of the two types of timing signals is a timing signal suitable for making a standard video signal such as the NTSC system, and the second timing signal is more than the first timing signal. This is a low-frequency timing signal.

  When a video signal is output from the video output terminal 26, an image signal is read out from the CCD 12 or the memory 22 using the first timing signal, a standard video signal is output from the video output terminal 26, and the LCD panel. When only the image display at 30 is performed, the image signal is read from the CCD 12 or the memory 22 by the second timing signal, and a video signal having a frame rate slower than the standard video signal is output to the LCD panel 30. Then, the LCD panel 30 is driven with a corresponding drive pulse.

  That is, the microcomputer 20 detects whether the video output from the video output terminal 26 or the liquid crystal display of only the LCD panel 30 is detected by the detector 34 or other selection means. A command for generating a typical video signal is output to the timing signal generation circuit 14. On the other hand, if the liquid crystal display is selected, the command for liquid crystal display is output to the timing signal generation circuit 14.

  As a result, the timing signal generation circuit 14 outputs a first timing signal suitable for generating a standard video signal at the time of video output, and a video signal having a slower frame rate than the standard video signal at the time of liquid crystal display. A second timing signal for generating is output.

  Note that the lower the frequency of driving the CCD 12 and reading the image data from the memory 22, the lower the power consumption. In this embodiment, when performing only liquid crystal display, a standard video signal is used. Since it is not necessary to generate the video signal, a video signal having a slower frame rate than that of a standard video signal is generated, thereby reducing power consumption.

  Note that the liquid crystal driving circuit is not limited to a video signal input for the NTSC system or the like, but may be a signal input for R, G, B signals.

FIG. 1 is a block diagram showing an electronic camera according to the present invention. FIG. 2 is a block diagram showing details of the liquid crystal driving circuit and the LCD panel 30 shown in FIG. FIG. 3 is a timing chart of signals in the liquid crystal driving circuit shown in FIG.

Explanation of symbols

10 ... Photography lens 12 ... Solid-state image sensor (CCD)
DESCRIPTION OF SYMBOLS 13 ... CCD drive circuit 14 ... Timing signal generation circuit 16 ... CDS circuit 18 ... Signal processing circuit 20 ... Microcomputer 22 ... Memory 24 ... Video output circuit 26 ... Video output terminal 28 ... Liquid crystal drive circuit 28A ... Driver circuit 28B ... Drive pulse generation Circuit 30 ... LCD panel 30A ... Horizontal gate switch unit 30B ... Horizontal shift register 30C ... Vertical shift register 30D ... Display unit 32 ... External interface 34 ... Detector

Claims (3)

Image acquisition means for acquiring image data;
An image memory for temporarily storing the image data acquired by the image acquisition means;
A liquid crystal display,
A selection means for selecting whether to output the image data stored in the image memory to an external device or to the liquid crystal display;
When the image data stored in the image memory is video-outputted to the external device, a first timing signal for generating a video signal is generated, and the image data stored in the image memory is output to the liquid crystal display. A timing signal generating means for generating a second timing signal having a frequency lower than that of the first timing signal;
When video data of the image data stored in the image memory is output to the external device, the image data is read from the image memory by the first timing signal, and the video data is output to the external device. A video output means for converting the video signal into a video signal suitable for the external device and outputting the video signal to the external device;
When outputting the image data stored in the image memory to the liquid crystal display, the image data is read from the image memory by the second timing signal, and the image data is displayed on a liquid crystal display suitable for liquid crystal display. Liquid crystal driving means for converting to a liquid crystal display and outputting a driving pulse corresponding to the liquid crystal display video signal together with the liquid crystal display video signal to the liquid crystal display;
A liquid crystal display device comprising: Imaging means for driving the imaging device to acquire image data indicating a subject;
An image memory for temporarily storing image data acquired by the imaging means;
A liquid crystal display,
A selection means for selecting whether to output the image data stored in the image memory to an external device or to the liquid crystal display;
When the image data stored in the image memory is video-outputted to the external device, a first timing signal for generating a video signal is generated, and the image data stored in the image memory is output to the liquid crystal display. A timing signal generating means for generating a second timing signal having a frequency lower than that of the first timing signal;
When video data of the image data stored in the image memory is output to the external device, the image data is read from the image memory by the first timing signal, and the video data is output to the external device. A video output means for converting the video signal into a video signal suitable for the external device and outputting the video signal to the external device;
When outputting the image data stored in the image memory to the liquid crystal display, the image data is read from the image memory by the second timing signal, and the image data is displayed on a liquid crystal display suitable for liquid crystal display. Liquid crystal driving means for converting to a liquid crystal display and outputting a driving pulse corresponding to the liquid crystal display video signal together with the liquid crystal display video signal to the liquid crystal display;
An electronic camera characterized by comprising: Imaging means for driving the imaging device to acquire image data indicating a subject;
A liquid crystal display,
Selection means for selecting whether to output image data acquired by the imaging means to an external device or to the liquid crystal display;
When the image data acquired by the imaging unit is video-outputted to the external device, a first timing signal for generating a video signal is generated, and the image data acquired by the imaging unit is output to the liquid crystal display. A timing signal generating means for generating a second timing signal having a frequency lower than that of the first timing signal;
When video data of the image data acquired by the imaging means is output to the external device, the image sensor is driven by the first timing signal, and the video data is suitable for video output to the external device. Video output means for converting into a signal and outputting the video signal to the external device;
When outputting the image data acquired by the image pickup means to the liquid crystal display, the image pickup device is driven by the second timing signal, and the image data is a video signal for liquid crystal display suitable for liquid crystal display. Liquid crystal driving means for outputting to the liquid crystal display a driving pulse corresponding to the video signal for liquid crystal display together with the video signal for liquid crystal display,
An electronic camera characterized by comprising:

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