JP2006201399A - Display device and display control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device and a display control method which realize prolongation of a battery life while preventing degradation in luminance of a liquid crystal display (LCD) section. <P>SOLUTION: When a remaining amount of a battery 42 becomes equal to or below a predetermined amount, the power which is supplied to a backlight 50 is controlled to become small (104) and a gain (amplitude) of an image signal to an LCD 46 is controlled to become large (106). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display device including a liquid crystal display unit that displays an image based on an image signal, a backlight that illuminates the liquid crystal display unit, and a display control method for the display device.

  Conventionally, a transmissive liquid crystal display device is known in which an image displayed on a liquid crystal display unit is visualized by a backlight illuminating the liquid crystal display unit. Such a liquid crystal display device is mounted on various portable devices such as a digital camera and a PDA because it is light and thin.

  A portable device mainly uses a battery as a power source. Since batteries are consumed with the use of portable devices, various techniques have been proposed in the past to extend the life of batteries.

  For example, there has been proposed a method of reducing the power of the backlight of the display device by automatically determining whether the liquid crystal display device is driven by commercial power or battery (see, for example, Patent Document 1).

  In addition, an automatic dimming circuit that reduces the current consumption of the backlight by performing duty control when the battery voltage decreases has been proposed (see, for example, Patent Document 2).

As described above, conventionally, when the battery voltage is monitored while the battery is driven and the remaining amount of the battery is reduced, the power supply to the load (backlight) is restricted to extend the life of the battery, and the portable device is lengthened. It was possible to use it continuously.
JP-A-5-276656 JP-A-6-205343

  However, in the above conventional technology, the current consumption (power consumption) of the backlight is reduced in order to extend the battery life. However, since the brightness of the liquid crystal display surface is lowered (that is, the screen becomes dark), the mobile phone is not portable. There is a problem that the quality, performance, and operability of the device (liquid crystal display device) deteriorate.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a display device and a display control method capable of extending the battery life while preventing a decrease in luminance of a liquid crystal display unit.

  In order to achieve the above object, a display device of the present invention includes a liquid crystal display unit that displays an image based on an image signal, a backlight that illuminates the liquid crystal display unit, and the liquid crystal display unit and the backlight are driven. A power source that supplies power for power supply, a detection unit that detects a remaining capacity of the power source, and a power that is supplied to the backlight when the remaining capacity of the power source detected by the detection unit falls below a predetermined amount And a control means for controlling the gain of the image signal to the liquid crystal display unit to be increased.

  The display device includes a liquid crystal display unit that displays an image based on an image signal, a backlight that illuminates the liquid crystal display unit, and a power source that supplies driving power to the liquid crystal display unit and the backlight. It is a transmissive liquid crystal display device. The detecting means detects the remaining capacity of the power supply. The control unit controls the power supplied to the backlight to be small when the remaining capacity of the power source detected by the detection unit becomes a predetermined amount or less, and the gain of the image signal to the liquid crystal display unit is Control to increase.

  As a result, when the remaining capacity of the battery mounted on the display device is reduced to a predetermined amount, the power supplied to the backlight that illuminates the liquid crystal display unit can be reduced, so that the battery life can be extended. it can. Furthermore, in the present invention, it is possible to prevent a decrease in the luminance of the liquid crystal display unit that occurs when the power to the backlight is decreased by increasing the gain (amplitude) of the image signal to the liquid crystal display unit. . Note that even if the gain of the image signal to the liquid crystal display unit is increased, the power consumption does not increase.

  In order to reduce the power supplied to the backlight, the voltage value applied to the backlight may be reduced, but the current value flowing through the backlight may be reduced.

  In addition, the display control method of the present invention includes a liquid crystal display unit that displays an image based on an image signal, a backlight that illuminates the liquid crystal display unit, and power for driving the liquid crystal display unit and the backlight. Display control method for a display device comprising: a power supply for controlling the power supply to the backlight to be reduced when the remaining capacity of the power supply becomes a predetermined amount or less, and the liquid crystal display Control is performed so that the gain of the image signal to the unit increases.

  Since the display control method of the present invention also operates in the same manner as the display device of the present invention, the battery life can be extended without reducing the luminance of the liquid crystal display unit.

  According to the display device and the display control method according to the present invention, when the remaining capacity of the power source that supplies driving power to the liquid crystal display unit and the backlight becomes a predetermined amount or less, the power supplied to the backlight is small. In addition to controlling so that the gain of the image signal to the liquid crystal display unit is increased, it is possible to extend the power source (battery) life while preventing the luminance of the liquid crystal display unit from decreasing. Has an effect.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in this embodiment mode, a mode in which the display device of the present invention is applied to a digital still camera (hereinafter simply referred to as “digital camera”) will be described. First, a schematic configuration of the digital camera 10 according to the present embodiment will be described with reference to FIG.

  As shown in the figure, the digital camera 10 includes a lens 12, a CCD (Charge Coupled Device) 14 disposed behind the optical axis of the lens 12, and a correlated double sampling circuit (hereinafter referred to as "CDS"). 16, an analog / digital converter (hereinafter referred to as “ADC”) 18 that converts an input analog image signal into a digital image signal, and a microcomputer (hereinafter referred to as “microcomputer”) that controls the operation of the entire digital camera 10. 20) and a line buffer having a predetermined capacity, and subjecting the input digital image signal to predetermined digital signal processing, an object image and various menu screens indicated by the digital image signal obtained by photographing Display operation on a liquid crystal display (hereinafter referred to as “LCD”) 46 for displaying messages and the like. In order to drive the CCD 14, a signal processing circuit 22 constituted by a DSP (Digital Signal Processor), a memory 26 constituted mainly by an SDRAM (Synchronous Dynamic Random Access Memory) that stores digital image signals obtained by photographing. And a timing signal generating unit 30 for supplying a required timing signal to each unit such as the CDS 16, the signal processing circuit 22, and the CCD driving unit 28. Yes.

  Here, the correlated double sampling processing by the CDS 16 is a feed included in the output signal for each pixel of the solid-state image sensor for the purpose of reducing noise (particularly thermal noise) included in the output signal of the solid-state image sensor. This is a process for obtaining an accurate pixel signal by taking the difference between the through component level and the pixel signal component level.

  The output terminal of the CCD 14 is connected to the input terminal of the CDS 16, the output terminal of the CDS 16 is connected to the input terminal of the ADC 18, and the output terminal of the ADC 18 is connected to the input terminal of the signal processing circuit 22. The signal processing circuit 22 is connected to each of the microcomputer 20 and the data bus BUS, and the memory 26 is also connected to the data bus BUS. Further, the microcomputer 20 is an input terminal of the timing signal generating unit 30, an output terminal of the timing signal generating unit 30 is an input terminal of the CDS 16, the signal processing circuit 22, the CCD driving unit 28, etc., and an output terminal of the CCD driving unit 28 is the CCD 14. Are respectively connected to the input terminals.

  A part of the digital signal processing by the signal processing circuit 22 is executed according to the control by the microcomputer 20, and the generation of various timing signals by the timing signal generator 30 is also executed by the control by the microcomputer 20.

  In addition, the digital camera 10 includes an external interface (hereinafter referred to as “external I / F”) 24 connected to the data bus BUS. The external I / F 24 is connected to the digital camera 10 with smart media, In a state where a portable recording medium 52 such as an IC card, CD-R, or CD-RW is mounted, it controls access to the recording medium 52 and inputs / outputs other digital information to / from the outside.

  In addition, a release button (so-called shutter) 32 that is pressed by the user when shooting is performed, a menu button that is pressed when various menu screens are displayed on the LCD 46, a power switch that turns the power on / off, and the display of the LCD 46 An operation unit 34 such as a select button that is pressed to specify a desired item from the contents and a determination button that is pressed to confirm the specification result by the select button is connected to the microcomputer 20. 20 can always grasp the operation state of these buttons.

  The signal processing circuit 22 is connected to the above-described LCD 46 via the LCD driving circuit 44. The microcomputer 20 outputs a control signal to the LCD drive circuit 44 and outputs a YUV signal (or YCrCb signal) composed of, for example, a luminance signal and a color difference signal to the LCD drive circuit 44 via the signal processing circuit 22, whereby the LCD 46. Display an image on.

  The LCD drive circuit 44 generates a signal for causing the LCD 46 to display an image such as a subject image or a menu screen based on the image signal input from the signal processing circuit 22 in accordance with the control signal input from the microcomputer 20. To supply.

  The LCD 46 is a transmissive type excellent in visibility, contrast, and the like, and is composed of a light receiving element that does not emit light by itself. Therefore, the backlight 46 is disposed as a light source on the back surface of the LCD 46. The image displayed on the LCD 46 is visualized by the backlight 50 illuminating the LCD 46. A current limiting circuit 48 is connected to the backlight 50. The current limiting circuit 48 is connected to the microcomputer 20 and limits the current flowing through the backlight 50 under the control of the microcomputer 20.

  Here, the LCD drive circuit 44 and the LCD 46 will be described in detail.

  FIG. 2 is a block diagram showing a detailed configuration of the LCD drive circuit 44 and the LCD 46. The LCD drive circuit 44 includes a signal processing unit 60, a digital / analog (D / A) conversion unit 70, a buffer (BF) 72, a control unit 74, an internal clock circuit (VCO) 76, a timing controller (T / T). C) 78 and a high voltage circuit 80 for liquid crystal.

  The signal processing unit 60 includes a serial / parallel conversion unit (SPCONV) 61, an RGB conversion unit (RGB-MAT) 62, a sample hold setting unit (SHLD) 63, a sharpness setting unit (PICT) 64, a contrast setting unit (CONT) 65, And a brightness setting unit (BRT) 66.

  The SPCONV 61 converts the YUV signal serially output from the signal processing circuit 22 into 3-channel parallel data and outputs it. The RGB-MAT 62 converts the YUV signal output in parallel from the SPCONV 61 into an RGB format image signal. The SHLD 63 samples and holds the image signal output from the RGB-MAT 62. Further, the PICT 64 performs sharpness processing, the CONT 65 adjusts contrast, and the BRT 66 performs brightness adjustment.

  The D / A conversion unit 70 converts the digital image signal output from the signal processing unit 60 into an analog image signal. The BF 72 buffers the analog signal obtained by the conversion by the D / A conversion unit 70 and outputs it to the LCD 46.

  The control unit 74 controls the signal processing unit 60 in accordance with a control signal from the microcomputer 20.

  HD (horizontal synchronization signal), VD (vertical synchronization signal), and MCLK (master clock) are input to the VCO 76 from the microcomputer 20. The VCO 76 generates an internal clock from the MCLK, and outputs HD and VD to the T / C 78 together with the generated internal clock. The T / C 78 outputs an H-drive pulse signal and a V-drive pulse signal to the LCD 46 based on the rising edge of the input internal clock, and supplies the internal clock to the signal processor 60 and the D / A converter 70. The output is synchronized with both the signal processing unit 60 and the D / A conversion unit 70.

  The high voltage circuit for liquid crystal 80 boosts the input voltage to a predetermined voltage (+8.5 V as an example in FIG. 2) and supplies it to the LCD 46.

  On the other hand, the LCD 46 includes an H-side level shifter 90, an H-driver 92, a V-side level shifter 94, a V-driver 96, and a display unit 98.

  The H-side level shifter 90 generates a clock signal used by the H-driver 92 using the H-drive pulse signal input from the T / C 78 of the LCD drive circuit 44 as a timing signal. The V-side level shifter 94 generates a clock signal used by the V-driver 96 using the V-drive pulse signal input from the T / C 78 of the LCD drive circuit 44 as a timing signal.

  An image signal is input to the H-driver 92 from the BF 72 of the LCD drive circuit 44. The H-driver 92 uses the clock signal from the H-side level shifter 90 as a timing signal to generate a signal voltage corresponding to the input image signal. Apply to the signal electrode of the display unit 98. The V-driver 96 applies a predetermined scanning voltage to the scanning electrodes of the display unit 98 using the clock signal from the V-side level shifter 94 as a timing signal. As a result, an image corresponding to the input image signal is displayed on the display unit 98 of the LCD 46.

  Further, a battery 42 for supplying driving power to each unit is built in the digital camera 10. In FIG. 1, only the power supply lines for the current limiting circuit 48 and the LCD drive circuit 44 among the power supply lines from the battery 42 to each unit are illustrated, and the other power supply lines are not illustrated. . In the digital camera 10 according to the present embodiment, as the battery 42, a rechargeable secondary battery represented by a nickel cadmium battery, a nickel hydride battery, a lithium ion battery, or the like is applied. A primary battery that cannot be charged, such as a battery, can also be applied.

  The digital camera 10 includes a battery remaining capacity detection unit 40 that detects the remaining capacity (remaining capacity) of the battery 42. The battery remaining capacity detection unit 40 according to the present embodiment is configured to detect the output voltage value of the battery 42 as a value corresponding to the remaining capacity of the battery 42. Here, it will be described with reference to FIG. 3 that the remaining capacity of the battery 42 can be detected from the output voltage value of the battery 42.

  FIG. 3 shows a change in the output voltage with respect to the discharge capacity of the battery 42. As shown in the figure, the characteristics of the battery are generally that the output voltage value gradually decreases until a certain discharge capacity, and the output voltage value rapidly decreases as the discharge capacity increases. Therefore, it is possible to detect that the discharge capacity is large, that is, the remaining capacity of the battery is small using the output voltage value, and particularly when the remaining capacity of the battery is small, the measurement error is reduced and the remaining capacity of the battery is reduced. The excess of the measurement error that should be included in the threshold value for determining is reduced.

  In the figure, the low voltage value Vth reduces the current value supplied to the backlight 50, and increases the gain (amplitude) of the image signal output to the LCD 46, thereby preventing the luminance of the LCD 46 from decreasing and saving power. This is a threshold value for starting the process of achieving the above.

  Next, the operation of the digital camera 10 according to the present embodiment will be described. First, the overall processing flow at the time of photographing with the digital camera 10 will be briefly described.

  A signal indicating the subject image output from the CCD 14 is sequentially input to the CDS 16 and subjected to correlated double sampling processing, and then input to the ADC 18. The ADC 18 receives R (red), G (green), The B (blue) signal is converted into a 12-bit R, G, B signal (digital image signal) and output to the signal processing circuit 22.

  The signal processing circuit 22 accumulates digital image signals sequentially input from the ADC 18 in a built-in line buffer and temporarily stores them in the memory 26.

  The digital image signal stored in the memory 26 is read out by the signal processing circuit 22 under the control of the microcomputer 20, and white balance adjustment is performed by applying a digital gain corresponding to the type of light source to these, as well as gamma processing and sharpness. Processing is performed to generate an 8-bit digital image signal, and further signal processing is performed to generate a YUV signal (or YCrCb signal), which is stored in the memory 26 again.

  The LCD 46 is configured to display a moving image (through image) obtained by continuous imaging by the CCD 14 and can be used as a finder. When the LCD 46 is used as a finder, the signal processing circuit 22 sequentially outputs the generated YUV signal to the LCD 46 via the LCD driving circuit 44. As a result, a through image is displayed on the LCD 46.

  Here, when still image shooting is set by the user, when the release button 32 is fully pressed by the user, the YUV signal (or YCrCb signal) stored in the memory 26 at this time is After being compressed in a predetermined compression format (in this embodiment, JPEG format) by a compression / decompression unit (not shown), it is recorded on the recording medium 52 via the external I / F 24.

  In addition, when moving image shooting is set by the user, a period from when the release button 32 is fully pressed to the next time when the release button 32 is fully pressed, that is, shooting of a moving image. During a given period, the YUV signal (YCrCb signal) stored in the memory 26 is converted into a predetermined compression format (in the present embodiment, the Motion JPEG format) by a compression / decompression unit (not shown) for each predetermined period. After compression, the data is recorded on the recording medium 52 via the external I / F 24.

  Next, a battery monitoring process executed in the digital camera 10 will be described with reference to FIG. FIG. 4 is a flowchart showing a flow of battery monitoring processing executed by the microcomputer 20 of the digital camera 10 when a power switch (not shown) is turned on and the power saving mode is set by the user. .

  In step 100, the microcomputer 20 takes in the output voltage value of the battery 42 detected by the battery remaining capacity detection unit 40.

  In step 102, the microcomputer 20 determines whether or not the output voltage value of the captured battery is equal to or less than the threshold value Vth. Here, if it is determined that the output voltage value of the battery exceeds the threshold value Vth, the process returns to step 100. On the other hand, if it is determined that the output voltage value of the battery is equal to or less than the threshold value Vth, the process proceeds to step 104. That is, until the output voltage value of the battery becomes equal to or lower than the threshold value Vth, the processing from step 100 to step 102 (processing for taking in the output voltage value of the battery and checking the remaining capacity of the battery) is repeated at predetermined time intervals.

  In step 104, the microcomputer 20 controls the current limiting circuit 48 so that the power supplied to the backlight 50 is reduced. Here, control is performed so that the value of the current flowing through the backlight 50 is reduced to a predetermined value.

  In step 106, the microcomputer 20 controls the LCD drive circuit 44 so that the gain of the image signal output to the LCD 46 is increased. Specifically, the microcomputer 20 outputs a control signal for increasing the gain (amplitude) of the image signal output to the LCD 46 to the LCD drive circuit 44.

  The control signal is input to the control unit 74 of the LCD drive circuit 44 as described above. The control unit 74 controls the BRT 66 of the signal processing unit 60 to increase the gain (amplitude) of the RGB image signal output to the LCD 46 by a predetermined amount and adjust the luminance of the display unit 98 of the LCD 46.

  In step 108, it is determined whether or not the power switch of the operation unit 34 is turned off. Here, until it is determined that the power switch is turned off, the digital camera is in a state where the current value flowing through the backlight 50 is reduced as described above and the gain value of the image signal to the LCD 46 is increased. 10 is driven. On the other hand, when it is determined that the power switch is turned off, the driving of the digital camera 10 is stopped and the battery monitoring process is ended.

  As described above in detail, in the digital camera 10 according to the present embodiment, when the remaining battery capacity decreases, the power supplied to the backlight 50 is reduced and the gain of the image signal to the LCD 46 is increased. Therefore, the brightness of the liquid crystal display unit can be prevented from being lowered and the battery life can be extended.

  Furthermore, in the digital camera 10 according to the present embodiment, since the remaining capacity of the battery 42 is detected based on the output voltage value of the battery 42, it can be detected more easily than when the remaining capacity is directly detected. Can do.

  In the present embodiment, the case where the remaining capacity of the battery 42 is detected by detecting the output voltage value of the battery 42 has been described. However, the present invention is not limited to this, and the discharge current of the battery 42 is not limited thereto. The remaining capacity of the battery 42 may be detected by detecting the integrated value. In this case, the battery remaining capacity detection unit 40 of the digital camera 10 according to the present embodiment can be configured to perform the process of integrating the output current of the battery 42.

  In the above embodiment, an example in which the LCD drive circuit 44 is controlled so that the gain of the signal to the LCD 46 is increased after the current limiting circuit 48 is controlled so that the power supplied to the backlight 50 is reduced. However, the present invention is not limited to this, and after controlling the LCD drive circuit 44 so that the gain of the image signal to the LCD 46 is increased, the current is limited so that the power supplied to the backlight 50 is reduced. The circuit 48 may be controlled.

  In the above-described embodiment, an example has been described in which control is performed so that the current value flowing through the backlight 50 is reduced to a predetermined value in order to reduce the power supplied to the backlight 50. However, the present invention is not limited thereto. For example, the voltage value applied to the backlight 50 may be controlled to be lowered to a predetermined value.

  Furthermore, in the above-described embodiment, the power supplied to the backlight 50 is reduced and the gain of the image signal supplied to the LCD 46 is increased, thereby preventing the luminance of the LCD 46 from being lowered and saving power. An example of performing when the output voltage value of the battery is equal to or lower than the threshold value Vth has been described. However, the present invention is not limited to this. For example, a plurality of threshold values are set and the power saving process is performed for each threshold value. In this case, by setting the power supply value to the backlight 50 and the gain value of the image signal to the LCD 46, the power saving process can be performed step by step according to the remaining battery capacity.

It is a block diagram which shows schematic structure of the digital camera which concerns on embodiment. It is a block diagram which shows schematic structure of a LCD drive circuit and LCD. It is the figure which showed an example of the change of the output voltage with respect to the discharge capacity of a battery. It is a flowchart which shows the flow of the battery monitoring process performed by a microcomputer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Digital camera 20 Microcomputer 22 Signal processing circuit 40 Battery remaining capacity detection part 42 Battery 44 LCD drive circuit 46 LCD
48 Current Limiting Circuit 50 Backlight 60 Signal Processing Unit 66 Brightness Setting Unit (BRT)
74 Control Unit 90 H Side Level Shifter 92 H-Driver 98 Display Unit

Claims (3)

A liquid crystal display for displaying an image based on an image signal;
A backlight for illuminating the liquid crystal display unit;
A power source for supplying driving power to the liquid crystal display unit and the backlight;
Detecting means for detecting a remaining capacity of the power source;
When the remaining capacity of the power source detected by the detection means becomes a predetermined amount or less, the power supplied to the backlight is controlled to be small, and the gain of the image signal to the liquid crystal display unit is large. Control means for controlling so that
Display device.   The display device according to claim 1, wherein the control unit reduces power supplied to the backlight by reducing a value of a current flowing through the backlight. Display of a display device comprising: a liquid crystal display unit that displays an image based on an image signal; a backlight that illuminates the liquid crystal display unit; and a power supply that supplies driving power to the liquid crystal display unit and the backlight A control method,
Display control for controlling the power supplied to the backlight to be small when the remaining capacity of the power source becomes a predetermined amount or less and controlling the gain of the image signal to the liquid crystal display unit to be large Method.

Images