JP3859623B2 - Backlight control method for liquid crystal display device - Google Patents

Description

  The present invention relates to a backlight control method for a liquid crystal display device, and more particularly to a control method for the purpose of power saving of a backlight of a liquid crystal display device used in a mobile phone or the like.

  Since mobile phones using this type of liquid crystal display device are battery-powered, reducing power consumption is a major issue. This type of liquid crystal display device has a small amount of power consumption by itself, but includes a backlight for illuminating the liquid crystal display panel from behind in order to enable visual recognition in a dark place.

  Since the power consumption of the backlight occupies a large proportion of the power consumption of the entire mobile phone, various proposals have been made for reducing this power consumption.

  For example, if the time without key operation continues for a certain period of time, it is generally determined that the user is not looking at the display screen and automatically turns off the backlight to save power. ing.

  Alternatively, a method of saving power by controlling the luminance of the backlight according to the ambient brightness is also known. For example, there is this conventional example shown in FIG. FIG. 3 is a block diagram showing a conventional example in which the luminance of the backlight is controlled in accordance with the ambient brightness.

  Hereinafter, this conventional example will be described. The liquid crystal display device shown in FIG. 3 includes an optical sensor 31, an amplifier 32, a CPU 33, a backlight power supply device 34, and a liquid crystal display 35. The liquid crystal display 35 is provided with a liquid crystal display panel 36 and a backlight 37 so that the CPU 13 displays necessary information on the liquid crystal display panel 36 and the backlight 37 can illuminate the liquid crystal display panel 36 from the back side. To do. In this embodiment, the backlight 37 is configured by connecting in parallel a plurality of light emitting diode groups each formed by connecting a plurality of light emitting diodes D in series.

  The backlight power supply 34 is provided with a power supply 40 and a power supply control circuit 41, and the power supply 40 is controlled by the CPU 33 based on the output of the optical sensor 31, as will be described later. The backlight 37 is configured to be turned on / off and to control the light emission amount.

  The operation of this conventional example is based on the output from the optical sensor 31 and detects the brightness of incident light incident on the display surface side of the liquid crystal display panel 36 and ambient light in front of the display surface side in the CPU 33, Depending on the brightness, the switch circuit X of the power supply control circuit 41 is turned on and off by the CPU 33 to reduce the light emission amount of the backlight 37 when the incident light and the ambient light are dark, and when the light is bright Control is made to turn off the light and increase the amount of light emission between them.

  As described above, in this conventional example, when the incident light and the ambient light are dark, the light emission amount of the backlight 37 is decreased, and when the light is bright, the light is turned off. At intermediate brightness, the amount of light emitted from the backlight 37 is increased, so that the display is easier to see than in the prior art. (For example, refer to Patent Document 1.)

JP-A-8-114801 (page 3-4)

  In the above-described conventional example, the brightness of incident light and ambient light incident on the display surface side of the liquid crystal display panel is detected, and the amount of light emitted from the backlight is uniquely controlled according to the brightness. Depending on the type of information, the visibility may be lowered.

    That is, if the information to be displayed is character information, it can be said that the contrast is generally high, but in the case of an image or a photograph, the contrast varies. In general, when the contrast is high, the screen can be visually recognized even if it is somewhat dark, and vice versa when the contrast is low. Therefore, in this conventional example, there is a problem that the visibility is lowered in the case of an image or a photograph having a low contrast when the light emission amount of the backlight is lowered particularly when the incident light and the ambient light are dark.

    Particularly in recent mobile phones and the like, the types of information to be handled are diversified, so the contrast varies. For this type of control, control in consideration of contrast is important in order to ensure visibility.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight control method for a liquid crystal display device capable of realizing reduction in power consumption while ensuring visibility by controlling the amount of light emitted from a backlight according to the contrast of information to be displayed. There is.

  According to the backlight control method of the liquid crystal display device of the present invention, the information displayed on the liquid crystal display panel is classified into character information, image information (information such as illustrations including characters), and photographic information, and for each classified information. A contrast value is detected, and the brightness of the backlight that illuminates the liquid crystal display panel is controlled based on the detected value.

  Alternatively, in the backlight control method of the liquid crystal display device of the present invention, the information displayed on the liquid crystal display panel is classified into character information, image information (information such as illustrations including characters) and photo information from the display data, In the case of the character information, the luminance of the backlight that illuminates the liquid crystal display panel is lowered to a first minimum luminance value that allows the display character to be identified on the screen. In the case of the image information, the contrast value is first determined from the display data. When the detected value is higher than a predetermined reference value, the display image is lowered to the second lowest luminance value that can be identified on the screen. In the case of the photographic information, first, the contrast value is detected from the display data, and When the detected value is higher than a predetermined reference value, the display photograph is controlled to be lowered to the third lowest luminance value that can be identified on the screen.

  In particular, the first lowest luminance value, the second lowest luminance value, and the third lowest luminance value are: the first lowest luminance value <the second lowest luminance value <the third lowest luminance value. You may make it set the value so that it may become a relationship of a value.

  The first minimum luminance value, the second minimum luminance value, and the third minimum luminance value may be arbitrarily variable.

  Further, the means for classifying the information into the character information, the image information, and the photographic information may be classified from gradation information calculated from luminance information possessed by each pixel signal of the display data.

  Further, the contrast value may be obtained from a difference between a maximum value and a minimum value of brightness calculated from luminance information of each pixel signal of the display data.

  According to the backlight control method of the liquid crystal display device of the present invention, the information displayed on the liquid crystal display panel is classified into character information, image information, and photographic information, a contrast value is detected for each classified information, and the contrast When the value is higher than the reference value, the backlight brightness is controlled so that the displayed information is lowered to the lowest brightness value that can be identified on the screen, thus reducing power consumption while ensuring visibility. There is an effect that can be done.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flowchart for explaining the operation of FIG.

  The embodiment of the present invention is a case where the present invention is applied to a mobile phone. In the following description, the general functions of the mobile phone are omitted, and only the portion related to the present invention is described.

  First, the configuration will be described with reference to FIG. An RF reception unit 1 that receives a radio reception signal from an antenna, demodulates and outputs a reception signal in a low frequency band, and a display data acquisition unit 2 that acquires display data 101 to be displayed on the liquid crystal display unit 9 from the reception signal. Information classification unit for classifying whether display information of the display data is character information, image information (graphic information such as an illustration including characters) or photographic information from the display data 101, and outputting a classification signal 102 indicating the result 3 and the display data 101 and the classification signal 102 are input. When the display data 101 is image information or photographic information, the contrast value is calculated and the contrast value signal 103 indicating the value is output. A liquid crystal display unit 9 comprising a calculation unit 4, a liquid crystal display panel 91 for displaying display data 101, and a backlight 92 for illumination; A backlight drive unit 8 that supplies power for driving the backlight 92 in accordance with an instruction of the control signal 104, a storage unit 7 that stores a reference value for determining the level of contrast between image information and photographic information, and a storage unit 7 The control unit 6 is configured to perform overall operations such as setting of the reference value, and the control unit 5 is configured to perform overall control operations including the luminance of the backlight 92.

  The control unit 5 controls the luminance of the backlight 92 that illuminates the liquid crystal display panel 91. When the classification signal 102 indicates character information, the control signal lowers the displayed character to a minimum luminance value 1 that can be identified on the screen. 104 is sent to the backlight drive unit 8. When the classification signal 102 indicates an image signal or photographic information, each contrast value indicated by the contrast value signal 103 is compared with each reference value stored in the storage unit 7, and the contrast value exceeds the reference value. If the display information is displayed, a control signal 104 for lowering the display information to a minimum luminance value 2 or 3 that can be identified on the screen is sent to the backlight drive unit 8. The backlight driving unit 8 controls the luminance of the backlight 92 by this control signal 104.

  Next, the operation will be described with reference to FIG. First of all, if you check the type of information handled by your mobile phone, you will find the “character information” that includes the most common numbers such as phone books, emails, and various messages, for example, Here, it is classified into “graphic information” or “image information” combined with a pictorial background, and “photo information” sent by a camera-equipped mobile phone.

  First, the radio reception signal from the antenna is demodulated into a low frequency band reception signal by the RF receiver 1. Then, display data 101 to be displayed on the liquid crystal display unit 9 is extracted from the received signal (201). The display data 101 is sent to the liquid crystal display panel 91 via the control unit 5 and simultaneously sent to the information classification unit 3 and the contrast value calculation unit 4.

  The information classification unit 3 classifies the type of information based on the gradation value calculated from the luminance information possessed by each pixel signal of the display data 101. That is, the smallest gradation is classified as character information, the largest number is photograph information, and the middle is classified as image information. Then, a classification signal 102 indicating the classification result is output. Alternatively, when this classification signal can be obtained from the outside, it may be used (202).

  On the other hand, the contrast value calculation unit 4 receives the display data 101 and the classification signal 102, and when the classification signal 102 indicates image information or photo information, the contrast value of each display data 101 is set to the display data 101. Obtained from the difference between the maximum value and the minimum value of brightness calculated from the luminance information of each pixel signal, a contrast value signal 103 indicating the value is output (204, 208).

  When the classification signal 102 indicates character information, the control unit 5 sends the control signal 104 for lowering the display character to the minimum luminance value 1 that can be identified on the screen without obtaining the contrast value, and sends it to the backlight drive unit 8. .

  When the classification signal 102 indicates an image signal or photographic information, each contrast value indicated by the contrast value signal 103 is referred to, and this value is compared with each reference value read from the storage unit 7. When the contrast value exceeds the reference value, the backlight luminance is the lowest luminance value whose display information can be identified on the screen, that is, the lowest luminance value 2 for image information, and the lowest luminance value for photo information. The control signal 104 to be lowered to 3 is sent to the backlight drive unit 8 (205, 209).

  Then, the backlight drive unit 8 changes the power supply voltage to the backlight 92 by the control signal 104 and sets the backlight 92 to a specified minimum luminance value (206, 210).

  When the contrast value does not exceed the reference value, a control signal 104 for setting the backlight brightness to a predetermined standard value is sent to the backlight drive unit 8, and the backlight drive unit 8 uses the control signal 104 to return the backlight. The power supply voltage to the light 92 is changed to set the backlight 92 to a designated standard value (207, 211).

  Since each reference value stored in the storage unit 7 can be arbitrarily set by an operation from the operation unit 6, a practically optimal value can be selected and set.

  The output voltage of the backlight drive unit 8 is set so that the minimum luminance value 1, the minimum luminance value 2, and the minimum luminance value 3 of the backlight 92 have a relationship of minimum luminance value 1 <minimum luminance value 2 <minimum luminance value 3. Set. That is, visibility is improved by setting the image and photo information brighter than the character information.

  Note that the minimum luminance value 1, the minimum luminance value 2, and the minimum luminance value 3 can be set to arbitrary values by changing the output voltage of the backlight drive unit 8, so that the values can be practically used. The optimum value can be selected and set.

  In the embodiment described above, the present invention is applied to a mobile phone alone. However, as described in the prior art, power is saved by controlling the luminance of the backlight according to the ambient brightness. It can also be used in combination with the method. That is, when the backlight brightness is lowered according to the ambient brightness, the present invention is applied, and the degree of reduction is determined in consideration of the contrast value of the display information at that time, so that power saving with more visibility can be secured. An effect is obtained.

  It can be used for all light-emitting display devices.

It is a block diagram which shows the example of embodiment of this invention. It is a flowchart for demonstrating the operation | movement of FIG. It is a block diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 RF receiving part 2 Display data acquisition part 3 Information classification part 4 Contrast value calculation part 5 Control part 6 Operation part 7 Memory | storage part 8 Backlight drive part 9 Liquid crystal display part 91 Liquid crystal display panel 92 Backlight

Claims (6)

Information displayed on the liquid crystal display panel is classified into character information, image information (information such as illustrations including characters), and photographic information, and a contrast value is detected for each classified information, and the liquid crystal display is based on the detected value. A backlight control method for a liquid crystal display device, characterized by controlling the brightness of a backlight that illuminates a panel. Information displayed on the liquid crystal display panel is classified into character information, image information (information such as illustrations including characters), and photographic information from the display data, and the brightness of the backlight that illuminates the liquid crystal display panel is determined by the character information. In this case, the display character is lowered to the first minimum luminance value that can be identified on the screen. In the case of the image information, first, the contrast value is detected from the display data, and the detected value is higher than a predetermined reference value. The display image is lowered to a second lowest luminance value that can be identified on the screen. In the case of the photographic information, first, a contrast value is detected from the display data, and if the detected value is higher than a predetermined reference value, the display photo is displayed on the screen. A backlight control method for a liquid crystal display device, characterized in that control is performed so as to lower the third lowest luminance value that can be identified above. The first lowest luminance value, the second lowest luminance value, and the third lowest luminance value are: the first lowest luminance value <the second lowest luminance value <the third lowest luminance value. 3. The backlight control method for a liquid crystal display device according to claim 2, wherein the values are set so as to satisfy the relationship. 4. The back of the liquid crystal display device according to claim 2, wherein the first lowest luminance value, the second lowest luminance value, and the third lowest luminance value can be arbitrarily changed. Light control method. The means for classifying the information into the character information, the image information, and the photographic information classifies from the gradation information calculated from the luminance information possessed by each pixel signal of the display data. , 3 or 4 backlight control method for a liquid crystal display device. The said contrast value is calculated | required from the difference of the maximum value and the minimum value of the brightness computed from the luminance information which each pixel signal of the said display data has, The 1, 2, 3, 4 or 5 characterized by the above-mentioned. A backlight control method for a liquid crystal display device.

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