JP2005121997A - Method for dimming backlight of liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device to be set up especially in a place where illumination is partially varied by shades caused by comings and goings of people and objects in relation to a technique to automatically dim a backlight of the liquid crystal display device corresponding to brightness and darkness of external light illumination. <P>SOLUTION: Optical sensor groups 111-112 are disposed on the liquid crystal panel display surface side of a casing of the liquid crystal display device keeping a distance between each other, for example, on both sides of the liquid crystal panel and detect the external light illumination which is then subjected to digital conversion by an A/D converter 12. An ROM 14, in which an operation program, comparing the digital converted external light illumination data of the optical sensor groups 111-112 with each other and making backlight luminance vary only when both data vary to the same extent and not vary when only one of them is abnormal, is stored, carries out computing at established periods with a computing device 13 and an RAM 15. Thereby, in an automatic dimming device of the liquid crystal backlight utilizing the optical sensor, in which the backlight is automatically dimmed corresponding to variation of the external light illumination, difficulty associated with the fact that the backlight is automatically dimmed even when illumination is partially varied only on the periphery of the optical sensor and a dimming operation corresponding to variation of illumination in the room is not realized is solved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technology for automatically dimming a backlight of a liquid crystal display device according to the brightness of external light illuminance, and in particular, a liquid crystal installed in a place where the illuminance changes partially due to shadows caused by traffic of people and objects. The present invention relates to a display device.

  When viewing an image comfortably on a liquid crystal panel, the brightness of the panel increases when the surroundings are bright, and decreases when it is dark due to human visual characteristics. It is troublesome to adjust the brightness every time the ambient illuminance changes when viewing the video.For natural light, the illuminance changes without being noticed, and sometimes the brightness is difficult to see. May get tired or feel sick. In particular, the present invention considers incident light that is installed in public places, public vehicles, etc., and the illuminance around the liquid crystal panel is partially lowered by the shadows of people and objects, or from other places The illuminance increases partially.

  Patent Documents 1 and 2 can be cited as conventional backlight automatic light control methods for liquid crystal display devices.

  FIG. 7 is an operation pattern of the backlight automatic light control method provided with the optical sensor of Patent Document 1. The ambient light is ambient ambient light illuminance of the optical sensor, and ambient light illuminance data is captured every unit time T seconds by a trigger signal. a (i) is ambient light illuminance data and b (i) luminance data. For the sake of specific explanation, a (i) changes step by step in accordance with the intensity of external light between 1 and 8, and the closer to 8, the brighter the surroundings. The b (i) changes step by step in accordance with the size of a (i) between 1 and 8, and the closer to 8, the higher the luminance. The external light illuminance a (i) is taken in at every unit time, and the data is compared with the external light illuminance a (i-1) one unit time before. If a (i) = a (i−1), the luminance b (i) corresponding to the current time a (i) is set. If a (i) ≠ a (i−1), one unit time before The luminance b (i-1) of the above is maintained. According to the above, the luminance does not change for a short-term illuminance change below the unit time.

The backlight automatic light control method of Patent Document 2 includes a plurality of optical sensors in a liquid crystal display device, calculates an average value of detected ambient light illuminance data, and automatically adjusts the backlight according to the average value. is there.
JP-A-10-282923 Japanese Patent Laid-Open No. 9-146073

  In public places and public vehicles, there are frequent movements such as people and traffic, and people stopping, and the degree varies depending on the situation and time zone. When a liquid crystal display device is installed in such an environment and the illuminance near the liquid crystal panel changes due to a human shadow or the like, in the background art, the brightness of the liquid crystal panel is inappropriate for the brightness of the installed environment. A situation also arises.

  In the backlight automatic light control method described in Patent Document 1, in order to avoid a change in luminance when, for example, a person stops in the vicinity of the liquid crystal panel and the ambient illuminance changes for several tens of seconds to several minutes, the illuminance change The illuminance capturing unit time must be lengthened according to the time, and the timing of the luminance change greatly shifts when the original illuminance changes.

  In the backlight automatic dimming described in Patent Document 2, the luminance is set according to the average value of the external light illuminance of the plurality of photosensors attached to the liquid crystal panel. However, since the degree of change becomes low, the luminance changes.

  It is an object of the present invention to more appropriately determine the case where there is a traffic of these people or objects and to better control the luminance of the liquid crystal panel.

  In order to solve the above-described problem, the liquid crystal display device backlight dimming method of the present invention has a plurality of photosensors attached at different positions around the liquid crystal panel display surface side, and takes in external light illuminance data every unit time, Make a comparison operation. When the numerical value of the comparison operation exceeds a predetermined value, it is considered that the illuminance around the liquid crystal panel is partially changed, and backlight dimming is not performed, and the numerical value of the comparison operation is within the predetermined value. In this case, the optimum value of the backlight dimming control is calculated according to a predetermined calculation procedure for the ambient light illuminance data, and the backlight is automatically dimmed.

  According to the backlight dimming method of the liquid crystal display device of the present invention, the backlight luminance does not change even if the illuminance around the liquid crystal panel partially changes, and the illuminance changes uniformly in the environment where the liquid crystal panel is installed. Only when the backlight is automatically dimmed according to the ambient illuminance, it is possible to realize an optimal environment for viewing images.

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

(Embodiment 1)
The first embodiment will be described in detail with reference to FIGS. 1, 2, and 3.

  FIG. 1 is a block diagram of a liquid crystal display device having a first photosensor 111 and a second photosensor 112 with automatic backlight dimming. The first optical sensor 111 and the second optical sensor 112 detect external light illuminance, and the external light illuminance is converted into external light illuminance digital data by the A / D converter 12.

  The external light illuminance digital data is sent to the arithmetic unit 13 and sequentially stored in the RAM 15, and the arithmetic is executed by the ROM 14 storing the arithmetic program. Then, the calculation result is transferred to the D / A converter 16, and a dimming voltage corresponding to the calculation result data is output. After the dimming voltage is applied to the inverter circuit 17, the backlight 18 is dimmed, and the brightness of the liquid crystal panel 19 is adjusted.

  FIG. 2 is a flowchart of the backlight dimming method of the liquid crystal display device in FIG. Here, i is the time, j is the optical sensor number, N is the number of optical sensors, Do (i) is the backlight dimming digital data at time i, and x is the backlight dimming digital data at time i = 1 (initial value). ), T is an external light illuminance data capturing time interval, Din (j) (i) is external light illuminance digital data of the optical sensor 11 (j) at time i, and Din1 (i) is external light illuminance digital data of the optical sensor 111 at time i. , Din2 (i) is the external light illuminance digital data of the optical sensor 112 at time i, and y is the illuminance difference allowable determination value of the optical sensor.

  After the start of processing, the initial value i = 1 is set (S201), the initial value Do (1) = x of the backlight dimming digital data is set (S202), and is output at the first time (S203).

  i is incremented by +1, and after waiting for T seconds (S204), the external light illuminance digital data Din1 (2) of the photosensor 111 and the external light illuminance digital data Din2 (2) of the photosensor 112 at the second time are shown in FIG. It is stored in the RAM 15 via the arithmetic unit 13 (S205 to S206).

  Next, the difference between the Din1 (2) and the Din2 (2) is calculated and compared with the illuminance difference allowable determination value y (S207).

If the result of step S207 is greater than the illuminance difference allowable determination value y, it indicates that any of the reactions of the photosensors 111 to 112 is abnormal, and the backlight dimming digital data Do (1) one unit time before (S208), if it is smaller than the illuminance difference allowable determination value y, it is determined that the photosensors 111 to 112 have reacted uniformly, and the photosensor 111 based on (Equation 1) in the next step S209. Average value of -112 Do (2) = [Din1 (2) + Din2 (2)] / 2 (Formula 1)
Is calculated.

  As described above, the backlight dimming digital data Do (i) is processed in either S208 or S209 at every unit time, transferred to the D / A converter 16 in FIG. 1 (S210), and waited for T seconds. Later (S211), the process returns to step S205, and steps S205 to S211 are repeated at the third time (i = 3).

  Thereafter, S205 to S211 are repeated until the power of the liquid crystal display device is turned off.

  Next, FIG. 3 is a diagram showing an example of input / output of the liquid crystal display device in FIG. 1 and will be described in detail with reference to FIGS.

  The ambient light 1 is the ambient ambient light illuminance of the optical sensor 111 in FIG. 1, the ambient light 2 is the ambient ambient light illuminance of the optical sensor 112 in FIG. 1, and the ambient light illuminance is generated by the trigger signal output from the arithmetic unit 13 in FIG. Digital data is stored in the RAM 15 via the arithmetic unit 13 every unit time T seconds. The external light intensity digital data Din1 (i) of the external light 1 and the external light intensity digital data Din2 (i) of the external light 2 are described in detail. Change step by step, and the closer to 8, the brighter the surroundings.

  At time (1), the initial value x of the backlight dimming digital data is set in step S202 of FIG. In FIG. 3, Do (1) = 4 where x = 4.

At time (2), in step S207 of FIG. 2, assuming that the illuminance difference allowable determination value y = 3, | Din1 (2) −Din2 (2) | = | 8−8 | <3 (Expression 2)
The determination is YES and the process proceeds to step S209.
Do (2) = [Din1 (2) + Din2 (2)] / 2 = (8 + 8) / 2 = 8 (Formula 3)
Is calculated and output as backlight dimming control data in step S210.

At time (3), after the external light illuminance digital data Din1 (3) and Din2 (3) are captured, in step S207, | Din1 (3) −Din2 (3) | = | 8−8 | <3 (Expression 4)
The determination is YES and the process proceeds to step S209.
Do (3) = [Din1 (3) + Din2 (3)] / 2 = (8 + 8) / 2 = 8 (Formula 5)
Is calculated and output as backlight dimming control data in step S210 (S210).

At time (4), after taking in external light illuminance digital data Din1 (4) and Din2 (4), in step S207,
| Din1 (4) -Din2 (4) | = | 8-3 |> 3 (Formula 6)
Thus, the determination is NO, and in step S208,
Do (4) = Do (3) = 8 (Formula 7)
The same backlight dimming control data as before one unit time is output (S210).

At time (5), after taking in external light illuminance digital data Din1 (5) and Din2 (5), in step S207, | Din1 (5) −Din2 (5) | = | 8-1 |> 3 (Equation 8)
Thus, the determination is NO, and the process proceeds to step S208.
Do (5) = Do (4) = 8 (Formula 9)
The same backlight dimming control data as before one unit time is output (S210).

At time (6), after the outside light 2 returns to the original state and the outside light illuminance digital data Din1 (6) and Din2 (6) are captured, in step S207,
| Din1 (6) -Din2 (6) | = | 8-8 | <3 (Formula 10)
The determination is YES and the process proceeds to step S209.
Do (6) = (Din1 (6) + Din2 (6)) / 2 = (8 + 8) / 2 = 8 (Formula 11)
The same backlight dimming control data as before one unit time is output (S210).

At time (7), after the external light illuminance digital data Din1 (7) and Din2 (7) are captured, in step S207,
| Din1 (7) -Din2 (7) | = | 6-6 | <3 (Formula 12)
The determination is YES and the process proceeds to step S209.
Do (7) = (Din1 (7) + Din2 (7)) / 2 = (6 + 6) / 2 = 6 (Formula 13)
The backlight dimming control data is output in this order (S210).

At time (8), after taking outside light illuminance digital data Din1 (8) and Din2 (8), the process proceeds to step S207.
| Din1 (8) -Din2 (8) | = | 1-1 | <3 (Formula 14)
The determination is YES and the process proceeds to step S209.
Do (8) = [Din1 (8) + Din2 (8)] / 2 = (1 + 1) / 2 = 1 (Formula 15)
The backlight dimming control data is output in this order (S210).

At time (9), after the external light illuminance digital data Din1 (9) and Din2 (9) are captured, in step S207,
| Din1 (9) −Din2 (9) | = | 1-1 | <3 (Expression 16)
The determination is YES and the process proceeds to step S209.
Do (9) = (Din1 (9) + Din2 (9)) / 2 = (1 + 1) / 2 = 1 (Formula 17)
The backlight dimming control data is output in this order (S210).

Note that step S207 in FIG. 2 is determined by taking the difference between the two illuminances, but the illuminance ratio Din1 (i) / Din2 (i), the illuminance ratio allowable determination value lower limit y1, and the illuminance ratio allowable determination value lower limit y2 Y1 <Din1 (i) / Din2 (i) <y2 (Formula 18)
The same effect can be obtained even if it is replaced.

  In step S209, the average value of the two external light illuminance digital data is taken as the backlight dimming digital data, but this step is a flow when the difference between the two external light illuminance digital data is small. Then, it may be based on either one of the data.

(Embodiment 2)
The second embodiment will be described in detail with reference to FIGS. 4 and 5.

  FIG. 4 is a block diagram of a liquid crystal display device with automatic backlight dimming that includes a first photosensor 411, a second photosensor 412, and a third photosensor 413. The first optical sensor 411, the second optical sensor 412, and the third optical sensor 413 detect external light illuminance, and the external light illuminance is converted into external light illuminance digital data by the A / D converter 42. .

  The external light illuminance digital data is sent to the arithmetic unit 43, and the arithmetic is executed by the ROM 44 in which the arithmetic program is stored while being sequentially stored in the RAM 45. The calculation result is transferred to the D / A converter 46, and a voltage corresponding to the calculation result data is output as a dimming voltage. After the dimming voltage is applied to the inverter circuit 47, the backlight 48 is dimmed and an image is displayed on the liquid crystal panel 49.

  FIG. 5 is a flowchart of the backlight dimming method of the liquid crystal display device in FIG. Here, i is the time, j is the optical sensor number, N is the number of optical sensors, Do (i) is the backlight dimming digital data at time i, and x is the backlight dimming digital data at time i = 1 (initial value). ), T is the external light illuminance data capturing time interval, Din (j) (i) is the external light illuminance digital data of the optical sensor 41 (j) at time i, and Din1 (i) is the external light illuminance digital data of the optical sensor 411 at time i. , Din2 (i) is the external light illuminance digital data of the optical sensor 412 at time i, Din3 (i) is the external light illuminance digital data of the optical sensor 413 at time i, and y is the illuminance difference allowable determination value of the optical sensor.

  After the start of processing, an initial value i = 1 is set (S501), an initial value Do (1) = x of backlight dimming digital data is set (S502), and output at the first time (S503).

  i is incremented by +1, and after waiting for T seconds (S504), the external light illuminance digital data Din1 (2) to Din3 (2) of the optical sensors 411 to 413 at the second time are stored in the RAM 45 via the arithmetic unit 43 of FIG. Stored (S505 to S506).

  Next, two different differences of Din1 (2) to Din3 (2) are sequentially calculated and compared with an illuminance difference allowable determination value y (S507 to S512).

If any one of steps S507, S509, or S511 is larger than the illuminance difference allowable determination value y, it indicates that any of the reactions of the optical sensors 411 to 413 is abnormal, and the backlight one unit time before If the dimming digital data Do (i-1) is validated (S508, S510, S512) and smaller than the illuminance difference allowable determination value y, it is determined that the photosensors 411 to 413 have reacted uniformly, and the next step S513 is performed. The average value of the optical sensors 411 to 413 Do (2) = [Din1 (2) + Din2 (2) + Din3 (2)] / 3 (Equation 19)
Is calculated.

  As described above, the backlight dimming digital data Do (i) is set to one of S508, S510, S512, or S513 every unit time, and transferred to the D / A converter 46 in FIG. 4 (S514). After waiting for T seconds (S515), the process returns to step S505, and then, at a third time (i = 3), steps S505 to S515 are repeated.

  Thereafter, S505 to S515 are repeated until the power of the liquid crystal display device is turned off.

  In addition, by changing N = 4, 5,... And calculating the ambient light illuminance difference as in steps S507 to S512 and increasing the number of steps to compare with the illuminance difference allowable determination value, the number of the optical sensors is four or more. Case processing is also possible.

Further, in the present embodiment, steps S507, S509, and S511 in FIG. 5 are performed using the illuminance ratios Din1 (i) / Din2 (i), Din1 (i) / Din3 (i), and Din2 (i) / Din3 (i). Illuminance ratio allowable range values y1, y2,
y1 <Din1 (i) / Din2 (i) <y2 (Formula 20)
y1 <Din1 (i) / Din3 (i) <y2 (Formula 21)
y1 <Din2 (i) / Din3 (i) <y2 (Formula 22)
The same effect is obtained even if it is replaced.

(Embodiment 3)
The third embodiment will be described in detail with reference to FIGS. 4 and 6.

  FIG. 6 is a flowchart of the backlight dimming method of the liquid crystal display device in FIG. Here, i is the time, j is the optical sensor number, N is the number of optical sensors, Do (i) is the backlight dimming digital data at time i, and x is the backlight dimming digital data at time i = 1 (initial value). ), T is the external light illuminance data capturing time interval, Din (j) (i) is the external light illuminance digital data of the optical sensor 41 (j) at time i, and Din1 (i) is the external light illuminance digital data of the optical sensor 411 at time i. , Din2 (i) is the external light illuminance digital data of the optical sensor 412 at time i, Din3 (i) is the external light illuminance digital data of the optical sensor 413 at time i, and Dmax (i) is Din1 (i) to Din3 ( i) is the maximum value, Dmin (i) is the minimum value of Din1 (i) to Din3 (i) at time i, and y is the optical sensor. A photometric tolerance determination value.

  After the start of processing, an initial value i = 1 is set (S601), an initial value Do (1) = x of backlight dimming digital data is set (S602), and output at a first time (S603).

  i is incremented by +1, and after waiting for T seconds (S604), the external light illuminance digital data Din1 (2) to Din3 (2) of the optical sensors 411 to 413 at the second time are taken into the arithmetic unit 43 of FIG. (S605 to S606).

  Next, a difference between the maximum value Dmax (2) and the minimum value Dmin (2) among the Din1 (2) to Din3 (2) is calculated and compared with the illuminance difference allowable determination value y (S607 to S609).

If it is larger than the illuminance difference allowable determination value y, it means that any of the reactions of the optical sensors 411 to 413 is abnormal, and the backlight dimming digital data Do (1) one unit time before is validated (S610). ), If it is smaller than the illuminance difference allowable determination value y, it is determined that the optical sensors 411 to 413 reacted uniformly, and the average value Do (2) = [Din1 (2) of the optical sensors 411 to 413 is determined in the next step S611. ) + Din2 (2) + Din3 (2)] / 3 (Formula 23)
Is calculated.

  As described above, the backlight dimming digital data Do (i) is set to either S610 or S611 every unit time, transferred to the D / A converter 46 of FIG. 4 (S612), and waited for T seconds. Later (S613), the process returns to step S605, and then, at a third time (i = 3), steps S605 to S613 are repeated.

  Thereafter, S605 to S613 are repeated until the power of the liquid crystal display device is turned off.

  By changing N = 4, 5,..., Processing when there are four or more optical sensors is also possible.

In the present embodiment, step S609 in FIG. 6 is set to illuminance ratio Dmax (i) / Dmin (i), illuminance ratio allowable range values y1, y2,
y1 <Dmax (i) / Dmin (i) <y2 (Formula 24)
The same effect is obtained even if it is replaced.

  As described above, the backlight automatic dimming of the liquid crystal display device according to the present invention has a function of automatically dimming the backlight only when the illuminance around the liquid crystal panel changes uniformly. This is suitable for installation in an environment where the illuminance changes partially around the LCD panel due to traffic.

1 is a block diagram of a liquid crystal display device according to Embodiment 1 of the present invention. Flowchart of Liquid Crystal Display Device Backlight Dimming Method in Embodiment 1 of the Present Invention The figure which shows an example of the input-output of the liquid crystal display device in Embodiment 1 of this invention Block diagram of a liquid crystal display device according to Embodiment 2 and Embodiment 3 of the present invention Flowchart of Liquid Crystal Display Device Backlight Dimming Method in Embodiment 2 of the Present Invention Flowchart of liquid crystal display device backlight dimming method according to Embodiment 3 of the present invention The figure which shows an example of the input / output of the conventional liquid crystal display device

Explanation of symbols

12, 42 A / D converter 13, 43 Arithmetic unit 14, 44 ROM (Read Only Memory)
15, 45 RAM (Random Access Memory)
16, 46 D / A converter 17, 47 Inverter circuit 18, 48 Backlight 19, 49 Liquid crystal panel 111, 112, 411, 412, 413 Optical sensor

Claims (6)

A liquid crystal display device backlight dimming method comprising a liquid crystal panel, a backlight, a first illuminance detection means, and a second illuminance detection means,
An illuminance recording step of recording the illuminance detected by the first illuminance detection means and the illuminance detected by the second illuminance detection means at predetermined time intervals;
An illuminance difference calculating step of calculating a difference between the illuminance detected by the first illuminance detecting means and the illuminance detected by the second illuminance detecting means recorded at the same time in the illuminance recording step;
A difference determining step for determining whether or not the difference calculated in the illuminance difference calculating step is smaller than a predetermined value;
Backlight dimming based on one or both of the illuminance detected by the first illuminance detection means and the illuminance detected by the second illuminance detection means when the difference is smaller than a predetermined value in the difference determination step, The liquid crystal display device backlight dimming method characterized by maintaining the immediately preceding backlight dimming when the difference is equal to or greater than a predetermined value in the difference determination step. A liquid crystal display device backlight dimming method comprising a liquid crystal panel, a backlight, and a plurality of three or more illuminance detection means,
Illuminance recording step for recording the illuminance detected by the plurality of illuminance detection means at predetermined time intervals,
An illuminance difference calculating step for obtaining a maximum value and a minimum value of illuminance detected by a plurality of illuminance detection means recorded at the same time in the illuminance recording step and calculating a maximum value / minimum value difference thereof;
A difference determination step for determining whether the maximum value minimum value difference calculated in the illuminance difference calculation step is smaller than a predetermined value;
When the difference is smaller than a predetermined value in the difference determination step, backlight dimming is performed based on one or more of the illuminances detected by the plurality of illuminance detection means, and immediately before the difference is greater than or equal to a predetermined value in the difference determination step. A backlight dimming method for a liquid crystal display device, characterized in that the backlight dimming is maintained. The illuminance difference calculating step calculates the difference sequentially for all two combinations selected from a plurality of illuminance detection means, and maintains the immediately preceding backlight dimming when the difference exceeds a predetermined value. The liquid crystal display device backlight dimming method according to claim 2. A liquid crystal display device backlight dimming method comprising a liquid crystal panel, a backlight, a first illuminance detection means, and a second illuminance detection means,
An illuminance recording step of recording the illuminance detected by the first illuminance detection means and the illuminance detected by the second illuminance detection means at predetermined time intervals;
An illuminance ratio calculating step of calculating a ratio of the illuminance detected by the second illuminance detecting means to the illuminance detected by the first illuminance detecting means recorded at the same time in the illuminance recording step;
A ratio determination step for determining whether the ratio calculated in the illuminance ratio calculation step is within a predetermined range;
Backlight dimming is performed based on one or both of the illuminance detected by the first illuminance detecting means and the illuminance detected by the second illuminance detecting means when the ratio is within a predetermined range in the ratio determining step. A backlight dimming method for a liquid crystal display device, wherein the backlight dimming immediately before is maintained when the ratio is outside a predetermined range in the ratio determining step. A liquid crystal display device backlight dimming method comprising a liquid crystal panel, a backlight, and a plurality of three or more illuminance detection means,
Illuminance recording step for recording the illuminance detected by the plurality of illuminance detection means at predetermined time intervals,
An illuminance ratio calculating step for obtaining a maximum value and a minimum value of illuminance detected by a plurality of illuminance detection means recorded at the same time in the illuminance recording step and calculating a maximum value / minimum value ratio thereof;
A ratio determination step for determining whether the maximum value minimum value ratio calculated in the illuminance ratio calculation step is within a predetermined range;
When the ratio is within a predetermined range in the ratio determination step, backlight dimming is performed based on one or more of the illuminances detected by the plurality of illuminance detection means, and the ratio is outside the predetermined range in the ratio determination step. A backlight dimming method for a liquid crystal display device, characterized by maintaining the previous backlight dimming. In the illuminance ratio calculation step, ratios are sequentially calculated for all two combinations selected from a plurality of illuminance detection means, and the immediately preceding backlight dimming is maintained when the ratio exceeds a predetermined value. The liquid crystal display device backlight dimming method according to claim 5.

Images