Image display device with daytime and nighttime information screens and brightness control method for the same

Abstract: To constantly obtain a satisfactorily bright screen in both nighttime and daytime map screens and, particularly to suppress an occurrence of inversion of the screen in the nighttime map screen as compared with prior art. A nighttime bright and/or contrast voltage and a daytime bright and/or contrast voltage set by the operation of a brightness and/or contrast adjustment means 24 are stored in an EEPROM 16. When the screen is switched to the nighttime map screen in accordance with a daytime/nighttime switch signal, the nighttime bright and/or contrast voltage is read from the EEPROM 16. When the screen is switched to the daytime map screen, the daytime bright and/or contrast voltage is read from the EEPROM 16. A CPU 18 performs such a brightness and/or contrast control that the brightness and/or contrast of an LCD 10 is adjusted to a brightness and/or contrast corresponding to the read bright and/or contrast voltage.

Description: The present invention relates to an image display device and to a brightness control method having a function of selectively switching a nighttime information screen, in particular map screen, and a daytime information screen, in particular map screen, by a switching device. Normally, a liquid crystal display (hereinafter, "LCD") is used in a navigation system to be installed in a vehicle as an image display device. As disclosed in Japanese Unexamined Patent Publications Nos. 6(HEI)-95102 and 6(HEI)-102504, the LCD has a so-called inverse region where black and white portions of a displayed image are inverted as in a negative image of a picture. The inverse region is created by a change in contrast (white-to-black ratio) according to an angle of view. This constrast varies according to an input signal voltage of the LCD. For example, relationships between the input signal voltage and the contrast in the cases where the LCD is viewed from a direction A of about 12 o'clock, from a right above direction B, and from a direction C of about 6 o'clock as shown in FIG. 4 are shown in FIGS. 5(a), 5(b) and 5(c), respectively. As is clear from FIG. 5(a), contrast rises again when the input signal voltage exceeds a specified level. From this, it is known that the inverse region is created in the direction of 12 o'clock of LCD1. In recent years, navigation systems have proposed which have a function of selectively switching a daytime map screen and a nighttime map screen. Generally, the LCD screen in the daytime map screen tends to be whitish, whereas the LCD screen in the nighttime map screen tends to be blackish. Since the above inversion is likely to occur in the black screen, the inversion is likely to occur at the time of the nighttime map screen while being difficult to occur at the time of the daytime map screen in the navigation systems having such daytime/nighttime switching function. However, in the known systems having the daytime/nighttime switching function, there is provided no particular means for preventing such an inversion, and a bright voltage for adjusting the brightness of the screen is always constant regardless of whether the daytime or nighttime map screen is set. As a means for preventing the inversion, a brightness adjustment switch or the like for adjusting the brightness of the screen which switch is provided at the system may be operated so as to adjust the brightness of the screen, particularly at the time of the nighttime map screen to such a level which does not cause the inversion of contrast. However, if the screen is turned into such a satisfactory white screen to the extent that the inversion is unlikely to occur at the time of the nighttime map screen, the screen becomes too white when being switched to the daytime map screen, making it difficult to read the names on the displayed map. Further, if the bright voltage is adjusted such that satisfactory brightness is obtained at the time of the daytime map screen, the inversion is likely to occur when the screen is switched to the daytime map screen. WO 90/03024 discloses an image display device which may be selectively switched between a night time modus and a daytime modus on the basis of a threshold value switch. GB-A-2 285 329 discloses a display device having a photo sensor for determining a light intensity and a variation time function. It is the object of the invention to provide an improved image display device which may provide a satisfactorily bright screen in both night time and daytime and which has a simplified construction and which may be manufactured at low costs. This object is fulfilled by a device having the features disclosed in claim 1 and a method having the features disclosed in claim 7. Preferred embodiments are defined in the dependent subclaims. According to the invention, the nighttime bright and/or contrast voltage and the daytime bright and/or contrast voltage preferably set by the operation of the brightness and/or contrast adjustment means are stored in a storage device. When the screen is switched to the nighttime map screen, the nighttime bright and/or contrast voltage is read from the storage device. When the screen is switched to the daytime map screen, the daytime bright and/or contrast voltage is read from the storage device. The brightness and/or contrast control is so performed as to adjust the brightness and/or contrast of the liquid crystal display to the brightness and/or contrast corresponding to the read bright and/or contrast voltage. Accordingly, a satisfactorily bright and/or contrasted screen can constantly be obtained in both nighttime and daytime map screens. Particularly, an occurrence of the inversion in the nighttime map screen can be suppressed as compared with the prior art. Therefore, there can be provided an image display device having an excellent visibility which is suitable for a navigation system to be installed in a vehicle. Also a control of the display device can be performed according to ambient light conditions or occurrence, e.g. when the car is driven into a tunnel the brightness and/or contrast of the display device can be modified (e.g. by switching it to the nighttime brightness and/contrast) to achieve a better readability. According to a preferred embodiment, the image display device further comprises brightness and/or contrast adjustment means for setting a bright and/or contrast voltage which adjusts the brightness and/or contrast of the display means by setting the nighttime bright and/or contrast voltage for the nighttime information screen and the daytime bright and/or contrast voltage for the daytime information screen. Preferably, the display means comprises a liquid crystal display. Further preferably, the storage means comprises: a permanent data storage, in particular a ROM for storing at least one initial value of the nighttime bright and/or contrast voltage and/or of the daytime bright and/or contrast voltage. a rewritable data storage, in particular an EEPROM for storing at least one newly set value of the nighttime bright and/or contrast voltage and/or of the daytime bright and/or contrast voltage, being in particular set by the brightness and/or contrast adjusting means. Still further preferably, the switching device comprises a switch for head a light diode for detecting a brightness and/or contrast inside and/or outside a vehicle. Most preferably, the controller performs the brightness and/or contrast control of the display means so as to adjust the brightness and/or contrast of the display means such that the brightness and/or contrast is stepwisely and/or continuously varied between the brightness and/or contrast corresponding to the nighttime bright and/or contrast voltage and the daytime bright and/or contrast voltage read by the reading device, preferably depending on a signal corresponding to a brightness and/or contrast inside and/or outside a vehicle. According to the invention, there is further provided a brightness and/or contrast control method for controlling an image display device, in particular to the invention, comprising the steps of: discriminating which of a night time or first information screen mode and a day time or second information screen mode has been chosen based upon a switch signal from a switching device; reading a nighttime bright and/or contrast voltage value or a daytime bright and/or contrast voltage value from a storage means based upon the chosen screen mode, D/A-converting the read voltage value to an analog voltage and outputting the analog voltage to a display means of the image display device. According to a preferred embodiment, the method further comprises the steps of: detecting whether a brightness and/or contrast adjustment has been performed based upon one or more adjustment signals of a brightness and/or contrast adjustment means, and writing the nighttime bright and/or contrast voltage value and/or the daytime bright and/or contrast voltage value corresponding to the adjustment signals of the brightness and/or contrast adjustment means in the storage means. Preferably, the method further comprises the step of initializing the storage means, in particular by reading a predetermined or predeterminable initial value from an initial value storage means and writing the initial value for the nighttime and/or daytime bright and/or contrast voltage value in the storage means. According to a further preferred embodiment, there is provided an image display device having a function of selectively switching a nighttime map screen and a daytime map screen by a switching device, comprising: brightness and/or contrast adjustment means for setting a bright and/or contrast voltage which adjusts the brightness and/or contrast of a screen or liquid crystal display, storage means for storing a nighttime bright and/or contrast voltage for the nighttime map screen and a daytime bright and/or contrast voltage for the daytime map screen which are set by the operation of the brightness and/or contrast adjustment means, a reading device for reading the nighttime bright and/or contrast voltage when a screen is switched to the nighttime map screen by the switching device, and the daytime bright and/or contrast voltage when the screen is switched to the daytime map screen by the switching device, and a controller for performing a brightness and/or contrast control so as to adjust the brightness and/or contrast of the liquid crystal display to a brightness and/or contrast corresponding to the nighttime bright and/or contrast voltage or the daytime bright and/or contrast voltage read by the reading device. In this invention, when being set by the operation of the brightness and/or contrast adjustment means, the nighttime bright and/or contrast voltage and the daytime bright and/or contrast voltage are stored in the storage device. When the screen is switched to the nighttime map screen, the nighttime bright and/or contrast voltage is read from the storage means by the reading device, and the controller controllably adjusts the brightness and/or contrast of the liquid crystal display to a brightness and/or contrast corresponding to the read nighttime bright and/or contrast voltage. Likewise, when the screen is switched to the daytime map screen, the daytime bright and/or contrast voltage is read and the brightness and/or contrast of the liquid crystal display is controllably adjusted to a brightness and/or contrast corresponding to the read daytime bright and/or contrast voltage. According to a further preferred embodiment of the invention there is provided an image display device for displaying images in a selected one of a first visibility condition and a second visibility condition on an electrically operated display, comprising: storage means for storing a first voltage for the display and a second voltage for the display; switch means for selectively switching between first and second positions corresponding respectively to the first visibility condition and the second visibility condition; a reading device for reading the first voltage in the storage means when the switch means is in said first position and for reading the second voltage from the storage means when the switch is in the second position; and a controller for adjusting output of the display between a first display condition and a second display condition in accordance with the voltage read by the reading device, such that the first display condition displays images selected for said first visibility condition and such that said second display condition displays images selected for said second visibility condition. Preferably, the first visibility condition defines a condition of low ambient light, and wherein said second visibility condition defines a condition of high ambient light, said first and second voltages being set such that said first display condition defines a display of images brighter than the second display condition. Further preferably, the first visibility condition defines a condition of low ambient light, and wherein said second visibility condition defines a condition of high ambient light, said first and second voltages being set such that said second display condition defines greater image contrast than said first display condition. Still further preferably, the display means comprises a liquid crystal display. Most preferably, the switching device comprises a light diode for detecting ambient light conditions. These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings in which: FIG. 1 is a block diagram of one embodiment of the invention, FIGS. 2 and 3 are a flow chart showing the operation of the embodiment, FIG. 4 is a diagram showing a prior art image display device, and FIGS. 5(a), 5(b), 5(c) are graphs showing the characteristics of the prior art image display device. FIG. 1 is a block diagram of one embodiment of the invention, and FIGS. 2 and 3 are a flow chart showing the operation of this embodiment. First, the overall construction is described. As shown in FIG. 1, a monitor unit 6 and a navigation unit 7 are provided. The monitor unit 6 includes a storage means, e.g. an EEPROM 16 for storing a nighttime bright voltage for a nighttime map screen and a daytime bright voltage for a daytime map screen which are set by operating a brightness adjustment means 24 constructed by a touch switch, a remote controller, a variable resistance knob or the like. A CPU 18 which functions as a reading device and a controller writes and reads the nighttime and daytime bright voltages in and from the EEPROM 16. The read nighttime and daytime bright voltages are output to a display means, e.g. an LCD 10, a projection screen (e.g. integrated in the windshield), an electron beam tube, etc. after being digital to analog (D/A) converted by a D/A converter 19. The navigation unit 7 outputs R-, G-, B-signals and a composite synchronization signal C-Sy based on a navigation data such as a map data stored in advance in an unillustrated storage means such as a built-in memory. Alternatively also other color signals (such as C-, M-, Y-signals) and/or synchronization or control signals may be used. These output signals are input to the LCD 10, whereon a navigation screen including a road map corresponding to the navigation data is displayed. The nighttime and daytime map screens are switched in accordance with a daytime/nighttime switch signal sent to the navigation unit 7. Generally, as this daytime/nighttime switch signal, an on-off signal for head lights or tail lights is used as it is additionally also a light diode sensing or detecting the brightness inside and/or outside the vehicle can be used as a switching device. This switch signal is also input to the CPU 18, which in turn discriminates a selected mode and switches thereto. The nighttime and daytime bright voltages are written in the EEPROM 16 in accordance with this mode. Identified by 14 in FIG. 1 is a permanent storage means, e.g. a ROM for storing an initial value of the nighttime bright voltage set, e.g. at the time of shipment from a factory, and by 15 a rewritable storage means, e.g. a RAM for providing an operation work area of the CPU 18. Next, a brightness control is described with respect to the flow chart of FIGS. 2 and 3. First, as shown in FIG. 2, whether an effective voltage value has already been written in a write area of the EEPROM 16 for the nighttime bright voltage is discriminated (Step S1). If the discrimination result is "NO", the initial value of the nighttime bright voltage set, e.g. at the time of shipment is read from the ROM 14 and written in the EEPROM 16 (Step S2). On the other hand, if the discrimination result in Step S1 is "YES", Step S3 follows in the same way as the operation of Step S2 is completed. In Step S3, whether the effective voltage has already been written in the write area of the EEPROM 16 for the daytime bright voltage is discriminated . If the discrimination result is "NO", the initial value of the daytime bright voltage set, e.g. at the time of shipment is read from the ROM 14 and written in the EEPROM 16 (Step S4). On the other hand, if the discrimination result in Step S3 is "YES", Step S5 follows in the same way as the operation of Step S4 is completed. The nighttime map screen is set in accordance with the daytime/nighttime switch signal (Step S5), and the nighttime bright voltage is read from the EEPROM 16 (Step S6). After the read nighttime bright voltage is D/A converted by the D/A converter 19, a digital value of the nighttime bright voltage is output to the LCD 10 (Step S8). Further, whether the screen has been switched to the daytime map screen is discriminated (Step S9). If the discrimination result is "NO", whether a brightness control in the nighttime map screen has been performed is discriminated (Step S10). If this discrimination result is "NO", Step S9 follows. On the other hand, if the discrimination result in Step S10 is "YES", the nighttime bright voltage set by the brightness adjustment means 24 during the brightness control is newly written in the EEPROM 16 (Step S11). Thereafter, Step S8 follows. If the discrimination result in Step S9 is "YES", as shown in FIG. 3, the daytime map screen is set in accordance with the daytime/nighttime switch signal (Step S15); the daytime bright voltage is read from the EEPROM 16 (Step S16); and after the read daytime bright voltage is D/A converted by the D/A converter 19 (Step S17), a digital value of the daytime bright value is output to the LCD 10 (Step S18). Further, whether the screen has been switched to the nighttime map screen is discriminated (Step S19). If the discrimination result is "NO", whether the brightness control in the navigation mode has been performed is discriminated (Step S20). If this discrimination result is "NO", Step S19 follows. On the other hand, if the discrimination result in Step S20 is "YES", the daytime bright voltage set by the brightness adjustment means 24 during the brightness control is newly written in the EEPROM 16 (Step S21) and Step S18 follows thereafter. If the discrimination result in Step S19, Step S5 follows. As described above, when the nighttime bright voltage is set in the nighttime map screen or the daytime bright voltage is set in the daytime map screen by the operation of the brightness adjustment means 24, the set bright voltage is written in the EEPROM 16. When the screen is switched to the nighttime map screen, the CPU 18 reads the nighttime bright voltage from the EEPROM 16 and controls the brightness of the LCD 10 so as to conform to the read nighttime bright voltage. Likewise, when the screen is switched to the daytime map screen, the daytime bright voltage is read and the brightness of the LCD 10 is controlled so as to conform to the read daytime bright voltage. Since the brightness control is performed in both nighttime and daytime map screens, there can be prevented an occurrence of inconveniences residing in the prior art: even if a satisfactorily bright screen is obtained in the daytime map screen, the screen becomes too dark when being switched to the nighttime map screen, thereby creating an inverse area; or even if a satisfactorily bright screen is obtained in the nighttime map screen, the screen becomes too bright when being switched to the daytime map screen, thereby making it difficult to read the names on a displayed map. Thus, a satisfactorily bright screen can constantly be obtained in both nighttime and daytime map screens. The invention was exemplarily described with respect to a map screen (as a displaying device). However it is to be understood that the invention may also be applied to any other type of information display means such as a radio frequency or station display, a broadcast information display or a vehicle data (e.g. speed, oil temperature or oil pressure etc.) display.

Claims: An image display device having a function of selectively switching a nighttime information screen and a daytime information screen by a switching device, characterized by storage means (16; 14) for storing a nighttime bright and/or contrast voltage for the nighttime information screen and a daytime bright and/or contrast voltage for the daytime information screen, a reading device (18) for reading the nighttime bright and/or contrast voltage when a display means (10) is switched to the nighttime information screen by the switching device, and the daytime bright and/or contrast voltage when the display means (10) is switched to the daytime information screen by the switching device, and a controller (18) for performing a brightness and/or contrast control of the display means (10) so as to adjust the brightness and/or contrast of the display means (10) to a brightness and/or contrast corresponding to the nighttime bright and/or contrast voltage or the daytime bright and/or contrast voltage read by the reading device (18), wherein the switching device comprises a switch for head lights and/or tail lights. An image display device according to claim 1, further comprising brightness and/or contrast adjustment means (24) for setting a bright and/or contrast voltage which adjusts the brightness and/or contrast of the display means (10) by setting the nighttime bright and/or contrast voltage for the nighttime information screen and the daytime bright and/or contrast voltage for the daytime information screen. An image display device according to one or more of the preceding claims, wherein the display means (10) comprises a liquid crystal display (LCD). An image display device according to one or more of the preceding claims, wherein the storage means (16;14) comprises: a permanent data storage (14), in particular a ROM (14) for storing at least one initial value of the nighttime bright and/or contrast voltage and/or of the daytime bright and/or contrast voltage. a rewritable data storage (16), in particular an EEPROM (16) for storing at least one newly set value of the nighttime bright and/or contrast voltage and/or of the daytime bright and/or contrast voltage, being in particular set by the brightness and/or contrast adjusting means (24). An image display device according to one or more of the preceding claims, wherein the switching device comprises a light diode for detecting a brightness and/or contrast inside and/or outside a vehicle. An image display device according to one or more of the preceding claims, wherein the controller (18) comprises means arranged to perform the brightness and/or contrast control of the display means (10) so as to adjust the brightness and/or contrast of the display means (10) such that the brightness and/or contrast is stepwisely and/or continuously varied between the brightness and/or contrast corresponding to the nighttime bright and/or contrast voltage and the daytime bright and/or contrast voltage read by the reading device (18), preferably depending on a signal corresponding to a brightness and/or contrast inside and/or outside a vehicle. A brightness and/or contrast control method for controlling an image display device, in particular according to one or more of the preceding claims, comprising the steps of: discriminating (S9; S19) which of a night time information screen mode and a day time information screen mode has been chosen based on a switch signal from a switching device; characterized by the steps of: providing the switch signal on the basis of a switch for head lights and/or tail lights, reading (S6; S16) a nighttime bright and/or contrast voltage value or a daytime bright and/or contrast voltage value from a storage means (16; 14) based on the chosen screen mode, D/A-converting (S7; S17) the read voltage value to an analog voltage and outputting (S8; S18) the analog voltage to a display means (10) of the image display device. A method according to claim 7, further comprising the steps of: detecting (S10; S20) whether a brightness and/or contrast adjustment has been performed based upon one or more adjustment signals of a brightness and/or contrast adjustment means (24), and writing (S11; S21) the nighttime bright and/or contrast voltage value and/or the daytime bright and/or contrast voltage value corresponding to the adjustment signals of the brightness and/or contrast adjustment means in the storage means (16). A method according to claim 7 or 8, further comprising the step of initializing (S1, S2; S3, S4) the storage means (16), in particular by reading a predetermined or predeterminable initial value from an initial value storage means (14) and writing the initial value for the nighttime and/or daytime bright and/or contrast voltage value in the storage means (16).

Inventors: MORIGUCHI MASAKATSU, MORIGUCHI, MASAKATSU, Moriguchi, Masakatsu, Sumitomo Wiring Systems Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1997
Main classification: G09G3
IPC codes: G08G1, G01C21, G09B29, B60Q3, G09G3