JP2006106495A - Image display apparatus and portable terminal apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display apparatus and a portable terminal apparatus capable of attaining low power consumption and displaying image information of high visibility. <P>SOLUTION: At the time of power saving operation, a light emission control means 16 controls the light emission intensity of a light source means 14 to intensity lower than that of normal operation, and a gradation control means 12 controls gradations displayed by respective pixels in a light modulation means 10 to a level larger than that of normal operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image display device capable of reducing power consumption and improving image quality, and a portable terminal device including the image display device.

  2. Description of the Related Art Conventionally, a liquid crystal display including a liquid crystal panel and a backlight is widely used as a thin image display device.

  This type of liquid crystal display displays an image on a liquid crystal panel based on an input video signal and irradiates the liquid crystal panel with light from a backlight. The liquid crystal display displays video information corresponding to the input video signal by obtaining a transmitted light image by irradiating light from a backlight onto an image displayed on the liquid crystal panel. The user can know the video information by viewing the transmitted light image.

  Liquid crystal displays are used in a wide range of fields such as televisions, monitors for personal computers (personal computers) or display screens of portable terminal devices typified by mobile phones.

  As liquid crystal displays become more widespread, it is desired that liquid crystal displays have higher image quality and lower power consumption.

  Especially in portable terminal devices, the usage time has expanded with the expansion of applications, and it has become indispensable to extend the battery life, so the low power consumption of liquid crystal displays that consume a lot of power Is required.

  Control technology to improve the image quality of the liquid crystal display detects the maximum luminance, minimum luminance, average luminance, etc. of the input video signal, and amplifies the gradation of the image data of the image displayed on the liquid crystal panel according to the detected values At the same time, there is one that modulates the light output intensity of the backlight to expand the dynamic range.

  For example, Japanese Patent Laid-Open No. 9-244548 (Patent Document 1) reduces the amount of light emitted from the backlight and increases the amount of light reduction in the liquid crystal panel by controlling the image data when the input video signal relates to dark video information. Let On the other hand, when the input video signal is related to bright video information, a display device is disclosed that increases the amount of light emitted from the backlight and controls the image data to reduce the amount of light reduction in the liquid crystal panel.

  This achieves the purpose of improving the contrast of the image displayed on the liquid crystal panel and supplying a video with a wide range of expression.

  In addition, in a battery-driven portable terminal device typified by a mobile phone, the remaining battery level is monitored at a certain time interval in order to extend the life of the battery. There is a control technology that reduces the light output intensity of the backlight to save power.

  For example, Japanese Patent Laying-Open No. 2000-250455 (Patent Document 2) discloses an information processing for reducing the brightness of a backlight and changing a color palette according to the remaining battery level when the remaining battery level falls below a certain level. An apparatus is disclosed.

Thereby, the power consumption of the backlight is reduced, and the visibility is improved by adding a difference in saturation in addition to the brightness.
JP-A-9-244548 JP 2000-250455 A

  However, the above-described conventional image display device has the following problems.

  In the control technology for modulating the light output intensity of the backlight and the image data according to the brightness of the video information related to the input video signal as shown in Patent Document 1, the maximum luminance, minimum luminance, and average of the input video signal If a circuit for detecting image features such as luminance is provided, the circuit scale and power consumption increase.

Furthermore, it is necessary to appropriately modulate the image data for each input image data, resulting in an increase in circuit scale and an increase in power consumption. Further, when the resolution of the display unit increases, the amount of image data that needs to be modulated per image increases, which causes a problem that the scale of the modulation circuit must be increased or the processing speed must be increased. End up.
Further, depending on the brightness of the input image data, the light output of the backlight cannot be reduced, and the power consumption cannot be reduced.

  When reducing the power consumption by reducing the luminance (light emission intensity) of the backlight according to the remaining battery level as shown in Patent Document 2, the amount of light irradiation to the liquid crystal panel is reduced and the display of the liquid crystal panel is displayed. The brightness and contrast of the image are lowered, and eventually the visibility is lowered.

  Furthermore, although the method of changing the color palette is good only for character display, there is a problem that the color, which is an important element for the image, is changed, so that the image quality is deteriorated.

  The present invention has been made in view of the above problems, and provides an image display device and a portable terminal device that can reduce power consumption and display video information with high visibility. It is the purpose.

  The present invention relates to a light modulation means for displaying an image with a plurality of pixels capable of gradation display, a gradation control means for controlling a gradation displayed by each pixel of the light modulation means, and irradiation to the light modulation means. An image display device having light source means for emitting light and light emission control means for controlling light emission intensity of the light source means, wherein the light emission control means normally sets the light emission intensity of the light source means during power saving operation. An image that is controlled to be smaller than that during operation, and wherein the gradation control unit controls the gradation displayed by each pixel of the light modulation unit to be larger than that during normal operation. It is a display device.

  In the present invention, when the power saving operation is performed, it is preferable that the light emission control unit controls the light emission intensity of the light source unit to be smaller at a constant rate than in the normal operation.

  The present invention relates to a light modulation means for displaying an image with a plurality of pixels capable of gradation display, a gradation control means for controlling a gradation displayed by each pixel of the light modulation means, and irradiation to the light modulation means. An image display device having a light source means for emitting light and a light emission control means for controlling the light emission intensity of the light source means, comprising an average luminance detection means for detecting an average luminance of an input video signal, and a power saving operation The light emission control means controls the light emission intensity of the light source means to change according to the average luminance, and the gradation control means controls the gradation displayed by each pixel of the light modulation means. Is an image display device that is controlled to be larger than that during normal operation.

  In the present invention, during power saving operation, the gradation control means controls each pixel of the light modulation means so as to display a video signal obtained by adding a certain gradation to the input video signal. It is preferable that

  Further, in the present invention, during the power saving operation, the gradation control means fixes the maximum gradation of the input video signal and displays the video signal in which the value of the other gradation is increased. It is preferable to control each pixel of the light modulation means.

  Further, in the present invention, during the power saving operation, the gradation control means fixes the minimum gradation of the input video signal and displays the video signal in which the value of the other gradation is increased. It is preferable to control each pixel of the light modulation means.

  In the present invention, each pixel of the light modulation unit has red, green, and blue sub-pixels. During the power saving operation, the gradation control unit is configured to output the red and green sub-pixels of the input video signal. The gradation for the pixel is increased at a constant rate, and the gradation for the blue sub-pixel of the input video signal is increased to a certain gradation or more, and the gradation that is less than the certain value exceeds the certain value. It is preferable to control each pixel of the light modulation means so as to display a video signal that is enlarged in a non-existing range.

  Further, in the present invention, it is preferable to have battery remaining amount detecting means for detecting the remaining battery level, and to switch between the normal operation and the power saving operation according to the value detected by the remaining battery amount detecting means.

  In the present invention, it is preferable that the light modulation means is constituted by a liquid crystal panel.

  In the present invention, it is preferable that the light source means is constituted by a light emitting diode.

  The present invention is a portable terminal device comprising the image display device as a display means.

  In the image display device of the present invention, the light emission control means controls the light emission intensity of the light source means to be smaller than that in the normal operation during the power saving operation, and the gradation control means includes the light modulation means. The gradation displayed by each pixel is controlled to be larger than that during normal operation. As a result, during power saving operation, the light emission intensity of the light source means is reduced to reduce power consumption, and even when the light emission intensity of the light source is reduced, the gradation displayed by each pixel of the light modulation means is normally operated. It is possible to increase the average luminance of the display screen by increasing the time and to provide an image display device with high visibility.

  In addition, when performing the power saving operation, the light emission control means controls the light emission intensity of the light source means to be smaller at a constant rate than in the normal operation, so that the average luminance, minimum luminance, Since it is only necessary to uniformly reduce the light emission intensity of the light source means without detecting image features such as average luminance, the circuit scale can be reduced and the size can be reduced.

  The image display apparatus according to the present invention has an average luminance detecting means for detecting the average luminance of the input video signal, and the light emission control means uses a light source according to the average luminance detected by the average luminance detecting means during the power saving operation. The light intensity of the means is controlled to change, and the gradation control means controls the gradation displayed by each pixel of the light modulation means to be larger than that during normal operation. As a result, the light emission intensity of the light source is reduced to reduce power consumption, and even when the light emission intensity of the light source is reduced, the gradation can be increased to increase the average luminance of the display screen, and the visibility is high. Image display is possible.

  In the image display device of the present invention, during the power saving operation, each of the light modulators displays so that the gradation control unit displays a video signal obtained by adding a certain gradation to the input video signal. Control the pixels. Thereby, it is not necessary to perform separate gradation conversion for every gradation, the circuit constituting the gradation control means can be reduced, and the power consumption in the circuit can be reduced. Further, power consumption can be reduced regardless of the input video signal.

  Further, during the power saving operation, each pixel of the light modulation unit is controlled to display a video signal in which the maximum gradation of the input video signal is fixed and other gradation values are increased. Thereby, since the brightness of the display image can be increased while maintaining the relativity of each gradation of the input video signal, it is possible to reduce power consumption and improve the visibility of the display screen. Further, power consumption can be reduced regardless of the input video signal.

  In the present invention, during the power saving operation, each pixel of the light modulation means is controlled so that the video signal with the minimum gradation of the input video signal fixed and the other gradations increased is displayed. What is to be done is suitable. As a result, the average luminance of the display screen can be increased and the contrast can be improved, so that power consumption can be reduced and the visibility of the display screen can be improved.

  In the present invention, each pixel of the light modulation means has red, green, and blue sub-pixels, and during power saving operation, the gradation control means applies to the red and green sub-pixels of the input video signal. A range in which the gradation is increased at a certain rate, and the gradation for the blue sub-pixel of the input video signal is increased to a certain gradation or more, and the gradation less than the certain value is not exceeded the certain value. Each pixel of the light modulation means is controlled so as to display the video signal enlarged by. As a result, when additive color mixture of red, green, and blue light is performed, in the white area where the surrounding gradation is less than a certain value and the gradation near the center is the maximum gradation in the input image, Since the blue gradation around the area is a constant value and the gradation near the center of the white area is displayed at or near the maximum gradation, the color temperature in the white area is higher than the surrounding color temperature in the white area. The central color temperature can be increased to express a bright white color, and the image quality of the display image can be improved.

  In the image display device of the present invention, it is preferable that the image display apparatus further includes a remaining battery level detection unit that detects the remaining battery level, and the normal operation and the power saving operation are switched according to a value detected by the remaining battery level detection unit. . As a result, when the remaining amount of the battery is low, the power consumption can be reduced and the battery life can be extended, and a display with improved visibility becomes possible.

  In the image display device of the present invention, it is preferable that the light modulation means is a liquid crystal panel. Thereby, it is possible to easily realize the light modulation means.

  In the image display device of the present invention, the light source means is preferably a light emitting diode. Thereby, the light emission intensity of the light source can be easily controlled by changing the voltage, current, light emission time, and the like.

  According to the portable terminal device of the present invention, by providing the display unit with an image display device with reduced power consumption and high visibility, a portable terminal with a long battery life and capable of good display can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the size and positional relationship are exaggerated for easy understanding, and the actual image display apparatus is not limited to this size and interval.

[Embodiment 1]
FIG. 1 is an explanatory diagram showing a schematic configuration of Embodiment 1 of an image display apparatus according to the present invention. 2 to 4 are diagrams showing light source means (light emission intensity thereof), gradation data control, and the like for specifically explaining the control according to the first embodiment. FIG. 5 is an explanatory diagram of the relationship between the gradation of the input video signal and the display gradation when each control (method) shown in FIGS. 2 to 4 is used.

  As shown in FIG. 1, the image display apparatus according to the first embodiment controls the light modulation unit 10 that displays an image using a plurality of pixels that can perform gradation display, and the gradation that each pixel of the light modulation unit 10 displays. An image display apparatus having a gradation control means 12 for performing light emission, a light source means 14 for emitting light for irradiating the light modulation means 10, and a light emission control means 16 for controlling the light emission intensity of the light source means 14. The light emission control means 16 controls the light emission intensity of the light source means 14 to be smaller than that during normal operation, and the gradation control means 12 and the gradation displayed by each pixel of the light modulation means 10 are normal. Control to be larger than that during operation.

  In the first embodiment, the light emission control means 16 is controlled so that the light emission intensity of the light source means 14 is reduced at a constant rate compared with the normal operation when performing the power saving operation.

  The light modulation means 10 has a plurality of pixels capable of gradation display, and displays an image with the plurality of pixels. In this embodiment, the light modulation means 10 is a liquid crystal panel 102 in which a plurality of pixels capable of gradation display are arranged in a plane, and a video signal corresponding to the plurality of pixels is input to thereby display a screen. The image data is displayed in part or in whole.

  The gradation control means 12 controls the gradation displayed by each pixel of the light modulation means 10. The gradation control means 12 controls the gradation (luminance) of each pixel of the liquid crystal panel 102 by the liquid crystal panel control unit 104.

  The light source means 14 emits light for irradiating the light modulation means 10. In the present embodiment, as shown in FIG. 1, the light source means 14 includes a light source 100 and a light guide plate 101 on which light emitted from the light source 100 is incident from a side end face (light incident end face 101i). As the light source 100, a cold cathode tube, a light emitting diode, or the like can be used, but a light emitting diode is preferable because the light emission intensity can be easily changed by controlling the light emission time.

  As shown in FIG. 1, the light guide plate 101 has a substantially wedge shape, and light incident from the light incident end surface 101 i is reflected on the inclined surface to change the light propagation angle and does not satisfy the total reflection condition. Light is emitted from the light guide plate 101. The light guide plate 101 is not limited to such a substantially wedge shape, and a rectangular parallelepiped provided with diffusion dots and irregularities may be used. In addition, it is possible to improve the light utilization efficiency by disposing a reflective sheet made of white PET (PolyEthylene Terephthalate) or the like on the end surface of the light guide plate 101 shown in FIG. 1 excluding the light incident end surface 101i and the light irradiation surface 101o. It is.

  The liquid crystal panel 102 is arranged on the light irradiation surface 101 o side of the light guide plate 101 so that the light emitted from the light guide plate 101 is irradiated onto the liquid crystal panel 102. Although not shown, an optical sheet that provides desired optical characteristics, such as a diffusion sheet, a prism sheet, and a reflective polarizing sheet, may be disposed between the light guide plate 101 and the liquid crystal panel 102.

  The light emission control means 16 controls the light emission intensity of the light source means 14. In the present embodiment, the light emission control means 16 includes a light source control unit 103 that controls the light emission intensity of the light source 100 given by the light source control signal. The light emission intensity can be changed by controlling the light emission time. For example, when the light emission duty of the light source is changed from 100% to 50%, the light emission intensity can be halved from the initial state.

  In the present embodiment, the video signal and the light source control signal are switched to the display method according to the present invention described later in accordance with the input of the power saving signal. As shown in FIG. 1, a light emission intensity reducing unit 108 that decreases the input light source control signal at a constant rate and a luminance increasing unit 109 that increases the luminance of the input video signal at a constant rate are provided. When shifting from the normal operation to the power saving operation in which the power saving signal is inputted, the light source control signal whose emission intensity is reduced by the emission intensity reducing unit 108 is inputted to the light source control unit 103 and the luminance (109) Each signal is switched so that a video signal having an increased (gradation) is input to the liquid crystal panel control unit 104.

  During normal operation, the light intensity L0 indicated by the light source control signal is input to the light source control unit 103, and the luminance x0 indicated by the video signal is input to the liquid crystal panel control unit 104.

As the light source control signal during the power saving operation, a light source control signal having a light emission intensity L1 that is reduced from the light emission intensity L0 by A1 (0 <A1 <L0) is input to the light source control unit 103 as shown in Expression (1). . Here, as a method of reducing the light emission intensity, the light emission intensity L2 during the power saving operation may be obtained by multiplying a constant A2 (0 <A2 <1) and L0 as shown in Expression (2). That is, when A2 is 0.8, 80% brightness during normal operation is the brightness during power saving operation.
L1 = L0−A1 (1)
L2 = L0 × A2 (2)

  As the video signal during the power saving operation, a video signal whose fixed value is increased to the input gradation is input to the liquid crystal panel control unit 104 by a method described later.

  Here, as long as the power saving signal is switched from the normal operation to the power saving operation (such as a switch input by the user), the power saving signal may be generated in a fixed manner until the normal operation is restored thereafter. Other power-saving signals include a method that allows the user to arbitrarily set the conditions for generating the power-saving signal, a method that automatically controls the generation of the power-saving signal based on ambient brightness and video signals, It is preferable to perform a method of automatically controlling the generation of a power saving signal by a signal indicating the amount or the like because appropriate display can be performed according to the display environment and the remaining battery level.

  In particular, in a portable terminal device, it is important to extend the battery life, and it is necessary to reduce power consumption. That is, when the remaining battery level is low, it is preferable to perform control so as to switch between normal operation and power saving operation.

  FIG. 2 is an explanatory diagram showing the control of the light emission intensity and the display luminance during the power saving operation.

  2A is a perspective view showing the positions of the pixels arranged on the liquid crystal panel 102, and the positions of the pixels in the horizontal direction correspond to the horizontal axis of the graphs shown in FIGS. 2B to 2D. Also, the vertical axis of the graphs of FIGS. 2B to 2D represents the luminance (gradation) of the video signal displayed by each pixel in the horizontal direction shown in FIG.

  FIG. 2B shows a video signal input to the image display device. That is, it represents the luminance displayed by each pixel during normal operation. FIG. 2 (c) shows the luminance (gradation) displayed by the pixel when the intensity of light irradiated from the light source means 14 to the light modulation means 10 is lowered by the light emission intensity control means, and FIG. The luminance (gradation) displayed in each pixel during the power saving operation is shown.

  By reducing the light emission intensity in the light emission intensity reducing unit 108, the light emission intensity of the light source means 14 controlled by the light emission control means 16 is lowered at a constant rate to reduce the power consumption. That is, control is performed so that the light emission of the light source means 14 becomes dark according to the power saving signal. The state at this time is shown in FIG. Since the light emission intensity of the light source means 14 is reduced from the state of FIG. 2B, the displayed luminance is lowered as a whole as compared with FIG.

  In addition, the luminance increasing unit 109 adds a certain numerical value to the gradation of the input video signal, so that the gradation that is increased at a certain ratio is set as a display gradation to be displayed by the light modulation means 10. The state at this time is shown in FIG. As shown in FIG. 2 (d), the brightness of the displayed image is reduced by the amount of light emission intensity of the light source means 14, but the display brightness is increased because the gradation of the light modulation means 10 is increased, and the image is increased. It becomes possible to improve the visibility.

  In the present embodiment, control is performed so that the light emission intensity of the light source is reduced at a constant rate regardless of the input video signal. Therefore, since it is not necessary to detect video features such as the maximum luminance, minimum luminance, and average luminance of the input video, it is not necessary to provide a circuit for detecting video features, and the circuit scale is reduced and the size is reduced. It is possible.

  Even if a circuit for detecting the above-mentioned video feature is provided, the power consumption of the circuit can be reduced if power is not supplied to the circuit for detecting the video feature when the power saving operation is performed. Is possible.

  In the method described above, the display luminance of the light modulation means 10 is controlled by adding a certain numerical value to the luminance of the input video signal by the luminance increasing unit 109, but the method shown in FIGS. The same effect can be obtained also.

  In the method shown in FIG. 3, the luminance increasing unit 109 performs control by fixing the maximum gradation of the input video signal and increasing other gradations. According to this method, the luminance of the display image can be improved while maintaining the relativity of each gradation of the input video signal, and the power consumption can be reduced and the visibility of the display screen can be improved.

  The method shown in FIG. 4 is a case where the brightness increasing unit 109 fixes the minimum gradation of the input video signal and increases other gradations. According to this method, the contrast between the minimum luminance and the maximum luminance can be obtained, so that it is possible to reduce power consumption and improve the visibility of the display screen.

3 (a), 3 (b), and 4 (c) can be performed in the same manner as the method of FIG.
In FIG. 3D, since the maximum gradation is fixed and other gradations are increased by the luminance increasing unit 109, the gradation excluding the maximum gradation is increased and the average luminance of the displayed image is increased. is doing. At this time, the relative gradation of each pixel is maintained. Therefore, the brightness of the display image can be improved while maintaining the relativity of each gradation, and the power consumption can be reduced and the visibility of the display screen can be improved.
In FIG. 4D, since the minimum gradation is fixed and other gradations are increased by the luminance increasing unit 109, the gradation excluding the minimum gradation is increased and the average luminance of the displayed image is increased. is doing. At this time, since the other gradations are increased while the minimum gradation is maintained, the contrast of the display image is increased. Therefore, the contrast between the maximum luminance and the minimum luminance can be obtained, and the power consumption can be reduced and the visibility of the display screen can be improved.

  FIG. 5 is an explanatory diagram of the relationship between the gradation of the input video signal and the display gradation when the method (control method) shown in FIGS. 2 to 4 is used. When FIG. 5A uses the input video signal as it is for display gradation, FIG. 5B uses the method shown in FIG. 2, and FIG. 5C uses the method shown in FIG. FIG. 5D shows a case where the method shown in FIG. 4 is used.

  When an arbitrary pixel has a gradation of 0 to 255, the gradation of the input video signal is x0, the display gradation of the light modulation means 10 during the power saving operation of the method shown in FIG. 2 is x1, and FIG. The display gradation of the light modulation means 10 during the power saving operation of the method shown is x2, the display gradation of the light modulation means 10 during the power saving operation of the method shown in FIG. 4 is x3, and C1, C2 and C3 are constants. To do.

  At this time, for example, in the method shown in FIG. 2, the display gradation x1 is expressed by the relational expression shown in the equation (3), and in the method shown in FIG. In the method shown, the display gradation x3 can be obtained by the relational expression shown in Expression (5).

  However, if the obtained gradation exceeds 255, it is assumed to be 255.

  x1 = x0 + C1 (3)

  x2 = C2 × (x0-255) +255 (4)

  x3 = C3 × x0 (5)

  Therefore, in each method, by setting the constants C1, C2, and C3 in advance, the display gradation is sequentially obtained based on the maximum luminance, minimum luminance, average luminance, backlight brightness, etc. of the input video signal. In comparison, the display gradation of the liquid crystal panel 102 can be easily obtained.

In the methods shown in FIGS. 2 to 4, the relationship between the display gradation and the input gradation is a straight line. However, the present invention is not limited to this relationship, and although not shown, the display gradation x4 and As shown in the equation (6) using the constant C4, the effect of the present invention can be obtained even when the relationship between x0 and x4 is a curve.
x4 = √ (255 × x0) + C4 (6)

  Therefore, according to the first embodiment, the above-described control reduces the light emission intensity of the light source at a certain rate and increases the display gradation of the liquid crystal panel 102 at a certain rate, thereby reducing the power consumption. An image display device with good visibility can be obtained even when the backlight is darkened.

  Here, in the first embodiment, the light source means 14 has been described using a side-edge type backlight using the light guide plate 101 and a transmissive liquid crystal panel 102. It is preferable to use a direct-type backlight provided with the light source 100 on the back surface of the liquid crystal panel 102, a backlight using an anti-transmissive liquid crystal panel, or a front light that emits light from the front side of the reflective liquid crystal panel. In these cases, similar effects can be obtained.

[Embodiment 2]
Hereinafter, Embodiment 2 of the present invention will be described in detail with reference to the drawings.

  FIG. 6 is an explanatory diagram showing the relationship between the gray level of the input video signal and the gray level displayed by the light modulation means 10, and FIG. 6 (a) shows the case where the gray level of the input video signal is directly used as the display gray level. FIG. 6B is a diagram showing the relationship between the gradation of the input video signal and the gradation displayed by the light modulation means 10 in the red and green sub-pixels, and FIG. FIG. 6 is a diagram showing the relationship between the gradation of an input video signal and the gradation displayed by the light modulation means 10 in the blue sub-pixel.

  The difference between the second embodiment and the first embodiment is that when the gradation displayed on the liquid crystal panel is controlled, the same processing is performed for all the pixels in the first embodiment. Different gradations are controlled in each sub-pixel of the modulation means 10. As other configurations, those shown in the first embodiment can be used. In addition, the same reference numerals in the second embodiment denote the same parts as in the first embodiment.

  In the image display apparatus according to the second embodiment, the light source unit 14 that is the same component as the first embodiment reduces the light emission intensity by the light emission intensity reducing unit 108 when a power saving signal is input, thereby reducing the power consumption. Control to reduce.

  In the light modulation unit 10, each pixel has red, green, and blue sub-pixels. That is, a display image is formed by additive color mixture of red, green, and blue. During power-saving operation, the gradation for the red and green sub-pixels of the input video signal is increased at a constant rate, and the gradation for the blue sub-pixel of the input video signal is increased to a certain value or higher. The lower gradation is enlarged within the range not exceeding this fixed value to obtain the display gradation.

  At this time, when reducing the light emission intensity of the light source means 14 to reduce the power consumption, the display gradations of red and green are increased at a constant rate as shown in FIG. . FIG. 6A is a diagram when the gradation of the input video signal is used as the display gradation.

  On the other hand, the blue gradation is controlled to be the display gradation as shown in FIG. 6C with respect to the gradation of the input video signal.

  That is, when the displayable gradation of the liquid crystal panel 102 is 0 to 255, the display gradation is increased to 255 when the blue gradation of the input video signal is 240 (an example of a constant value) or more.

  For the gray level of the input video signal whose blue gray level is less than 240, control is performed so that the gray level of the input video signal is increased at a certain rate and the gray level to be displayed does not exceed 240.

  When such control is performed, for example, in the image of the input video signal, when there is a white region whose surrounding gradation is less than 240 and whose gradation near the center is 240 or more, the blue color around the white region is displayed. The gradation is 240, and the gradation near the center in the white region is 255.

  At this time, the change in luminance in the white region is not large, but the color temperature differs between the periphery and the center in the white region.

  That is, the image quality can be improved by expressing a bright white color by increasing the central color temperature in the white region rather than the surrounding color temperature in the white region.

  Here, when additive color mixture of red, green, and blue light is performed, the luminance of the mixed light is greatly influenced by the green light, and the influence from the blue light is small. This is because the spectral sensitivity is high at the wavelength of green light and low at the wavelength of blue light. That is, even when the blue gradation is controlled by the above-described method, the influence of the luminance change on the display screen is small.

  Therefore, according to the second embodiment, the light emission intensity of the light source means 14 is decreased by decreasing the light emission intensity of the light source means 14 and the display gradation of the light modulation means 10 is increased at a constant ratio. Even when the power consumption is reduced by lowering, the display luminance can be increased, and a bright and highly visible image display device can be obtained.

  Note that the gradations of red, green, and blue are not limited to the range of 0 to 255, and can be implemented with gradations in other ranges. Also, the fixed value is not limited to 240, and is preferably set to a fixed value set between the median value of gradation and the maximum value.

[Embodiment 3]
Hereinafter, Embodiment 3 of the present invention will be described in detail with reference to the drawings.

  FIG. 7 is an explanatory diagram showing a schematic configuration of Embodiment 3 of the image display apparatus according to the present invention. FIG. 8 is a diagram illustrating the control of the light emission intensity of the light source means 14 with respect to the average luminance. 9 and 10 are diagrams illustrating a method of controlling the light emission intensity of the light source unit 14 (light source 100) and the display luminance of the light modulation unit 10 (liquid crystal panel 102) with respect to the input video signal in the third embodiment. .

  The difference between the third embodiment and the first embodiment described above is a method for controlling the light emission intensity of the light source means 14. About the same part as Embodiment 1, the same code | symbol is attached | subjected and detailed description of each part is abbreviate | omitted.

  In the third embodiment, the average luminance detecting means 20 is configured by an average luminance detecting unit 105 that detects the average luminance in one image of the input video signal. The light emission control unit 16 performs control so as to change the magnitude of the light emission intensity of the light source unit 14 in accordance with the average luminance detected by the average luminance detection unit 105.

  Specifically, the average luminance detection unit 105 detects the average luminance in one image of the input video signal, and according to the average luminance, the emission intensity reduction unit 108 responds to the average luminance from the input light source control signal. The light emission control signal is reduced, and the reduced light source control signal is input to the light source control unit 103 of the light emission control means 16. The light source control unit 103 controls the light emission intensity of the light source 100 of the light source means 14 according to the input light source control signal. As a result, the light applied to the liquid crystal panel 102 of the light modulation means 10 is controlled to a light emission intensity smaller than the light emission intensity during normal operation.

  For example, when the average luminance is high, the degree of lowering the light emission intensity of the light source 100 is reduced, and when the average luminance is low, the degree of lowering the light emission intensity of the light source 100 is increased. That is, as shown in FIG. 8, the magnitude of light emission intensity of the light source is changed according to the magnitude of the average brightness. The relationship between the average luminance and the light emission intensity can be an arbitrary curved relationship in addition to a linear relationship as shown in FIG.

  Here, the change of the light emission intensity of the light source 100 based on the average luminance of the input video signal may be performed every several frames. That is, the light emission intensity of the light source 100 is changed in accordance with the average luminance of one arbitrary image, and the light emission intensity of the light source 100 is kept constant for the subsequent several frames. Thereby, it is not necessary to change the light emission intensity of the light source 100 according to the average luminance of each frame of the input video signal, and it is not necessary to increase the average luminance and the processing speed of the light source control.

  Further, the control of the display brightness of the liquid crystal panel 102 in the third embodiment uses the method of FIG. 2 described in the first embodiment (determining the display gradation by the equation (3)). That is, a display gradation is obtained by adding a certain value to the gradation of the input video signal.

  FIG. 9 is a diagram showing the control when the average luminance is large. FIG. 9A is a perspective view showing the positions of the pixels arranged on the liquid crystal panel 102, and the horizontal pixel positions are shown in FIG. 9 corresponds to the horizontal axis of the graph shown in (b) to (d). 9B shows the luminance of the input video signal as it is, FIG. 9C shows the luminance when the light source is controlled, and FIG. 9D shows the luminance when the gradation is controlled. FIG.

  FIG. 10 is a diagram showing the control when the average luminance is small, and FIG. 10A is a perspective view showing the positions of the pixels arranged in the liquid crystal panel 102, and the horizontal pixel positions. Corresponds to the horizontal axis of the graphs shown in FIGS. 10B shows the luminance of the input video signal as it is, FIG. 10C shows the luminance when the light source is controlled, and FIG. 10D shows the luminance when the gradation is controlled. FIG. The reference value for determining the magnitude of the average luminance may be a predetermined reference value or may be obtained as a reference value by obtaining an average luminance history of a plurality of frames.

  Therefore, according to the third embodiment, not only display with reduced power consumption and improved visibility is possible, but also the display image is displayed by controlling the light emission intensity of the light source based on the average luminance of the input video signal. A sense of contrast can be produced and good display can be achieved.

[Embodiment 4]
FIG. 11 is a diagram showing a schematic configuration of an image display apparatus according to Embodiment 4 of the present invention.

  In FIG. 11, the same parts as those of the image display apparatus according to the third embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the fourth embodiment, as shown in FIG. 11, the battery remaining amount detecting means is provided, and the battery remaining amount detecting unit 106 detects the remaining amount of the battery and outputs a signal based on the detected value. Specifically, the remaining battery level detection unit 106 detects the remaining battery level and outputs a power saving signal based on the detected result to the light emission control unit 16 and the gradation control unit 12.

  Therefore, it is preferable to automatically control the power saving operation of the fourth embodiment by automatically outputting a power saving signal when the remaining battery level becomes smaller than a predetermined value. It is.

  Further, the remaining battery level may be set in a plurality of stages, and the control method of the power saving operation for reducing the power consumption may be switched according to the remaining battery level. That is, a plurality of control methods having different emission intensity reduction ratios and display gradation increase ratios during the power saving operation may be switched according to the remaining battery level. Note that the light emission intensity of the light source means 14 and the display gradation control method of the light modulation means 10 during the power saving operation can be realized by Embodiments 1 to 3 or a combination thereof.

  For example, when the remaining battery level is reduced to about half, the control method during the power saving operation shown in the third embodiment of the present invention is used, and when the remaining battery level is reduced to about 1/4, The control method during the power saving operation shown in the first or second embodiment of the present invention can be used. As a result, when the remaining amount of the battery is about half, it is possible to construct a highly functional image display device that can display images with higher contrast and higher image quality, and the remaining amount of the battery is further reduced. When it becomes about 1/4, the power consumption can be further reduced and the configuration of a bright and highly visible image display apparatus can be obtained.

  The image display devices according to the first to fourth embodiments are most preferably used as an image display unit of a portable terminal device such as a mobile phone, but in addition, a monitor for a portable or stationary personal computer and a television receiver. It can also be used for monitors and the like.

  Needless to say, the present invention is not limited to the configuration of the above embodiment, and can be freely modified within the scope of the invention.

It is explanatory drawing which shows schematic structure of Embodiment 1 of the image display apparatus which concerns on this invention. It is explanatory drawing which shows control of the light emission intensity of a light source, and gradation control in the image display apparatus of FIG. 1, Comprising: (a) is a perspective view which shows each position of the several pixel arranged in a liquid crystal panel, (b) ) Is an input video signal, (c) is a luminance (gradation) displayed in each pixel when the intensity of irradiation light is reduced, and (d) is a luminance (gradation) displayed in each pixel during power saving operation. FIG. 6 is a diagram illustrating the position corresponding to each position illustrated in FIG. FIGS. 2A and 2B are explanatory views showing light source control and gradation control in the image display apparatus of FIG. 1, wherein FIG. 1A is a perspective view showing positions of a plurality of pixels arranged on a liquid crystal panel, and FIG. (C) is a luminance (gradation) displayed in each pixel when the intensity of irradiation light is reduced, (d) is a luminance (gradation) displayed in each pixel during power saving operation, (a) It is a figure shown corresponding to each position shown in FIG. FIGS. 2A and 2B are explanatory views showing light source control and gradation control in the image display apparatus of FIG. 1, wherein FIG. 1A is a perspective view showing positions of a plurality of pixels arranged on a liquid crystal panel, and FIG. (C) is a luminance (gradation) displayed in each pixel when the intensity of irradiation light is reduced, (d) is a luminance (gradation) displayed in each pixel during power saving operation, (a) It is a figure shown corresponding to each position shown in FIG. FIGS. 2A and 2B are explanatory diagrams of the relationship between the gradation of the input video signal and the display gradation when the control method shown in FIGS. 2 to 4 is used, where FIG. 2 shows a case where the control method of FIG. 2 is used, (c) shows a case where the control method of FIG. 3 is used, and (d) shows a case where the control method of FIG. 4 is used. FIG. 7 is an explanatory diagram showing the relationship between the gradation of an input video signal and the display gradation in Embodiment 2 of the present invention, where (a) is a diagram when the gradation of the input video signal is used as a display gradation; ) Is a diagram showing the relationship between the input video signal of the red and green sub-pixels and the display gradation, and (c) is a diagram showing the relationship between the input video signal of the blue sub-pixel and the display gradation. It is explanatory drawing which shows schematic structure of Embodiment 3 of the image display apparatus which concerns on this invention. It is a figure which shows the relationship between the average brightness | luminance of the input video signal in Embodiment 3 of this invention, and the emitted light intensity of a light source. It is a figure which shows the light source control and gradation control in Embodiment 3 of this invention, Comprising: It is a case where the average brightness | luminance of an input video signal is high, (a) shows each position of the several pixel arranged in a liquid crystal panel. It is a perspective view, (b) is an input video signal, (c) is a luminance (gradation) displayed in each pixel when the intensity of irradiation light is reduced, and (d) is each pixel during power saving operation. It is a figure which shows the brightness | luminance (gradation) to display corresponding to each position shown by (a), respectively. It is a figure which shows the light source control and gradation control in Embodiment 3 of this invention, Comprising: It is a case where the average brightness | luminance of an input video signal is low, (a) shows each position of the several pixel arranged in a liquid crystal panel. It is a perspective view, (b) is an input video signal, (c) is a luminance (gradation) displayed in each pixel when the intensity of irradiation light is reduced, and (d) is each pixel during power saving operation. It is a figure which shows the brightness | luminance (gradation) to display corresponding to each position shown by (a), respectively. It is explanatory drawing which shows schematic structure of Embodiment 4 of the image display apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light modulation means 12 Gradation control means 14 Light source means 16 Light emission control means 20 Average brightness detection means 100 Light source 101 Light guide plate 101i Light incident end surface 101o Light irradiation surface 102 Liquid crystal panel 103 Light source control part 104 Liquid crystal panel control part 105 Average brightness detection Unit 106 remaining battery level detection unit 108 emission intensity decreasing unit 109 luminance increasing unit

Claims (11)

Light modulation means for displaying an image by a plurality of pixels capable of gradation display;
Gradation control means for controlling the gradation displayed by each pixel of the light modulation means;
Light source means for emitting light for irradiating the light modulation means;
An image display device having light emission control means for controlling light emission intensity of the light source means,
During the power saving operation, the light emission control unit controls the light emission intensity of the light source unit to be smaller than that during normal operation, and the gradation control unit displays each pixel of the light modulation unit. An image display device that controls gradation to be larger than that during normal operation.   2. The image display apparatus according to claim 1, wherein, during the power saving operation, the light emission control unit controls the light emission intensity of the light source unit to be reduced at a constant rate than during normal operation. Light modulation means for displaying an image by a plurality of pixels capable of gradation display;
Gradation control means for controlling the gradation displayed by each pixel of the light modulation means;
Light source means for emitting light for irradiating the light modulation means;
An image display device having light emission control means for controlling light emission intensity of the light source means,
While having an average luminance detection means for detecting the average luminance of the input video signal,
During power saving operation, the light emission control means controls the light emission intensity of the light source means to change according to the average luminance, and the gradation control means displays each pixel of the light modulation means. An image display device that controls the gradation to be larger than that during normal operation.   In the power saving operation, the gradation control unit controls each pixel of the light modulation unit so as to display a video signal obtained by adding a certain gradation to the input video signal. The image display device according to claim 1.   In the power saving operation, each pixel of the light modulation unit displays the video signal in which the gradation control unit fixes the maximum gradation of the input video signal and increases the value of other gradations. The image display device according to claim 1, wherein the image display device is controlled.   In the power saving operation, each pixel of the light modulation unit displays the video signal in which the gradation control unit fixes the minimum gradation of the input video signal and increases other gradation values. The image display device according to claim 1, wherein the image display device is controlled. Each pixel of the light modulation means has red, green and blue sub-pixels,
During the power saving operation, the gradation control means increases the gradation for the red and green sub-pixels of the input video signal at a constant rate, and the gradation for the blue sub-pixel of the input video signal Wherein each pixel of the light modulation means is controlled so as to display a video signal in which a gradation greater than a certain value is increased and a gradation less than the certain value is increased within a range not exceeding the certain value. The image display device according to any one of claims 1 to 3. A battery remaining amount detecting means for detecting the remaining amount of the battery;
The image display device according to claim 1, wherein the normal operation and the power saving operation are switched according to a value detected by the battery remaining amount detection unit.   9. The image display device according to claim 1, wherein the light modulation means is a liquid crystal panel. The image display device according to claim 1, wherein the light source means is a light emitting diode.   A portable terminal device comprising the image display device according to claim 1 as a display unit.

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