Display apparatus with dynamic blinking backlight and control method and device thereof

CROSS-REFERENCE TO RELATED APPLICATION

0001This application claims the priority benefit of Taiwan application serial no. 94139396, filed on Nov. 10, 2005. All disclosure of the Taiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

00021. Field of Invention

0003The present invention relates to a control method and device of a backlight. More particularly, the present invention relates to a control method and device of a dynamic blinking backlight.

00042. Description of Related Art

0005As some types of display panels cannot emit light themselves, they need to be disposed with backlights. For example, liquid crystal displays (LCDs) need backlights for the aid of displaying frames. With considerable improvement of the viewing angle and significant reduction in price, the trend of LCDs replacing cathode ray tube (CRT) displays as computer screens has already developed. And its next ambition focuses on a broader market, the household television. To achieve dynamic image quality display rivaling the CRT display, various well-known LCD manufacturers have started exploring the improvement of the dynamic features of LCDs. Quality degradation of LCDs when displaying dynamic images includes: reduction in dynamic contrast, edge-blur, and stroboscopic motion. The main reason lies in that the response speed of the liquid crystal is slow and the so-called Hold-type data writing feature.

0006To reduce the influence of the Hold-type data writing feature, the applicable methods can be divided into two categories: image temporary interruption and non-image interruption. The former imitates the CRT display to temporarily interrupt the image, not being received by the visual system; while the later increases the data renewal speed or compensates the dynamic track. Though the blinking backlight is a basic method for improving the dynamic image quality, it causes worries about extra power consumption and decrease in the service life of the lamp.

0007U.S. Pat. No. 4,958,915 discloses a liquid crystal apparatus, including a method of making the low-level brightness of the blinking backlight synchronous with the period of writing data to the display panel. This conventional technology makes the backlight blink at a fixed frequency, so as to imitate the CRT display to temporarily interrupt the image, thereby improving the dynamic features of LCDs. However, keeping the backlight blinking at a fixed frequency will cause extra power consumption and shorten the service life of the lamp.

0008U.S. patent application No. 20020154088 discloses a transmissive-type liquid crystal display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp based on the parameters of dynamic images, so as to turn off all the cold cathode lamps in the vertical blank period of a frame period, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the cold cathode lamp.

0009U.S. patent application No. 20040246242 discloses a display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp in a frame period based on the parameters of dynamic images. In other words, the ratio of lightening time to darkening time of the cold cathode lamp in a frame period is determined by the movement amount of the dynamic images, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the lamp.

0010U.S. patent application No. 20040051692 discloses a liquid crystal display device. This conventional technology controls the brightness of the backlight by adjusting the time proportion of the lightening and the darkening period in accordance with the brightness information in the display signal. This conventional cold cathode lamp is kept blinking at a fixed frequency without the capability of dynamically adjusting the blinking frequency in accordance with the features of the displayed image. As the cold cathode lamp is kept blinking at a fixed frequency, it will cause extra power consumption and shorten the service life of the lamp.

SUMMARY OF THE INVENTION

0011Accordingly, one object of the present invention is to provide a dynamic blinking backlight control method. In accordance with the motion condition of a frame, the method dynamically determines the scanning frequency of the backlight or even stops the backlight from blinking so as to keep the backlight lit without blinking; various requirements such as improving dynamic image quality, reducing power consumption, and prolonging the service life of the backlight can be fulfilled.

0012Another object of the invention is to provide a dynamic blinking backlight control device, which fulfills the above objects by hardware architecture.

0013Yet another object of the invention is to provide a display apparatus with a dynamic blinking backlight, which reduces power consumption and improves image quality by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlight.

0014Based on the above and other objects, the present invention provides a dynamic blinking backlight control method, used for controlling the lighting status of multiple backlights of a display panel. The dynamic blinking backlight control method includes the following steps. First, the motion condition of a frame to be displayed on the display panel is detected to obtain a motion detection result. Then, the scanning frequency is determined in accordance with the motion detection result. Also, the lighting status of the backlights is controlled sequentially and respectively in accordance with the determined scanning frequency.

0015From another point of view, the present invention provides a dynamic blinking backlight control device. The dynamic blinking backlight control device includes a motion detection circuit, a control circuit, multiple backlights and a light source driving circuit. The motion detection circuit detects the motion condition of a frame to output a motion detection result. The control circuit is electrically connected to the motion detection circuit to determine the scanning frequency in accordance with the motion detection result. The light source required for displaying images on the display panel is provided by various backlights. The light source driving circuit is electrically connected to the control circuit and various backlights, wherein the lighting status of the backlights is controlled sequentially and respectively by the light source driving circuit in accordance with the scanning frequency determined by the control circuit.

0016The present invention provides another display apparatus with dynamic blinking backlight, which includes a display panel, a display driver, a motion detection circuit, a control circuit, multiple backlights, and a light source driving circuit. The display panel is used for displaying images. The display driver is electrically connected to the display panel to scan the display panel in accordance with the scanning frequency, and to drive the display panel to display the corresponding images in accordance with a frame. The motion detection circuit detects the motion condition of a frame to output the motion detection result. The control circuit, electrically connected to the motion detection circuit and the display driver, is used for determining the scanning frequency in accordance with the motion detection result. The light source required for displaying images on the display panel is provided by various backlights. The light source driving circuit is electrically connected to the control circuit and various backlights, wherein the lighting status of the backlights is controlled sequentially and respectively by the light source driving circuit based on the scanning frequency determined by the control circuit.

0017By modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlights in accordance with the motion condition of a frame, and even by stopping blinking backlights and keeping the backlights lit without blinking, the present invention fulfills the various requirements of improving the dynamic image quality, reducing power consumption, and prolonging the service life of the backlight.

0018In order to the make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.

0019It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

0020<figref idref="DRAWINGS">FIG. 1</figref> is a flow chart illustrating a dynamic blinking backlight control method in accordance with an embodiment of the invention.

0021<figref idref="DRAWINGS">FIGS. 2A and 2B</figref> are schematic views illustrating respectively a slow moving frame and a quick moving frame.

0022<figref idref="DRAWINGS">FIG. 3</figref> is a schematic example illustrating the dynamic scanning backlight control in accordance with the invention.

0023<figref idref="DRAWINGS">FIG. 4</figref> is a block view illustrating a display apparatus with dynamic blinking backlight in accordance with the embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

0024<figref idref="DRAWINGS">FIG. 1</figref> is a flow chart illustrating a dynamic blinking backlight control method in accordance with an embodiment of the invention. Referring to <figref idref="DRAWINGS">FIG. 1</figref>, this dynamic blinking backlight control method is used to control the lighting status of multiple backlights of a display panel (for example, a liquid crystal display panel). First, step S<b>105</b> is carried out, i.e., the motion condition of a frame to be displayed is detected to obtain a motion detection result. The aforementioned frame to be displayed will be displayed on a display panel.

0025Step S<b>105</b> can be implemented by those skilled in the art in any ways. For example, compare the pixel data in the corresponding positions in the previously displayed frame and the frame to be displayed presently, obtain a differential pixel percentage in accordance with the changing proportion between both data, and take the differential pixel percentage as the motion detection result. Or, the motion detecting is carried out for the provided previously displayed frame and the frame to be displayed presently to obtain a motion vector as the motion detection result.

0026Then step S<b>110</b> is carried out, wherein it is determined whether or not the frame is a static frame in accordance with the motion detection result. As the static frame does not need to imitate the CRT display to temporarily interrupt the image, the backlight is kept lit without blinking when the motion detection result shows that the frame is a static frame (step S<b>115</b>), thereby reducing the power consumption and prolonging the service life of the backlight.

0027When the motion detection result shows that the frame is a dynamic frame, steps S<b>120</b> to S<b>135</b> are carried out to improve the power consumption and image quality by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlight modular. This embodiment uses the motion detection result to activate the dynamic blinking backlight control mechanism, but it is not limited to this. For example, a button can be disposed. A user can press the button to send a command to activate (or turn off) the dynamic blinking backlight control mechanism, so as to perform steps S<b>120</b> to S<b>135</b>. Or, the application (for example, a movie playing program) executed by a host (for example, a personal computer) generates a command when outputting (or stopping output) the dynamic images, so as to activate (or turn off) the dynamic blinking backlight control mechanism.

0028In step S<b>120</b>, the scanning frequency is determined in accordance with the motion detection result. Those skilled in the art can set a reference value to determine the scanning frequency in accordance with the relationship between the motion detection result and the reference value. To avoid an incorrect determination caused by the unexpected factors such as a few abruptly skipping images in the frame (for example, the quick motion of the mouse pointer), or to avoid the scanning frequency being switched too often, a hysteresis function can be added into step S<b>120</b>. For example, if the motion detection result is the above-mentioned differential pixel percentage, when the differential pixel percentage (i.e., the changing proportion of the frame) is larger than an upper limit value (for example, 10%) (showing that the frame is a quick moving frame, for example, as shown in <figref idref="DRAWINGS">FIG. 2B</figref>), the scanning frequency will be switched from a low frequency (for example, 60 Hz) to a high one (for example, 120 Hz) to improve the display quality of the frame. If the differential pixel percentage is smaller than a lower limit value (for example, 5%) (showing that the frame is a slow moving frame, for example, as shown in <figref idref="DRAWINGS">FIG. 2A</figref>), the scanning frequency will be switched from a high frequency back to a low one to reduce power consumption and to prolong the service life of the backlight. Or, when the number of successive times in which the differential pixel percentage is larger than an upper limit value reaches a predetermined number (for example, the differential pixel percentages of two successive frames are all larger than the upper limit value), the scanning frequency will be switched from a low frequency to a high one. And when the number of successive times in which the differential pixel percentage is smaller than a lower limit value reaches a predetermined number, the scanning frequency will be switched from a high frequency back to a low one. Furthermore, if the motion detection result is represented by the motion vector, its operating steps can also refer to the above description.

0029In this embodiment, the backlight is, for example, a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), with its manner of arrangement shown in <figref idref="DRAWINGS">FIG. 3</figref>. In <figref idref="DRAWINGS">FIG. 3</figref>, the backlights <b>301</b>-<b>306</b> are disposed at the back of the display panel along the direction of a scan line of the display panel. When the dynamic blinking backlight control mechanism is activated, the averaged brightness of the backlight will be reduced. In step S<b>125</b>, the brightness of every backlight when it is lit will be increased in accordance with the scanning frequency, so as to compensate the averaged brightness of the backlight.

0030In step S<b>130</b>, the lighting status of the backlights <b>301</b>-<b>306</b> is controlled respectively in accordance with the scanning frequency determined in step S<b>120</b> and the brightness determined in step S<b>125</b>. For example, when the scanning frequency is determined to be 60 Hz or 120 Hz, as shown in <figref idref="DRAWINGS">FIG. 3</figref>, at least one of the backlights <b>301</b>-<b>306</b> is lit in accordance with the determined scanning frequency and the other backlights are turned off. Of course, the backlights <b>301</b>-<b>306</b> can also be lit, turned off or kept blinking at the same time in accordance with the determined scanning frequency.

0031This embodiment continues to carry out step S<b>135</b> after finishing step S<b>125</b>, i.e., the scanning frequency determined by Step S<b>120</b> is used to scan the display panel, so as to make the display panel display the corresponding images in accordance with the frame. Therefore, the display panel and the backlights can be scanned synchronously to display the frame, thereby improving the frame display quality.

0032<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating a display apparatus with dynamic blinking backlight in accordance with the embodiment of the invention. Referring to <figref idref="DRAWINGS">FIG. 4</figref>, the display apparatus <b>400</b> includes a dynamic blinking backlight control device, a display driver <b>450</b>, a display panel <b>460</b>, a memory <b>470</b>, and a graphic unit <b>480</b>. The dynamic blinking backlight control device includes a motion detection circuit <b>410</b>, a control circuit <b>420</b>, a light source driving circuit <b>430</b>, and backlights <b>440</b>. In this embodiment, the display panel <b>460</b> is, for example, liquid crystal display panel, and the backlights <b>440</b> can be composed by CCFLs or LEDs. The backlights <b>440</b> can be disposed at the back of the display panel <b>460</b> in accordance with the arrangement as shown in <figref idref="DRAWINGS">FIG. 3</figref>.

0033A central processing unit (CPU) <b>490</b> is electrically connected to the memory <b>470</b> and the graphic unit <b>480</b>. The graphic unit <b>480</b> continuously outputs frames to carry out the graphic operation based on the control of the CPU <b>490</b>. The graphic unit <b>480</b> is not only transmitted to the motion detection circuit <b>410</b>, but is also stored in the memory <b>470</b> at the same time. The motion detection circuit <b>410</b> compares the presently displayed frame output by the graphic unit <b>480</b> and the previously displayed frame stored in the memory <b>470</b> to detect the motion condition of the frame, and accordingly outputs the motion detection result to the control circuit <b>420</b>. The control circuit determines the scanning frequency in accordance with the motion detection result output by the motion detection circuit <b>410</b>.

0034Those skilled in the art can implement the motion detection circuit <b>410</b> by any means. For example, the motion detection circuit <b>410</b> compares the pixel data in the corresponding positions in the previously displayed frame and the frame to be displayed presently to obtain a differential pixel percentage in accordance with the changing proportion between both data, and take the differential pixel percentage as the motion detection result. Or, the motion detection circuit <b>410</b> carries out the motion detection for the previously displayed frame and the frame to be displayed presently to obtain a motion vector as the motion detection result.

0035The control circuit <b>420</b> is electrically connected to the motion detection circuit <b>410</b>. The control circuit <b>420</b> determines whether the frame to be displayed on the display panel <b>460</b> is a static frame in accordance with the motion detection result output by the motion detection circuit <b>410</b>. As the static frame needs not to imitate the CRT display to temporarily interrupt the image, when the motion detection result shows that the frame is a static frame, the control circuit <b>420</b> keeps the backlights <b>440</b> lit without blinking via the light source driving circuit <b>430</b>, thereby reducing power consumption and prolonging the service life of the backlights.

0036When the motion detection result output by the motion detection circuit <b>410</b> shows that the frame is a dynamic frame, the power consumption can be reduced and image quality can be improved by modulating the light source of the display panel, i.e., the control circuit <b>420</b> dynamically changes the lighting frequency of the backlight <b>440</b> via the light source driving circuit <b>430</b>. This embodiment uses the motion detection result to activate the dynamic blinking backlight control mechanism, but it is not limited to this. For example, a button can be disposed. A user can press the button to send out a command to activate (or turn off) the mechanism, so as to carry out dynamic blinking backlight control. Or, the application (for example, a movie playing program) executed by a host (for example, a personal computer) generates a command when outputting (or stopping output) the dynamic images, so as to activate (or turn off) the dynamic blinking backlight control mechanism.

0037Then, the control circuit <b>420</b> determines the scanning frequency in accordance with the motion detection result. Those skilled in the art can set a reference value to determine the scanning frequency based on the relationship between the motion detection result and the reference value. To avoid the incorrect determination caused by the unexpected factors such as a few abruptly skipping images in the frame (for example, the quick motion of the mouse pointer), or to avoid the scanning frequency being switched too often, a hysteresis function can be added to the control circuit <b>420</b>. For example, if the motion detection result is the above-mentioned differential pixel percentage, when the differential pixel percentage (i.e., the changing proportion of the frame) is larger than an upper limit value (for example, 10%) (showing that the frame is a quick moving frame, for example, as shown in <figref idref="DRAWINGS">FIG. 2B</figref>), the scanning frequency will be switched from a low frequency (for example, 60 Hz) to a high one (for example, 120 Hz) to improve the display quality of the frame. If the differential pixel percentage is smaller than a lower limit value (for example, 5%) (showing that the frame is a slow moving frame, for example, as shown in <figref idref="DRAWINGS">FIG. 2A</figref>), the scanning frequency will be switched from a high frequency back to a low one, so as to reduce the power consumption and to prolong the service life of the backlights. Or, when the number of successive times in which the differential pixel percentage is larger than an upper limit value reaches a predetermined number (for example, the differential pixel percentages of two successive frames are larger than the upper limit value), the scanning frequency will be switched from a low frequency to a high one. And when the number of successive times in which the differential pixel percentage is smaller than a lower limit value reaches a predetermined number, the scanning frequency will be switched from a high frequency back to a low one. Furthermore, if the motion detection result is represented by a motion vector, its operating manner can also refer to the above description.

0038When the control circuit <b>420</b> activates the dynamic blinking backlight control mechanism, the averaged brightness of the backlights will be reduced. The control circuit <b>420</b> will raise the brightness of the backlights <b>440</b> when they are lit via the light source driving circuit <b>430</b> in accordance with the determined scanning frequency, so as to compensate the averaged brightness of the backlights. The control circuit <b>420</b> controls the lighting status of the backlights <b>440</b> respectively via the light source driving circuit <b>430</b> in accordance with the determined scanning frequency and brightness. For example, when the scanning frequency is 60 Hz or 120 Hz as shown in <figref idref="DRAWINGS">FIG. 3</figref>, at least one of the backlights <b>301</b>-<b>306</b> is lit in accordance with the determined scanning frequency and the other backlights are turned off. Of course, the backlights <b>301</b>-<b>306</b> (i.e., the backlights <b>440</b> in <figref idref="DRAWINGS">FIG. 4</figref>) can also be lit, turned off, or kept blinking at the same time in accordance with the determined scanning frequency.

0039The display driver <b>450</b> is electrically connected to the display panel <b>460</b> to scan the display panel <b>460</b> based on the scanning frequency determined by the control circuit <b>420</b>, and to drive the display panel <b>460</b> to display the corresponding images in accordance with the frame. In this embodiment, the display driver <b>450</b> includes a timing controller <b>451</b>, a scanning driver <b>452</b> and a data driver <b>453</b>. The timing controller <b>451</b> is electrically connected to the graphic unit <b>480</b> to receive the frame to be displayed presently. The timing controller <b>451</b> is further electrically connected to the control circuit <b>420</b> to scan the display panel <b>460</b> via the scanning driver <b>452</b> based on the scanning frequency determined by the control circuit <b>420</b>. The data driver <b>453</b> cooperates with the scanning timing of the scanning driver <b>452</b> to transmit the scan line data to the display panel <b>460</b> to display the frame.

0040In sum, by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlights in accordance with the motion condition of a frame, and even by stopping blinking backlights and keeping the backlights lit without blinking, the present invention fulfils the various requirements of improving dynamic image quality, reducing power consumption and prolonging the service life of the backlights.

0041Though the present invention has been disclosed above by the preferred embodiments, it is not intended to limit the invention. Anybody skilled in the art can make some modifications and variations without departing from the spirit and scope of the invention. Therefore, the range of protection of the invention shall be defined by the appended claims.