Patent Publication Number: US-8994638-B2

Title: Backlight scanning method and liquid crystal display

Description:
BACKGROUND 
     One or more embodiments of the disclosed technology relate to a backlight scanning method for a liquid crystal display and a liquid crystal display. 
     Liquid crystal displays (LCDs) suffer from two main shortcomings in application to televisions: severe motion artifacts (which occur when displaying moving scenes or an action movie) and inadequate contrast (in a dark field condition). A black frame insertion technology is a common technology for shortening a response time. A fast pulse modulation effect similar to that in cathode ray tube (CRT) display can be produced by interpolating a black frame for every image frame. A flickering light-emitting diode (LED) backlight can also produce an effect similar to the insertion of a black frame, and it achieves the black frame insertion effect by regularly turning off the backlight. Furthermore, a good effect can also be obtained by a backlight scanning method for driving the backlight in a pulse modulation manner. One of current trends is to combine these fast response technologies so as to attain a shorter gray-to-gray response time. 
       FIG. 1  shows a schematic view showing the principle of improving a motion smear (streaking) by backlight blinking and backlight scanning, where an LED backlight is turned on or off at a proper place of a liquid crystal response curve. The backlight is turned off when the liquid crystal response curve is in a slow ascending phase or a descending phase (a tailing phase), and is turned on when the liquid crystal response curve is in a stable phase. To realize a backlight source employing a backlight scanning technology and also ensure lightness and thinness, a side-light type backlight scanning technology has become a hot research concern. A difficulty in application of the side-light type backlight scanning technology lies in that it is necessary to assure that the light in a region radiated by an LED group will not diffuse into other regions and ensure that a corresponding LED group is turned on in the stable response phase of liquid crystals in pixels. It is important to ensure that a corresponding LED group is in an off-state in the stable response phase of liquid crystals in pixels, so that pixels not in the stable response phase are imperceptible by human eyes. 
     SUMMARY 
     Embodiments of the disclosed technology provide a backlight scanning method and a liquid crystal display capable of performing a backlight scanning by light bars on the left and right sides, to thereby improve the display effect. 
     According to an embodiment of the disclosed technology, there is provided a backlight scanning method for controlling a backlight for a liquid crystal display panel, the backlight comprising light groups on left and right sides, the method comprising steps of: determining a time period for turning on and off the light groups on the left and right sides in accordance with a control signal for pixels in the liquid crystal display panel; and in scanning, turning on and off the light groups on the left and right sides alternately in sets, and during the course of displaying one frame by the liquid crystal display, turning on or off the light groups on the left and right sides at least two times. 
     According to another embodiment of the disclosed technology, there is provided a liquid crystal display comprising: a liquid crystal display panel, a backlight, a backlight control unit, and a pixel control unit. The backlight comprises light groups on left and right sides, and each of the light groups on the left and right sides are connected to the backlight control unit which is connected to the pixel control unit; the pixel control unit is adapted to provide a control signal for liquid crystal response in pixels of the liquid crystal display panel to the backlight control unit; and the backlight control unit is adapted to determine a time period for turning on and off the light groups on the left and right sides in accordance with the received control signal, and to turn on and off the light groups on the left and right sides alternately in sets. During the course of displaying one frame by the liquid crystal display panel, the light groups on the left and right sides are controlled to be turned on or off at least two times. 
     Further scope of applicability of the disclosed technology will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosed technology, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosed technology will become apparent to those skilled in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed technology will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the disclosed technology and wherein: 
         FIG. 1  is a schematic view showing the principle of improving a motion smear by blinking backlights and scanning backlights in a conventional technology; 
         FIG. 2  is a schematic view showing the joints of light guide plates in the conventional technology; 
         FIG. 3  is a schematic view showing light groups on the left and right sides are turned on and off alternately in sets according to an embodiment of the disclosed technology; 
         FIG. 4  is a schematic view showing a turn-on and -off time period of a light group within one frame scanning according to an embodiment of the disclosed technology; 
         FIGS. 5 and 6  are schematic views showing a turn-on and -off time period of light groups and pixel rows according to an embodiment of the disclosed technology; 
         FIG. 7  is a structural view showing a liquid crystal display according to an embodiment of the disclosed technology; and 
         FIG. 8  is a structural view showing a backlight according to an embodiment of the disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     In the side-light type backlight scanning technology, the light emitted from the backlight scanning will be processed by light guide plates  903 . There will occur shadow portions at junction sites  905  among the light guide plates  903 , as shown in  FIG. 2 . A common method for solving the shadow problem due to the joint between the light guide plates  903  is providing a light mixing element or increasing a light mixing distance. The inventors have found that two adjacent light guide plates  903  have quite high luminance with slightly low luminance therebetween and give rise to strong contrast. Even though the shadow portions at the joints of the light guide plates  903  are very narrow, it will still be perceptible by human eyes if it is not processed, which will adversely affect the display performance. 
     According to an embodiment of the disclosed technology, a plurality of light sources (e.g., light groups or LED groups) on the left and right sides of a backlight module with a row interval (i.e., arranged along the direction perpendicular to the pixel row direction with an interval) are turned on or off simultaneously, i.e., two adjacent sets (which are adjacent in the direction perpendicular to the pixel row direction) are not turned on or off simultaneously, thereby increasing a distance between lighting areas. A light distribution becomes more uniform with light guide plates  903 . Therefore, the problem that the display effect is adversely affected by a strong contrast between joints of the light guide plates  903  and the surrounding can be solved. Furthermore, in the conventional technology, all the light sources on both the left and right sides are always turned on simultaneously during the course of a whole frame scanning, so that shadow portions at the joints of the light guide plates  903  stay for relatively long time period and is more easily perceptible by human eyes, adversely affecting display performance. In contrast, during the course of one frame scanning according to the embodiment of the disclosed technology, light sources on both the left and right sides are turned on or off at least twice so that a turn-off time of the light groups of the backlight in one frame is shortened and the contrast between light portions and dark portions can reduced, improving display performance. 
     A flow of a backlight scanning method according to the embodiment is as follows: 
     The backlight scanning method according to the embodiment is adapted to control a backlight for a liquid crystal display panel, the backlight comprising light sources (e.g., light groups or LED groups) on both the left and right sides. Here, light groups are taken for example for description, and each light group may comprise at least one light. 
     In step  301 , a time period for turning on and off the light groups on the left and right sides is determined in accordance with a control signal for pixels in the liquid crystal display panel. 
     In step  302 , in scanning, the light groups on the left and right sides are turned on and off alternately in sets, and during the course of displaying one frame of picture by the liquid crystal display, the light groups on the left and right sides are turned on or off at least two times. 
     In the embodiment, the light groups on the left and right sides are turned on and off alternately in sets, as shown in  FIG. 3 , the contrast between joints of light guide plates and the surroundings can be reduced, thereby improving the display effect. Furthermore, the light groups on the left and right sides are turned on or off more than one time during the stable phase of pixel response (liquid crystal response), so that the time period during which the relatively darker sites or portions of the display affects human eyes can be shortened, thereby improving display effect. As shown in  FIG. 4 , for the light groups on both the left and right sides in a corresponding row, they are turned off when the pixel response starts to become stable (i.e., the shadow area in the first column on the left in  FIG. 4 ), turned on as time goes by (i.e., the white area in the first column on the left in  FIG. 4 ), and then turned off and turned on once more. Preferably, during the course of scanning one frame, the light groups on the left and right sides are turned on and off at least three times. The light groups on the left and right sides being turned on and off alternately in sets may be implemented by dividing the light groups both the left and right sides into two set kinds arranged in an interlace manner (e.g., odd sets and even sets) and turning off and on alternately the light groups of the two set kinds. Each set may comprise at least one light group. 
     If the light groups on the left and right sides are turned on or off at least two times during the course of scanning one frame, the light groups on the left and right sides of a panel for the whole pixel region may comprise at least three sets; correspondingly, the pixel rows of the whole pixel region can be divided into at least three sets, and each pixel set may comprise at least one row of pixels. In the embodiment, the three pixel sets may have the same size or different sizes. In one example, preferably the three pixel sets have substantially the same size. Because the number of rows in the whole pixel region is not necessarily the times of 3, it may be possible for the three sets to have an identical size. ‘Substantially the same’ means that the difference among the number of pixel rows of the three pixel sets is not more than one row in the embodiment. 
     Specifically, at each time that one set of light groups is scanned, the light group of the scanned set and other light groups in synchronization with the light group (in the same set kind) are turned on, and meanwhile the asynchronous light groups with respect to the light group (in a different set kind) are turned off. In the embodiment, the light groups on the left and right sides are divided into two set kinds in advance, and the set(s) of light groups in a first partial area corresponding to the first set kind, and the set(s) of light groups in a second partial area corresponding to the second set kind are arranged alternately. The light groups corresponding to the scanned set and other light groups of the set(s) belonging to the same partial area are turned on, and meanwhile the light groups in another partial area are turned off. That is, the light groups on the left and right sides belonging to the same partial area will be turned on or off synchronously, and the light groups on the left and right sides belonging to different partial areas will be turned on or off asynchronously. For instance, when the light groups on the left and right sides in the first partial area are turned on, the light groups on the left and right sides in the second partial area are turned off; when the light groups on the left and right sides in the second partial area are turned on, the light groups on the left and right sides in the first partial area is turned off. As shown in  FIG. 3 , the light groups on the left and right sides corresponding to black areas belong to the first partial area, and the light groups on the left and right sides corresponding to white areas belong to the second partial area. 
     Preferably, when pixels in the last row in a scanned set start to respond stably (i.e., in a stable phase), the light groups corresponding to the set and other light groups belonging to the set(s) of the same partial area are turned on, and meanwhile light groups in another partial area are turned off, so as to further improve the display effect. As shown in  FIG. 5 , the whole pixel region (from the first row to the nth row of pixels) is divided into 9 sets for example, and when pixels in the last row in the first set start to respond stably, the light groups on the left and right sides corresponding to the first set and the light groups on the left and right sides corresponding to other sets in the first partial area, which comprise the light groups on the left and right sides corresponding to the third set, the light groups on the left and right sides corresponding to the fifth set, the light groups on the left and right sides corresponding to the seventh set, and the light groups on the left and right sides corresponding to the ninth set, are turned off. At the same time, the light groups on the left and right sides of the sets corresponding to the second partial area, which comprise the light groups on the left and right sides corresponding to the second set, the light groups on the left and right sides corresponding to the fourth set, the light groups on the left and right sides corresponding to the sixth set, and the light groups on the left and right sides corresponding to the eighth set, are turned on. When pixels in the last row in the second set start to respond stably, the light groups on the left and right sides corresponding to the second set and the light groups on the left and right sides corresponding to other sets in the second partial area, are turned off; meanwhile, the light groups on the left and right sides of the sets corresponding to the first partial area are turned on. The operation is performed by the same way until the scanning of one frame ends, and the pixel response starts to change gradually. 
     In another example, as shown in  FIG. 6 , when pixels in the last row in the first set start to respond stably, the light groups on the left and right sides corresponding to the first set and the light groups on the left and right sides in other sets corresponding to the first partial area are turned on; meanwhile, the light groups on the left and right sides corresponding to the second partial area are turned off. The operation is performed by the same way until the scanning of one frame ends, and the pixel response starts to change gradually. 
     The backlight scanning scheme in the embodiment can be applied into a liquid crystal display (LCD). Hereinafter, a structure and function of the liquid crystal display will be described. 
     As shown in  FIG. 7 , the liquid crystal display in the embodiment comprises: a panel, a backlight  801 , a backlight control unit  802  and a pixel control unit  803 . The panel comprises a pixel region and a peripheral region, and the backlight  801  is typically provided behind the panel for providing it with light for display. The liquid crystal display in the embodiment can be applied into various applications or devices, such as liquid crystal television, computer monitor, cell phone, and so on. The backlight control unit  802  and the pixel control unit  803  each can be implemented by software, hardware, firmware, or any combination thereof. 
     The backlight  801  may comprise a light guide plate and the light groups on the left and right sides of the light guide plate, and each of the light groups is connected to the backlight control unit  802  which is connected to the pixel control unit  803 . 
     The pixel control unit  803  is adapted to provide control signals for liquid crystal response in pixels of the liquid crystal display panel, and to provide the backlight control unit  802  with the control signals for response of liquid crystals in pixels of the liquid crystal display panel. 
     The backlight control unit  802  is adapted to determine a time period for turning on and off the light groups on the left and right sides of the backlight  801  in accordance with the received control signals, and to turn on and off the light groups on the left and right sides alternately in sets. During the course of displaying one frame by the liquid crystal display panel, the light groups on the left and right sides of the backlight  801  are controlled to be turned on or off at least two times. 
     Specifically, at each time when the pixel control unit  803  scans a set of pixels (also the corresponding light group set), the backlight control unit  802  turns on a light group (or light groups) corresponding to the scanned set pixels and other light groups belonging to the set(s) of the same partial area, and meanwhile turns off light groups in another partial area. Preferably, the backlight control unit  802  turns on, when pixels in the last row in a scanned set begin to respond stably, the light group (or light groups) corresponding to the set and other light groups belonging to the set(s) of the same partial area, and meanwhile, turns off light groups in another partial area. One pixel set comprises at least one row of pixels in the embodiment, and the whole pixel region comprises at least three pixel sets; correspondingly, the light groups can be divided into at least three sets, and one light group set corresponds at least one pixel. The three sets can have the substantially same size or different sizes. 
     As shown in  FIG. 8 , the backlight  801  comprises a back plate  901 , light bar plates  902 , light guide plates  903  and light groups  904 . 
     The light guide plates  903  are located above the back plate  901 . The light bar plates  902  are located on two sides of the back plate  901 , and a plurality of light groups  904  are located on each of the light bar plates  902 . Each of the light groups  904  may comprise a plurality of light emitting devices such as lights or LEDs. Herein, for example, an area covered by all of the light guide plates  903  corresponds to the pixel region. 
     In the embodiment of the disclosed technology, a plurality of light groups on the left and right sides are simultaneously turned on or off alternately in sets, i.e., two adjacent sets (which are adjacent in the direction perpendicular to the pixel row) are not turned on or off simultaneously, thereby increasing a distance between lighting areas. The light distribution becomes uniform with the light guide plates  903 . Therefore, the problem that the display effect is adversely affected by the strong contrast between joints of the light guide plates  903  and surroundings can be solved. Furthermore, light groups on the left and right sides are always turned on during the course of scanning one whole frame in the conventional technology, so that shadow portions at the joints of the light guide plates  903  stay relatively long and are more easily perceptible by human eyes, thereby adversely affecting the display effect. While during the course of scanning one frame in the embodiment of the disclosed technology, light groups on the left and right sides are turned on or off at least two times so that the turn-off time period of the backlight in one frame can be shortened and the contrast between light portions and dark portions can reduced, improving display performance. 
     It should be understood by those skilled in the art that, one or more embodiments of the disclosed technology can be provided as a method, a system and a computer program product. Thus, the disclosed technology can be implemented in the form of embodiments of full hardware, embodiments of full software, or embodiments of combining software and hardware. Furthermore, the disclosed technology can be implemented in the form of a computer program product which is stored on a storage medium or a plurality of storage mediums available for a computer (comprising but not limited to a disk storage device, an optical storage device and the like) containing a program code executable by the computer therein. 
     The embodiment of the disclosed technology being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosed technology, and all such modifications as would be obvious to those skilled in the art are intended to be comprised within the scope of the following claims.