Patent Publication Number: US-2023148216-A1

Title: Image display device and control method thereof

Description:
This application claims the benefit of People&#39;s Republic of China application Serial No. 202111331873.7, filed Nov. 11, 2021, the subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an electronic device and a control method thereof, and more particularly, relates to an image display device and a control method for suppressing backlight afterimages. 
     BACKGROUND 
     Due to the characteristic of visual persistence of human visual perception, when the image frame of the display is updated, afterimage of previous image frame may interfere with visual perception of the current image frame, resulting in dragging of picture of display and causing motion blur. 
     In order to improve the phenomenon of motion blur, the display may support a mechanism of “moving picture response time (MPRT)” to insert a black image frame between normal image frames, referred to as an operation of “black frame insertion (BFI)”. Alternatively, the backlight module may be turned off between intervals of displaying normal image frames, so as to simulate the operation of black frame insertion. 
     When simulating the operation of black frame insertion, although the backlight module has been turned off and stops providing backlight, however, due to characteristic of visual persistence, the backlight before the backlight module is turned off may still cause afterimages. The red afterimage of red light source has the longest duration length and interferes with visual perception seriously. Traditionally, color gamut range of phosphor powder of backlight sources with various colors is reduced, so as to change spectral components of red light source to reduce the red afterimage. 
     However, in order to change color gamut range of phosphor powder of backlight sources, hardware of the backlight module must be changed, which will consume more hardware costs. To address the aforementioned technical problems, skilled ones of related industries in the technical field of display are devoted to develop a more effective method, so that operation of black frame insertion may be simulated under MPRT, and red afterimages may be reduced. 
     SUMMARY 
     The present disclosure provides an image display device and an operation method thereof, which are used to control the backlight module of an image display device to provide backlights with different intensities in different intervals of an image frame cycle, so that afterimage of the image display device may be reduced. 
     According to an aspect of the present disclosure, an image display device is provided. The image display device includes a display unit and a backlight module. The display unit is used for displaying pictures in an image frame cycle. The backlight module includes a plurality of light sources of different colors. The image frame cycle is divided into a first interval, a second interval and a third interval in sequence, the second interval is adjacent to the first interval, the backlight module provides a white light source with a first intensity in the first interval and provides a white light source with a second intensity in the second interval, the second intensity is smaller than the first intensity, and the backlight module is turned off in the third interval. 
     According to another aspect of the present disclosure, an image display device is provided. The image display device includes a display unit and a backlight module. The display unit is used for displaying pictures in an image frame cycle, and the image frame cycle has a first interval and a third interval. The backlight module includes a plurality of light sources of different colors, the backlight module is used for providing a white light source with a first intensity to the display unit in the first interval, and the backlight module is turned off in the third interval. The image frame cycle further includes a second interval and a fourth interval, the second interval and the fourth interval are between the first interval and the third interval, the second interval is adjacent to the first interval and the fourth interval is adjacent to the second interval, the backlight module provides a white light source with a second intensity in the second interval, the second intensity is smaller than the first intensity, and the backlight module provides a white light source with a third intensity in the fourth interval, the third intensity is smaller than the second intensity. 
     According to still another aspect of the present disclosure, a control method of an image display device is provided. The control method includes the following steps. Dividing an image frame cycle of a display unit into a first interval, a second interval and a third interval in sequence, wherein the second interval is adjacent to the first interval. In the first interval, a backlight module is controlled to provide a white light source with a first intensity to the display unit. In the second interval, the backlight module is controlled to provide a white light source with a second intensity to the display unit, wherein the second intensity is smaller than the first intensity. In the third interval, the backlight module is turned off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an image display device according to an embodiment of the present disclosure. 
         FIG.  2    is a timing diagram of each control signal of the image display device according to an embodiment of the present disclosure. 
         FIGS.  3 A- 3 D  are schematic diagrams of afterimages of the backlight module. 
         FIG.  4    is a timing diagram illustrating backlight control of the backlight module according to an embodiment of the present disclosure. 
         FIG.  5    is a timing diagram illustrating backlight control of the backlight module according to another embodiment of the present disclosure. 
         FIGS.  6 A- 6 C  are timing diagrams illustrating backlight control of the backlight module according to another three embodiments of the present disclosure. 
         FIGS.  7 A and  7 B  are timing diagrams of each control signal of the image display device corresponding to the embodiments of  FIGS.  6 A and  6 B . 
         FIG.  8    is a flow diagram of a control method of the image display device according to an embodiment of the present disclosure. 
     
    
    
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically illustrated in order to simplify the drawing. 
     DETAILED DESCRIPTION 
       FIG.  1    is a block diagram of an image display device  1000  according to an embodiment of the present disclosure. Referring to  FIG.  1   , the image display device  1000  includes a display unit  100 , a scalar IC  200 , a backlight control unit  300  and a backlight module  400 . The image display device  1000  is, for example, an external screen of a desktop computer or a built-in screen of a laptop computer, and may also be a display screen of a home TV or a display screen of a video wall of a commercial exhibition hall. The display unit  100  is a display panel of the image display device  1000 . The display unit  100  has a plurality of pixels, and these pixels may form a whole picture. 
     Please also refer to  FIG.  2   , which is a timing diagram of each control signal of the image display device  1000  according to an embodiment of the present disclosure. In operation, the display unit  100  defines an image frame cycle according to a vertical synchronization signal Vsync and updates the image frame according to the vertical synchronization signal Vsync. Accordingly, the display unit  100  displays a picture of the corresponding image frame in each image frame cycle. For example, the picture of the first image frame is displayed in the first image frame cycle Fc 1 , and the picture of the second image frame is displayed in the second image frame cycle Fc 2 , and so on. In one example, the display updating frequency of the display unit  100  is 80 fps, i.e., 80 image frames are displayed per second. In other words, the duration length of each image frame cycle is 1/80 second (i.e., 0.0125 seconds). In the operating schemes of the display unit  100 , each image frame cycle may be further divided into at least a first interval T 1 , a second interval T 2  and a third interval T 3  in sequence. The display unit  100  may display a normal picture including video content in the first interval T 1 . 
     Please refer to  FIG.  1    again, the backlight module  400  is, for example, a backlight plate of the image display device  1000 . The backlight module  400  may dispose a plurality of light emitting diodes (LED) or micro light emitting diodes (micro LED) to form a plurality of light sources (i.e., backlight sources), thereby providing the backlight of the image display device  1000 . Moreover, these light sources have different colors, such as red light sources, blue light sources and green light sources. The red light sources, blue light sources and green light sources may be mixed as white light sources. In the operating scheme of the backlight module  400 , as shown in  FIG.  2   , when the display unit  100  displays a normal picture in the first interval T 1 , the backlight module  400  correspondingly provides a white light source in the first interval T 1 . That is, the backlight module  400  entirely turns on the red light source, blue light source and green light source, and the three types of light sources are mixed as the white light source. 
     On the other hand, the scalar IC  200  and the backlight control unit  300  may provide a plurality of control signals or driving signals to control the operation of the backlight module  400 . In this embodiment, the scalar IC  200  may provide a first control signal S_PWM 1  and a second control signal S_ADC to the backlight control unit  300 , and the backlight control unit  300  may correspondingly generate a third control signal COMP. The third control signal COMP may be further converted to a first driving signal LB_C through the circuit element RC 1  and the transistor SW 1 , and the first driving signal LB_C is used to drive the backlight module  400 . As shown in  FIG.  2   , in the first interval T 1 , the first control signal S_PWM 1  and the second control signal S_ADC are both in an enable state (e.g., a state of high voltage level). Correspondingly, the third control signal COMP is also in the enable state (not shown in  FIG.  2   ). Accordingly, the first driving signal LB_C of the enable state may be provided to drive the backlight module  400 . In this embodiment, the first driving signal LB_C is a driving current, and the backlight module  400  may adjust the intensity of the light sources according to the current value of the first driving signal LB_C. For example, the current value I 1  of the first driving signal LB_C generates a white light source with a first intensity L 1 . 
     However, the white light source may have an afterimage after the first interval T 1 , as shown in the schematic diagrams of the afterimages of the backlight module  400  in  FIGS.  3 A- 3 D . The white light source W 1  in the first interval T 1  has a red light component R 1 , a blue light component B 1  and a green light component G 1 . The red light component R 1  has a red afterimage R 2  after the first interval T 1 , and the duration length of the red afterimage R 2  is TR. Furthermore, the blue light component B 1  has a blue afterimage B 2  with a duration length of TB. Moreover, the green light component G 1  has a green afterimage G 2  with a duration length of TG. More particularly, the red light sources, blue light sources and green light sources of the backlight module  400  may be realized by, for example, red light diodes, blue light diodes and green light diodes. The above-mentioned colorful diodes use phosphor powders of different colors. Different colors of phosphor powders have different response times in human visual perception, wherein the response time of red phosphor powders is the longest. Therefore, the red afterimage R 2  of the red light component R 1  has the longest duration length TR (i.e., the duration length TR of the red afterimage R 2  is greater than the duration length TG of the green afterimage G 2  and the duration length TB of the blue afterimage B 2 ). Therefore, for human visual perception, the red afterimage R 2  is the most significant, which is referred to as “red afterimage phenomenon”. The technical solution of the present disclosure refers to control backlight of the backlight module  400  by software or firmware so as to suppress or eliminate the above-mentioned red afterimage phenomenon. 
     Please refer to  FIG.  4   , which shows a timing diagram of backlight control of the backlight module  400  according to an embodiment of the present disclosure. In the backlight control mechanism of the present embodiment, the backlight module  400  is controlled to continuously provide a white light source after the first interval T 1  to shield or cover the red afterimage R 2 . Specifically, in the second interval T 2  adjacent to the first interval T 1  (the second interval T 2  is after the first interval T 1 ), the backlight module  400  may provide a white light source W 2  with the second intensity L 2  (that is, the duration length of the white light source W 2  is equal to the duration length of the second interval T 2 ) so as to shield or cover the red afterimage R 2 . Compared with the white light source W 1  in the first interval T 1 , the second intensity L 2  of the white light source W 2  in the second interval T 2  is smaller (i.e., the second intensity L 2  is smaller than the first intensity L 1 ). Moreover, the duration length of the white light source W 2  (i.e., the duration length of the second interval T 2 ) is at least greater than the duration length TR of the red afterimage R 2 . Therefore, for human visual perception, the white light source W 2  may effectively shield or cover the red afterimage R 2  and eliminate the red afterimage phenomenon. 
     Next, a “Moving Picture Response Time (MPRT)” mode of the display is supported, and the backlight module  400  is turned off in the third interval T 3  (which is after the second interval T 2  and adjacent to the second interval T 2 ) to simulate an operation of black frame insertion, thereby suppressing motion blur of the display unit  100 . 
     The above-described embodiments may be applied to each image frame cycle. For example, in the second interval T 2  of the first image frame cycle Fc 1 , the backlight module  400  provides a white light source W 2  with a second intensity L 2  to cover the red afterimage R 2 . Based on the same implementation, the white light source W 2  of the second intensity L 2  is also provided in the second interval T 2  of the second image frame cycle Fc 2 , and so on. Referring to  FIG.  2    again, in order to control and drive the backlight module  400  to provide white light sources with a first intensity L 1  and a second intensity L 2  in the first interval T 1  and the second interval T 2  respectively, the second control signal S_ADC of the scalar IC  200  in the second interval T 2  has a voltage level lower than the voltage level in the first interval T 1 , so that the current value I 2  of the first driving signal LB_C of the backlight control unit  300  in the second interval T 2  is smaller than the current value I 1  in the first interval T 1 . Furthermore, the current value of the first driving signal LB_C is substantially reduced to zero in the third interval T 3 , so as to turn off the backlight module  400 . 
       FIG.  5    is a timing diagram illustrating backlight control of the backlight module  400  according to another embodiment of the present disclosure (only one image frame cycle Fc 1  is shown). Referring to  FIG.  5   , the second intensity L 2 ′ of the white light source W 2  in this embodiment may be smaller than the second intensity L 2  of the white light source W 2  in  FIG.  4   . In addition, the duration length of the white light source W 2  in this embodiment (i.e., the duration length of the second interval T 2 ′) may be smaller than the duration length of the white light source W 2  of  FIG.  4    (i.e., the duration length of the second interval T 2 ). That is, in this embodiment, the intensity and duration length of the white light source W 2  are reduced, so that the white light source W 2  has a smaller profile, but can still cover the red afterimage R 2 . 
     For example, in the first interval T 1 , the current value I 1  of the first driving signal LB_C for generating the white light source W 1  is 106 mA, so that the white light source W 1  has the first intensity L 1 . The ratio of duration length of the white light source W 1  (i.e., duration length of the first interval T 1 ) to the entire image frame cycle Fc 1  is 31.9%. Correspondingly, in the second interval T 2 ′, the current value I 2 ′ of the first driving signal LB_C is set as 15 mA, so that the white light source W 2  has the first intensity L 2 ′. The ratio of duration length of the white light source W 2  (i.e., duration length of the second interval T 2 ′) is set as 19.2%. Under the above-mentioned settings for intensity and duration length, the white light source W 2  in the second interval T 2 ′ can still substantially cover the red afterimage R 2 . 
     In this embodiment, even though the white light source W 2  in the second time interval T 2 ′ still has a red afterimage R 3 , the intensity of the white light source W 2  has been reduced to a smaller value of second intensity L 2 ′. The red afterimage R 3  generated by the white light source W 2  has reduced intensity and duration length, hence human visual perception is less affected. 
     As described above, in the embodiments shown in  FIGS.  4  and  5   , after the first interval T 1  the backlight module  400  provides white light source with constant intensity, for example, the intensity of the white light source W 2  is a constant value of second intensity L 2  (or second intensity L 2 ′). On the other hand, since the intensity of the red afterimage R 2 , the blue afterimage B 2  and the green afterimage G 2  is gradually decreasing, the red afterimage can be substantially covered by providing white light source W 2  with decreasing intensity.  FIGS.  6 A- 6 C  are timing diagrams illustrating backlight control of the backlight module  400  according to another three embodiments of the present disclosure. First, please refer to  FIG.  6 A , the second intensity L 2  of the white light source W 2  may gradually decrease in the second interval T 2 . For example, the second intensity L 2  decreases from the first intensity L 1  to zero in a ramp-down manner (i.e., ramped decrease). On the other hand, referring to  FIG.  6 B , the second intensity L 2  of the white light source W 2  may decrease to the third intensity L 3  in a stepped manner (i.e., stepped decrease) in the second interval T 2 . 
     The embodiment of  FIG.  6 B  may also be represented as the aspect of  FIG.  6 C . As shown in  FIG.  6 C , the image frame cycle Fc 1  may be further divided into a fourth interval T 4 . The fourth interval T 4  is between the second interval T 2  and the third interval T 3 , and the fourth interval T 4  is adjacent to the second interval T 2 . The backlight module  400  provides the white light source W 2  during the second interval T 2  and provides the white light source W 3  during the fourth interval T 4 . In other words, the embodiment of  FIG.  6 C  further divides the white light source into a white light source W 2  and a white light source W 3  to cover the red afterimages R 2  and R 3  respectively. Moreover, the third intensity L 3  of the white light source W 3  is smaller than the second intensity L 2  of the white light source W 2 . That is, the white light source W 2  decreases to the white light source W 3  in a stepped manner. Furthermore, the duration length of the white light source W 3  (i.e., the duration length of the fourth interval T 4 ) is at least greater than the duration length of the red afterimage R 3  after the second interval T 2 . 
       FIGS.  7 A and  7 B  respectively illustrate timing diagrams of each control signal of the image display device  1000  corresponding to the embodiments of  FIGS.  6 A and  6 B . For the backlight module  400  to control the second intensity L 2  of the white light source W 2  to decrease in a ramp-down manner in the second interval T 2  (the embodiment of  FIG.  6 A ), as shown in  FIG.  7 A , the scalar IC  200  has a second control signal S_ADC with a voltage level ramped decreasing in the second interval T 2 , and the current value I 2  of the first driving signal LB_C of the backlight control unit  300  also ramped decreases in the second interval T 2 . 
     On the other hand, for the backlight module  400  to control the second intensity L 2  of the white light source W 2  to decrease in a stepped manner in the second interval T 2  (as the embodiment of  FIG.  6 B ), as shown in  FIG.  7 B , the voltage level of the second control signal S_ADC of the scalar IC  200  and the current value I 2  of the first driving signal LB_C of the backlight control unit  300  also decrease in a stepped manner in the second interval T 2 . 
       FIG.  8    is a flow diagram of a control method of the image display device  1000  according to an embodiment of the present disclosure. Referring to  FIG.  8   , in step S 110 , each image frame cycle of the display unit  100  of the image display device  1000  is sequentially divided into a first interval T 1 , a second interval T 2  and a third interval T 3 . The second interval T 2  is adjacent to the first interval T 1 . Then, in step S 120 , the backlight control unit  300  is controlled according to the vertical synchronization signal Vsync of the image display device  1000 , so to generate a first driving signal LB_C. The backlight module  400  is driven by the first driving signal LB_C. The intensity of the light source generated by the backlight module  400  may be controlled according to the current value of the first driving signal LB_C, so that the backlight module  400  may provide light sources with different intensities in different intervals of the image frame cycle. 
     Then, in step S 130 , the backlight module  400  of the image display device  1000  is controlled to provide the white light source W 1 , which has a first intensity L 1 , to the display unit  100  during the first interval T 1 . Then, in step S 140 , the backlight module  400  is controlled to provide the white light source W 2 , which has a second intensity L 2 , to the display unit  100  in the second interval T 2 . The second intensity L 2  is smaller than the first intensity L 1 . Then, in step S 150 , the intensity of the white light source W 2  is controlled and adjusted, so that the intensity of the white light source W 2  is constant (maintained as the second intensity L 2 ) or decreased in the second interval T 2 . It may have a ramped type of decreasing or a stepped type of decreasing. 
     In the examples of the stepped type of decreasing, the image frame cycle may be further divided into a fourth interval T 4 , which is between the second interval T 2  and the third interval T 3 . In addition, the backlight module  400  is controlled to provide the white light source W 3  in the fourth interval T 4 . The third intensity L 3  of the white light source W 3  is smaller than the second intensity L 2 . Accordingly, the white light source W 2  provided by the backlight module  400  decreases to form the white light source W 3  in a manner of stepped decreasing. 
     Then, in step S 160 , duration length of the white light source W 2  (i.e., duration length of the second interval T 2 ) is controlled and adjusted to be greater than duration length of the red afterimage R 2  of the backlight module  400  after the first interval T 1 . Accordingly, the white light source W 2  with the second intensity L 2 , which is provided in the second interval T 2 , can shield or cover the red afterimage R 2 , after the first interval T 1 . Hence, the red afterimage phenomenon may be suppressed or eliminated. Then, in step S 170 , the backlight module  400  is turned off to simulate the operation of black frame insertion. 
     On the other hand, for the examples where the white light source W 2  gradually decreases to form the white light source W 3  in a manner of stepped decreasing, duration length of the white light source W 3  (i.e., duration length of the fourth interval T 4 ) is also controlled. So that duration length of the white light source W 3  is greater than that of the red afterimage R 3  of the backlight module  400  after the second interval T 2 . Hence, the red afterimage R 3  is shielded or covered by the white light source W 3 . 
     From the above, in the image display device  1000  and the control method thereof according to the embodiments of the present disclosure, between the interval when the image display device  1000  displays a normal picture and the interval when the backlight module is turned off to simulate the operation of black frame insertion, white light sources with different intensities are provided (i.e., the brightness are segmented). Intensity of the white light source is controlled to be constant, ramped decreasing or stepped decreasing, so as to achieve segmented brightness. The white light source is used to cover afterimages of the normal picture, especially covering the red afterimage with the longest duration length, hence technical effect of suppressing or eliminating red afterimage phenomenon is achieved. The technical solution of the present disclosure needs not change the color gamut range of the backlight phosphor powders of the backlight module (i.e., needs not change hardware of the backlight module). Instead, the technical solution of the present disclosure only needs to control the backlight of the backlight module with software or firmware to suppress or eliminate red afterimage phenomenon. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.