Patent Publication Number: US-2012033060-A1

Title: Shutter glasses and method for controlling a pair of shutter glasses

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of viewing stereo images, and more particularly, to a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus and a method for controlling the pair of shutter glasses. 
     2. Description of the Prior Art 
     With the development of science and technology, users are pursing stereoscopic and more real image displays rather than high quality images. There are two techniques of present stereo image display. One is to use a video output apparatus which collaborates with glasses (such as anaglyph glasses, polarization glasses or shutter glasses), while the other one to directly use a video output apparatus without any accompanying glasses. No matter which technique is utilized, the main theory of stereo image display is to make the left eye and the right eye see different images, thus the brain will regard the different images seen from two eyes as stereo images. 
     For a pair of shutter glasses, they are widely used for users to view stereo images presented by a video output apparatus. The pair of shutter glasses includes two shutter lenses, and allow user&#39;s left eye to see left-eye images and right eye to see right-eye images by properly switching the shutter lenses between an on-state (or called open state) and an off-state (or called close state). In general, as to the pair of shutter glasses of video output apparatus operated in a lower refresh rate (e.g., 60 Hz or 120 Hz), each shutter lens is continuously switched between the on-state and the off-state. For example, when the shutter lens corresponding to left eye is in an on-state in a certain time period, the shutter lens corresponding to right eye is in an off-state, and when the shutter lens corresponding to right eye is in an on-state, the shutter lens corresponding to left eye is in an off-state. However, if the shutter-on period of the shutter lens is not properly controlled, the user&#39;s left eye may probably see part of the right-eye image and/or the user&#39;s right eye may probably see part of the left-eye image, which significantly degrades the quality of the stereo image the user views. 
     Besides, since each shutter lens of the pair of shutter glasses is switched between the on-state and the off-state, therefore, the ambient brightness perceived by the user is lower than real ambient brightness. Moreover, according to the polarization direction of the image light output generated from the video output apparatus, the shutter lenses of the pair of shutter glasses have corresponding polarization setting. However, as the ambient light comprises light beams of different angles, so when the shutter lens of the pair of shutter glasses is in an on-state, only light beams which conform to the polarization setting of the shutter lens will penetrate through the shutter lens. Thus, the ambient brightness perceived by the user is lower than the real ambient brightness. If the user feels lack of ambient brightness when wearing the pair of shutter glasses, he/she may not identify items, such as a keyboard or remote control, beyond the screen of the video output apparatus clearly, leading to inconvenience in stereo image viewing for users. 
     Moreover, suppose that a liquid crystal layer is employed in the shutter lens of the pair of shutter glasses to control the switching between an on-state and an off-state. In general, when there is no voltage applied on the liquid crystal layer, the shutter lens is in an on-state and allows light beams to penetrate therethrough. As described above, under the control of well known control mechanism, the two shutter lenses of the pair of shutter glasses stay in an on-state alternately. Therefore, when there is no voltage applied on the liquid crystal layer of one shutter lens for allowing light beams to penetrate therethrough, the liquid crystal layer of the other shutter lens requires a voltage applied thereto for blocking light beams to penetrate therethrough. Thus, if the shutter lens stays in an off-state longer, the power consumption of the pair of shutter glasses is increased accordingly. 
     In conclusion, how to provide a reasonable image quality when the user is viewing stereo images presented by the video output apparatus, and increase the ambient brightness users feel when the user wears the pair of shutter glasses and/or decrease power consumption of the pair of shutter glasses without affecting user&#39;s viewing of stereo images is an issue to be solved immediately in this technical field. 
     SUMMARY OF THE INVENTION 
     Therefore, one of the objectives of the present invention is to provide a pair of shutter glasses and a method for controlling the pair of shutter glasses, which can provide a reasonable image quality when the user is viewing stereo images presented by the video output apparatus, and lengthen the shutter-on period of the shutter lens of the pair of shutter glasses to thereby increase the ambient brightness users feel and/or decrease power consumption of the pair of shutter glasses effectively. 
     According to a first aspect of the present invention, a method for controlling a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus is provided. The video output apparatus outputs a group of first images and a group of second images, alternately, and successively outputs a primary first image and at least a secondary first image included in the group of first images in order, during a successive plurality of first image output periods, respectively, and successively outputs a primary second image and at least a secondary second image included in the group of second images in order, during a successive plurality of second image output periods, respectively. One of the group of first images and the group of second images is a group of left-eye images, and the other one of the group of first images and the group of second images is a group of right-eye images. The method includes: controlling a first shutter lens of the pair of shutter glasses to be switched between an on-state and an off-state, wherein the shutter lens stays in an on-state within a first image output period corresponding to a specific secondary first image, and stays in the off-state within a second image output period corresponding to a specific primary second image immediately following the specific secondary first image; and controlling a second shutter lens of the pair of shutter glasses to be switched between an on-state and an off-state, wherein the second shutter lens stays in the off-state within a second image output period corresponding to the specific primary second image, and stays in the on-state within a second image output period corresponding to a specific secondary second image immediately following the specific primary second image. One of the first shutter lens and the second shutter lens is utilized for viewing left-eye images, and the other one of the first shutter lens and the second lens is utilized for viewing right-eye images. The first shutter lens and the second shutter lens simultaneously stay in the off-state only within a single continuous time period of the second image output period corresponding to the specific primary second image. 
     According to a second aspect of the present invention, a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus. The video output apparatus outputs a group of first images and a group of second images, alternately, and successively outputs a primary first image and at least a secondary first image included in the group of first images in order, during a successive plurality of first image output periods, respectively, and successively outputs a primary second image and at least a secondary second image included in the group of second images in order, during a successive plurality of second image output periods, respectively. One of the group of the first images and the group of second images is a group of left-eye images, and the other one of the group of the first images and the group of second images is a group of right-eye images. The pair of shutter glasses comprises a first shutter lens, a second shutter lens and a control circuit. One of the first shutter lens and the second shutter lens is utilized for viewing left-eye images, and the other one of the first shutter lens and the second shutter lens is utilized for viewing right-eye images. The control circuit is electronically connected to the first shutter lens and the second shutter lens, in order to control the first shutter lens to be switched between an on-state and an off-state, and control the second shutter lens to be switched between an on-state and an off-state. The control circuit controls the first shutter lens to stay in the on-state within a first image output period corresponding to a specific secondary first image, and stay in the off-state within a second image output period corresponding to a specific primary second image immediately following the specific secondary first image; besides, the control circuit further controls the second shutter lens to stay in the off-state within the second image output period corresponding to the specific primary second image, and stay in the on-state within a second image output period corresponding to a specific secondary second image immediately following the specific primary second image. The first shutter lens and the second shutter lens simultaneously stay in the off-state only within a single continuous time period of the second image output period corresponding to the specific primary second image. 
     According to a third aspect of the present invention, a method for controlling a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus is provided. The video output apparatus respectively outputs a first image and a second image during a plurality of image output periods, alternately. One of the first image and the second image is a left-eye image, and the other one of the first image and the second image is a right-eye image. Each image output period comprises an image driving period and an image stabilization period. The method comprises: controlling a first shutter lens of the pair of shutter glasses to be switched between an on-state and an off-state, wherein the shutter lens stays in an on-state within an image stabilization period corresponding to a specific first image, and stays in the off-state within an image driving period corresponding to a specific second image immediately following the specific first image; and controlling a second shutter lens of the pair of shutter glasses to be switched between an on-state and an off-state, wherein the shutter lens stays in the off-state within the image driving period corresponding to the specific second image, and stays in the on-state within an image stabilization period corresponding to the specific second image. One of the first shutter lens and the second shutter lens is utilized for viewing left-eye images, and the other one of the first shutter lens and the second lens is utilized for viewing right-eye images. The first shutter lens and the second shutter lens simultaneously stay in the off-state only within a single continuous time period of the image driving period corresponding to the specific second image. Besides, the video output apparatus comprises a scanning backlight module, and the single continuous time period is at least overlapped with the backlight off period in which the scanning backlight module is in an off-state. 
     According to a fourth aspect of the present invention, a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus are provided. The video output apparatus respectively outputs a first image and a second image during a plurality of image output periods, alternately. One of the first image and the second image is a left-eye image, and the other one of the first image and the second image is a right-eye image. Each image output period comprises an image driving period and an image stabilization period. The pair of shutter glasses comprises a first shutter lens, a second shutter lens and a control circuit. One of the first shutter lens and the second shutter lens is utilized for viewing left-eye images, and the other one of the first shutter lens and the second lens is utilized for viewing right-eye images. The control circuit is electronically connected to the first shutter lens and the second shutter lens, in order to control the first shutter lens to be switched between an on-state and an off-state, and control the second shutter lens to be switched between an on-state and an off-state. The control circuit controls the first shutter lens to stay in the on-state within an image stabilization period corresponding to a specific first image, and stay in the off-state within an image driving period corresponding to a specific second image immediately following the specific first image; moreover, the control circuit further controls the second shutter lens to stay in the off-state within the image driving period corresponding to the specific second image, and stay in the on-state within an image stabilization period corresponding to the specific second image. The first shutter lens and the second shutter lens simultaneously stay in the off-state only within a single continuous time period of the image driving period corresponding to the specific second image. Besides, the video output apparatus comprises a scanning backlight module, and the single continuous time period is at least overlapped with the backlight off period in which the scanning backlight module is in an off-state. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a function block diagram of the pair of shutter glasses utilized for viewing stereo images presented by video output apparatus of present invention. 
         FIG. 2  is a sequence diagram of the first control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
         FIG. 3  is a continued sequence diagram of the operation in  FIG. 2  based on the concept of using mixed glasses cycles. 
         FIG. 4  is a sequence diagram of the second control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
         FIG. 5  is a diagram illustrating the operation of a scanning backlight module. 
         FIG. 6  is a sequence diagram of the third control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
         FIG. 7  is a continued sequence diagram of the operation in  FIG. 6  based on the concept of using mixed glasses cycles. 
         FIG. 8  is a sequence diagram of the fourth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
         FIG. 9  is a sequence diagram of the fifth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
         FIG. 10  is a continued sequence diagram of the operation in  FIG. 9  based on the concept of using mixed glasses cycles. 
         FIG. 11  is a sequence diagram of the sixth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a function block diagram of a pair of shutter glasses utilized for viewing stereo images presented by a video output apparatus. In present exemplary embodiment, pair of shutter glasses  100  comprises, but is not limited to, a first shutter lens  102 , a second shutter lens  104  and a control circuit  106 . One of the first shutter lens  102  and second shutter lens  104  (e.g., the first shutter lens  102 ) is utilized for viewing left-eye images, and the other one of the first shutter lens  102  and the second shutter lens  104  (e.g., the second shutter lens  104 ) is utilized for viewing right-eye images. Besides, the control circuit  106  respectively outputs control signals S 1  and S 2  to the first shutter lens  102  and the second shutter lens  104 , in order to control the first shutter lens  102  to be switched between an on-state (or called open state) and an off-state (or called a close state), and control the second shutter lens  104  to be switched between an on-state and an off-state. For example, the first shutter lens  102  and the second shutter lens  104  have liquid crystal layers, respectively. Therefore, the control signal S 1 /S 2  may be a control voltage utilized for controlling the rotation of the liquid crystal cells (LC cells) in the liquid crystal layer to control light transmission rate. However, this is for illustrative purposes only, and is not meant to be a limitation of the present invention. For example, any structure that can control light transmission rate may be utilized for realizing the first shutter lens  102  and the second shutter lens  104 . This also achieves the objective of controlling the first shutter lens  102  and the second shutter lens  104  to be switched between the on-state and the off-state. 
     In the present invention, the “off-state” described above means that the first shutter lens  102 /the second shutter lens  104  is totally opaque (i.e., the light transmission rate is 0%). Therefore, as long as the first shutter lens/the second shutter lens is not totally opaque (i.e., the light transmission rate is not 0%), it may be regarded as staying in the “on-state”. For example, when the first shutter lens  102 /the second shutter lens  104  is fully open (e.g., the light transmission rate is 100%), half open (e.g., the light transmission rate is 50%), or slightly open (e.g., the light transmission rate is 0.1%), the first shutter lens  102 /the second shutter lens  104  may be regarded as staying in an on-state. In brief, when the light transmission rate of the first shutter lens  102 /the second shutter lens  104  is larger than 0% (but smaller than or equal to 100%), the first shutter lens  102 /the second shutter lens  104  is staying in an on-state. 
     A user may wear the pair of shutter glasses  100  to view stereo images presented by the video output apparatus  100 . For example, the video output apparatus  110  may be a liquid crystal display (LCD), and therefore comprises, but is not limited to, a display screen (e.g., an LCD panel)  112  and a backlight module  114 . Backlight module  114  provides light source needed by the display screen  112 , and the pair of shutter glasses  100  control whether image light output generated by the display screen  112  may reach user&#39;s left eye or right eye. Please note that the video output apparatus  110  is not limited to be realized by an LCD apparatus, that is, the video output apparatus  110  may by any video output apparatus that collaborates with the pair of shutter glasses  100  for presenting stereo images to the user. For example, the video output apparatus  110  may be an organic light-emitting diode (OLED) display, a plasma display, a digital light processing (DLP) display/projector, a liquid crystal on Silicon (LCoS) display/projector, etc. 
     The pair of shutter glasses  100  may receive reference information SC from the video output apparatus  110  through wired or wireless transmission (e.g., infrared transmission, ZigBee transmission, ultrawideband (UWB) transmission, WiFi transmission, radio frequency (RF) transmission, DLP light signal transmission or Bluetooth transmission). For example, as shown in  FIG. 1 , the signal transmitter  120  is externally connected to the video output apparatus  110 , and controlled by the video output apparatus  110  in order to transmit the reference information SC generated by the video output apparatus  110  to the pair of shutter glasses  100 . However, in another exemplary embodiment, the signal transmitter  120  may be embedded in the video output apparatus  110 . Thus, the control circuit  106  may generate control signals S 1  and S 2  according to the reference information SC. For example, the reference information SC may be timing sequence of image output presented by the display screen  112 , and the control circuit  106  may automatically generate needed control signals S 1  and S 2  according to the reference information SC. In other words, the video output apparatus  110  only provides a synchronization signal rather than the control information of the time points at which the first shutter lens  102  and the second shutter lens  104  should be open or close; instead, the control circuit  106  controls the timing when the first shutter lens  102  and the second shutter lens  104  should be open or close according to the synchronization signal provided by the video output apparatus  110 . In an alternative design, reference information SC may be directly the control information of the first shutter lens  102  and the second shutter lens  104  (i.e., the video output apparatus  110  dominates the timing when the first shutter lens  102 /the second shutter lens  104  should be open or close). In this way, the control circuit  106  generates corresponding control signals S 1  and S 2  simply according to the received reference information SC. Please note that what described above is only an exemplary embodiment, and is not meant to be a limitation to the present invention. 
     In one exemplary embodiment of the present invention, the video output apparatus  110  is operated under a higher refresh rate (e.g., 200 Hz, 240 Hz, 400 Hz or 480 Hz). In the following, a plurality of examples are given to provide further illustration for the control mechanism of the first shutter lens  102  and the second shutter lens  104 . 
     Please refer to  FIG. 2 , which is a sequence diagram of the first control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . In the present exemplary embodiment, the video output apparatus  110  is operated under a higher refresh rate such as 240 Hz. However, the video output apparatus  110  may also be operated under even higher refresh rate such as 480 Hz. Thus, as to the same primary image, there are more secondary images included in the display output of the video output apparatus  110  operated under a higher refresh rate such as 480 Hz. However, no matter whether the video output apparatus  110  is operated under a refresh rate of 240 Hz or a higher refresh rate (e.g., 480 Hz), the control method of the pair of shutter glasses is basically the same. For clarity and brevity, the following paragraphs only provide a control method of the pair of shutter glasses  100  under a condition where the video output apparatus is operated under a refresh rate of 240 Hz. As shown in  FIG. 2 , the video output apparatus  110  displays a group of first images (e.g., (L 1 , L 1 ′) or (L 2 , L 2 ′)) and a group of second images (e.g., (R 1 , R 1 ′) or (R 2 , R 2 ′)), alternately. Besides, the video output apparatus  110  successively displays a primary first image (e.g., L 1  or L 2 ) and a secondary first image (e.g., L 1 ′ or L 2 ′) both included in the group of first images in order during a plurality of first image output periods (e.g., (T 11 , T 11 ′) or (T 12 , T 12 ′)), respectively, and successively displays a primary second image (e.g., R 1  or R 2 ) and a secondary second image (e.g., R 1 ′ or R 2 ′) both included in the group of second images in order during a plurality of second image output periods (e.g., (T 21 , T 21 ′) or (T 22 , T 22 ′)), respectively. It should be noted that one of the group of first images and the group of second images is a group of left-eye images, and the other one of the group of first images and the group of second images is a group of right-eye images. In other words, in one exemplary embodiment, the first images L 1 , L 1 ′, L 2 , and L 2 ′ stand for left-eye images, and the second images R 1 , R 1 ′, R 2 , and R 2 ′ stand for right-eye images; however, in another exemplary embodiment, the first images L 1 , L 1 ′, L 2 , and L 2 ′ stand for right-eye images, and the second images R 1 , R 1 ′, R 2 , and R 2 ′ stand for left-eye images. 
     Analogously, when the video output apparatus  110  is operated under a higher refresh rate such as 480 Hz, the video output apparatus  110  will also display a group of first images and a group of second images, alternately. For example, in one exemplary embodiment, the display order of the images is: L 1 , L 1 ′, R 1 , R 1 ′, L 2 , L 2 ′, R 2 , and R 2 ′, wherein L 1  and L 2  are primary first images, L 1 ′ and L 2 ′ are secondary first images, R 1  and R 2  are primary second images, and R 1 ′ and R 2 ′ are secondary second images. Therefore, groups of first images are composed of (L 1 , L 1 ′) and (L 2 , L 2 ′), respectively, and groups of second images are composed of (R 1 , R 1 ′) and (R 2 , R 2 ′), respectively. Besides, in the present exemplary embodiment, the number of the secondary first images and the number of the secondary second images are for illustrative purposes only. In another exemplary embodiment, the display order of the images is: L 1 , L 1 ′, L 1 ″, L 1 ′″, R 1 , R 1 ′, R 1 ″, R 1 ′″, wherein L 1  is a primary first image, L 1 ′, L 1 ″ and L 1 ′″ are secondary first images, R 1  is a primary second image, and R 1 ′, R 1 ″ and R 1 ′″ are secondary second images. Therefore, a group of first images is composed of (L 1 , L 1 ′, L 1 ″, L 1 ′″), and a group of second images is composed of (R 1 , R 1 ′, R 1 ″, R 1 ′″). Besides, in the present exemplary embodiment, the number of the secondary first images and the number of the secondary second images are for illustrative purposes only. Please note that, in an actual application, the backlight module  114  provides a brighter backlight to secondary first images L 1 , L 1 ′, L 1 ″, and L 1 ′″ and secondary second images R 1 , R 1 ′, R 1 ″, and R 1 ′″. However, this is for illustrative purposes only, and is not meant to be a limitation to the present invention. Besides, in a case where the video output apparatus  110  (e.g., liquid crystal display, OLED display, plasma display, or display/projector of other display techniques) is operated under a higher refresh rate such as 240 Hz or above, regarding the same group of first/second images, the length of all secondary first/second images is longer than or equal to the length of the primary first/second images. 
     In one exemplary embodiment, the secondary first image is a primary first image in the same group of the first images that is displayed again, and the secondary second image is a primary second image in the same group of the second images that is displayed again. Each of the first image output periods and the second image output periods comprises an image driving period and an image stabilization period (e.g., the first image output period T 11  comprises an image driving period TP 1  and an image stabilization period TH 1 , the image output period T 11 ′ comprises an image driving period TP 1 ′ and an image stabilization period TH 1 ′, and so on). Please note that, according to the display technique applied, each image stabilization period may comprise a non-image driving period or an image maintaining period. For example, finishing transmitting an image driving signal within an image driving period or not transmitting any image driving signal within an image stabilization period would make the image now regarded as being in a stabilizing state. For example, regarding pixels such as liquid crystal cells of OLED units), a pixel may be regarded as operating in an image stabilization period starting from the time point when the pixel becomes stable due to being driven by the image driving signal transmitted within the image driving period. On the other hand, a pixel may also be regarded as operating in an image stabilization period starting from the time point when there is no image driving signal transmitted to the pixel. 
     As to the liquid crystal display, controlling the rotation of the liquid crystal cell is needed in order to reach the aim of controlling light transmission rate. Regarding the liquid crystal display operated under a lower refresh rate (e.g., 60 Hz or 120 Hz), the needed rotation time of liquid crystal cell is taken into consideration, and thus the image stabilization period immediately following the image driving period is mainly utilized for displaying stereo images. Regarding the liquid crystal display operated under a higher refresh rate (e.g., 240 Hz or 480 Hz), the length of each image stabilization period is shorter; however, in the same time period, the liquid crystal display will output more images under a higher refresh rate. Therefore, the image output periods corresponding to the secondary images may be utilized for providing stabilized images and opening the first shutter lens  102 /the second shutter lens  104  in order to provide stereo images for the user. In brief, each primary image (e.g., L 1 , L 2 , R 1  or R 2  described above) is responsible for updating the content of the displayed previous image (i.e., the content of the previous primary first image). Therefore, before the current primary image to be displayed has totally replaced the displayed previous image, the output result of the display screen  112  (e.g., an LCD panel) comprises part of the current primary images and part of the previous primary image within the image driving period corresponding to the primary image to be displayed. In addition, the following secondary images (e.g., L 1 ′, L 2 ′, R 1 ′, R 2 ′, L 1 ′-L 1 ′″ or R 1 ′-R 1 ′″) are responsible for stabilizing images in order to provide stereo images for the user through the pair of shutter glasses  100 . 
     Besides, in another exemplary embodiment, the secondary first image is a continuous output result of the primary first image included in the same group of first images. That is, within the image driving period corresponding to the primary image, the display screen  112  successively sets pixels according to the display data, wherein pixels are driven line by line from the top to the bottom in an image and pixel by pixel from the left to the right in each line of the image to thereby output the primary image to be displayed. Alternatively, according to a different placement setting or hardware design of the LCD panel, the display screen  112  may output the primary image to be displayed by successively setting pixels according to the display data, wherein the pixels are driven line by line from the bottom to the top in an image and pixel by pixel from the right to the left in each line in the image, or may be driven according to other pixel updating order). However, within the image driving period corresponding to the following secondary image, the display screen  112  does not perform display driving operation according to any display data, so the display screen  112  still continuously displays the content of the primary image due to the inherent characteristic of the LCD panel. Moreover, the secondary first image may also be a black image or an adjusted image that is generated by applying a fine-tuning adjustment, such as a compensation for the crosstalk of images, to the primary first image included in the same group of first images. 
     Besides, in yet another exemplary embodiment, the primary first/second image may also be a black image, and the backlight module  114  stays in the on-state within the image output period corresponding to the secondary first/second image in order to provide stereo images for the user. 
     The control circuit  106  controls the first shutter lens  102  to be switched between an on-state (“ON”) and an off-state (“OFF”), and controls the second shutter lens  104  to be switched between an on-state (“ON”) and an off-state (“OFF”). In the present exemplary embodiment, the control circuit  106  controls the first shutter lens  102  to stay in the on-state within the first image output period (e.g., T 11 ′ or T 12 ′) corresponding to the specific secondary first image (e.g., L 1 ′ or L 2 ′), and stay in the off-state within the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image immediately following the specific secondary first image (e.g., R 1  or R 2 ). As shown in  FIG. 2 , in the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state from the start point of the first image output period corresponding to the specific secondary first image, and is switched from the on-state to the off-state at the end point of the first image output period corresponding to the specific secondary first image. Afterwards, the first shutter lens  102  maintains at the off-state from the start point to the end point of the second image output period corresponding to the following specific primary second image. Moreover, the control circuit  106  further controls the second shutter lens  104  to stay in the off-state within the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image (e.g., R 1  or R 2 ), and stay in the on-state within the second image output period (e.g., T 21 ′ or T 22 ′) corresponding to the specific secondary second image (e.g., R 1 ′ or R 2 ′) immediately following the specific primary second image. As shown in  FIG. 2 , in the present exemplary embodiment, the shutter lens  104  maintains at the off-state from the start point to the end point of the second image output period corresponding to the specific primary second image, is switched from the off-state to the on-state within the second image output period corresponding to the following specific secondary second image, and then is switched from the on-state to the off-state at the end point of the second image output period corresponding to the specific secondary second image. Besides, as shown in the figure, the first shutter lens  102  and the second shutter lens  104  simultaneously stay in the off-state only within a single continuous time period (e.g., P 1  or P 2 ) of the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image (e.g., R 1  or R 2 ). 
     Please note that,  FIG. 2  only shows that the control circuit  106  controls the first shutter lens  102  and the second shutter lens  104  during an operating time period including, for example, image output periods T 11 -T 22 ′. In fact, the control circuit  106  will repeat the same control mechanism mentioned above for controlling the first shutter lens  102  and the second shutter lens  104  to be switched between the on-state and the off-state by referring to the same glasses cycle (i.e., the cycle that the left eye and the right eye respectively view the image once) or different glasses cycles during the previous operating period(s) (e.g., the image output period(s) before the image output period T 11 ) and the following operating period(s) (e.g., the image output period(s) after the image output period T 22 ′). 
     As to the operation with mixed glasses cycles, please refer to  FIG. 2  in conjunction with  FIG. 3 .  FIG. 3  is a continued sequence diagram of the operation in  FIG. 2  based on the concept of using mixed different glasses cycles. As shown in  FIG. 3 , the original glasses cycle is equal to a sum of image output periods of four images (e.g., T 11 +T 11 ′+T 21 +T 21 ′). However, after the second image output period T 21 ′ ends, the original glasses cycle is expanded to a sum of image output periods of eight images (e.g., T 12 +T 12 ′+T 22 +T 22 ′+T 13 +T 13 ′+T 23 +T 23 ′). In the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state at the start point of the following first image output period T 14 ′ corresponding to the secondary first image L 4 ′, and the second shutter lens  104  is switched from the off-state to the on-state at the start point of the second image output period T 24 ′ corresponding to the secondary second image R 4 ′. Please note that using a sum of image output periods of eight images as another glasses cycle is for illustrative purposes only, and is not meant to be a limitation to the present invention. In fact, the number of image output periods covered in one glasses cycle may be adjusted according to the actual application requirement/consideration. Besides, in the aforementioned exemplary embodiment of mixed glasses cycles, the same control mechanism is repeated in another longer glasses cycle. However, in this longer glasses cycle, other control mechanism(s) may be employed. Thus, within the time period (e.g., T 13 -T 23 ′) that the original control mechanism has no control over the on/off-state of the shutter lenses, other control mechanism(s) may be active to control the on/off-state of the shutter lenses. This alternative design also obeys the spirit of the present invention. 
     As described above, before the present primary image to be displayed has totally replaced the displayed previous image, the output result, which is to be displayed within the image driving period corresponding to present primary image, of the display screen  112  (e.g., an LCD panel) comprises part of the present primary image and part of the previous primary image. Thus, in order to block trash images from reaching user&#39;s eyes, in the present exemplary embodiment, in addition to the control of the first shutter lens  102  and the second shutter lens  104 , the backlight module  114  stays in the on-state (“ON”) only within the image driving period TP 1 ′, TP 2 ′, TP 3 ′, TP 4 ′ respectively corresponding to the secondary first and second image. In other words, the backlight module  114  is disabled to stay in the off-state (“OFF”) within the image driving period TP 1 , TP 2 , TP 3 , TP 4  respectively corresponding to the primary first and second images. Therefore, in the present exemplary embodiment, the backlight module  114  stays in the on-state only when the first shutter lens  102  and the second shutter lens  104  stay in the on-state, so the aforementioned single continuous time period is at least partly overlapped with the backlight-off period in which the backlight module  114  stays in the off-state. In short, by a proper control of the first shutter lens  102 , the second shutter lens  104  and the backlight module  114 , the system may provide a reasonable image quality for the user when the user is viewing stereo images presented by the video output apparatus. 
     Please note that, in another exemplary embodiment, the backlight module  114  is enabled to stay in the on-state within the image driving period TP 1 ′, TP 2 ′, TP 3 ′, TP 4 ′ respectively corresponding to the secondary first and second images; additionally, the backlight-on period of the backlight module  114  may also slightly expand forward or shrink backward from the start point of the image driving periods TP 1 ′, TP 2 ′, TP 3 ′, TP 4 ′ respectively corresponding to the secondary first and second images, and/or slightly expand backward or shrink forward at the end point of the image driving periods TP 1 ′, TP 2 ′, TP 3 ′, TP 4 ′ respectively corresponding to the secondary first and second images. For example, an exemplary backlight-on period expansion is shown in the figure by dotted lines. Taking the secondary first image L 1  for example, in the first exemplary embodiment, the backlight-on period of the backlight module  114  only includes the image driving period TP 1 ′, in the second exemplary embodiment, the backlight-on period of backlight module  114  includes the image driving period TP 1 ′ and the image stabilization period TH 1 ′, while in the third exemplary embodiment, the backlight-on period of the backlight module  114  includes the image driving period TP 1 ′ and the image stabilization periods TH 1  and TH 1 ′. In other words, the backlight module  114  may be switched from the off-state to the on-state before the start point of the image driving period corresponding to the secondary first image/the secondary second image, and/or be switched from the on-state back to the off-state after the end point of the image driving period corresponding to the secondary first image/secondary second image. According to above disclosure, the backlight-on period of the backlight module  114  staying in the on-state may cover and extend beyond the image driving period corresponding to the secondary first image/secondary second image, wherein the backlight module  114  stays in the on-state within the image driving period corresponding to the secondary first image/secondary second image, and stays in the off-state within the image stabilization period corresponding to the adjacent primary first image/primary second image. A length of a time period in which the backlight module  114  stays in the off-state within the adjacent image stabilization period is shorter than or equal to a length of the adjacent image stabilization period. 
     As described above, the first shutter lens  102  is switched from the off-state to the on-state at the start point of the first image output period corresponding to the specific secondary first image, and is switched from the on-state to the off-state at the end point of the first image output period corresponding to the specific secondary first image. The second shutter lens  104  is switched from the off-state to the on-state at the start point of the second image output period corresponding to the specific secondary second image, and is switched from the on-state to the off-state at the end point of the second image output period corresponding to the specific secondary second image. However, it is not meant to be a limitation to the present invention. Please refer to  FIG. 4 .  FIG. 4  is a sequence diagram of the second control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . In the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state before the start point of the first image output period (e.g., T 11 ′ or T 12 ′) corresponding to the specific secondary first image (e.g., L 1 ′ or L 2 ′), and is switched from the on-state to the off-state after the end point of the first image output period (e.g., T 11 ′ or T 12 ′) corresponding to the specific secondary first image (e.g., L 1 ′ or L 2 ′). The second shutter lens  104  is switched from the off-state to the on-state before the start point of the second image output period (e.g., T 21 ′ or T 22 ′) corresponding to the specific secondary second image (e.g., R 1 ′ or R 2 ′), and is switched from the on-state to the off-state after the end point of the second image output period (e.g., T 21 ′ or T 22 ′) corresponding to the specific secondary second image (e.g., R 1 ′ or R 2 ′). Please note that, like the exemplary embodiment shown in  FIG. 2 , the first shutter lens  102  and the second shutter lens  104  in this exemplary embodiment simultaneously stay in the off-state only within a single continuous time period (e.g., P 1  or P 2 ) of the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image (e.g., R 1  or R 2 ). Besides, the aforementioned single continuous time period, such as P 1  or P 2 , is at least partly overlapped with the backlight-off period in which the backlight module  114  stays in the off-state. In the present exemplary embodiment, the single continuous time period in which the first shutter lens  102  and the second shutter lens  104  simultaneously stay in the on-state totally lies within the backlight-off period of the backlight module  114 . 
     Similarly, in order to prevent trash images from coming into user&#39;s eyes, the present exemplary embodiment controls the first shutter lens  102  and the second shutter lens  104  as well as the backlight module  114 , wherein the backlight module  114  is enabled to stay in the on-state (“ON”) only within the image driving periods TP 1 , TP 2 , TP 3 , and TP 4  respectively corresponding to the secondary first and second images. By a proper control of the first shutter lens  102 , the second shutter lens  104  and the backlight module  114 , the system may provide a reasonable image quality for the user when the user is viewing stereo images presented by the video output apparatus  110 . Moreover, the backlight module  114  is disabled to stay in the off-state (“OFF”) within the image driving periods TP 1 ′, TP 2 ′, TP 3 ′, and TP 4 ′ respectively corresponding to the primary first and second images. Due to lack of backlight source needed, the display output presented by the display screen  112  within the image output periods T 11 , T 21 , T 12 , and T 22  will not be seen by user&#39;s eyes. Thus, though the first shutter lens  102  and the second shutter lens  104  are open (i.e., stay in the on-state) within image output periods T 11 , T 21 , T 12 , and T 22 , they have no effect on user&#39;s viewing of stereo images. However, since the length of the shutter-on period of the first shutter lens  102 /the second shutter lens  104  is increased, the ambient brightness perceived by the user is increased when compared with the perceived ambient brightness in the exemplary embodiment shown in  FIG. 2 . Besides, since the shutter-on period of the first shutter lens  102 /the second shutter lens  104  is increased, the length of the shutter-off period of the first shutter lens  102 /the second shutter lens  104  is decreased accordingly, thereby reducing the power consumption of the pair of shutter glasses  100 . 
     Moreover, in another exemplary embodiment, the backlight module  114  is enabled to stay in the on-state within the image driving periods TP 11 , TP 2 ′, TP 3 ′, and TP 4 ′; additionally, the backlight-on period of the backlight module  114  may also slightly expand forward or shrink backward at the start point of the image driving periods TP 11 , TP 2 ′, TP 3 ′, and TP 4 ′, and/or slightly expand backward or shrink forward at the end point of the image driving periods TP 11 , TP 2 ′, TP 3 ′, and TP 4 ′. These alternative designs all fall within the scope of the present invention. 
     Besides, the above disclosure directed to the backlight module  114  is only utilized to assist in illustrating the control mechanism of the pair of shutter glasses  100  of the present invention. That is, whatever the design of the backlight-on period of the backlight module  114  is, the display system which allows the user to view stereo images falls within the scope of the present invention as long as the operations of switching the first shutter lens  102  and the second shutter lens  104  between the on-state and the off-state obey the spirit of the present invention. 
     Please note that the exemplary embodiment shown in  FIG. 4  is for illustrative purposes only, and is not meant to be a limitation to the present invention. That is, under the premise of not departing from the spirit of present invention, changes/modifications made to the exemplary embodiment shown in  FIG. 4  are feasible. In other words, it is not necessary to make the shutter-on periods of the first shutter lens  102  and the second shutter lens  104  expand forward/backward together. For example, any control mechanism would be regarded as obeying the spirit of the present invention and thus falling within the scope of the present invention as long as one of the operations listed below or a combination of multiple operations selected from the operations listed below is employed: making the first shutter lens  102  be switched from the off-state to the on-state before the start point of the image driving period corresponding to the specific secondary first image, making the first shutter lens  102  be switched from the on-state to the off-state after the end point of the image driving period corresponding to the secondary first image, making the second shutter lens  104  be switched from the off-state to the on-state before the start point of the image driving period corresponding to the specific secondary second image, and making the second shutter lens  104  be switched from the on-state to the off-state after the end point of the image driving period corresponding to the secondary second image. 
     In the exemplary embodiment described above, the backlight module  114  may be realized by a plain backlight module. That is, when the backlight module  114  is enabled, all pixels in the display screen  112  receive backlight offered by the backlight module  114 . However, it is not meant to be a limitation to the present invention. The backlight module  114  may be realized by a scanning backlight module. Please refer to  FIG. 5 , which is a diagram illustrating an operation of the scanning backlight module. All pixels in the display screen  112  may be categorized into several display areas, and the scanning backlight module offers backlight to the display areas in turn. Therefore, the display areas with no backlight applied thereto may be utilized for hiding the shadow-trail and image crosstalk generated by the display screen  112  (e.g., an LCD panel). As shown in  FIG. 5 , the display screen  112  is separated into several display areas from the top to the bottom, such as four display areas  402 ,  404 ,  406 , and  408 . Therefore, during the backlight-on period TL in which the scanning backlight module stays in the on-state, the display areas  402 ,  404 ,  406 , and  408  are successively provided with backlight as shown by the blank blocks in  FIG. 5 . Compared with the backlight-on period of the plain backlight module, the backlight-on period of the scanning backlight module may be longer. For example, the backlight-on period of the scanning backlight module is longer than the length of the first image output period/second image output period corresponding to the secondary first image/secondary second image, and close to (shorter than) the sum of the length of the first image output period/the second image output period corresponding to the secondary first image/secondary second image and the length of the second image output period/first image output period corresponding to the primary second image/primary first image immediately following the secondary first image/secondary second image. However, it is not meant to be a limitation to the present invention. 
     When the scanning backlight module is employed in the video output apparatus  110 , the control mechanism employed by the control circuit  106  for controlling the first shutter lens  102  and the second shutter lens  104  needs to be properly adjusted according to the backlight-on period in which the scanning backlight module stays in the on-state. Please refer to  FIG. 6 , which is a sequence diagram of the third control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . In the present exemplary embodiment, the backlight module  114  is a scanning backlight module. As shown in the figure, the backlight module  114  is enabled within the image output periods T 11 ′, T 21 ′, T 12 ′, and T 22 ′ respectively corresponding to the secondary first and second images as well as time periods within the image output periods T 21 , T 12 , and T 22  corresponding to the following primary first and second images. Please note that, though the backlight module  114  is enabled to stay in the on-state in the time periods within the image output periods T 21 , T 12 , and T 22  respectively corresponding to the primary first and second images, no backlight is applied to a top half of the display screen  112  while the primary first image and the primary second image have pixel data updated from the top to the bottom during a first half of each of the image output periods T 21 , T 12 , and T 22 , as shown in  FIG. 5 . Therefore, the user will not see the updated pixel data. In other words, though the output result presented by the display screen  112  within the image driving period corresponding to the primary image to be displayed would include part of the current primary image to be displayed and part of the displayed previous primary image before the current primary image to be displayed has totally replaced the displayed previous image, the trash image will not reach user&#39;s eyes under a proper control of the scanning backlight module, the first shutter lens and the second shutter lens, however. As a result, the system may provide a reasonable image quality for the user when the user is viewing stereo images presented by the video output apparatus. 
     In the present exemplary embodiment, the backlight module  114  stays in the on-state only when the first shutter lens  102  and the second shutter lens  104  stay in the on-state; besides, the first shutter lens  102  and the second shutter lens  104  simultaneously stay in the off-state only within a single continuous time period (e.g., P 1  or P 2 ) within the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image (e.g., R 1  or R 2 ). Moreover, as shown in the figure, the length of the continuous backlight-on period that the backlight module  114  stays in the on-state (e.g., the backlight-on period TL shown in  FIG. 5 ) must be shorter than an image cycle (e.g., T 11 +T 11 ′, T 21 +T 21 ′, T 12 +T 12 ′ or T 22 +T 22 ′) for a single eye (left eye/right eye). 
     Please note that, in another exemplary embodiment, the backlight module  114  is enabled to stay in the on-state within the image output periods T 11 ′, T 21 ′, T 12 ′, and T 22 ′ respectively corresponding to the secondary first and second images and also stay in the on-state in time periods within the image output periods T 21 , T 12 , and T 22  corresponding to the following primary first and second images; additionally, the backlight-on periods of the backlight module  114  may also slightly expand forward or shrink backward at the start points of the image output periods T 11 ′, T 21 ′, T 12 ′, and T 22 ′ (i.e., start points of image driving periods TP 1 ′, TP 2 ′, TP 3 ′, and TP 4 ′) respectively corresponding to the secondary first and second images. For example, the backlight module  114  may be switched from the off-state to the on-state before the start points of the image output periods T 11 ′, T 21 ′, T 12 ′, and T 22 ′ (i.e., start points of the image driving periods TP 1 ′, TP 2 ′, TP 3 ′, and TP 4 ′) corresponding to the secondary first and second images. In other words, the continuous backlight-on period in which the backlight module  114  stays in the on-state, such as the backlight-on period TL shown in  FIG. 5 , may be expanded forward and/or backward. 
     Besides,  FIG. 6  only shows that the control circuit  106  controls the first shutter lens  102  and the second shutter lens  104  during an operating time period including, for example, image output periods T 11 -T 22 ′). In fact, the control circuit  106  will repeat the same control mechanism mentioned above to control the first shutter lens  102  and the second shutter lens  104  to be switched between the on-state and the off-state by referring to the same glasses cycle (i.e., the cycle that left eye and right eye respectively view the image once) or different glasses cycles within the previous operating time period(s) (e.g., the image output period(s) before the image output period T 11 ) and the following operating time period(s) (e.g., the image output period(s) after the image output period T 22 ′). 
     As to the operation with mixed glasses cycles, please refer to  FIG. 6  in conjunction with  FIG. 7 .  FIG. 7  is a continued sequence diagram of the operation in  FIG. 6  based on the concept of using mixed glasses cycles. As shown in  FIG. 6 , the original glasses cycle is equal to a sum of image output periods of four images (e.g., T 11 +T 11 ′ or T 21 +T 21 ′). However, after the image stabilization period T 21 ′ ends, the glasses cycle is expanded to a sum of image output periods of eight images (e.g., T 12 +T 12 ′+T 22 +T 22 ′+T 13 +T 13 ′+T 23 +T 23 ′). In the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state at the start point of the first image output period T 14 ′ corresponding to the secondary first image L 4 ′, and the second shutter lens  104  is switched from the off-state to the on-state at the start point of the second image output period T 24 ′ corresponding to the following secondary second image R 4 ′. Please note that using a sum of image output periods of eight images as another glasses cycle is for illustrative purposes only, and is not meant to be a limitation to the present invention. In fact, the number of image output periods covered in on glasses cycle may be adjusted according to the actual application requirement/consideration. Besides, in the exemplary embodiment of mixed different glasses described above, the same control mechanism is repeated in another longer glasses cycle. However, in this longer glasses cycle, other control mechanism(s) may be employed. Thus, within the time period that original control mechanism has no control over the on/off-state of the shutter lenses (e.g., T 13 -T 23 ′), other control mechanism(s) may be active to control the on/off-state of the shutter lenses. This alternative design also obeys the spirit of present invention. 
     As shown in  FIG. 6 , the first shutter lens  102  is switched from the off-state to the on-state at the start point of the first image output period corresponding to the specific secondary first image, and is switched from the on-state to the off-state after the end point of the first image output period corresponding to the specific secondary first image. Besides, the second shutter lens  104  is switched from the off-state to the on-state before the start point of the second image output period corresponding to the specific secondary second image, and is switched from the on-state to the off-state at the end point of the second image output period corresponding to the specific secondary second image. However, it is not meant to be a limitation to the present invention. That is, like the exemplary embodiment shown in  FIG. 4 , the shutter-on period in which the first shutter lens  102  and the second shutter lens  104  stay in the on-state, as shown in the exemplary embodiment in  FIG. 6 , may be expanded forward and/or backward to thereby increase the ambient brightness the user feels and decrease the power consumption of the pair of shutter glasses  100 . Please refer to  FIG. 8 , which is a sequence diagram of the fourth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . Similarly, like the exemplary embodiment shown in  FIG. 6 , the first shutter lens  102  and the second shutter lens  104  simultaneously stay in the off-state only within a single continuous time period (e.g., P 1  or P 2 ) of the second image output period (e.g., T 21  or T 22 ) corresponding to the specific primary second image (e.g., R 1  or R 2 ). Besides, the aforementioned single continuous time period (e.g., P 1  or P 2 ) is at least partly overlapped with the backlight-off period in which the backlight module  114  stays in the off-state. In the present exemplary embodiment, the single continuous time period in which the first shutter lens  102  and the second shutter lens  104  simultaneously stay in the on-state totally lies within the backlight-off period of backlight module  114 . Please note that the exemplary embodiment in  FIG. 8  is for illustrative purposes only, and is not meant to be a limitation to the present invention. Under the premise of not departing from the spirit of the present invention, changes/modifications made to the exemplary embodiment shown in  FIG. 8  are feasible. For example, it is not necessary to make the shutter-on periods of the first shutter lens  102  and the second shutter lens  104  expand forward and/or backward together. These alternative designs all fall within the scope of the present invention. 
     Besides, within the image output periods respectively corresponding to the secondary first and second images (e.g., the image driving periods TP 1 ′, TP 2 ′, TP 3 ′, and TP 4 ′), the user is allowed to view images mainly by the enabling of the backlight module  114 . Regarding the first shutter lens  102 /the second shutter lens  104  within the shutter-on period, the liquid crystal cells in the liquid crystal layer of the first shutter lens  102 /the second shutter lens  104  start rotating before the image output period (e.g., the image driving period) corresponding to the secondary first image/the secondary second image for making the first shutter lens  102 /the second shutter lens  104  be switched from the off-state to the on-state, and start rotating after the image output period (e.g., the image driving period) corresponding to the secondary first image/the secondary second image for making the first shutter lens  102 /the second shutter lens  104  be switched from the on-state to the off-state. In this way, when the user views images within the image output periods (e.g., image driving periods) respectively corresponding to the secondary first and second images, the present invention may further decrease the brightness attenuation induced due to the response time period (i.e., the rotating process) of the liquid crystal cells. 
     According to the exemplary embodiments shown in  FIG. 6  and  FIG. 8 , the pair of shutter glasses control mechanism of the present invention may be utilized for controlling the video output apparatus  110  which is operated under a higher refresh rate (e.g., 240 Hz or 480 Hz) and adopts a scanning backlight module. However, the pair of shutter glasses control mechanism of the present invention may also control the video output apparatus  110  which is operated under a lower refresh rate (e.g., 60 Hz, 96 Hz, 100 Hz, 110 Hz or 120 Hz) and adopts a scanning backlight module. Please refer to  FIG. 9 , which is a sequence diagram of the fifth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . In the present exemplary embodiment, the backlight module  114  is a scanning backlight module, and the video output apparatus  110  is operated under a lower refresh rate such as 60 Hz or 120 Hz. As shown in  FIG. 9 , the video output apparatus  110  respectively outputs a first image (e.g., L 1 , L 2 , L 3  or L 4 ) and a second image (e.g., R 1 , R 2  or R 3 ) during a plurality of image output periods (e.g., T 1 -T 7 ), alternately, wherein one of the first image and the second image is a left-eye image, and the other one of the first image and the second image is a right-eye image. In other words, in one exemplary embodiment, the first images L 1 , L 2 , L 3  and L 4  stand for left-eye images and the second images R 1 , R 2  and R 3  stand for right-eye images; however, in another exemplary embodiment, the first images L 1 , L 2 , L 3  and L 4  stand for right-eye images and the second images R 1 , R 2  and R 3  stand for left-eye images. Besides, as shown in the figure, each image output period comprises an image driving period and an image stabilization period. Please note that, according to the display technique used, each image stabilization period may probably comprises a non-image-driving period or an image maintaining period. For example, the image output period T 1  comprises an image driving period TP 1  and an image stabilization period TH 1 , the image output period T 2  comprises an image driving period TP 1 ′ and an image stabilization period TH 1 ′, and so on. Within each image driving period, the display screen  112  (e.g., an LCD panel) successively sets pixels according to the display data, wherein the pixels are driven line by line from the top to the bottom in an image and pixel by pixel from the left to the right in each line of the image to thereby output the image to be displayed now. Alternatively, according to a different placement setting or hardware design of the LCD panel, the display panel  112  may output the image to be displayed by successively setting pixels according to the display data, wherein the pixels are driven line by line from the bottom to the top in an image and pixel by pixel from the right to the left in each line of the image, or may be driven according to other pixel updating sequence. In short, the display screen  112  will replace the displayed previous image with a current image to be displayed. Therefore, before the current image to be displayed has totally replaced the displayed previous image, the display screen  112  will output an image that comprises part of the current image and part of the previous image within the image driving period. In addition, within the following image stabilization period, the display screen  112  will wait for the image stabilization of the current image to be displayed. For example, the display screen  112  will not drive pixels according to any display date. That is, each image stabilization period may be a vertical blanking interval (VBI). 
     The control circuit  106  controls the first shutter lens  102  to be switched between an on-state (“ON”) and an off-state (“OFF”), and controls the second shutter lens  104  to be switched between an on-state (“ON”) and an off-state (“OFF”). In this exemplary embodiment, the control circuit  106  controls the first shutter lens  102  to stay in the on-state within the image stabilization period (e.g., TH 1 , TH 2  or TH 3 ) corresponding to a specific first image (e.g., L 1 , L 2  or L 3 ) and stay in the off-state within the image driving period (e.g., TP 1 ′, TP 2 ′ or TP 3 ′) corresponding to a specific second image (e.g., R 1 , R 2  or R 3 ) immediately following the specific first image, as shown in  FIG. 9 . In the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state at the start point of the image stabilization period, and is switched from the on-state to the off-state after the end point of the image stabilization period. In addition, the control circuit  106  controls the second shutter lens  104  to stay in the off-state within the image driving period (e.g., TP 1 ′, TP 2 ′ or TP 3 ′) corresponding to the specific second image (e.g., R 1 , R 2  or R 3 ) and stay in the on-state within the image stabilization period (e.g., TH 1 ′, TH 2 ′ or TH 3 ′) corresponding to the same specific second image (e.g., R 1 , R 2  or R 3 ). The second shutter lens  104  stays in the off-state within the image driving period, is switched from the off-state to the on-state at the start point of the following image stabilization period, and then is switched from the on-state to the off-state after the end point of the image stabilization period. The first shutter lens  102  and the second shutter lens  104  both stay in the off-state only within a single continuous time period (e.g., P 1  or P 2 ) of the image driving period (e.g., TP 1 ′ or TP 2 ′) corresponding to the specific second image (e.g., R 1  or R 2 ). Besides, the aforementioned single continuous time period (e.g., P 1  or P 2 ) is at least partly overlapped with the backlight off period in which the backlight module  114  stays in the off-state. In the present exemplary embodiment, they are totally overlapped with each other. 
     Please note that  FIG. 9  only shows that the control circuit  106  controls the first shutter lens  102  and the second shutter lens  104  during an operating time period including, for example, image output periods T 1 -T 6 ). In fact, the control circuit  106  will repeat the same control mechanism mentioned above to control the first shutter lens  102  and the second shutter lens  104  to be switched between the on-state to the off-state by referring to the same glasses cycle (i.e., the cycle that left eye and right eye respectively view the image once) or different glasses cycles within the previous operating time period(s) (e.g., the image output period(s) before the image output period T 1 ) and the following operating time period(s) (e.g., the image output period(s) after the image output period T 6 ). 
     As to the operation with mixed glasses cycles, please refer to  FIG. 9  in conjunction with  FIG. 10 .  FIG. 10  is a continued sequence diagram of the operation in  FIG. 9  based on the concept of using mixed glasses cycles. As shown in  FIG. 9 , the previous glasses cycle is equal to a sum of image output periods of two images (e.g., T 1 +T 2  or T 3 +T 4 ). However, after the image stabilization period TH 2 ′ ends, the glasses cycle is expanded to a sum of image output periods of four images (e.g., T 5 +T 6 +T 7 +T 8  or T 9 +T 10 +T 11 +T 12 ). In the present exemplary embodiment, the first shutter lens  102  is switched from the off-state to the on-state at the start point of the image stabilization period TH 5  corresponding to the first image L 5 , and the second shutter lens  104  is switched from the off-state to the on-state within the start point of image stabilization period TH 5 ′ corresponding to the second image R 5 . Please note that using a sum of image output periods of four images as another glasses cycle is for illustrative purposes only, and is not meant to be a limitation to the present invention. In fact, the number of image output periods of glasses cycle covered in one glasses cycle may be adjusted according to the actual application requirement/consideration. Besides, in the exemplary embodiment of using mixed different glasses described above, the same control mechanism is repeated in another longer glasses cycle. However, in this longer glasses cycle, other control mechanism(s) may be employed. Thus, within the time period that the original control mechanism has no control over the on/off-state of the shutter lenses (e.g., T 7 -T 8 ), other control mechanism(s) may be active to control the on/off-state of the shutter lenses. This alternative design also obeys the spirit of the present invention. 
     As described above, before the current image to be displayed has totally replaced the displayed previous image, the output result of the display screen  112  (e.g., an LCD panel) within the image driving period corresponding to the current image to be displayed comprises part of the current image and part of the previous image. Therefore, in order to prevent the trash image from reaching user&#39;s eyes, in the present exemplary embodiment, the backlight module  114  is enabled to stay in the on-state only when the first shutter lens  102  and the second shutter lens  104  both stay in the on-state. Please note that, though the backlight module  114  is enabled to stay in the on-state in the time periods within the image driving periods TP 1 -TP 3  and TP 1 ′-TP 3 ′ respectively corresponding to the first and second images, no backlight is applied to a top half of the display screen  112  while the first and second images have pixel data updated from the top to the bottom during a first half of the image driving periods TP 1 -TP 3  and TP 1 ′-TP 3 ′, as shown in  FIG. 5 . Therefore, the user cannot see the updated pixel data. In other words, by controlling the scanning backlight module, the first shutter lens and the second shutter lens properly, the trash image will not reach user&#39;s eyes. As a result, the system may provide a reasonable image quality for the user when the user views stereo images presented by the video output apparatus. 
     Please note that, in another exemplary embodiment, the backlight module  114  keeps staying in the on-state within each of the image stabilization periods TH 1 , TH 1 ′, TH 2 , TH 2 ′, and TH 3  and is switched from the on-state to the off-state at an end point of a certain time period immediately following the end point of each of the image stabilization periods TH 1 , TH 1 ′, TH 2 , TH 2 ′, TH 3 , and TH 3 ′; additionally, the backlight-on periods of the backlight module  114  may also slightly expand forward or shrink backward at the start points of the image stabilization periods TH 1 , TH 1 ′, TH 2 , TH 2 ′, Th 3 , and TH 3 ′. For example, the backlight module  114  may be switched from the off-state to the on-state before the start point of the image stabilization period. In summary, the backlight-on period of the backlight module  114  may expand forward at the start point of the image stabilization period and/or expand backward at the end point of the image stabilization period, and the length of the increment generating by expanding the original backlight-on period forward/backward depends on the design requirement. That is, by properly collaborating with the control mechanism used for controlling the pair of shutter glasses  100 , the backlight module  114  may stay in the on-state continuously or be switched between the on stage and the off-state alternately. 
     As shown in  FIG. 9 , the first shutter lens  102  is switched from the off-state to the on-state at the start point of the image stabilization period corresponding to the specific first image, and is switched from the on-state to the off-state after the end point of the image stabilization period. The second shutter lens  104  is switched from the off-state to the on-state at the start point of the image stabilization period corresponding to the specific second image, and is switched from the on-state to the off-state after the end point of the image stabilization period. However, it is not meant to be a limitation to the present invention. That is, like the exemplary embodiment shown in  FIG. 4 , the shutter-on period in which the first shutter lens  102 /the second shutter lens  104  stays in the on-state, as shown in the exemplary embodiment in  FIG. 9 , may also be expanded forward and/or backward to thereby increase the ambient brightness the user feels and decrease the power consumption of the pair of shutter glasses  100 . Please refer to  FIG. 11 , which is a sequence diagram of the sixth control method employed for controlling the pair of shutter glasses shown in  FIG. 1 . Similarly, like the exemplary embodiment shown in  FIG. 9 , the first shutter lens  102  and the second shutter lens  104  both stay in the off-state only within a single continuous time period (e.g., P 1 , P 2  or P 3 ) of the image driving period (e.g., TP 1 ′, TP 2 ′ or TP 3 ′) corresponding to the specific second image (e.g., R 1 , R 2  or R 3 ). Besides, the aforementioned single continuous time period (e.g., P 1 , P 2  or P 3 ) is at least partly overlapped with the backlight-off period that the backlight module  114  stays in the off-state. In the present exemplary embodiment, the single continuous time period when the first shutter lens  102  and the second shutter lens  104  both stay in the on-state totally lies within the backlight-off period of the backlight module  114 . 
     Please note that the exemplary embodiment shown in  FIG. 11  is for illustrative purposes only, and is not meant to be a limitation to the present invention. That is, under the premise of not departing from the spirit of the present invention, changes/modifications made to the exemplary embodiment shown in  FIG. 9  are feasible. In other words, it is not necessary to make the shutter-on periods of the first shutter lens  102  and the second shutter lens  104  expand forward and/or backward together. These alternative designs all fall within the scope of the present invention. Besides, since those skilled in the art will readily understand other alternative designs after reading above paragraphs, further description is omitted here for brevity. 
     In the exemplary embodiments described above, within the image stabilization periods such as TH 1 , TH 1 ′, TH 2 , TH 2 ′, TH 3 , and TH 3 ′, the user is allowed to view images mainly by the enabling of the backlight module  114 . Regarding the first shutter lens  102 /the second shutter lens  104  within the shutter-on period, the liquid crystal cells in the liquid crystal layer of the first shutter lens  102 /the second shutter lens  104  start rotating before the image stabilization period for making the first shutter lens  102 /the second shutter lens  104  be switched from the off-state to the on-state, and start rotating after the image stabilization period for making the first shutter lens  102 /the second shutter lens  104  be switched from the on-state to the off-state. In this way, when the user views images within the image stabilization periods, the present invention may further decrease the brightness attenuation induced due to the response time period (i.e., the rotating process) of the liquid crystal cells. 
     Moreover, in order to maintain the same brightness user&#39;s left eye and right eye perceive, in the exemplary embodiment, the ratio of the shutter-on period in which the first shutter lens  102  stays in the on-state to the shutter-off period in which the first shutter lens  102  stays in the off-state is substantially equal to the ratio of the shutter-on period in which the second shutter lens  104  stays in the on-state to the shutter-off period in which the second shutter lens  104  stays in the off-state. In other words, in the process that each of the first shutter lens  102  and the second shutter lens  104  continuously is switched between the on-state and the off-state, a total length of shutter-on periods that the first shutter lens  102  stays in the on-state is substantially equal to a total length of shutter-on periods that the second shutter lens  104  stays in the on-state (on the other hand, a total length of shutter-off periods that the first shutter lens  102  stays in the off-state is substantially equal to a total length of shutter-off periods that the second shutter lens  104  stays in the off-state). Since the lengths of integral shutter-on/shutter-off periods that the first shutter lens  102  and the second shutter lens  104  stay in the on-state/off-state are the same, user&#39;s left eye and right eye would feel the same brightness. However, it is only utilized as an exemplary embodiment, and is not meant to be a limitation to the present invention. For example, under the condition where the length of an integral shutter-on/shutter-off period of the first shutter lens  102  is equal to the length of an integral shutter-on/shutter-off period of the second shutter lens  104 , the number of shutter-on times and the number of shutter-off times of the first shutter lens  102  are not required to be equal to the number of shutter-on times and the number of shutter-off times of the second shutter lens  104 , respectively. 
     Besides, switching on and switching off the first shutter lens  102  and the second shutter lens  104  will determine the brightness perceived by the user Therefore, under the premise of increasing the shutter-on periods of the pair of shutter glasses, the number of shutter-on times, the number of shutter-off times, the ratio of the shutter-on period to the shutter-off period and/or the glasses cycle (i.e., the cycle that the left eye and the right eye respectively view the image once) of the first shutter lens  102  and the second shutter lens  104  are adjustable, thereby achieving the objective of adjusting the ambient brightness perceived by the user. 
     Please note that, as to the video output apparatus  110  operated under a lower refresh rate (e.g., 120 Hz) in the exemplary embodiment described above, a glasses cycle (i.e., the cycle that the left eye and the right eye respectively view the image once) is mainly composed of image output periods of two images. As to the video output apparatus  110  operated under a higher refresh rate (e.g., 240 Hz) in the exemplary embodiment described above, a glasses cycle (i.e., the cycle that the left eye and the right eye respectively view the image once) is mainly composed of image output periods of four images. However, these are for illustrative purposes only, and are not meant to be limitations to the present invention. For example, regarding the video output apparatus  110  that is operated under a lower refresh rate (e.g., 120 Hz), a glasses cycle may also be composed of image output periods of four or six images. In addition, one of the several aforementioned control methods or their combination may be employed to control the pair of shutter glasses  100 . The same objective of increasing the shutter-on periods of the pair of shutter glasses is achieved. In brief, the periodicity of the pair of shutter glasses  100  does not necessarily the same as the periodicity of image signals. 
     In addition, in the present invention, the on-state and the off-state of the backlight module  114  are not limited to fully switching on the backlight module  114  to make the backlight module  114  have 100% brightness output and fully switching off the backlight module  114  to make the backlight module  114  have 0% brightness output, respectively. For example, when the brightness output of the backlight module  114  is higher than a certain value (such as 80% brightness output), the backlight module  114  may be regarded as entering the on-state; besides, when the brightness output of the backlight module  114  is lower than a certain value (such as 20% brightness output), the backlight module  114  may be regarded as entering the off-state. In brief, the on-state and the off-state of the backlight module  114  may be defined according to the actual design requirement/consideration. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.