The present invention relates to a video display device. More specifically, the present invention relates to a video display device that can display a three-dimensional video by utilizing a time-sharing display approach and prevent an image quality from deteriorating due to the occurrence of a crosstalk.
In recent years, a video display device has been developed proactively which would display a three-dimensional video by using a plasma display panel (hereinafter abbreviated as a “PDP”). To display a three-dimensional video by the video display device, the time-sharing display approach is typically used. By the time-sharing display approach, different videos are alternately displayed to the user of the video display device so that he may perceive a three-dimensional video. The video to be displayed includes a right-eye video and a left-eye video which have a difference in parallax from each other. The user wears shutter-attached glasses to appreciate the video which is displayed. The shutter-attached glasses include a shutter which blocks the viewfield of his right eye and that which blocks the viewfield of his left eye. When the right-eye video is displayed, the left-eye side shutter is closed so that the relevant video may be seen by his right eye, and when the left-eye video is displayed, the right-eye side shutter is closed so that the relevant video may be seen by his left eye.
The following will specifically describe processing in which the video display device displays a three-dimensional video. The video display device opens/closes the LCD filter shutters respectively disposed to a right-eye lens and a left-eye lens in synchronization with the timing at which the right-eye video and the left-eye video to be displayed on a display panel are switched from each other. That is, in synchronization with the timing at which the right-eye image is switched on, the LCD filter shutter disposed to the right-eye lens is opened to let the light pass through and the LCD filter shutter disposed to the left-eye lens is closed to block the light, thereby permitting the right-eye video to be seen only by the right eye. In synchronization with the timing at which the left-eye image is switched on, the LCD filter shutter disposed to the left-eye lens is opened to let the light pass through and the LCD filter shutter disposed to the right-eye lens is closed to block the light, thereby permitting the left-eye video to be seen only by the left eye. The timing at which the right-eye video and the left-eye video are switched on/off and the timing at which the LCD filter shutters are opened/closed are synchronized with each other by connecting the display panel and the pair of glasses wirelessly by or wiredly. By repeating it continually, the viewer can see a three-dimensional video based on the right-eye video and the left-eye video.
One of the problems of the video display device for displaying videos is a crosstalk. A crosstalk occurs if the right-eye video or the left-eye video is perceived visually on the left eye or the right eye respectively. If a crosstalk occurs, the user cannot correctly appreciate the three-dimensional video.
A crosstalk occurs mainly owing to an afterglow of the video. More precisely, it occurs due to an afterglow produced by picture elements of the PDP. A video appears on the PDP when a video signal is applied to the PDP. On the PDP, a phosphor formed of a lot of picture elements is disposed. When the phosphor emits light in continual patterns, the PDP expresses a video. However, the surface of the phosphor has properties that light stays behind slightly. Therefore, even after the video signal is switched off, the PDP still displays the previous video even for a short lapse of time. That is, by the time-sharing display approach, the left-eye video filters in the right-eye video. Further, the right-eye video may possibly filter in the left-eye video. A video generated by the filtering in is referred to as a crosstalk.
To solve the problem of such a crosstalk, various solutions have been worked out. The typical one is a method described in, for example, Unexamined Japanese Patent Publication No. 2001-54142, by which a crosstalk due to the previous video is subtracted from the subsequent video. An input video is multiplied by coefficient α to calculate a crosstalk and the crosstalk is subtracted from the subsequent video. If the value of coefficient α can be defined precisely, the crosstalk can be prevented logically.
However, even this conventional technology cannot solve the problem of the crosstalk. That is, in Unexamined Japanese Patent Publication No. 2001-54142, coefficient α to calculate a crosstalk is assumed to be calculated inductively from a video signal beforehand. It is considered that if coefficient α corresponding to the video signal is predetermined, the crosstalk can be prevented logically.
However, on the PDP, a crosstalk is not simply determined uniquely from the video signal. That is, the PDP employs a drive method by use of subfields, so that the same video may possibly be expressed with the different video signals A and B. Therefore, a crosstalk of a video expressed with the video signal A may possibly be different from that of a video expressed with the video signal B.
A reason why the same video has different crosstalks will be described in detail as follows. The PDP performs operations to superimpose a plurality of different videos (subfields) which are switched on momentarily. This display method is referred to as the subfield method. The user would perceive the combined subfield as one sheet of video.
The drive method by use of subfields will be outlined as follows. The purpose of using the drive method by use of subfields is to express the gradation of a video by displaying a plurality of subfields in different period. Typically, four to 14 subfields are used for one sheet of video. Each sheet of the subfield has a different display period. A method for setting the period will be described as follows. The PDP displays an image only momentarily each time it discharges. The number of times the discharge is performed during the subfield may be said to give the period of time to display the subfield. The number of times of performing discharge (=number of times of emitting light) is referred to as the weight of the subfield. For example, assuming that the eight sheets of subfield are displayed sequentially and their weights are set in order of 1, 2, 4, 8, 16, 32, 64, and 128. Such setting enables expressing 256 levels of gradation. For example, to display a video having a brightness of 10, the second and fourth subfield can be displayed.
Taking into account the characteristics of the subfield method, the technology described in Unexamined Japanese Patent Publication No. 2001-54142 described above cannot be applied as it is. Because they have the different order of subfield weighting and the different filtering-in amounts for the subfields to be displayed. As described above, an afterglow occurs on a video. The subfield is one kind of video. Therefore, precisely, the PDP involves generation of afterglows having the different characteristics of the different sheets of subfields not of the video signal. That is, for example, it is understood that the order in which the subfields are weighted has a large influence on a crosstalk.
That is, the conventional technologies have not completely been able to prevent the crosstalk on the PDP. Therefore, there has been a problem in that the user cannot correctly appreciate the three-dimensional video.
A video signal processing device of the present invention includes a subfield conversion unit, a drive parameter setting unit, a calculation unit, and a subtraction unit. The subfield conversion unit converts a frame signal, which is a video signal corresponding to one frame of video, into a plurality of subfields corresponding to the frame signal. The drive parameter setting unit sets a luminance weight and a light emitting position in the plurality of subfields for each of the plurality of subfields. The calculation unit calculates the filtering-in amount of the frame signal corresponding to the plurality of subfields based on a signal level of the frame signal as well as the setup luminance weight and light emitting position. The subtraction unit subtracts the filtering-in amount from a signal level of a frame signal input to the subfield conversion unit subsequent to the frame signal.
By such a configuration, the filtering-in amounts for the subfields are summed and subtracted from the subsequent frame, so that the filtering-in amount can be reduced accurately. As a result, it is possible to prevent a crosstalk from occurring between the frames.
The following will describe one exemplary embodiment of the present invention with reference to the drawings.
First, a description will be given of a configuration of a video signal processing device of the present exemplary embodiment with reference to
Input unit 101 is supplied with a video signal. The video signal is formed of various components. The video signal may be, for example, a signal obtained by decoding a broadcast signal or may be a signal sent from a hard disk drive or media player connected inside or outside. The video signal is any one of the three primary color signals and the other two primary color signals may undergo almost the same signal processing. The video signal supplied to input unit 101 is transferred to frame memory 102 and addition unit 103.
Frame memory 102 extracts and accumulates one frame worth of video signal (hereinafter abbreviated as “frame signal”). Frame memory 102 extracts the frame signal from the video signal transferred from input unit 101. The frame signal is accumulated in frame memory 102 until the subsequent frame is written. The accumulated frame signal is transferred to combination unit 109 at the timing when the subsequent frame signal is written. That is, the video signal undergoes delay processing as much as one frame worth in frame memory 102.
Addition unit 103 subtracts a filtering-in amount from the video signal to produce a second video signal. The filtering-in amount refers to a signal level of afterglow that contributes to a crosstalk. Specifically, the filtering-in amount is calculated by spuriously converting a component of afterglow generated in the previous frame that is mixed into a video to be displayed in the subsequent frame into a video signal level. The second video signal is transferred to subfield conversion unit 104. The filtering-in amount calculation method will be described in detail later.
Subfield conversion unit 104 converts the second video signal into a subfield signal for each frame.
A description will be given of subfield signal 200 with reference to
Subfield conversion unit 104 determines which subfield is to make panel 107 emit light. For example, it determines that subfields 203 and 204 are to make the panel emit light for frames of the input second video signal (subfields 202, 205, and 206 are not lit up). That is, the fact that subfield conversion unit 104 converts the second video signal into the subfield signal for each frame involves the generation of information to the effect that which subfield is to make panel 107 emit light and which subfield is not to make it emit light in the relevant frame. Generally, the more brightly a frame displays a video, the more subfields it has to make panel 107 emit light. The number of times a specific one of the subfields is to make panel 107 emit light (how many pulses are included in each subfield) is set by drive parameter setting unit 105 described below. Subfield signal 200 is transferred to panel drive unit 106. As described above, subfield conversion unit 104 converts the frame signal, which is a video signal corresponding to one frame of video, into a plurality of subfields corresponding to the frame signal.
Drive parameter setting unit 105 generates a drive parameter. The drive parameter is information that relates to weights and light emitting positions of subfields 202 to 206. The weight of the subfield is a setting of the number of times a specific subfield is to make panel 107 emit light. That is, it is the setting of how many pulses to make panel 107 emit light are included in each subfield. Further, the light emitting position of the subfield denotes the timing at which the subfield makes panel 107 emit light in a one frame of period of time. The weight and the light emitting position are determined by a setup state in which the video signal processing device is set. This setup state can be set also by the user of the video signal processing device. For example, an adjustment of the image quality of a video which is displayed on panel 107 has an influence on the parameters of the weight and the light emitting position. The drive parameter is input to panel drive unit 106 and calculation unit 108. As described above, drive parameter setting unit 105 sets a luminance weight and a light emitting position in a plurality of subfield for the individual one of the plurality of subfields.
Further, drive parameter setting unit 105 includes a circuit for controlling the shutter-attached glasses and a circuit for transmitting a control signal of the glasses. Those circuits switches the timing at which the shutter of the LCD filter disposed to each of a right-eye lens and a left-eye lens is opened/closed in synchronization with the timing at which a right-eye video and a left-eye video to be displayed on the display panel are switched from each other. That is, it opens the LCD filter shutter on the right-eye lens in synchronization with the timing at which the right-eye video is switched on so that the light may pass through and then closes the LCD filter shutter on the left-eye lens so that the light may be blocked, thereby permitting only the right eye to see the right-eye video. It opens the LCD filter shutter on the left-eye lens in synchronization with the timing at which the left-eye video is switched on so that the light may pass through and then closes the LCD filter shutter on the right-eye lens so that the light may be blocked, thereby permitting only the left eye to see the right-eye video.
Panel drive unit 106 generates a signal which drives panel 107 based on the subfield signal and the drive parameter. The subfield signal transferred from subfield conversion unit 104 includes information to the effect that which subfield is to make panel 107 emit light. The drive parameter transferred from drive parameter setting unit 105 includes information about the weight and the light emitting position of the subfield.
The following will describe one example where panel drive unit 106 generates a signal which drives panel 107. For example, it is assumed that the subfield signal includes the information to the effect that subfields 203 and 204 are to make panel 107 emit light. It is assumed that the drive parameter includes the information to the effect that subfields 202, 203, 204, 205, and 206 are to make panel 107 emit light 8 times, 128 times, 64 times, 32 times and 16 times respectively and the information about the light emitting order and timing of subfields 202 to 206. Then, panel drive unit 106 controls panel 107 so that it may emit light 128 times at the light emitting timing of subfield 203 and 64 times at the light emitting timing of subfield 204.
Panel 107 emits light under the control of panel drive unit 106. The scope in which the present invention is applied is not limited to a plasma display panel but broadly covers displays which are driven by the drive method by use of subfields.
Calculation unit 108 is configured to set the value of coefficient α in accordance with the drive parameter. The value of coefficient α is set on the basis of a luminance weight and a light emitting position. The value of coefficient α will be described in detail with reference to
From
If attention is focused on afterglows 301 to 305 individually, it may be understood that some of them have an afterglow amount even after the subsequent frame starts. Specifically, afterglow 301 is based on the subfield that makes the panel emit light first in the current frame and has a smaller number of times of light emission and, therefore, gives little afterglow to the subsequent frame.
On the other side, afterglow 305 is based on the subfield that makes the panel last in the current frame and has a larger number of times of light emission and, therefore, gives about a half of the maximum afterglow amount at the start of the subsequent frame. A sum of the afterglow amounts of afterglows 301 to 305 at a predetermined point in time in the subsequent frame gives a filtering-in amount. This predetermined point in time should preferably be a point in time when a video corresponding to the subsequent frame is displayed in this subsequent frame and the user would perceive it. A value corresponding to a sum of the afterglow amounts of afterglows 301 to 305 at the predetermined point in time in the subsequent frame gives the value of coefficient α. The value of coefficient α is not the sum itself of the afterglow amounts that occurred in the subfields but corresponds to the amount of an afterglow that occurred in the subfields and is determined from a sum of the afterglow amounts at the predetermined point in time. That is, if the sum of the afterglow amounts that occur in the subfields of the subfield signal is the same as that of the other subfield signal, they have the same value of α.
Although the value of coefficient α has been described schematically with reference to
As described above, calculation unit 108 calculates filtering-in amounts of the frame signals corresponding to a plurality of the subfields based on the signal level of the frame signal, the setup luminance weight, and the light emitting position. Further, the calculation unit 108 calculates a greater amount of the setup luminance weight at the greater filtering-in amount of the frame signal. The value of coefficient α calculated by calculation unit 108 is transferred to combination unit 109.
Combination unit 109 obtains a filtering-in amount by computing the frame signal delayed in frame memory 102 and the value of coefficient α. One example will be described for obtaining the filtering-in amount by multiplying the frame signal and the value of coefficient α. The frame signal includes the values of signal levels of a plurality of picture elements. It is assumed that the green signal level of one of the picture elements is 100. If the value of coefficient α is assumed to be 0.1, the filtering-in amount becomes 10. By performing this computation on all of the picture elements, the frame signal is formed in which the signal levels of the picture elements are each multiplied by 0.1. This formed frame signal provides a filtering-in amount. The frame signal is delayed in frame memory 102 in order to calculate the filtering-in amount of the relevant frame signal by computing a sum of the afterglow amounts occurring due to this frame signal by feeding back the sum to this frame signal. The calculated filtering-in amount is transferred to addition unit 103.
As described above, addition unit 103 subtracts the filtering-in amount from the video signal to generate a second video signal. Therefore, the filtering-in amount of the previous frame signal is subtracted from that of the current frame signal. That is, addition unit 103 is substantially a subtraction unit and subtracts the filtering-in amount from a signal level of a frame signal input to the subfield conversion unit subsequent to the frame signal.
A description will be given to operations of the equipment by using the above-described video signal processing device with reference to an example of processing a three-dimensional video signal.
The three-dimensional video signal is a video signal having a right-eye video frame and a left-eye video frame. The right-eye video frame and the left-eye video frame are input to input unit 101 alternately. Panel 107 displays a right-eye video and a left-eye video alternately.
The user wears the shutter-attached glasses to appreciate the displayed video. The shutter-attached glasses include a shutter which blocks the right-eye viewfield and a shutter which blocks the left-eye viewfield. If the right-eye video is displayed, the left-eye shutter is closed so that this right-eye video may be seen on the right eye. If the left-eye video is displayed, the right-eye shutter is closed so that this left-eye video may be seen on the left eye.
In
Comparison between the middle stage and the bottom stage in
As described above, calculation unit 108 calculates the value of coefficient α based on the drive parameter set to subfield signal 400. This value of coefficient α should preferably be calculated at the timing when the right-eye shutter is opened in the right-eye video frame subsequent to the left-eye video frame. This is because the user perceives the right-eye video when the right-eye shutter is opened and, simultaneously, perceives the afterglows, that is, the filtering-in amounts of the subfields of subfield signal 400. As described above, the calculation unit 108 calculates a smaller amount of the filtering-in amount at a greater distance of the light emitting position from a shutter open timing in a frame period subsequent to the frame signal.
The thus calculated value of coefficient α is computed with the left-eye video signal accumulated in frame memory 102 to determine a filtering-in amount occurring due to subfield signal 400. The obtained filtering-in amount is subtracted from a signal level of the subsequent right-eye video signal. In such a manner, the filtering-in amount occurring due to subfield signal 400 in the left-eye video frame is subtracted from the subsequent right-eye video signal, thereby solving the problem of crosstalks.
The shutter is opened at a timing that provides a starting point at which coefficient α corresponding to a sum of afterglows shown in
That is, preferably drive parameter setting unit 105 should completely open the shutter on the glasses on the side corresponding to a video of the current frame before the end of first address portion 510 included in the subfield ends. In such a manner, the starting point at which coefficient α is calculated can be set later, thereby reducing the value of coefficient α. As a result, it is possible to suppress the occurrence of a crosstalk in the subsequent frame. Further, the timing at which the shutter corresponding to a video of the current frame of the shutter-attached glasses starts to be closed can be made a timing at which the fifth subfield (5SF) providing the last light emitting period in the frame completes.
As hereinabove described, the video signal processing device of the present exemplary embodiment calculates a sum of filtering-in amounts due to the subfields and subtracts it from a signal level of the subsequent frame and, therefore, can reduce the filtering-in amount accurately. As a result, it is possible to prevent a crosstalk from occurring between the video frames.
The video signal processing described with reference to the present exemplary embodiment solves the problems of crosstalks between the video frames and, therefore, is well suited in particular for applications involving the processing of a three-dimensional video signal including a left-eye video signal and a right-eye video signal. However, there is a case where dissipation power may possibly increase due to such video signal processing always. Therefore, a configuration to detect the type of the video signal may be added separately to decide whether the video signal is of a three-dimensional video and, if so, perform the video signal processing.
There is a case where a video may blur due to a crosstalk between the current frame and the subsequent frame also in the processing of an ordinary video signal not of a three-dimensional video, so that it is possible to apply the video signal processing described with reference to the present exemplary embodiment to the processing of the ordinary video signal.
Further, as shown in
Further, as described above, the larger the luminance weight is, the larger the afterglow amount becomes. Therefore, by disposing a subfield having a luminance weight equal to or greater than a predetermined value in the first half of one frame, coefficient α can be reduced sufficiently. In this case, the predetermined luminance weight value may be set to, for example, a half of the maximum luminance weight. Therefore, drive parameter setting unit 105 may dispose a subfield having equal to or greater than the predetermined luminance weight value in the first half of one frame and may dispose a subfield having the smaller luminance weight than the predetermined value in a latter half of the one frame. Furthermore, drive parameter setting unit 105 may dispose the subfield having equal to or greater than the predetermined luminance weight value in the first half of one frame and the subfields having the smaller luminance weight than the predetermined value in the latter half of the one frame in descending order of the luminance weight. By disposing the subfields in such a manner, coefficient α, which corresponds to the sum of the afterglows, can be reduced. As a result it is possible to prevent a crosstalk from occurring between the video frames.
Number | Date | Country | Kind |
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JP 2011-041355 | Feb 2011 | JP | national |