JP2005275357A - Device and method for video display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform proper masking display without using a frame memory and to enable real-time letter box display even with a video signal whose vertical blanking period is very short. <P>SOLUTION: A video display device which reads in a video signal and displays it on a display part through line sequential scanning generates a clock for timing the display of the video signal with respective pixels of the display part, compresses effective scanning line areas in nearly the same time with an effective scanning line period to display the video part of the display part, and increases the frequency of the clock in a vertical blanking period to display a non-video part of the display part. The clock frequency of the video part and the clock frequency of the non-video part are made different from each other. Further, scanning of the video part and scanning of the non-video part are equalized in horizontal frequency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a video display device that appropriately displays various video signals and a video display method thereof.

  In recent years, the broadcasting system has also become various, and the specifications of the video signal sent are also various. For this reason, it is required that a single video display device displays an appropriate video corresponding to various video signals.

  In the current market, there are video display devices such as televisions and PC monitors with screen sizes of 4: 3, 5: 4, and 16: 9 (hereinafter simply referred to as A: B). A: B.), Video signals transmitted to these video display devices are subjected to resolution conversion such as compression and decompression called scaling, and video of other screen sizes. Displayed on the display device. Currently, 4: 3 is adopted for terrestrial broadcasting and the like, and 16: 9 is adopted for high-definition broadcasting.

  For example, when displayed on a 16: 9 video display device, a plurality of perfect circles are displayed as shown in FIG. 11C. A video signal diagram 11a for a 16: 9 video display device is shown in 4: 3. When displayed as it is on the video display device, a plurality of perfect circles are displayed in a vertically long ellipse as shown in FIG. This is because if the number of 4: 3 and 16: 9 vertical display lines is the same, the display time per line will be the same, so a 4: 3 video display device is a 16: 9 video display device. This is because if the video signal for use is projected as it is, the video display is compressed in the horizontal direction. Conversely, when a 4: 3 video display device is used to display a 4: 3 video signal display image 12a for a 4: 3 video display device in which a plurality of perfect circles are displayed as shown in FIG. When displayed as it is on the video display device, a plurality of perfect circles are displayed in a horizontally long ellipse as shown in FIG.

  Therefore, when a video signal as shown in FIG. 11A for a 16: 9 video display device is displayed on a 4: 3 video display device while maintaining roundness, the video signal is generally vertically scaled by scaling. In addition, the display image 131 is displayed as shown in FIG. Such display is called letterbox display.

  Similarly, when a video signal as shown in FIG. 12A for a 4: 3 video display device is displayed on a 16: 9 video display device while maintaining roundness, the left and right sides of the display video 141 are black bands. Display as shown in FIG. 14 masked by 142 and 143 is performed.

  In FIG. 11 and FIG. 12, 1V is one vertical period that is a time for displaying one frame of a video signal, and 1H is one horizontal period that is a time for displaying one line of a video signal.

  Here, taking a liquid crystal display device as an example of the video display device, details of general video display and letterbox display will be described.

  As shown in FIG. 15, the liquid crystal display device includes a signal line driving circuit 152 that drives signal lines of the liquid crystal panel 151 and a scanning line driving circuit 153 that drives scanning lines of the liquid crystal panel 151. In a state where the scanning line is being scanned, the signal line driver circuit outputs a gradation voltage corresponding to the input video signal to any one of the signal lines, so that the gradation is applied to the pixel electrode through the TFT which is in the on state. The regulated voltage is written, and the amount of light transmission is controlled by the potential difference between the common electrode set to a constant potential and the pixel electrode to which the gradation voltage is applied, and a desired pixel display is performed.

  As shown in FIG. 16, the video signal is transmitted as a × b (all scanning lines a, number of clocks b per line), and an effective scanning period (effective scanning lines x, 1 The number of clocks per line y) and a blanking period (there is a horizontal blanking period Hb and a vertical blanking period Vb). In the horizontal blanking period Hb, a horizontal synchronizing signal which is a write synchronizing signal for one line. However, the vertical blanking period Vb includes a vertical synchronization signal which is a one-frame write synchronization signal. A region including x lines is referred to as an effective scanning line region, and a region including lines ax is referred to as a blanking region. Video signal types are 525i (525 scanning lines, 480 effective scanning lines), 525p (525 scanning lines, 480 effective scanning lines), 750p (750 scanning lines, effective) depending on the scanning method. There are 720 scanning lines), 1125i (1125 scanning lines, 1080 effective scanning lines), and the like.

  When a video signal is input to the liquid crystal display device configured as shown in FIG. 15, as shown in FIG. 17, a gate start pulse signal (hereinafter referred to as GSP) generated based on the vertical synchronization signal of the video signal is displayed. As a reference, the video signal of the first line is stored in the signal line drive circuit 152 and then written to the first line of the liquid crystal panels 151 and 171 and generated based on the horizontal synchronization signal (hereinafter referred to as GCK). ), The writing line is shifted to the second line, the third line,..., And when the liquid crystal panels 151 and 171 are VGA panels, for example, the writing lines are shifted to 480 lines. In this way, the liquid crystal display device displays the video signal.

  Next, for example, when displaying a 4: 3 video signal for a video display device on a 16: 9 video display device and letterbox display with the black and white portions 142 and 143 masking the left and right sides of the display video 141 as shown in FIG. After the video signal is compressed in the horizontal direction, as shown in FIG. 18, black is written with j clocks in the first half and the latter half of one horizontal period, and the video signal is written with i clocks therebetween. The above writing is performed in timing with a clock (CLK) that is constantly generated in the video display device, and in principle, one pixel is written in one clock (hence, also referred to as pixel clock, pixel clock, etc.). .

  However, in order to display a video signal for a 16: 9 video display device with a 4: 3 video display device in which the upper and lower sides of the display video 131 are masked by the black belt portions 132 and 133 as shown in FIG. There is a problem like this.

  When a video signal for a 16: 9 video display device that is horizontally compressed when displayed on a 4: 3 video display device as shown in FIG. 19A is read and compressed as shown in FIG. 19B In order to perform the display in real time, the writing time of the compressed video portion (the portion displaying a plurality of perfect circles) must be the same as the reading time of the transmitted video signal (referred to as “T” time). I must. When the liquid crystal panel is a VGA panel, the time for reading a video signal of 480 lines that is not compressed and the time for displaying 360 lines of an image portion compressed 3/4 times in the vertical direction of the screen are the same T time. Then, in order to display 480 lines including the black belt portion in FIG. 19 (b), originally (4/3) × T time is required, and accordingly, the GSP generation period is the length including the black belt portion. This period must be secured (FIG. 20). As can be seen from FIG. 20, the GSP generated in synchronization with one vertical period V starts, for example, prior to the start time of the vertical period A in FIG. Must be generated as follows. In addition, the writing of the image started in this way is continued even after the end time of the vertical period A has elapsed. If an image is displayed using such a GSP, the video signal of the next frame is input before the scanning for one frame is completed, and normal display cannot be performed.

  This phenomenon will be described with reference to FIG. 21 by following the actual writing scan. First, a GSP is generated to display an image in the vertical period A, but the GSP is started earlier by the time secured for inserting the black band portion. (A ′ in FIG. 21). Then, the video signal writing scan is performed by selecting GCKn started in synchronization with GSPa ′. At this time, GSPa ′ is started earlier than the start time of the vertical period A. The video signal for the period is written.

  On the other hand, the writing scan period for one screen by the selection of GCKn-1 is also long in consideration of the insertion of the black belt portion, and the writing scanning period for one screen by the selection of GCKn-1 is not completed until the selection of GCKn. By starting the writing scan for one screen, two lines of the first line and about the 400th line are simultaneously turned on, and the same video signal is written (FIG. 22). The video signal is written as it is for two lines at the same time. After that, the black band in the vertical blanking period is written, the video (1) in the vertical period A is written by selecting GCKn-1, and the scanning is completed. The video (2), (3)... In the vertical period A is written by selecting GCKn. Then, when scanning is completed between a 'and b', the image displayed on the screen is as shown in FIG. The reason why scanning by selecting GCKn-1 does not end when GSPa 'is generated is that a DC voltage is applied when writing is stopped halfway, so that it is necessary to scan to the last line to prevent this. It is.

  The above-described problems have been solved by using a conventional frame memory. This will be described with reference to FIG.

  The input video signal is compressed by the scaler 244 for one frame of the video signal in the vertical direction, for example, 3/4 times, and the compressed video signal for one frame is stored in the frame memory 245. Since the compressed video signal is read from the frame memory and written in (3/4) T time, the total including the black belt portions 132 and 133 can be displayed in T time.

  In this way, an appropriate letterbox display can be performed by using the frame memory, but there is a drawback that the frame memory itself is very expensive. In addition, since it is stored in the frame memory and then displayed, there is a disadvantage that real-time letterbox display cannot be performed and a delay occurs between reading and display of the video signal.

  Therefore, there is a high expectation for an image display device that can appropriately perform letterbox display in real time without using an expensive member such as a frame memory, and many attempts have been made so far to solve the above problems. ing.

  For example, the liquid crystal display device of patent document 1 is mentioned as the example. A block diagram of this liquid crystal display device is shown in FIG. 25, and its operation will be described with reference to FIG.

  When a video signal is input to the liquid crystal display device (assuming that the video signal shown in FIG. 16 is input), the number of effective scanning lines (x) of the input video signal and the display capability scan of the liquid crystal panel 251 are scanned. The number of lines (n) is compared by the scanning line number discrimination circuit 256. When it is determined by the scanning line number determination circuit 256 that x <n, the following operation is performed so that the black belt portion can be displayed in the short vertical blanking period Vb in order to perform letterbox display as shown in FIG. I do.

  First, the blanking control circuit 257 gives a black signal to the signal line driver circuit 252. In the vertical blanking period Vb, a period for increasing the GCK period of the scanning line driving circuit 253 by the high-speed scanning line driving circuit 255 is provided (262 in FIG. 26). At the same time, the period of the GCK period is high. In order to turn off the switching element of the liquid crystal panel 251, the output of the scanning voltage generation circuit 254 is fixed to the off voltage (263 in FIG. 26). In the vertical blanking period Vb, in addition to the high-speed GCK period, a period for generating GCK having the same period as that for writing in the video portion is provided (264 in FIG. 26). The normal GCK generation period is the liquid crystal panel 251. The switching element is turned on, and the black signal applied to the signal line driver circuit 252 is written in the line selected by the scanning line driver circuit 253. This writing line is changed for each frame. For example, in one frame, a black line is written immediately after the vertical blanking period Vb as shown in FIG. 26A, and in the next frame, it is written in FIG. 26A as shown in FIG. Write a black line from the next line. As shown in FIG. 26 (c), an appropriate letterbox display is displayed in real time as an image to be displayed in one vertical period by changing the black writing line for each frame so that the black writing line is distributed over the black belt portion. To be made.

  The display of the black band portion is based on so-called frame thinning driving, and the voltage once applied to the switching element of the liquid crystal panel 251 is not changed as long as the switching element is in an off state, and thus a certain frame is displayed. The line in which black is written is kept in the off state in another frame, so that the black display of the line is held in another frame.

  The reason why the GCK is operated at high speed in the vertical blanking period Vb is the same as the video part because the vertical blanking period Vb for displaying the black belt portion is very short as described above. This is because the display is as shown in FIG. 23 when written in GCK. Therefore, a period during which GCK is operated at high speed is provided to display the black belt portion with an appropriate width.

  In Patent Document 2, a normally black liquid crystal panel is used as the liquid crystal panel 251 in FIG. 25 in the above Patent Document 1, and the entire period of the vertical blanking period Vb in FIG. 26 is output from the scanning voltage generation circuit 254. Is fixed to an off-voltage, and the GCK cycle of the scanning line driver circuit 253 is made faster. Accordingly, since the switching element remains off, the signal from the signal line driver circuit 252 is not written, and during that period, black, which is a color displayed when no signal is written, is displayed. In this way, although black is not written, letterbox display can be made appropriate without using a frame memory.

  Further, as similar to Patent Document 1, black is written every several lines in the vertical blanking period Vb, and writing for each several lines is shifted for each frame (field sequence between frames), thereby maintaining the liquid crystal. There are some which perform letterbox display that does not require a frame memory by using (Patent Document 3 and Patent Document 4). Note that Patent Document 3 discloses a method of displaying black on a large number of horizontal lines in one horizontal period by using the fact that the horizontal period of VGA is longer than the horizontal period of SXGA, or a plurality of independent lines simultaneously. It also describes performing letterbox display without a frame memory by writing a black line.

In addition, the video signal and the discrimination flag for discriminating the aspect ratio thereof are read from the storage medium, and the 4: 3 full video display or 4: 3 letterbox display video signal is combined with the 16: 9 video display device. There is also a document disclosing a video signal reproduction apparatus that can display a correct aspect ratio and display subtitles (Patent Document 5).
Japanese Patent Laid-Open No. 10-187105 Japanese Patent Laid-Open No. 11-3064 JP 2001-142044 A JP-A-10-240195 Japanese Patent Laid-Open No. 2002-16884

  The technique of Patent Document 1 requires a special scanning line driving device that turns off or on the output of the scanning voltage generation circuit 254, and cannot use a general-purpose scanning line driving device, which also increases costs.

  In addition, black is not written to all the lines in the black belt portion in one frame, but uses the holding characteristics of the liquid crystal panel, so there are parts that depend on the performance of the liquid crystal panel (charge holding performance, etc.). In addition, not only can the black strips be displayed in full form on all types of display devices, including liquid crystal panels, but a special scanning line driving device is required to drive the scanning lines in a complex sequence. It becomes. This also applies to Patent Documents 3 and 4.

  The technique of Patent Document 2 utilizes the fact that the display color of the liquid crystal panel when no voltage is applied is black, and can only be realized with a normally black liquid crystal panel.

  Further, another letterbox display method that uses the difference between the horizontal period of the input signal and the horizontal period of the liquid crystal panel depends on the input video signal and the standard of the liquid crystal panel. When letterbox display is performed without a frame memory by simultaneously writing black lines on a plurality of independent lines, a gate driving device for simultaneously writing the plurality of lines is required.

  The present invention does not have the above-mentioned problems, and an image signal sent for a display device having a certain aspect ratio can be displayed in an appropriate manner in real time without using a frame memory on a video display device having a different aspect ratio. The purpose is to do.

  In order to achieve the above object, the present invention provides a video display device that reads a video signal having an effective scanning line period and a vertical blanking period and displays the video signal on a display unit by line-sequential scanning. A clock that takes a timing for displaying a video signal on each pixel is generated, and the effective scanning line area is compressed to display the video portion of the display unit at substantially the same time as the effective scanning line period, and the vertical blanking is performed. In the period, the non-video part of the display part is displayed by increasing the frequency of the clock.

  Further, the clock frequency in the video part and the clock frequency in the non-video part are made different.

  Further, the horizontal frequency is made equal between the scanning in the video portion and the scanning in the non-video portion.

  As a result, it is possible to increase the area of the non-video portion in the vertical blanking period, and to perform many displays in a short period. Therefore, it is possible to display an appropriate letterbox in real time. Further, it is not necessary to use an expensive member such as a frame memory.

  According to the present invention, an appropriate video display can be stably performed in real time in any video display device using any module for a display unit without using a frame memory.

First, the preconditions of the present invention are confirmed with reference to FIG. When the read video signal FIG. 19A is compressed in the vertical direction by, for example, 3/4 times and letterbox display as shown in FIG. 19B is performed in real time, it always takes the same T time as the read time. Therefore, the black belt portions 132 and 133 must be displayed in the vertical blanking period Vb shown in FIG. That is, when the writing times of the upper and lower black belt portions 132 and 133 are t1 and t2, respectively.

1V ≧ T + t1 + t2 (Formula 1)

It is necessary to satisfy. However, since the vertical blanking period Vb is a very short period in which the synchronization signal is usually inserted, the black belt portions 132 and 133 cannot be sufficiently displayed in this short period. In particular, when the scanning method is 750p, 1125i, since the ratio of the vertical blanking period Vb is smaller than that of 525i, 525p, the period for displaying the black belt portions 132 and 133 is further shorter. However, since 1V and T in (Expression 1) are unchanged, it is required to display the black belt portions 132 and 133 with an appropriate width during the period of t1 and t2.

  In the present invention, the vertical blanking period Vb refers to a period other than the period for displaying the effective scanning line x.

  An example of a block diagram of a video display device according to the present invention is shown in FIG. A display unit 11 such as a liquid crystal panel for displaying video, a controller 12 for driving and controlling the display unit 11, image processing such as image quality adjustment for the input video signal, and expansion / compression of the video signal 13 And a clock that synchronizes the number of lines (horizontal frequency) in which a video signal can be written to the display unit 11 per unit time and the writing timing of the video signal in units of pixels (pixels) that are constantly generated in the video display device ( CLK) The operation unit 17 that gives a command to change the frequency, the horizontal frequency adjustment unit 14 that sets the number of lines (horizontal frequency) that can be written per unit time, and the clock frequency are adjusted by the command of the operation unit 17 The clock frequency adjusting unit 15 that controls the horizontal frequency adjusting unit 14 and the clock frequency adjusting unit 15 are controlled based on a command from the operation unit 17. Comprising a microcomputer 16.

  In the present embodiment, the case where the display unit 11 is the liquid crystal panel 151 illustrated in FIG. 15 will be described as an example. In this case, the controller 12 corresponds to the signal line driving circuit 152 and the scanning line driving circuit 153 in FIG. Further, it is assumed that the aspect ratio of the display unit 11 is 4: 3.

  When the input video signal is a 4: 3 video signal shown in FIG. 12A, if there is no command from the operation unit 17, the image processing / scaler unit 13 can perform image quality adjustment without being expanded / compressed. After the display is performed, the display unit 11 performs a display maintaining the roundness as shown in FIG.

  When the input video signal is the 16: 9 video signal shown in FIG. 11A, when displayed on the display unit 11, the circle is compressed in the horizontal direction as shown in FIG. 11B. Therefore, it is desirable to perform letterbox display as shown in FIG. Therefore, when a circle is displayed in a compressed form in the horizontal direction as shown in FIG. 11B, a command to perform letterbox display is given by the operation unit 17 (a picture compressed in the horizontal direction is displayed). If it is desired to display, the operation unit 17 is not operated).

  In the present embodiment, when the letterbox display as shown in FIG. 13 is performed in real time, the clock frequency is set as a whole so that the black writing time is not too short and the inappropriate display as shown in FIG. As shown in FIG. 2, the number of clocks per line of the black belt portions 132 and 133 is changed from the normal b to c, which is smaller than b. That is, since the clock frequency adjusting unit 15 sets the clock frequency to f ′ higher than f, one clock period (1 / clock frequency) is shortened, and one pixel (pixel) black is written in one clock. The horizontal frequency adjusting unit 14 sets the (minimum necessary) number of clocks necessary for writing one line to the black belt portions 132 and 133 (increasing the horizontal frequency). As a result, the horizontal period for writing in one line of the black belt portions 132 and 133 is shortened. Since the time for writing to one line is shortened, the number of lines to be written can be increased and the width of the black belt portions 132 and 133 can be increased.

  The video signal is subjected to predetermined image processing by the image processing / scaler unit 13 and compressed in the vertical direction. The compression process is performed, for example, by thinning out lines. When this compressed video signal is displayed in letterbox, for example, if it is compressed 3/4 times in the vertical direction, the reading time of the video signal of one frame is the same as the writing time of the compressed video signal (T time (See FIG. 19), the horizontal period of the compressed video signal must be long. For example, when the display unit 11 is a VGA panel, the horizontal period when the video signal before compression is written is T / 480, while the horizontal period after compression is T / 360. Therefore, as shown in FIG. 2, in the letterbox display in which the upper and lower portions of the video portion 131 are masked by the black belt portions 132 and 133, the number of clocks per line when writing the video portion 131 is from the normal b to b. Let b 'be more. That is, the horizontal frequency adjusting unit 14 sets the number of clocks per line so that the time for writing one line to the video unit is T / 360 (lowering the horizontal frequency).

From the above, referring to FIG. 2, one vertical period is

V = ((3/4) x * b '+ (a- (3/4) x) * c) / f' (Formula 2)

It becomes. In addition, since the reading time of the input video signal and the writing time of the video portion 131 after compression are the same T time,

T = (x × b) / f = ((3/4) x × b ′) / f ′ (Formula 3)

Must hold. The relationship between the number of clocks b and b ′ per line satisfying (Expression 2) and (Expression 3) and the clock frequencies f and f ′ is as follows:

b <b ′, f <f ′ (Formula 4)

It becomes. By selecting the number of clocks c per line and the clock frequency f ′ satisfying the above expression, the video part 131 and the black band parts 132 and 133 can be displayed within the reading time of the input video signal (1 The number of clocks b ′ per line is uniquely determined by setting f ′). Note that the clock frequency of the black belt portions 132 and 133 and the video portion 131 during letterbox display is constant at f ′.

  The above contents will be described in more detail with reference to FIG. FIG. 3 shows GCK (gate clock) of each line based on the horizontal frequency set by the horizontal frequency adjusting unit 14 and a clock (CLK) based on the clock frequency of each line. GSP is a gate start pulse based on the vertical synchronizing signal of the input video signal. The 1-a line displays the upper black belt portion 132, the a + 1-b line displays the video portion 131, and the b + 1-c lines display the lower black belt portion 133, respectively. At the bottom of FIG. 3, GCK based on the horizontal synchronizing signal of the input video signal is shown as a reference, and each line of the input video signal has the number of clocks corresponding to i clocks.

  First, after setting the clock frequency to f ′, the black band portions 132 and 133 reduce the number of clocks per line so that each line includes (ij) clocks. 131 increases the number of clocks per line so that (i + k) clocks are included. That is, by changing the horizontal frequency between the video unit 131 and the masking units 132 and 133 (the clock frequency is constant at f ′), the number of clocks per line is different.

  Therefore, in order to make the total display time of the black strips 132 and 133 and the video part 131 in the letterbox display equal to the reading time of the input video signal, the total number of pixels (clocks) of the input video signal The number of clocks b ′ and c per line may be set so that the total number of pixels (clocks) in the letterbox image is equal. Note that, although the number of clocks per line is as small as possible, ij cannot be smaller than the number of pixels per line of the display unit 11.

Taking the example of the input video signal as shown in FIG. 16, the total number of all scanning lines of the input video signal is a, the total number of effective scanning lines is x, and the vertical blanking period. The total number of lines of Vb is a−x. When the video portion is compressed and displayed at 3/4 times as shown in FIG. 2, the total number of lines in the video portion is (3/4) x, and the total number of lines in the black belt portion is a- (3/4) x. The total number of pixels (clocks) of the input video signal “a × i” and the total number of pixels (clocks) of the letterbox image “(3/4) ×× (i + k) + (a− (3/4)” x) × (i−j) ”

a * i = (3/4) xx (i + k) + (a- (3/4) x) * (ij) (Formula 5)

It becomes.

Further, the total number of pixels (clocks) “(3/4) x × (i + k)” in the video section must be equal to the total number of pixels (clocks) “x × i” in the effective scanning line.

xxi = (3/4) xx (i + k) (Formula 6)

The following conditional expression holds. Also, the total number of pixels (clocks) of the black belt portions 132 and 133 “(a− (3/4) x) × (ij)” and the total number of pixels (clocks) in the vertical blanking period Vb “(a− x) × i ”is made equal,

(3/4) x * (i + k) = (a- (3/4) x) * (ij) (Formula 7)

The following conditional expression holds.

  Therefore, since a, x, and i are values determined by the scanning method and the image display device, the number of pixels (clocks) per line satisfying (Expression 5) to (Expression 7) (i + k) Based on (i−j), the horizontal frequencies of the video part 131 and the black belt parts 132 and 133 can be determined.

  In addition, the operation unit 17 does not give a command as to whether the input video signal is displayed as it is or the letterbox display, but the input video signal may be an input video signal such as a video signal for a video display device having any aspect ratio. Of course, letterbox display may be automatically performed by determining the type.

  Next, referring to the flowchart of FIG. 4, the video display method according to the present embodiment is displayed on the 4: 3 video display device as an example of the video signal sent to the 16: 9 video display device. While explaining.

  First, it is determined whether or not the switching process is performed from the video signal 4: 3 to 16: 9 by scaling (S1). This may be performed by issuing a switching command or automatically determining the type of the input video signal.

  When it is determined in S1 that the switching process is not performed, the video signal is displayed in a state compressed in the horizontal direction (S8), and when it is determined that the switching process is performed, the clock frequency is increased.

  If the writing line is the black belt portion 132 or 133 in S3, the number of clocks per line is reduced by lowering the horizontal frequency (S4), and one line is written (S6). If the writing line is not the black belt portion 132 or 133 in S3, the number of clocks per line is increased by increasing the horizontal frequency (S5), and one line is written (S6).

  S3 to S6 are repeated until the last line, and when one frame is written, the process proceeds to the next frame.

  Next, a video signal (FIG. 5) having a resolution of D3 having a scanning method of 1125i (1125 scanning lines and 1080 effective scanning lines) is displayed in a letterbox on the XGA display unit 11 (FIG. 6). ) Taking a case as an example, a numerical example is shown.

First, when displaying 16: 9 with XGA, the number of lines in the video section 61 is

1024 × (9/16) = 576 (Formula 8)

(Thus, the total number of black belt portions 62 and 63 is 192). If the video portion 61 becomes 95% due to overscan, the video signal 61 has 1125 scanning lines and 1080 effective scanning lines, so the display time G of the video portion 61 when letterbox display is performed in real time. Is the same as the display time of one frame when displaying the video signal normally instead of letterbox display.

G = (1080 × 0.95) / 1125 × 1/60 [s] (Formula 9)

It becomes. Since the black belt portions 62 and 63 must be displayed in the vertical blanking period Vb, the display time M of the black belt portions 62 and 63 is

M = 1 / 60−G [s] (Formula 10)

It becomes. Therefore, if the number of clocks per line of the video unit 61 during letterbox display is α, the number of clocks of the video unit 61 is 576 × α, and the total number of clocks of the black belts 62 and 63 is 192 × 1024 ( From the case where the number of clocks per line of the black belt portions 132 and 133 is set to the minimum necessary),

G: M = 576 × α: 192 × 1024 (Formula 11)

And

α = (192 × 1024 × G) / (576 × M)
= 35377.4549 (Formula 12)

It becomes. Therefore, the clock frequency Pckf is

Pckf = (576 × α + 192 × 1024) × 60
= 134.050924MHz

It becomes.

  As described above, according to the present embodiment, the blanking period of the input video signal is very short because letterbox display is performed by increasing the horizontal frequency of the masking section after increasing the clock frequency. Even so, it is possible to display appropriately.

<Second Embodiment>
In the above embodiment, letterbox display is performed by increasing the clock frequency and then increasing the horizontal frequency of the masking portion (lowering the horizontal frequency of the video portion). However, in this embodiment, the clock frequency is increased. Is made constant, the horizontal frequency of the black band portions 132 and 133 is increased, and the horizontal frequency of the video portion 131 is decreased, so that an appropriate letterbox display is performed.

  A block diagram of this embodiment is shown in FIG. Since it is the same as that of the above-mentioned embodiment except not having the clock frequency adjustment part 15, detailed description is abbreviate | omitted.

  Hereinafter, this embodiment will be described with reference to FIG. In the present embodiment, the clock frequency as shown in FIG. 2 is not changed to f ′. Then, the horizontal frequency (number of writable lines per unit time) of the black belt portions 132 and 133 is increased. That is, if the horizontal frequency is increased by the horizontal frequency adjusting unit 84, the time for writing to one line (horizontal period) is shortened. Since the time for writing to one line is shortened, the number of lines that can be written increases, and many lines can be written in a short time. Since this is performed by the black belt portions 132 and 133, many black lines can be written.

  However, since the reading time of the video signal and the video display time in the video unit 131 must be the same, when the video signal is written in the video unit 131, the horizontal frequency adjustment unit 14 must lower the horizontal frequency. Don't be.

From the above, referring to FIG. 2, one vertical period is

V = ((3/4) x * b '+ (a- (3/4) x) * c) / f (Formula 13)

It becomes. In addition, since the reading time of the input video signal and the writing time of the video portion 131 after compression are the same T time,

T = (x × b) / f = ((3/4) x × b ′) / f (Formula 14)

Must hold. The relationship between the number of clocks b, b ′, c per line satisfying (Equation 13) and (Equation 14) is as follows:

c <b <b ′ = 4 / 3b (Formula 15)

It becomes.

  As described above, according to the present embodiment, it is possible to perform appropriate letterbox display. However, when the vertical blanking period Vb of the video signal is extremely short, or when the number of pixels per line of the display unit 81 is extremely large, the black belt portion 132. 133 may not be secured, but the clock frequency adjusting unit 15 can be reduced under the conditions of the video signal and the display unit 81 that can secure the black band portions 132 and 133 having appropriate widths. It is valid.

<Third Embodiment>
Next, another embodiment according to the present invention will be described. The block diagram according to this embodiment is the same as FIG. Since the functions of the horizontal frequency adjusting unit 14 and the clock frequency adjusting unit 15 are the same as in FIG. 1, detailed description thereof is omitted.

In this embodiment, the clock frequency is increased when displaying the black belt portions 132 and 133, and the writing speed to one line at t1 and t2 shown in (Equation 1) is increased. Specifically, the clock frequency adjustment unit 85 adjusts the black band portions 132 and 133 so that the clock frequency is f ′ ″ and the video portion 131 is f ″. The horizontal frequency is the same for the black belt portions 132 and 133 and the video portion 131 (therefore, the number of clocks per line is the same for all lines b ″). Assuming that the number of clocks per line is b ″ and the normal clock frequency is f, with reference to FIG.

V = ((3/4) x × b ″) / f ′ ″ + (a− (3/4) x) × b ″ / f ″ (Formula 16)

Since the video signal read time and write time must be the same,

x × b / f = ((3/4) xx × b ″) / f ′ ″ (Expression 17)

F ″ and f ′ ″ are determined so as to satisfy the above. In order to satisfy both (Equation 16) and (Equation 17), the relationship between the clock frequencies f, f ″, f ′ ″ and the number of clocks b, b ″ per line is

f ″ ′ <f <f ″, b ″> b (Formula 18)

It becomes. In order to satisfy (Equation 16) and (Equation 17) as in (Equation 15), it is necessary that b ″> b. Therefore, the horizontal frequency adjustment unit 14 sets the number of clocks per line to b. Set the horizontal frequency to be ''.

  Next, a video display method according to the present embodiment will be described with reference to FIG.

  First, it is determined whether or not the switching process is performed from the video signal 4: 3 to 16: 9 by scaling (S1). This may be performed by issuing a switching command or automatically determining the type of the input video signal.

  When it is determined in S1 that the switching process is not performed, the video signal is displayed in a state compressed in the horizontal direction (S8). When it is determined that the switching process is performed, the black belt portions 132 and 133 and the video portion 131 are displayed. Set the clock frequency. If the writing line is the black belt portion 132 or 133 in S3, the number of clocks per line is reduced by lowering the horizontal frequency (S4), and one line is written (S6). If the writing line is not the black belt portion 132 or 133 in S3, the number of clocks per line is increased by increasing the horizontal frequency (S5), and one line is written (S6).

  S3 to S6 are repeated until the last line, and when one frame is written, the process proceeds to the next frame.

  As described above, letterbox display can be appropriately performed according to the present embodiment.

  By the way, according to the letterbox display according to the present invention, black writing in the black belt portions 132 and 133 does not include a pure video signal to be written in the video portion 131 during the blanking period of the input video signal. The fact that 0 level (black) is displayed when writing is used. Therefore, an appropriate letterbox display can be performed with any module (for example, a plasma display, an organic EL, etc.). Therefore, the display unit of the present invention is not limited to the liquid crystal display device.

However, the present invention can also be realized by providing a control unit that generates black data, such as the blanking control unit 257 of Patent Document 1, without black writing using an input video signal. The portion is not limited to black, and can be replaced with a display of other colors, a fixed pattern, a pattern, or the like (in this respect, a portion other than the video portion can be referred to as a “non-video portion”).
In addition, the present invention aims to display the video signal in a letterbox in real time. However, in the video display device that displays the video portion in the display portion in approximately the same time as the reading time of the effective scanning line, even if not in real time. It goes without saying that can be used.

  Further, the present invention has been described with an example of masking the upper and lower sides of the display image. However, as described with reference to FIG. Of course we can do it.

  The present invention can be used in a video display device that displays video such as a television receiver.

These are examples of a block diagram of a video display device according to the present invention. These are explanatory drawings of 1st Embodiment concerning this invention. These are timing charts of a first embodiment according to the present invention. These are the image | video display methods in 1st Embodiment concerning this invention. These are the outline | summary of the input video signal of D3. These are explanatory drawings in the case of letterbox display on an XGA standard display device. These are the timing diagrams of the numerical example of 1st Embodiment concerning this invention. These are an example of the block diagram of the video display apparatus of 2nd Embodiment concerning this invention. These are explanatory drawings of 3rd Embodiment concerning this invention. These are the image | video display methods in 3rd Embodiment concerning this invention. These are explanatory drawings showing a case where a video signal for a 16: 9 video display device is displayed. These are explanatory drawings showing a case where a video signal for a 4: 3 video display device is displayed. These are figures which show the letterbox display which masked the upper and lower sides of the image part. These are figures which show the letterbox display which masked the right and left of the image | video part. These are block diagrams which show a general liquid crystal display device. These are figures which show the structure of a video signal. These are diagrams showing a process of writing a video signal to the liquid crystal panel. These are timing charts when displaying letterboxes with the left and right sides of the video portion masked. These are explanatory drawings when the video signal is compressed and the upper and lower parts of the video part are masked and displayed. These are diagrams showing GSP when a video signal is compressed in the vertical direction on the screen and displayed in letterbox. FIG. 8 is a diagram for explaining scanning writing when it is assumed that GSP is generated in consideration of the insertion time of the black belt portion. These are the figures which show the scanning write line when it is assumed that GSP was generated in consideration of the insertion time of the black belt part. These are figures which show a screen at the time of displaying on the assumption that GSP was generated in consideration of insertion time of a black belt part. These are block diagrams of a video display device using a frame memory. These are the block diagrams of the video display apparatus of patent document 1. FIG. These are figures which show operation | movement of the video display apparatus of patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Display part 12 Controller 13 Image processing and scaler part 14 Horizontal frequency adjustment part 15 Clock frequency adjustment part 16 Microcomputer 17 Operation part

Claims (6)

A video display device that reads a video signal having an effective scanning line period and a vertical blanking period and displays it on a display unit by line sequential scanning,
Generating a clock that takes a timing to display a video signal on each pixel of the display unit;
In approximately the same time as the effective scanning line period, the effective scanning line region is compressed to display the video portion of the display unit,
The video display device, wherein the non-video part of the display part is displayed by increasing the frequency of the clock during the vertical blanking period. The video display device according to claim 1,
A video display device, wherein a clock frequency in the video unit and a clock frequency in the non-video unit are different. 2. The video display device according to claim 1, wherein the horizontal frequency is the same in scanning in the video section and scanning in the non-video section. A video display method for reading a video signal having an effective scanning line period and a vertical blanking period and displaying it on a display unit by line sequential scanning,
Generating a clock that takes a timing to display a video signal on each pixel of the display unit;
A step of compressing the effective scanning line area and displaying the video part of the display unit at substantially the same time as the effective scanning line period;
And displaying the non-video part of the display part by increasing the frequency of the clock during the vertical blanking period. The video display device according to claim 1,
A video display method, wherein a clock frequency in the video unit and a clock frequency in the non-video unit are different. 2. The video display method according to claim 1, wherein the horizontal frequency is the same in the scanning in the video unit and the scanning in the non-video unit.

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