JP2004310128A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device capable of displaying an image faithfully even to video signals having a variety of parameter specifications. <P>SOLUTION: The image display device comprises an A/D conversion circuit that obtains frequency of standard clock signals composing picture signals by video signals consisting of horizontal synchronizing signals, vertical synchronizing signals, and the picture signals, and quantizes the picture signals by a sampling clock of generally the same frequency as the above frequency; an image memory circuit that retains a part corresponding to a picture period of the picture signals among the image data output from the above circuit; and a display means that displays an output from the memory circuit, thereby displaying the image faithful to the original picture signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  According to the present invention, a video signal is input, its signal parameters are determined, and the video signal is automatically converted into digital image data and coordinate information by using the signal parameters, and the image is output to a display device. It relates to a display device.

  2. Description of the Related Art In recent years, a video printer device has been developed which inputs image information (video signal) output from a video device such as a computer, a communication device, or a television for a display device and prints and records an image, a figure, and the like. .

  These video signals are becoming higher definition and multiple gradations, and video printers are also required to respond to higher definition and multiple gradations.

  2. Description of the Related Art Conventionally, as a video printer device for printing and recording this kind of video signal, for example, as disclosed in Patent Document 1 below as a still image recording device, a video signal of a general television broadcast or the like is temporarily converted into digital data. In addition, there is known an apparatus that prints and records an image using the image data.

  When converting a video signal into digital data, a video signal constituting the video signal is sampled at a timing based on a synchronization signal accompanying the video signal. Each digitized image data is managed together with coordinate position information in the whole image, and is reproduced based on the coordinate position information during printing and recording.

  Further, management in the horizontal direction and the vertical direction of an actual image period (a period during which an image signal constituting an actual screen is output among the image signals) in the image signal is performed as follows.

  FIG. 18 is a timing chart showing the structure of the video signal, showing the relationship between the vertical synchronizing signal (V synchronizing signal), the horizontal synchronizing signal (H synchronizing signal), and the video signal, and the enlarged H synchronizing signal and the video signal. The relationship is shown.

  In the figure, in the horizontal direction, an image period 450 as an output period of the image signal 453 and a blanking period 451 from the fall of the H synchronization signal to the start of the image period 450 are set in advance, and the H synchronization signal is After falling, the video signal is sampled only for the image period 450 from the point in time delayed by the blanking period 451, so that only the image signal is selectively sampled from the video signal for one line in the horizontal direction. I have.

  As a result, only the image signal 453 indicating the image period 450 is digitized and output as image data.

  In the vertical direction, a predetermined time (back porch period) 454 from the fall of the V sync signal to the input of the video signal including the image signal is set in advance, and after the V sync signal has fallen. The image period in the vertical direction is managed by sampling a video signal corresponding to the H synchronization signal starting from the time delayed by the back porch period 451.

  The above-mentioned conventional example relates to a video printer device, but there is a liquid crystal display device described in Patent Document 2 below as a display device in the same manner. In such a conventional example, a video signal (television signal) is input, and a video signal portion of the video signal is digitized and stored in an image memory capable of holding one screen of image data. Are read out in a predetermined order, and an image is displayed on the liquid crystal display.

JP-A-60-46733 JP-A-55-650

  The video printer and the liquid crystal display device having the above-described configuration operate correctly with respect to a certain type of video signal, but the type of video signal that can be handled is determined to be a predetermined type such as a television signal. There is a problem that it is not possible to cope with a video signal in which the values of signal parameters such as the blanking period and the back porch period are slightly different.

  An apparatus capable of handling video signals having different signal parameter values is described in JP-A-59-226581.

  In this conventional device, the time setting from the output of the synchronization signal to the start of the sampling process for the video signal is performed using a rewritable storage element (shift register), and the shift register is appropriately set. By rewriting, it is possible to cope with video signals having different signal parameter values.

  However, in this prior art, since the frequency of the timing signal (sampling clock) for performing the sampling process is fixed, when the type of the synchronization signal is different, that is, when the time per horizontal line is different, the sampling is performed. Since the aspect ratio of the resulting image data changes, and the aspect ratio between the original image and the print image changes, it is impossible to perform faithful printing.

  In addition, for the existing NTSC or PAL video signals, since the standards are known, various parameter values can be prepared in advance in accordance with each standard. Separate volume transistor technology SPECIAL, No. 5 (1987), pp. 106 to 136, there are widely known methods which are discussed under the titles of "image processing technology using personal computer" and "design and manufacture of image input board for personal computer".

  However, in recent computers and information terminal devices that handle video signals, the resolution of the display has been increased, and for example, it has been used for conventional television broadcasting such as 1280 pixels in the horizontal direction and 1024 pixels in the vertical direction. Devices that display about four times the amount of information as compared to signal formats are being developed.

  However, there is no generalized standard for this type of high-definition high-resolution video signal, and at present, different signal formats are used for each manufacturer of the computer as a signal source.

  Therefore, in a video printer or a liquid crystal display which performs image recording based on these high-definition and high-resolution video signals, the specifications must correspond to the video signal standards. The conventional technology used cannot fully support a video signal of a newly developed signal format.

  Furthermore, in the prior art, if the frequency of the sampling signal on the video printer device side is made sufficiently faster than the quantization frequency on the signal source side, the faithfulness of the video signal can be obtained without considering the quantization frequency on the signal source. Although sampling is possible, the frequency band of a high-definition high-resolution video signal is so high that the sampling frequency cannot be made sufficiently faster than the quantization frequency at the signal source. Must be adjusted to the quantization frequency of

  Further, dullness of a video signal due to connection conditions such as a cable connecting a signal source to a video printer device or a display device cannot be ignored. That is, if the peak value of the signal does not match the sampling position, such as when the image signal is a line image, the line image will not be accurately represented in the print image, or the display image will not be displayed correctly. appear.

  Therefore, in order to solve such a problem, it is necessary to match the timing at the time of quantization in the signal source with the sampling timing in the video printer or the display device depending on the situation. Cannot be performed using preset data.

  As described above, the conventional video printer or display device can cope with a case where the format of an input video signal is known, but has a problem that it cannot handle a video signal of an unknown format.

  An object of the present invention is to solve the above-described problems, determine the signal format of an input video signal, and set various parameters in accordance with the result, so that the video signal of any signal format can be input. Even so, an object of the present invention is to provide an image display device which automatically and faithfully converts the video signal into digital image data and coordinate information and outputs the digital image data and coordinate information to a terminal device such as a general-purpose video printer.

In order to solve the above problems, the present invention has taken the following measures.
(1) Corresponding to a video signal composed of a horizontal synchronization signal, a vertical synchronization signal, and a video signal having various signal parameter specifications, an image capable of displaying an image faithful to the video signal when the video signal is input. In the display device, A / D conversion means for quantizing the video signal with a sampling clock having substantially the same frequency as a reference clock constituting the video signal; It is characterized in that it comprises image memory means for holding corresponding image data, and a display unit for displaying the output of the memory means as an image.
(2) Further, it is characterized in that it comprises a phase adjusting means for adjusting the phase of the sampling clock when a video signal having a predetermined image pattern is input.

  Since the number of pixels in the horizontal and vertical directions substantially uniquely corresponds to the frequency of the horizontal synchronization signal, if the frequency of the horizontal synchronization signal is detected, the number of pixels in the horizontal and vertical directions is determined.

  If the number of pixels in the horizontal direction and the frequency of the horizontal synchronization signal are known, the approximate frequency at the time of quantization of the video signal can be obtained by multiplying the frequency by the number of pixels.

  By sampling the video signal at the above-described approximate frequency and referring to the image data, an image period in one cycle of the horizontal synchronization signal and an image period in one cycle of the vertical synchronization signal can be obtained.

  Then, the video signal is converted into digital image data and coordinate information according to the number of pixels, the image period, and the approximate frequency determined as described above, and this is output to a terminal device such as a video printer or a liquid crystal display device. Then, an image output display faithful to the original video signal becomes possible.

  In addition, the image data and the coordinate information are referred to, and the image period and the approximate frequency are further corrected.Therefore, the reference to the image data and the correction according to the reference result may be repeated. , And more faithful image printing and display becomes possible.

  Further, by correcting the difference between the phase of the video signal and the phase of the sampling signal with reference to image data or the like, more accurate image printing and display can be performed.

As is clear from the above invention, the following effects are achieved according to the present invention.
(1) By determining the frequency of the horizontal synchronization signal, the number of pixels in the image period of a video signal whose signal format is unknown can be automatically determined.
(2) The image period can be automatically determined based on the luminance information of the video signal.
(3) The frequency of the quantized clock signal of the video signal at the video signal source can be determined based on the determined number of pixels and the image period. It can be sampled at the same frequency as the signal.

Therefore, faithful image data can be output to a subsequent display device or the like without dropping pixels included in the image.
(4) Using the parameters determined as in (1) to (3) above, process a video signal having a video signal whose signal format is unknown and which repeats black and white in the horizontal direction, and performs digital processing. By generating image data and referring to the image data, it is possible to match the phase of the video signal with the phase of the sampling signal, thereby preventing loss of information at the time of quantization and deterioration of the image. The image data can be output to a subsequent display device or the like.
(5) The parameters determined as described in the above (1) to (4) are stored, and the stored parameters are read out as necessary, and can be used. Once the format is known, the video signal can be easily processed thereafter.
(6) If the video signal source is sampled at a frequency twice or more the quantization clock signal on the sending side, faithful image data can be output to a subsequent display device or the like without losing the original information amount. Can be.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of an image signal input device 1 according to one embodiment of the present invention.

  In the figure, a video signal 806 including a video signal 302, a horizontal (H) synchronization signal 303, and a vertical (V) synchronization signal 304 is output from a video signal output device 2 such as an electronic computer connected to the monitor 202. And input to the image signal input device 1.

  FIG. 3 is a timing chart showing a configuration of the video signal 806. FIG. 3A is a diagram showing a relationship among a V synchronization signal 304, an H synchronization signal 303, and a video signal 302. FIG. 4B shows sampling of the same frequency as the H synchronization signal 303, the video signal 302, and the reference clock used when sending the video signal 302 from the video signal output device 2 per one cycle Th of the H synchronization signal 303. FIG. 3 is a diagram illustrating a relationship with a signal.

  When the image is color, the video signal 302 is a signal for three colors of red (R), green (G), and blue (B), which are three primary colors of light. Since the same processing is performed for any of the colors, only one color will be described for simplicity of description, and description of the other two colors will be omitted.

  The V synchronization signal 304 sets the time for displaying one image, and the frequency is generally a period during which the afterimage phenomenon of the human eye can be used, for example, a frequency having a period of about 16 ms (60 Hz). Is often used.

  In FIG. 7A, a period (video period) 705 during which an H synchronization signal having an image signal constituting an actual image is output starts from one cycle of the V synchronization signal 304 and extends before and after the blanking periods 704 and 706. Is subtracted, and in the blanking periods 704 and 706, a video signal for displaying black is output.

  On the other hand, in FIG. 3B, of the video signals 302, each row of image signals 453 that actually constitutes an image is output at a timing that falls within one period of the H synchronization signal 303. However, the image signal 453 is output within one cycle of the H synchronization signal 303 only during the image period 711 obtained by subtracting the back porch period 710 and the front porch period 712 before and after the one cycle Th of the H synchronization signal 303. In the back porch and front porch periods 710 and 712, a video signal for displaying black is output.

  Returning to FIG. 1, the video signal 302 is converted into digital image data 305 by the A / D converter 301 and then output to the common bus 4, and the digital image data 305 is temporarily stored in an image memory as described later in detail. 5 is stored.

  The H synchronization signal 303 is supplied to the reset terminal of the first frequency divider 360 in the phase comparator 351 and the horizontal synchronization address generation means 27 of the PLL circuit 350 and to the vertical synchronization address generation means 28 in the horizontal input head position setting means 26. , A clock terminal of the second frequency divider 371 in the horizontal input head position setting means 29, a clock terminal of the third frequency divider 380, and one input terminal of the interlace detecting means 30. And the output signal of the third frequency divider 380 is input to the controller 381.

  The V synchronization signal 304 is input to the other input terminal of the interlace detecting means 30 and the reset terminal of the second frequency divider 371. The interlace detection unit 30 receives the H synchronization signal 303 and the V synchronization signal 304, compares the phases of the H synchronization signal 303 and the V synchronization signal 304, determines whether or not the scanning is interlaced, and outputs the determination result to the controller 381.

  The H address counter 361 in the horizontal synchronization address generating means 27 outputs an H address signal 364 for setting an address in the horizontal direction when the digital image data 305 is stored in the image memory 5 via the common bus 4. Output to the image memory 5.

  Similarly, the V address counter 370 in the vertical synchronization address generating means 28 transmits a V address signal 374 for setting an address in the vertical direction when the digital image data 305 is stored in the image memory 5 to the common bus 4. Output to the image memory 5 via the

  The output signal of the freeze switch 385, the output signal of the preset switch 386, and the output signal of the automatic adjustment switch 387 are input to the controller 381. A RAM 392, a ROM 393, and a backup power supply 394 are connected to the controller 381.

  The PLL circuit 350 includes a phase comparison circuit 351, a filter 352, an amplifier 353, a VCO (voltage controlled oscillator) 354, and a fourth frequency divider 355. The frequency division ratio of the fourth frequency divider 355 is as follows. It is determined by a parameter set in the frequency division ratio shift register 356, and the parameter is set by the controller 381.

  The H synchronization signal 303 input to the phase comparison circuit 351 is compared there with the signal output from the VCO 354 and frequency-divided by the fourth frequency divider 355, and the error signal after the comparison is passed through the filter 352 to the amplifier 353. Is input to The amplifier 353 outputs the amplified error signal to the VCO 354, and the VCO 354 outputs a clock signal 802 in which the phase error is corrected and synchronized with the H synchronization signal 303.

  That is, the clock signal 802 output from the PLL circuit 350 is synchronized with the H synchronization signal 303, and is further multiplied by the division ratio stored in the division ratio shift register 356 with respect to the original H synchronization signal 303. It becomes a clock signal.

  The clock signal 802 is input to the phase delay unit 382 in the phase delay unit 25, the clock terminal of the H address counter 361, the delay unit 390, and the clock terminal of the first frequency divider 360.

  The phase delay unit 382 delays the clock signal 802 by a time determined by a parameter set in the delay shift register 383, and outputs the delayed clock signal to the A / D converter 301 as a sampling signal 803. The delay unit 390 delays the clock signal 802 by a time corresponding to the processing in the H address counter 361, and outputs the H address signal 364 output from the H address counter 361 to the common bus 4 and the delay unit 390. The output timing of the sampling signal 803 output to the common bus 4 via the common bus 4 is matched.

  As a result, for example, if the frequency division ratio set in the frequency division ratio shift register 356 is 1700, the video signal per one cycle Th of the H synchronization signal 303 is divided into 1700 and 1700 image data per one cycle Th 305 is output to the image memory 5 via the common bus 4.

  As will be described later with reference to FIG. 6, the phase delay unit 25 converts the quantization frequency when the video signal output device 2 converts (quantizes) digital image data into a video signal which is an analog signal, This is used to match the phase with the sampling frequency on the input device 1 side. Parameters set in the delay shift register 383 are set by the controller 381.

  The horizontal synchronizing address generating means 27 includes a horizontal input head position setting means 26, an H address counter 361, and an H input number shift register 363. The horizontal input head position setting means 26 further includes a first frequency divider 360 And an H start shift register 362. The parameters of the H start shift register 362 and the H input number shift register 363 are determined by the controller 381.

  In the horizontal synchronizing address generating means 27, the first frequency divider 360 is reset by the H synchronizing signal 303, and divides the clock signal 802 by the frequency dividing ratio (parameter) set in the H start shift register 362. The peripheral output is output to the H address counter 361.

  When the frequency division output is input, the H address counter 361 inputs the number of H inputs to the parameter set in the shift register 363.

  On the other hand, the vertical synchronizing address generating means 28 includes a vertical input head position setting means 29, a V address counter 370, and a V input number shift register 373. The vertical input head position setting means 29 further includes a second frequency divider 371. And a V start shift register 372. The parameters of the V start shift register 372 and the V input number shift register 373 are determined by the controller 381.

  In the vertical synchronization address generating means 28, the second frequency divider 371 is reset by the V synchronization signal 304, and divides the H synchronization signal 303 by the division ratio (parameter) set in the V start shift register 372, The divided output is output to V address counter 370.

  The common bus 4 is connected to external devices, for example, an image printing unit 20 and an image storage unit 21 via an interface 22.

  Further, the image data 305 held in the image memory 5 is also output to the monitor 203, and the image is displayed.

  Next, the operation of the horizontal synchronization address generator 27 and the vertical synchronization address generator 28 will be described in detail.

  Here, the frequency division ratio parameter of the H start shift register 362 of the horizontal synchronization address generator 27 is set to X1, and the parameter of the H input number shift register 363 is set to X2. It is assumed that the start shift register 372 is set to Y1, the V input number shift register 373 is set to Y2, and the frequency division ratio shift register 356 is set to Z1.

  In the horizontal synchronization address generating means 27, when the H synchronization signal 303 falls, the first frequency divider 360 is reset. Then, the clock signal 802 output from the PLL circuit 350 is frequency-divided by X1 by the first frequency divider 360. Then, the preset signal 804 is output to the H address counter 361.

  The H address counter 361 reads the parameter X2 set in the H input number shift register 363 when the preset signal 804 is input, and thereafter generates an H address signal every time the clock signal 802 is input. To output X2 address signals.

As a result, in the image memory 5, of the video signals obtained by dividing one cycle of the H synchronization signal 303 into Z1, the (X1 + 1) th from the beginning is the start address, that is, X2, in other words, the (X1 + 1) th to (X1 + X2). ) -Th image data X2 are input to the image memory 5.

  Therefore, if the period corresponding to the back porch period 710 described with reference to FIG. 3B is set in the H start shift register 362 and the period corresponding to the image period 711 is set in the H input number shift register 363, the image period Is output to the image memory.

  On the other hand, in the vertical synchronization address generation means 28, when the V synchronization signal 304 falls, the second frequency divider 371 is reset. After that, when the H synchronization signal 303 is frequency-divided by Y1 by the second frequency divider 371, Preset signal 805 is output to V address counter 370.

  When the preset signal 805 is input, the V address counter 370 reads the parameter Y2 set in the V input number shift register 373, and thereafter generates a V address signal each time the H synchronization signal 303 is input, and 5 to output Y2 address signals.

As a result, in the image memory 5, Y2, in other words, the video signal corresponding to the (Y1 + 1) -th H synchronizing signal from the beginning of the H synchronizing signals after the V synchronizing signal 304 is output, in other words, , (Y1 + 1) th to (Y1 + Y2) th image data Y2 are input to the image memory 5.

  Therefore, if the period corresponding to the blanking period 704 described with reference to FIG. 3A is set in the V start shift register 372 and the image period 705 corresponding to one screen is set in the V input number shift register 373, the vertical As for the direction, only the image data corresponding to the video period 705 for one screen is output to the image memory 5.

  As a result, the image memory 5 stores X2 image data in the horizontal direction and Y2 image data in the vertical direction, that is, a total of X2 × Y2 image data.

  FIG. 2 is a perspective view of the image signal input device 1. The freeze switch 385, the preset switch 386, and the automatic adjustment switch 387 are attached to the front surface thereof. The use of each switch will be described as appropriate in the following embodiments.

  FIG. 4 is a diagram showing a configuration example of the number of pixels of an image generally used in a display method without interlace (sequential scanning method).

  The image example of FIG. 1I is an image composed of 1024 pixels in the vertical direction, and the image example of FIG. 2I is an image composed of 768 pixels in the vertical direction. Is an image composed of 400 pixels in the vertical direction.

  In addition, the frequency of the H synchronization signal in each image example is generally set in general in correspondence with the number of pixels in the vertical direction. That is, as described above, since the frequency of the V synchronization signal is set to about 60 Hz from the viewpoint of the afterimage phenomenon, if the frequency of the H synchronization signal is 64 kHz, the number of H synchronization signals in one cycle of the V synchronization signal becomes It is calculated as follows.

(64 kHz / 60 Hz) = 1067
Then, when the number of H synchronization signals in the vertical direction is obtained, it is determined that the number of pixels in the vertical direction according to the number of H synchronization signals is 1024.

  Similarly, when the frequency of the H synchronization signal is around 49 kHz, the number of pixels in the vertical direction is determined to be 768 pixels, and when the frequency of the H synchronization signal is around 24 kHz, the number of pixels in the vertical direction is determined to be 400 pixels. You.

  Similarly, in general, when the vertical direction is 1024 pixels, the horizontal direction is often 1280 pixels, and when the vertical direction is 768 pixels, the horizontal direction is often constituted by 1024 pixels. It is known that 400 pixels are often 640 pixels in the horizontal direction.

  The operation of each embodiment of the present invention, which will be described in detail below, uses a part of the estimation result as described above to determine parameters of a video signal of an unknown signal format, and reproduces a faithful image. .

  Hereinafter, the operation principle of the first embodiment shown in FIG. 1 will be described with reference to the flowchart of FIG.

In the present embodiment, each parameter of the input unknown signal format video signal is determined by the following three-stage automatic adjustment.
First stage: determination of the number of pixels (horizontal direction and vertical direction) in an image period in a video signal.
Second stage: determination of image period (blanking period and video period in horizontal and vertical directions) and sampling frequency.
Third stage: phase adjustment of the sampling signal.

  When a video signal of an unknown signal format output from the video signal output device 2 is input to the image signal input device 1 and the automatic adjustment switch 387 is operated, the first stage of the determination operation starts.

  In step S1, the H synchronization signal divided by the third frequency divider 380 is input to the controller 381, and the controller 381 determines the approximate frequency of the H synchronization signal based on the input signal as follows.

  That is, if the frequency division ratio of the third frequency divider 380 that divides the H synchronization signal is 100 and the period of the H synchronization signal after the frequency division is 1.5 ms, 100 / (1.5 × 10 -3) Based on the calculation result of 66.67 kHz, the controller 381 refers to data registered in the ROM 393 in advance based on the above estimation, and determines that the approximate frequency of the H synchronization signal is around 64 kHz.

  When the approximate frequency of the H synchronization signal is determined, in step S2, based on the determination result that the approximate frequency of the H synchronization signal is 64 kHz, the controller 381 refers to the data table registered in the ROM 393, and The number of pixels is determined to be, for example, 1280, and the number of pixels in the V direction is determined to be, for example, 1024. In step S3, values relating to the number of pixels are set in the H input number shift register 363 and the V input number shift register 373, respectively.

  In step S4, the controller 381 obtains the number of sampling clocks SC per one cycle of the H synchronization signal 303 with reference to the data table registered in the ROM 393, and sets this in the frequency division ratio shift register 356.

  As shown in FIG. 7, when the video signal for one cycle of the H synchronization signal 303 is divided into SC digital image data as shown in FIG. 7, the sampling clock number SC is divided into SC digital image data. Within at least the number of pixels (1280) in the H direction from the top of the digital image data, at least the periphery A around the boundary between the blanking period 710 and the image period 711 and the periphery B around the boundary between the image period 711 and the blanking period 712. This is a number that can include image data.

  In the following description, it is assumed that the sampling clock number SC is determined to be 1800. At this time, for example, 0 is set in the H start register 362 and the V start register 372 as an initial setting value.

  When the provisional setting of each parameter is completed in this way, in step S5a, the controller 381 outputs a write permission signal to the image memory 5 via the common bus. From the PLL circuit 350, a clock signal having a frequency of 115 MHz obtained by multiplying the value (1800) set in the frequency division ratio shift register 356 by the frequency (64 kHz) of the H synchronization signal 303 is output as a sampling clock 802. Is input to the A / D converter 301 via the phase delay unit 382 of the phase delay unit 25. The function of the delay unit 382 will be described later in detail with reference to FIG.

  The A / D converter 301 A / D converts the video signal 302 with the sampling signal 803, divides the video signal for one cycle of the H synchronization signal 303 into 1800, and converts this into digital image data 305 to the image memory 5. Output.

  At this time, the H address counter 361 of the horizontal synchronization address generator 27 starts the operation of generating an H (horizontal) direction address signal based on the sampling clock signal 802 as follows.

  That is, after being reset by the H synchronization signal 303, the first frequency divider 360 divides the frequency of the clock signal 802 by the frequency division ratio (currently 0) set in the H start shift register 362, and performs the frequency division. The output is sent to the H address counter 361 as a preset signal 804, and the preset value (1280) set in the H input number shift register 363 is set in the H address counter 361.

  The H address counter 361 counts 1280 sampling clocks from the H synchronization signal 303, generates a 1280 H direction address as an address for one line in the H direction of the image, and outputs the address to the image memory 5. .

  As a result, in the image memory 5, digital image data 305 obtained by sampling the video signal at a frequency of 115 MHz by the A / D converter 301 is stored in an area specified by the address.

  At this time, as described with reference to FIG. 7, the image data input to the image memory 5 is from the first part to the 1280th digital image data obtained by dividing the video signal for one cycle of the H synchronization signal by 1800. And the 1280 pieces of digital image data include digital image data around the boundary portion A between the blanking 710 and the video period 711 and digital image data around the boundary portion B between the video period 711 and the blanking 712. become.

  On the other hand, the second frequency divider 371 also divides the H synchronization signal 303 by the division ratio (currently 0) set in the V start shift register 372, and uses the frequency division output as a preset signal 805 as a V address counter. Then, the preset value (1024) set in the V input number shift register is set in the V address counter 370.

  Therefore, the V address counter 370 starts counting the H synchronization signal after the V synchronization signal 304 is output, generates a V-direction address for 1024 pixels in the vertical direction of the image, and sends this to the image memory 5. Output.

  As a result, 1280 image data corresponding to each H synchronization signal are stored in the image memory 5 in an area specified by the V address in the vertical direction.

  As described above, when the determination of the number of pixels in the image period in the video signal, which is the first stage of the automatic adjustment operation, and the registration of the image data obtained using the parameters to the image memory 5 are completed, The second stage of the determination operation starts.

  It is desirable that the image data to be registered in the image memory 5 in the first stage be selected so that the image becomes white in consideration of each operation in the second stage described later.

  In step S6a, the controller 381 reads out the contents of the image data stored in the image memory 5 via the common bus 4.

  In step S7a, first, referring to the image data corresponding to the V address, a blanking period from the fall of the V synchronization signal to the start of the video period is obtained as an address value as follows.

  That is, in the first stage, when a video signal whose image is white is stored in the image memory 5, the video signal 302 shows black (luminance 0) in the back porch portion other than the image area. Therefore, it can be determined that the period in which the image data is black is the back porch and the period in which the image data is white is the video period until the start of the video period.

  In this embodiment, it is assumed that the back porch period is determined to be 10 addresses.

  When the entire image is black, it is difficult to distinguish between the blanking period (back porch) and the video period. Therefore, when such automatic adjustment is performed, image data registered in the image memory 5 in advance is used. Needs to correspond to a video signal other than black at least at the beginning and end of the video period.

  When the determination of the video period in the vertical direction is completed in this way, the determination of the video period in the horizontal direction is started.

  By the way, the determination of the video period in the horizontal direction is not limited to simply calculating the image period and the blanking period according to the H synchronization signal 303, and it is necessary to determine the sampling frequency of the video signal in the video signal output device 2 at the same time. There is.

  That is, since most of the video signal output devices 2 create a video signal by converting digital information from an electronic computer or the like into an analog signal, the sampling frequency of the D / A conversion in the video signal output device 2 and the video If the sampling frequency of the A / D conversion on the signal input device 1 side does not match, moire fringes may occur in the image due to quantization errors.

  Therefore, when determining the video period in the horizontal direction, the blanking period, the video period, and the sampling frequency are obtained as follows.

  The controller 381 reads out the image data obtained in the horizontal direction from the image memory 5, and sets a blanking period from the fall of the H synchronization signal to the start of the video period and a subsequent video period as in the case of the vertical direction. Similarly, it is obtained as an address value.

  In this embodiment, it is determined that the blanking period is 50 addresses and the video period is 1220 addresses.

  When the blanking period in the V direction, the blanking period in the H direction, and the video period are obtained in this way, the sampling frequency at the time of D / A conversion in the video signal output device 2 is obtained as follows.

  That is, since the number of pixels in the horizontal image period is 1280 and the obtained video period is 1,220 addresses, it is necessary to match the sampling frequency, that is, to make the image period 1280 divided. It can be seen that the sampling frequency should be multiplied by 1280/1220 = 1.05 times. When the sampling frequency becomes 1.05 times, the blanking period (back porch) in the H direction also needs to be corrected to 50 addresses × 1.05 = 53.

  Similarly, in order to increase the sampling frequency by 1.05, it is understood that the division ratio of the PLL circuit 350, that is, the set value of the division ratio shift register 356 needs to be 1890.

  When each parameter is obtained in this way, in step S8, it is determined whether or not the value of each parameter is within a predetermined range.

  That is, in order to effectively utilize the function of the present embodiment, it is desirable to output a video signal for displaying a white screen in the first stage. However, when such a video signal is not input, The value of each parameter is out of the predetermined range. Then, when the subsequent processing is executed in this state, accurate parameters are not set.

  Therefore, in step S8, it is determined whether or not the value of each parameter is within a predetermined range. If the value is outside the predetermined range, the parameter for general setting set in the ROM 393 in step S9 is determined. Is read, the parameters are set to the respective parameters in step S10, and the respective parameters are stored in the RAM 392 in step S11, and the process ends.

  On the other hand, if it is determined in step S8 that the value of each parameter is within a predetermined range, each parameter is set or reset in a predetermined register in step S12.

  However, if such operation is performed only once, for example, when the blanking period or the video period is determined, if the boundary portion is not clear (the image data of the boundary portion indicates an intermediate value), the parameter may be changed. It will include errors.

  Therefore, in this embodiment, when the rough determination of the video period is completed as described above, it is determined in step S13 whether or not the determination result, that is, the parameter is correct. This determination is made by determining whether the image data at the address corresponding to the blanking period is substantially all 0 (black) and the image data at the address corresponding to the video period is substantially all 255 (white). Done. If not accurate, the process returns to step S5 to further improve the accuracy, and stores the video signal in the image memory 5 again using the parameter.

  Hereinafter, reprocessing after returning to step S5 will be briefly described.

In addition, as is clear from the above description, at this point,
The division ratio shift register 356 has 1890,
The H start shift register 362 has 53,
10 is stored in the V start shift register 372,
The H input number shift register 363 has 1280,
It is assumed that 1024 is set in the V input number shift register 373, respectively.

  In step S5, the controller 381 outputs a write enable signal to the image memory 5 via the common bus with the parameters set as described above. From the PLL circuit 350, a clock signal 802 having a frequency of 121 MHz obtained by multiplying the value (1890) set in the frequency division ratio shift register 356 by the frequency (64 kHz) of the H synchronization signal 303 is output as a sampling clock. The signal is input to the A / D converter 301 via the phase delay unit 382 of the phase delay unit 25.

  The A / D converter 301 performs A / D conversion on the video signal with the sampling clock 803, divides the video signal for one cycle of the H synchronization signal 303 into 1890, and outputs this to the image memory 5 as digital image data. .

  Further, after being reset by the H synchronization signal, the first frequency divider 360 divides the frequency of the clock signal 802 by the frequency division ratio (53 in this case) set in the H start shift register 362, and outputs the frequency divided signal. Is sent to the H address counter 361 as a set signal 804, and the preset value (1280) set in the H input number shift register is set in the H address counter 361.

  Therefore, the H address counter 361 outputs the 1280 address signals to the image memory 5 thereafter, with the 54th clock signal 802 as the start timing after the output of the H synchronization signal 303.

  As a result, the 54th image data of the digital image data obtained by sampling the video signal at the frequency of 121 MHz in the A / D converter 301 is used as the start address in the image memory 5, and thereafter, 1280 image data Will be stored.

  On the other hand, after being reset by the V synchronization signal 304, the second frequency divider 371 also divides the H synchronization signal 303 by the division ratio (10 in this case) set in the V start shift register 372, and The peripheral output is sent to the V address counter 370 as a set signal 805, and the preset value (1024) set in the V input number shift register is set in the V address counter 370.

  Therefore, the V address counter 370 starts address generation 10 cycles after the H synchronization signal after the V synchronization signal 304 is output, and generates a V address signal for 1024 pixels in the vertical direction of the image. Output to the image memory 5.

  As a result, 1024 address signals are set in the image memory 5 from the 11th H synchronization signal after the V synchronization signal is output.

  In step S6, the controller 381 reads out the contents of the image data stored in the image memory 5 via the common bus 4. In step S7, the controller 381 refers to the image data corresponding to the V address to generate the V synchronization signal. The blanking period from the fall to the start of the video period is obtained as an address value in the same manner as described above.

  In this embodiment, it is assumed that the back porch period is modified from 10 addresses to 11 addresses.

  When the determination of the video period in the vertical direction is completed in this way, the determination of the video period in the horizontal direction is started.

  The controller 381 refers to the image data obtained in the horizontal direction, and obtains a blanking period from the fall of the H synchronization signal to the start of the video period and the subsequent video period as address values in the same manner as described above. .

  Here, it is assumed that the blanking period has been corrected to 56 addresses and the video period has been corrected to 1260 addresses.

  When the blanking period and the video period are obtained in this manner, the sampling frequency is also obtained in the same manner as described above.

Sampling frequency =
1280/1260 × 121 = 123
Blanking period =
1280/1260 × 56 = 57
Similarly, it can be seen that the frequency division ratio of the PLL circuit 350 should be set to 1890 × 1.02 = 1927 to increase the sampling frequency by 1280/1260 = 1.02.

  When the rough determination of the video period is completed in this way, in the present embodiment, thereafter, the same processing as described above is performed in steps S8 and S12, and in step S13, it is determined that the obtained parameter values are accurate. Then, the adjustment of the second stage is completed.

  When the determination of the video period is completed in this way, next, the phase of the sampling clock is adjusted.

  In this phase matching, as described later, the video signal 302 input to the video signal input device 1 is dull due to the influence of a cable capacity or the like on the way, and the resulting video signal 302 and the sampling signal 803 are generated. This is performed to compensate for the phase shift.

  In performing the phase matching, after setting parameters relating to the video period obtained up to that point in each register, a video signal in which a stripe pattern is repeated in the horizontal direction is input as shown in FIG. .

  It is determined in step S14 whether a video signal in which a striped pattern is repeated is input. If the video signal is not such a pattern, each parameter is stored in the RAM 392 in step S11, and the process ends.

  In step S15, it is determined whether or not the phase of the video signal 302 matches the phase of the sampling signal 803. If they match, each parameter is stored in the RAM 392 in step S11 and the process ends. I do.

  The parameters stored in the RAM 392 in this manner can be appropriately read by operating the preset SW 386, and the read parameters are set in a predetermined register. Therefore, the video signal whose signal format has been clarified once can be easily processed thereafter without executing the above-described various determination processes.

  If they do not match, the image data does not change from white (image data is 255) to black (image data is 0) at the end of the stripe, and the boundary is shown in FIG. As described above, an area 750 in which the image data indicates an intermediate value between 0 and 255 appears.

  In such a case, the phase is adjusted in step S16 as follows. That is, the controller 381 changes the delay amount of the phase shifter 382 little by little by changing the value of the delay shift register 383, and sets the set value of the delay shift register 383 so that the image data at the end does not show an intermediate value. Is set.

  FIG. 6 is a diagram showing a relationship between the phase of the sampling clock 803 and the phase of the video signal 302.

  In the figure, at the output part of the video signal output device 2 which outputs a video signal in which a striped pattern is repeated in the horizontal direction, as shown in FIGS. Although being synchronized with the video signal 731, the video signal 731, when input to the image signal input device 1, has a dull waveform as shown in FIG. 732, and when sampling is performed with the sampling clock 733 (803) of the image signal input device 1, the image data becomes image data 734 indicating an intermediate value as shown in FIG.

  Therefore, in such a case, as shown in FIG. 7F, the video signal 732 is sampled by the sampling clock 736 shifted by, for example, 1/3 phase with respect to the sampling clock 733 of the video signal output device 2. Then, the image data becomes image data 737 corresponding to the original video signal 731 as shown in FIG.

  Therefore, in this embodiment, the controller 381 changes the delay amount of the phase delay unit 382 little by little by changing the value set in the delay shift register 383, and the image data at the boundary does not show an intermediate value. Thus, the set value of the delay shift register 383 is set, and finally the optimum delay time is set.

  The video signal input at this time may be any signal as long as it does not have an intermediate value and the value of the black and white changes several times within one horizontal period.

  The phase adjustment is performed in this way, and if it is determined in step S15 that the phases match, as described above, the parameters are stored in the RAM 392 in step S11, and the process ends.

  FIG. 9 is a block diagram showing a configuration of a main part of an embodiment in which the number of pixels (horizontal direction and vertical direction) in an image period in a video signal is determined by the pixel number setting means 33, and the same reference numerals as those in FIG. The same or equivalent parts are shown.

  In the embodiment described with reference to FIG. 1, the number of pixels in the image period is determined by the controller 381 by referring to the ROM 393 based on the output signal of the third frequency divider 380. At 381, the number of pixels can be determined and registered without performing an arithmetic process or the like.

  In the figure, the H synchronizing signal is inputted to one input terminal of the fh detecting means 31 and the interlacing detecting means 30, and the V synchronizing signal is inputted to the other input terminal of the interlacing detecting means 30. The output signal of the interlace detecting means 30 is input to an address bus of the ROM 32.

  A sampling frequency setting means 24, a horizontal synchronization address setting means 27, and a vertical synchronization address setting means 28 are input to the data bus of the ROM 32.

  In the device having such a configuration, the fh detection means 31 measures the frequency of the H synchronization signal by an appropriate means, and outputs a digital signal (for example, 3 bits) corresponding to the frequency to the lower 3 bits of the address bus of the ROM 32. I do.

  On the other hand, the interlace detecting means 30 detects the presence or absence of interlace, and outputs the detection signal to the upper one bit of the address bus of the ROM 32.

  The ROM 32 outputs digital data stored at an address corresponding to the data input to the address bus to the sampling frequency setting means 24, the horizontal synchronization address setting means 27, and the vertical synchronization address setting means 28.

  According to the present embodiment, data relating to the number of pixels is directly output from the ROM 32 to the horizontal synchronization address setting means and the vertical synchronization address setting means 28 based on the frequency of the H synchronization signal without performing calculations or the like by the controller 381. Therefore, the load on the controller 381 is reduced, and the processing speed is improved.

  FIG. 10 is a block diagram showing a configuration of a main part of a device for adjusting a phase shift of a sampling signal between an output side and an input side of a video signal as described with reference to FIG. 6, and is the same as FIG. Denotes the same or equivalent parts.

  In the figure, a video signal is input to an A / D converter 301, and a latch 33 for storing the maximum value and a latch 34 for storing a minimum value are connected to the A / D converter 301. Output signals of the latches 33 and 34 are input to an arithmetic circuit 35, respectively. The result of the operation (subtraction) in the operation circuit 35 is input to the controller 381.

  In the device having such a configuration, the video signal is sampled by the sampling signal output from the phase delay unit 25 in the A / D converter 301, and the maximum value and the minimum value within a predetermined period are respectively determined by the latch 33 and the latch 33. 34. The arithmetic circuit 35 obtains the difference between the image data stored in the latches 33 and 34 for each of the predetermined periods, and inputs the difference to the controller 381.

  The controller 381 detects a phase shift of the sampling signal from the difference, and controls the phase delay unit 25 so as to eliminate the shift.

  FIG. 11 is a block diagram showing a configuration of a main part of an apparatus for determining the image period without performing any arithmetic processing or the like by the controller 381, and the same reference numerals as those in FIG. 1 denote the same or equivalent parts.

  In the figure, the output signal of the A / D converter 301 is input to the edge detecting means 36. The detection signal of the edge detecting means 36 is input to the trigger input terminal of the counting means 37 of the display period detecting means 39, the reset terminal of the counting means 37 has an H synchronization signal, and the clock terminal has a clock signal from the VCO 354. Is entered.

  The counting result of the counting means 37 is input to the latch 38, and the output signal of the latch 38 is input to the controller 381.

  In the device having such a configuration, when the counting means 37 is reset by the H synchronization signal and the video signal is output after the blanking period ends, the video signal is converted into digital image data by the A / D converter 301. Then, it is inputted to the edge detecting means 36.

  The edge detecting means 36 detects an edge portion with reference to the digital image data, and inputs a detection signal to a trigger input terminal of the counting means 37. When the trigger is input, the counting means 37 starts counting the clock of the VCO 354.

  Thereafter, when the edge detecting means 36 detects the end of the image period, the latch 38 holds the count value of the counting means 37 and outputs the count value to the controller 381.

  FIG. 12 is a block diagram showing a configuration of a main part of an embodiment in which a function of changing a threshold for edge detection is added to the edge detecting means 36 described with reference to FIG. 11, and the same reference numerals as those in FIG. Or equivalent parts.

  In the figure, the output signal of the A / D converter 301 is input to one input terminal of the comparison means 41, and the output signal of the level setting means 40 is input to the other input terminal. A controller 381 is connected to the level setting means 40, and the output level of the level setting means 40 is adjusted by the controller 381.

  In the device having such a configuration, if the input video signal has an offset ΔV as shown in FIG. 17, the edge detecting means 36 described with reference to FIG. Cannot be distinguished from the edge portion D in the actual video period, resulting in an unnatural image.

  In such a case, in this embodiment, the controller 381 controls the level setting means 40 appropriately to change the offset of the comparing means 41 so that only the edge portion D is detected.

  According to the present embodiment, a faithful image can be reproduced even when the video signal has an offset ΔV.

  FIG. 13 is a block diagram showing a second embodiment of the present invention, and the same reference numerals as those in FIG. 1 denote the same or equivalent parts. FIG. 14 is a flowchart for explaining the operation of this embodiment.

  As is clear from the comparison with FIG. 1, the present embodiment is characterized in that a line memory 55 for storing only one line in the one-dimensional direction of the image is connected instead of the image memory 5.

  In FIG. 14, steps S1 to S4 are almost the same as the operations described with reference to FIG. 5, and thus description thereof will be omitted.

  Thereafter, in step S5b, one line of the video signal 302 output from the video signal output device 2 is stored in the line memory 55, and the stored one line of the video signal is read out to the controller 381.

  In step S6b, it is determined each time whether or not an image signal is included in the read one-line video signal. If no image signal is included, the process returns to step S5b and returns to step S5b. The storage of the signal, the reading to the controller 381, and the determination of the presence or absence of the image signal are repeated.

  If it is determined in step S6b that there is an image signal, in step S7b, the order of the H synchronization signal at this time is set as a blanking period in the vertical direction.

  The determination of the blanking period, the image period, and the sampling frequency in the horizontal direction is performed in the same manner as in the embodiment described with reference to FIG. 1 using the video signal having the image signal.

  Since the operation after step S8 is almost the same as the operation described with reference to FIG. 5, the description thereof will be omitted.

  According to this embodiment, since the capacity of the memory can be reduced, the size of the device can be reduced.

  FIG. 15 is a block diagram of the third embodiment of the present invention, and the same reference numerals as those in FIG. 1 represent the same or equivalent parts.

  As is clear from the comparison with FIG. 1 or FIG. 13, in this embodiment, no external memory for storing image data is particularly provided, and the image data is directly stored in the controller 381. The same determination processing as in the embodiment is performed.

  In this embodiment, a part of the controller 381 can be used as the image memory 5 shown in FIG. 1 or the line memory 55 shown in FIG. 13 depending on the processing method.

  FIG. 15 is a block diagram of the fourth embodiment of the present invention, and the same reference numerals as those in FIG. 1 represent the same or equivalent parts.

  In this embodiment, the sampling theorem is used, and the sampling frequency is twice or more that of the video signal output device 2 to generate image data that is twice or more that in each of the above-described embodiments. A characteristic feature is that the matching process is abolished by performing interpolation processing and outputting.

  Hereinafter, the operation of this embodiment will be described with reference to the flowchart of FIG. 5 on the assumption that the same video signal as that of the embodiment described with reference to FIG. 1 is input.

  That is, from the frequency of the H synchronization signal, it is determined in step S1 that the approximate frequency of the H synchronization signal is around 647 kHz, and in steps S2 and S3, the number of pixels in the H direction in the image period is 1280 and the number of pixels in the V direction is In step S4, the controller 381 determines the sampling clock number SC per one cycle of the H synchronization signal 303 in step S4 by referring to the data table registered in the ROM 393 in the same manner as described above. Is determined in the frequency division ratio shift register 356, and further, for example, 0 is set as an initial setting value in the H start register 362 and the V start register 372.

  From the PLL circuit 350, a clock signal having a frequency of 230 MHz obtained by multiplying the value (3600) set in the frequency division ratio shift register 356 by the frequency (64 kHz) of the H synchronization signal 303 is output as a sampling clock 802. Is input to the A / D converter 301 via the phase delay unit 382 of the phase delay unit 25.

  The A / D converter 301 performs A / D conversion of the video signal with the sampling clock 803, divides the video signal for one cycle of the H synchronization signal 303 into 3600, and outputs this to the image memory 5 as digital image data 305. I do.

  Hereinafter, in the same manner as described with reference to FIG. 1, the first step of the automatic adjustment operation is the determination of the number of pixels in the image period in the video signal, and the image memory of the image data obtained using the parameters. Upon completion of the registration with the image memory 5, the controller 381 reads out the contents of the image data stored in the image memory 5.

  In step S7a, first, the controller 381 refers to the image data to determine a blanking period of the V synchronization signal.

  In this embodiment, as in the case of the embodiment of FIG. 1, the period of the back porch is determined to be 10 addresses.

  When the determination of the video period in the vertical direction is completed, the determination of the video period in the horizontal direction is started. Here, since the sampling frequency is doubled as compared with the embodiment of FIG. The period is 100 addresses, and the video period is 2440 addresses.

  When the blanking period and the video period are calculated in this manner, the sampling frequency is calculated in the same manner as described above, and the parameters are reset.

  When the parameters are determined in this way and the actual printing operation is started, the digital image data output from the A / D converter 301 is twice as large as the original digital image data in the video signal output device 1. Become.

  The digital image data 305 output from the A / D converter 301 is subjected to an interpolation process in an interpolation device 650, and then stored in an image printing unit or an image storage unit via an interface.

  According to this embodiment, since the sampling frequency is at least twice the frequency of the original signal, the original video signal can be faithfully reproduced without performing phase adjustment of the sampling signal. .

  In the above-described embodiment, the determination of the number of pixels in the first stage in the signal format determination, the determination of the image period and the sampling frequency in the second stage, and the determination of the phase between the video signal and the sampling signal in the third stage. Although the matching has been described as being performed automatically, the present invention is not limited to this. Only the determinations in the first and second steps are automatically performed, and the phase matching in the third step is performed. May not be performed, or may be performed manually.

It is a block diagram of an image signal input device which is one example of the present invention. It is a perspective view of an image signal input device. 5 is a timing chart of a video signal. FIG. 4 is an explanatory diagram of image dimensions corresponding to a synchronization signal frequency. 2 is a flowchart illustrating the operation of FIG. FIG. 3 is a diagram illustrating a relationship between a sampling signal and a video signal. FIG. 9 is a diagram for explaining how to obtain the number of sampling clocks set in a frequency division ratio shift register. FIG. 3 is a diagram for explaining a phase shift of a sampling signal. FIG. 3 is a block diagram of an apparatus for determining a frequency of a horizontal synchronization signal. FIG. 3 is a block diagram of an apparatus for correcting a phase shift of a sampling signal. It is a block diagram of a device which detects an image period. FIG. 3 is a block diagram of an apparatus for detecting an image period of a video signal having an offset. FIG. 6 is a block diagram of a second embodiment of the present invention. 14 is a flowchart illustrating the operation of FIG. FIG. 9 is a block diagram of a third embodiment of the present invention. FIG. 14 is a block diagram of a fourth embodiment of the present invention. FIG. 13 is a diagram for explaining the operation of FIG. 12. 5 is a timing chart illustrating a configuration of a video signal.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Image signal input device, 2 ... Video signal output device, 4 ... Common bus, 5 ... Image memory, 20 ... Image printing means, 21 ... Image storage means, 22, 23 ... Interface, 25 ... Phase delay means, 26 ... Horizontal input head position setting means, 27: horizontal synchronization address generation means, 28: vertical synchronization address generation means, 29: horizontal input head position setting means, 30: interlace detection means, 55: line memory, 301: A / D conversion Vessel, 381 ... controller.

Claims (2)

In an image display device capable of displaying an image faithful to the video signal when the video signal is input in response to a video signal composed of a horizontal synchronization signal, a vertical synchronization signal, and a video signal having various signal parameter specifications. ,
A / D conversion means for quantizing the video signal with a sampling clock having substantially the same frequency as a reference clock constituting the video signal;
Image memory means for holding image data corresponding to a video period of the video signal among outputs of the conversion means;
Display means for displaying an image of the output of the memory means. In an image display device capable of displaying an image faithful to the video signal when the video signal is input in response to a video signal composed of a horizontal synchronization signal, a vertical synchronization signal, and a video signal having various signal parameter specifications. ,
A / D conversion means for quantizing the video signal with a sampling clock having the same frequency as a reference clock constituting the video signal;
Phase adjusting means for adjusting the phase of the sampling clock when a video signal having a predetermined image pattern is input;
Image memory means for holding image data corresponding to a video period of the video signal among outputs of the A / D conversion means;
Display means for displaying an image of the output of the memory means.

Images