KR950008127B1 - Image signal writing/reading apparatus - Google Patents

Abstract

The unit saves the image signal of high frequency band to a tape for folding in low frequency band and regenerates the image signal of high frequency band unfolding from low frequency band. It comprises an image signal regeneration device decoding image signal folding timely, an A/D converter(41) and spatial cut part (42) removing image signal in frequency band that the uses is difficult to recognize.

Description

Video signal recording / playback device for improving picture quality

1 is a video signal frequency band of a video home system (VHS).

2 is a conceptual diagram showing a three-dimensional frequency domain of the NTSC composite video signal.

3 is a two-dimensional frequency domain consisting of a horizontal frequency f _H and a vertical frequency f _V.

4 is a block diagram of a video signal recording apparatus in the SP system.

5 is a block diagram of a video signal reproducing apparatus in the SP system.

6 is a flowchart for data selection output.

7 is a block diagram of a video signal recording apparatus in the EP system.

8 is a block diagram of a video signal reproducing apparatus in the EP system.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal recording / reproducing apparatus for improving image quality. In particular, a video signal of a high frequency region is recorded on a tape by folding in a low frequency region. An unfolding video signal recording / reproducing method and apparatus thereof are provided.

FIG. 1 illustrates a video signal frequency band of a video home system (VHS). The horizontal axis represents a frequency band of a video signal in units of frequency (f) and the vertical axis is determined in decibels (dB). FIG. 1 (a) shows a low frequency luminance signal Y _L of 2.5 MHz or less in a frequency domain of a TV video signal transmitted from a broadcasting station, in particular, a luminance signal of 2.5 MHz or less, as a high frequency luminance signal Y _H. Fig. 1 (b) shows the frequency bands of the TV video signals recorded on the video tape.

The existing video home system (VHS) is difficult to record / reproduce video signals of 2.5 MHz or more as shown in FIG. 1 (b) due to the frequency characteristics of the head and tape. Therefore, many studies have been made to solve the problem of lowering the degree of correspondence caused by the high frequency signal loss of 2.5MHz or more. Representative among them is ID (Improved Definition) -VTR. A general video signal recording / reproducing method of ID-VTR will be described with reference to FIG. 2 and FIG.

A conceptual diagram showing the three-dimensional frequency domain of the NTSC composite video signal shown in FIG. 2. Displayed in a three-dimensional frequency space consisting of a horizontal frequency f _H , a vertical frequency f _V , and a frequency f _t corresponding to time. It is. Four blocks consisting of three blocks hatched the frequency signal of the color signal and one block not shown in the figure, and the remaining areas represent the frequency area of the luminance signal, especially the area enclosed by the roughly indicated dotted line is a Pukinuki Hall (Fukinuki Hole) is displayed.

FIG. 3 shows a two-dimensional frequency domain consisting of a horizontal frequency f _H and a vertical frequency f _V. FIG. 3 a corresponds to a horizontal frequency f _H of 5 MHz and one field of the NTSC method. Figure 2 shows the two-dimensional frequency domain of the video signal whose range is determined by the vertical frequency (f _H ) of 525/2, and Figure 3 (b) shows the frequency domain from which the four corners of the two-dimensional frequency domain are removed. It is shown. FIG. 3 (c) shows the frequency domain of the video signal actually recorded on the tape, and the hatched portion is called a diagonal component Y _D.

In general, the human eye is insensitive to changes in color signals, so the image quality is improved by adjusting the brightness. Therefore, in the ID-VCR, the luminance signal Y _H corresponding to the high range of 2.5 MHz or more is applied to the tape by using a blank area in the 2.5 MHz or less frequency area, that is, a Pkinuki keyhole area not used by the 2.5 MHz or less video signal. By recording, the luminance signal Y _{H in} the high frequency region can be saved and the image quality can be improved. In the following description, the insertion of a high frequency signal of 2.5 MHz or more into an area of 2.5 MHz or less for recording a video signal is referred to as 'folding', and the folded high frequency signal is restored to a frequency area of 2.5 MHz or more to reproduce a signal. This is called 'unfolding'.

Conventional ID-VCR method determines the movement of the image to record a video signal having a horizontal frequency of 2.5MHz or more on the tape. When the motion is small or the still picture, the frequency of the video signal related to the change of time is almost 0. Therefore, the video signal having the horizontal frequency of 2.5 MHz or more of the current field or frame is changed to the next field of the frequency domain where the horizontal frequency is 2.5 MHz or less. The frame, ie, 'temporal folding', is recorded in the frequency field of the next field or frame formed on the time-frequency frequency f _t axis perpendicular to the ground in FIG. In the case of moving images, a video signal having a horizontal frequency of 2.5 MHz or more is 'spatial folding', ie, spatial spatial cutting using a filter in a region having a horizontal frequency of 2.5 MHz or less in FIG. 3 (b). We are folding on the empty space created by cut). When the video signal is reproduced, the motion of the video is judged, and when there is little movement, temporal unfolding is used, and when there is much movement, spatial unfolding is used. Then, a motion detection method using data comparison between images is used to record information on the amount of motion of the image with 250 MHz four-phase amplitude modulation for resolving still and moving images, or to reproduce without recording motion information at the time of recording.

Standard play mode with play time of about 1 hour (Standatd Play mode; hereinafter referred to as 'SP method') and extended play mode with play time of about 3 hours (Extended Play mode; hereinafter referred to as 'EP method') In the case of not recording information on the amount of motion of the image, a motion detection error due to jitter occurs and the amount of motion of the image cannot be detected accurately. Therefore, the video signal is reproduced in a manner different from the recording method. A problem arises. When recording information on the amount of motion of an image, there is a problem that cross talk occurs between motion information and color signals. In particular, since the high-pass luminance signal is folded into the Pukinuki hole in the EP method, which is a high density recording method, the above-mentioned crosstalk problem still remains even when a carrier shift method is employed to overcome the cross-channel crosstalk problem.

An object of the present invention for solving the above problems is to use a temporal folding method when recording a luminance signal in a standard play mode with low channel crosstalk, and to select a temporal method selected by a predetermined comparison process during reproduction. The present invention provides an image signal recording / reproducing apparatus for improving image quality by reproducing a luminance signal by using one of unfolding and spatial unfolding.

Another object of the present invention for solving the above problems is that, in the extended play mode with large channel crosstalk, the odd field is signal processed by spatial folding when the luminance signal is recorded, and in the case of the even field, a general video groove is used. The present invention provides a video signal recording / reproducing method for improving image quality by resolving a shortage of diagonal components and a high frequency component due to spatial cutting during reproduction.

The object of the present invention is to provide a device for recording a video signal on a video tape in a standard play mode, wherein spatial cutting is performed to receive luminance data and delete luminance data in a frequency domain that is difficult for humans to detect. a third filter that receives spatial cut means, an output data of spatial unfolding means, and extracts a luminance signal of a high frequency region, and extracts luminance data belonging to a high frequency region by receiving an output luminance data of the spatial cutting means. And a means for temporally folding the luminance data output from the spatial cutting means and the output data of the first filter and luminance data of the high frequency region belonging to a current field or frame. Video signal recording device for improving picture quality, and video signal recorded on video tape in standard operation method An apparatus comprising: means for receiving a luminance signal recorded on a tape by the apparatus and spatially unfolding a luminance signal in a high frequency region of a current field or frame from a low frequency region, and the luminance signal recorded by the apparatus Means for temporally unfolding the luminance signal of the high frequency luminance signal region of the current field or frame from the low frequency region, and a third filter for receiving the output data of the spatial unfolding means to extract the luminance signal of the high frequency region; First data difference value detecting means for receiving the output data of the spatial unfolding means and detecting data difference values of respective elements between frames; and data difference of each pixel between the frames receiving the output data of temporal unfolding means. Second data difference value detecting means for detecting a value, and outputs of said unfolding means and data difference value detecting means; Data is inputted to determine the motion of the image in a predetermined unit. If the motion of the image is large, the output signal of the spatial unfolding means is selectively outputted. A video signal reproducing apparatus for improving image quality including a selective output means is achieved.

Another object of the present invention is to provide an apparatus for recording an image signal on a video tape in an extended play mode, and to receive spatial data, and to spatially cut a luminance signal in a frequency domain that is difficult for humans to detect. (spatial cut), a second filter for receiving the output luminance data of the spatial cutting means and extracting luminance data belonging to the high frequency region, and an output data of the spatial cutting means and the output data of the second filter. Spatial folding means for spatially folding the luminance data of the high frequency region belonging to the field or frame, luminance data inputted to the spatial cutting means, and output data of the spatial cutting means, and the spatial folding means for the odd field. Selective output of the output data, and the even field to the luminance data input to the spatial cutting means An image signal recording apparatus for improving image quality including an output first multiplexer, and an apparatus for reproducing an image signal recorded on a video tape in an extended operation method, comprising: receiving a luminance signal recorded by the apparatus and receiving a high frequency frequency Means for spatial unfolding the luminance signal of the region from the low frequency region, a fourth filter for extracting the luminance signal of the diagonal frequency region from the luminance signal input to the spatial unfolding means, and the spatial unfolding means of the spatial unfolding means. A third adder for adding an output signal and an output signal of the fourth filter, a fourth adder, a third adder, and a fourth adder for adding the luminance signal inputted to the spatial unfolding means and the luminance signal outputted from the third filter; Selects and outputs the output signal of the third adder in the odd field and the output signal of the fourth adder in the even field It is achieved by a video signal reproducing apparatus for improving image quality comprising a second multiplexer for output.

Hereinafter, a video signal recording / reproducing apparatus for improving image quality of the present invention will be described in detail with reference to the accompanying drawings.

4 is a block diagram of a video signal recording apparatus in the SP system, and shows a signal processing apparatus for recording a video signal on a video tape in the SP system.

The apparatus of FIG. 4 includes an A / D converter 41, a spatial cut section 42 for deleting a video signal corresponding to a frequency domain which is difficult for humans to detect, and a luminance signal Y _{H of} 2.5 MHz or more. The first filter 43 for extracting the signal, and the high-frequency luminance signal Y _{H that} is 2.5 MHz or more belonging to the current field of the spatially cut third diagram (b) in the two-dimensional frequency domain, and the low-frequency luminance signal that is 2.5 MHz or less in the next field ( Y _L ) and a three-dimensional temporal folding unit 44 and a D / A converter 45 to be folded. When the video signal for recording to the apparatus of FIG. 4 is input as a digital video signal by the A / D converter 41, the spatial cutting unit 42 connected to the output terminal of the A / D converter 41 is connected to the input video signal. The video signal corresponding to the hatched area of FIG. 3 (a), which is generated by the frequency range that is hard to be felt by humans, that is, the horizontal frequency f _H and the vertical frequency f _V is removed, and the remaining video signals are output. . The first filter 43 connected to the output terminal of the spatial cutting unit 42 extracts the high luminance signal Y _H having a horizontal frequency of 2.5 MHz or more from the input image signal. In addition, the three-dimensional temporal folding unit 44 connected in parallel with the above-described filter 43 at the output terminal of the spatial cutting unit 42 has a horizontal frequency f _H of the next field image signal output from the spatial cutting unit 42 at 2.5 MHz. The high-frequency luminance signal Y _H of the current field output from the filter 43 is temporally folded in the following area. The folded video signal is converted into an analog signal by the D / A converter 45 and recorded on the tape through a head not shown in the drawing. High-band luminance signals having a horizontal frequency f _{H of} 2.5 MHz or more are recorded on the tape in spite of the characteristics of the head and tape by temporal folding as described above.

FIG. 5 is a block diagram of a video signal reproducing apparatus in the SP method, and shows a video signal reproducing apparatus for restoring a video signal three-dimensionally folded by the apparatus of FIG.

The apparatus of FIG. 5 includes an A / D converter 51 connected to an image signal input terminal and a low luminance signal Y _L region connected to an output terminal of the A / D converter 51 and 2.5 MHz or less in FIG. Parallel connection to the spatial unfolding unit 52 and the spatial unfolding unit 52 for restoring the video signal of the current field folded to the video signal belonging to the current field of the high frequency luminance signal Y _{H which} is the original frequency domain. And unfolding the video signal of the current field, which is folded in the low-pass luminance signal Y _L region of FIG. 3 (b), into the high-frequency luminance signal region of the previous field, and the spatial unfolding unit ( A first frame delayer 54 and a second frame delayer 55 for delaying outputting the output data of the second data and the output data of the temporal unfolding unit 53 by one frame time interval, and a first frame delayer ( The output data of the first adder A1 and the second frame delay unit 55 which subtracts the output data of the spatial unfolding unit 52 from the output data of 54). The second adder A2 subtracts the output data of the temporal unfolding unit, the output data of the adders A1 and A2, and the output data of the spatial unfolding unit 52 and the temporal unfolding unit 53. And a data selection output section 56 for selectively outputting one of temporally unfolded data and spatially unfolded data by determining the amount of motion of the circuit.

When the video signal recorded on the tape is input to the apparatus of FIG. 5 through the A / D converter 51, the spatial unfolding unit 52 and the temporal unfolding unit 53 connected in parallel to the output terminal of the A / D converter 51 are provided. ) Processes the input image data in a predetermined manner. That is, the spatial unfolding unit 52 extracts the high-frequency luminance signal Y _H contained in the low-frequency luminance signal region Y _L among the input image data, and the temporal unfolding unit 53 continuously extracts the input image data. The high frequency luminance signal Y _H contained in the low frequency luminance signal Y _L region is extracted using the frame data.

The output data D1 of the spatial unfolding unit 52 is delayed by the frame time interval made by the first frame delay unit 54, and the data after one frame is subtracted from the first adder A1. The output data D2 of the temporal unfolding unit 53 is also delayed by one frame time interval by the second frame delay unit 55, and the delayed data is subtracted by one frame or more from the second adder A2. . Data addition of the adders A1 and A2 is performed for each pixel, and the output data D3 of the first adder A1 and the output data D4 of the second adder A2 are selected. Input to the output unit 56. The data selection output unit 56 receives the temporal unfolding unit 53 of the spatial unfolding unit 52 and the output data D1-D4 of the first and second adders A1 and A2. Selectively output the data according to the flowchart shown in the figure.

FIG. 6 is a flowchart for data selection output, and is for selectively outputting temporally unfolded data or spatially unfolded data using motion detection of an image. When the data D3 transmitted from the first adder A1 and the data D4 transmitted from the second adder A2 are input to the data select output unit 56, the data select output unit 56 is generated between frames. The number of pixels CNTY (i) whose data size difference values of each pixel are larger than the first predetermined reference value r ₁ is counted in each scanning line (step 61). Here, i means a predetermined scan line. The number of pixels counted per line is compared with a predetermined second reference value r ₂ ('5' in this embodiment) (step 62). The number of pixels counted per line (if CNTY (i) is smaller than r ₂ , the data D4 outputted from the second adder A2 is regarded as a small movement, and the data D4 is determined as a predetermined variable value P. ('10' in this embodiment) is set to the third reference value Q (step 63), and when the number of pixels CNTY (i) counted per line is greater than or equal to r ₂ , the line has a lot of motion. It is assumed that the data D3 outputted from the first adder A1 is set as the predetermined variable value P, and the above-described variable value Q for predetermined comparison of the predetermined data ('0' in this embodiment) is given. (Step 64).

When one of step 63 or step 64 is selected and executed, the absolute value | P | of the difference value between the frames of the pixel data is compared with the magnitude of the third reference value Q (step 65). If the absolute value | P | and the third reference value Q or more, the pixel is regarded as a moving image pixel, and the data D1 transmitted to the spatial unfolding unit 52 is selectively outputted (step 66). On the other hand, if the absolute value | P | is smaller than the third reference value Q, the pixel is regarded as a pixel of a still picture and temporally unfolded data, that is, data D2 transmitted from the temporal unfolding unit 53 Output (step 67). The above-mentioned data selectively outputted by the amount of motion between frames in the data selection output section 55 are output as an analog signal via the D / A converter 57 and used to reproduce an image on the screen.

7 is a block diagram of a video signal recording apparatus in the EP system. In the following description, the two-dimensional frequency region having a horizontal frequency of 2.5 MHz or less except for the diagonal component Y _D of FIG. 3 (c) is designated as the low luminance signal region Y _L , and the region of 2.5 MHz or higher is a high luminance. It is called a signal region (Y _H ).

The apparatus of FIG. 7 includes an A / D converter 71 and a D / A converter 76 for signal shape conversion, a spatial cut 72 for removing a frequency region in which the human eye is insensitive, and a low range of 2.5 MHz or less. The second filter 73 for extracting the high frequency frequency (Y _H ) from the frequency domain, the horizontal frequency (f _H ) of 2.5 MHz or more and the luminance signal of the current field belonging to the region are folded in the same field and the frequency domain of 2.5 MHz or less. And a first multiplexer 75 for receiving the output data of the A / D converter 71 and the output data of the 2D spatial folding unit 74 and selectively outputting the output data according to the field. do.

The video signal input through the A / D converter 71 outputs only data belonging to the frequency region Y _L + Y _H + Y _{D of} FIG. 3 b by the spatial cutting unit 72. The image data output from the spatial cutting unit 72 folds the high-intensity luminance signal Y _H into a 2.5 MHz or less region of the spatially cut image signal by the second filter 73. The image data output from the above-described A / D converter 71 and the two-dimensional spatial folding unit 74 is selectively output by the control signal C1 applied to the first multiplexer 75. That is, in the odd field, data belonging to the predetermined frequency region Y _L + Y _H is transmitted from the two-referential spatial folding unit 74 to the D / A converter 76, and in the case of the even field, the A / D converter ( 7 1) and outputs the image data belonging to another predetermined frequency range (Y _L + Y _H + Y _D ) to the D / A converter 76 as it is. The video data to be selectively output is output to the D / A converter 76. The video data to be selectively output is converted via the D / A converter 76 and recorded on the video tape according to a general video signal recording method. Due to the field characteristics of the head and non-eotape, in the odd field, the luminance signal of the predetermined frequency range (Y _L + Y _H ) is preserved by folding, but in the even field, the luminance belonging to the high frequency range (Y _H ) The signal is not recorded on the tape.

8 is a block diagram of a video signal reproducing apparatus in the EP system. The apparatus of FIG. 8 inputs an A / D converter 81, a third filter 83 connected to an output terminal thereof and extracting a high luminance signal Y _H , and output data of the A / D converter 81. A third adder A3 connected to add the fourth filter 84, which receives the diagonal luminance component Y _D , and the output data of the fourth filter 84, and the output data of the spatial unfolding unit 82. And an output of the fourth adder A, the third adder A3, and the fourth adder A4, which add the output data of the third filter 83 and the output data of the A / D converter 81 described above. And a second malt multiplexer 85 that receives data and selectively outputs the data using a predetermined control signal C2, and a D / A converter 86 connected to the output terminal thereof.

When the video signal read from the tape is converted into the digital form by the A / D converter 81, the spatial unfolding unit 82 receives the image data and low frequency in the same manner as the spatial unfolding unit 52 of FIG. Strip the conjugate luminance signal (Y _H ) that was scared in the area. The third filter 83 filters the data output from the spatial unfolding unit 82 and outputs only the high luminance signal Y _H. Since the data transmitted from the A / D converter 81 to the fourth filter 84 is filtered by the fourth filter 84, only the diagonal luminance signal Y _D appears at the output terminal of the fourth filter 84. In the odd field, the third adder A3 adds the output data of the spatial unfolding unit 82 and the output data of the fourth filter 84 to the frequency domain of Y _L + Y _H + Y _D. Outputs the luminance signal belonging to and outputs the luminance signal in the Y _L + Y _D frequency domain in the even field. The fourth adder A4 outputs only luminance signals in the Y _L + Y _H frequency domain in the odd field, and output data of the A / D converter 81 and output data in the third filter 83 in the even field. The luminance data of the predetermined frequency range Y _L + Y _H + Y _D generated by adding s is output. The second multiplexer 85 receives the output data of the third adder A3 and the fourth adder A4 and selectively outputs the output data according to the predetermined control signal C2. That is, in the case of the odd field, the output data of the third adder A3, that is, the luminance signal in the frequency domain Y _L + Y _H + Y _D is output by the control signal C2, and in the case of the even field, the fourth adder The output data of (A4), that is, the luminance signal in the frequency domain Y _L + Y _H + Y _D is output. The output data of the second multiplexer 85 is converted into an analog signal by the D / A converter 86 and used for image reproduction.

According to the video signal recording / reproducing apparatus for improving the image quality of the present invention as described above, the video signal is recorded in the temporal folding method in the SP mode, and the temporal unfolding or spatial unfolding data is selectively output by detecting the movement between frames. As a result, a luminance signal of about 5 MHz can be reproduced and a resolution of 400 or more can be obtained. In the EP mode, the odd field is recorded by spatial folding, the even field is recorded as the video groove method, and during reproduction, the loss compensation of the diagonal frequency component occurring in the odd field and the loss of the high frequency component occurring in the even field are compensated. There is an effect capable of reproducing a luminance signal of about 3 MHz.

Claims (6)

An apparatus for recording an image signal on a video tape in a standard play mode, the apparatus comprising: spatial cut means for receiving luminance data and deleting luminance data of a frequency domain which is difficult for humans to detect; A first filter which receives the output luminance data of the spatial cutting means and extracts luminance data belonging to the high frequency region; And a means for temporally folding the luminance data of the high frequency region belonging to the current field or frame by receiving the luminance data output from the spatial cutting means and the output data of the first filter. Logger. A device for reproducing a video signal recorded on a video tape in a standard operation method, comprising: receiving a luminance signal recorded on a tape by the apparatus of claim 1 and outputting a luminance signal in a high frequency region of a current field or frame from a low frequency region; Means for spatial unfolding; Means for receiving the luminance signal recorded by the apparatus of claim 1 and temporally unfolding the luminance signal in the high frequency region of the current field or frame from the low frequency region; First data difference value detecting means for receiving output data of the spatial cumulative folding means and detecting a data difference value of each pixel between frames; Second data difference value detecting means for receiving output data of the temporal unfolding means and detecting a data difference value of each pixel between frames; The output data of the unfolding means and the data difference value detecting means is input to determine an image movement in a predetermined unit. If the image movement is large, the output signal of the spatial unfolding means is selectively outputted. And a data selection output means for selectively outputting the output signal of the temporal unfolding means. 3. The image quality value according to claim 2, wherein the data difference value detecting means includes a frame delay for delaying the input data for one frame time interval, and an adder for subtracting the frame delayed data to unfolded data. Video signal reproduction device for improvement. 3. The data selection output means according to claim 2, wherein the data selection output means compares the output data of the second data difference value detecting means with a predetermined first reference value for each pixel to detect the number of pixels having data equal to or greater than the first reference value in each line. When the number of detected pixels is compared with a predetermined second reference value and the number of pixels is smaller than the second reference value, the line compares the output data of the second data difference detection means with a predetermined third reference value and compares the number of pixels by the comparison. If it is larger than the second reference value, the output data of the first data difference detection means is compared with the predetermined fourth reference value, and if the output data of the second data detection means is smaller than the third reference value, the output data of the temporal unfolding means is selected. If the data is greater than or equal to the third reference value, the output data of the spatial unfolding means is selected. If the output data of the first data detection means is less than the fourth reference value, the temporal unfolding is selected. In such a manner as to select the output data of the single spatial unfolding means or unloading time, select the output data of the folding means outputs a video signal reproducing apparatus for picture quality improvement which comprises. An apparatus for recording an image signal on a video tape in an extended play mode, the apparatus comprising: spatial cut means for receiving luminance data and deleting luminance signals in a frequency domain that are difficult for humans to detect; A second filter which receives the output luminance data of the spatial cutting means and extracts luminance data belonging to the high frequency region; Means for spatially folding the luminance data of the high frequency region belonging to the current field or frame by receiving the output data of the spatial cutting means and the output data of the second filter; The luminance data input to the spatial cutting means and the output data of the spatial cutting means are input and the output data of the spatial folding means is selected and output in the odd field, and the luminance data input to the spatial cutting means is output in the even field. An image signal recording apparatus for improving image quality of a first multiplexer. An apparatus for reproducing an image signal recorded on a video tape in an extended operation method, wherein the luminance signal recorded by the apparatus of claim 5 is input and spatial unfolding of a luminance signal in a high frequency region from a low frequency region Means for doing; A third filter which receives the output data of the spatial unfolding means and extracts the luminance signal in the high frequency region; A fourth filter for extracting a luminance signal in a diagonal frequency region from the luminance signal input to the spatial unfolding means; A third adder for adding the output signal of the spatial unfolding means and the output signal of the fourth filter; A fourth adder for adding the luminance signal input to the spatial unfolding means and the luminance signal output from the third filter; In response to the output signals of the third adder and the fourth adder, an odd field selects and outputs an output signal of the third adder, and an even field selects and outputs a second multiplexer for selectively outputting the output signal of the fourth adder. Video signal playback device.