Video signal processing apparatus

Abstract: A video signal processing apparatus, typically for use as a video tape recorder/recording for recording and reproducing high-definition television signals, includes an encoder (4) for converting a chrominance signal (P R , P B ) into a line sequential signal and multiplexing the line sequential signal with a luminance signal (Y) on time compression according to time-division multiplexing, thereby producing a time-division-multiplexed signal. A vertical emphasis circuit (31R, 31B) is connected to an input terminal of the encoder (4), for effecting vertical nonlinear emphasis on the chrominance signal (P R , P B ). The video signal processing apparatus also includes a vertical low-pass filter (32R, 32B) for removing aliasing distortions from the chrominance signal (P R , P B ) into the line sequential signal. The vertical nonlinear emphasis is effected on the chrominance signal (P R , P B ) after the chrominance signal (P R , P B ) has been processed by the vertical low-pass filter (32 R , 32 B ).

Description: This invention relates to video signal processing apparatus. More particularly, but not exclusively, this invention relates to video signal processing apparatus that may, for example, be used in a video tape recorder/reproducer which records and reproduces a high-definition television (HDTV) signal. Some video tape recorder/reproducers for recording and reproducing HDTV signals, particularly those for home use, convert chrominance signals into line sequential signals, and multiplex the line sequential signals with a luminance signal on time compression according to time-division multiplexing (TDM), thereby producing a TDM signal that is recorded and reproduced in a plurality of channels with multichannel heads (see Japanese Patent Application JP-A-63194494, for example). Figure 1 of the accompanying drawings shows such a video tape recorder/reproducer. In Figure 1, a luminance signal Y, which is demodulated from an HDTV signal, for example, is applied to an input terminal 1Y and supplied through a low-pass filter 2Y to an analog-to-digital (A/D) converter 3Y. The converted digital signal is then supplied to an TDM encoder 4. Chromatic signals P R , P B (colour difference signals R-Y, B-Y), which are demodulated from the HDTV signal, are applied to respective input terminals 1R, 1B and supplied through respective low-pass filters 2R, 2B to analog-to-digital (A/D) converters 3Y, 3B, respectively. The converted digital signals are then supplied to the TDm encoder 4. The TDM encoder 4 converts the chrominance signals into line sequential signals, and multiplexes them with the luminance signal according to time-division multiplexing. More specifically, when an HDTV signal is to be recorded, the luminance signal Y and the chrominance signals P R , P B are converted into digital signals at given sampling frequencies by the A/D converters 3Y, 3R, 3B, respectively, as shown in Figures 2A, 2B, 2C of the accompanying drawings, and the digital signals are stored in the TDM encoder 4. The sampling frequency for the luminance signal Y is selected to be an integral ratio, which is to be as simple as possible, of 72.25 MHz that is a fundamental clock frequency of the HDTV system, and also to be an integral multiple of a horizontal frequency (fH1 = 33.75 kHz) of the HDTV system. For example, the sampling frequency for the luminance signal Y is selected to be: (3/5) x 74.25 = 44.55 (MHz) = 1320 fH1. The sampling frequency for the chrominance signals P R , P B is selected to be 1/4 of the sampling frequency for the luminance signal Y. As shown in Figures 2A, 2B, 2C, the luminance signal Y and the chrominance signals P R , P B , which are sampled as 1320 and 330 samples over one horizontal scanning line, are stored in the TDM encoder 4. The stored signals are combined with each other, and the combined signals are supplied to digital-to-analog (D/A) converters 5A, 5B (Figure 1) which convert them into two-channel TDM signals as shown in Figures 2D, 2E. Figure 3 of the accompanying drawings shows such a TDM signal in specific detail. As shown in Figure 3, the TDM signal includes a signal of 1152 samples, which make up an effective screen image of the luminance signal Y, over one scanning line alternately for the channels, and a signal of 288 samples, which make up an effective screen image of each of the chrominance signals P R , P B , as a selectively omitted line sequential signal over one scanning line alternately for the channels. The TDM signal is composed of a total of 1530 samples over one scanning line, and includes, in addition to the luminance signal Y and the chrominance signals P R , P B , a synchronizing signal SYNC of 20 samples, a burst signal SB of 30 samples, and ID data ID1, ID2 each of 4 samples. The two-channel TDM signals from the D/A converters 5A, 5B are then supplied through respective low pass filters 6A, 6B to analogue signal processors 7A, 7B for preemphasis, for example. The processed signals are supplied from the analogue signal processors 7A, 7B to frequency modulators (FM) 8A, 8B, respectively, by which they are converted into respective frequency-modulated signals to be recorded. These converted TDM signals, i.e., the frequency-modulated signals, are then supplied to respective adders 9A, 9B. Stereophonic audio signals, for example, in righthand and lefthand channels are applied through respective input terminals 10L, 10R to a digital audio signal processor 11 which generates two-channel digital audio signals. These digital audio signals are supplied to the adders 9A, 9B by which they are added to the TDM signals from the frequency modulators 8A, 8B using time-division multiplexing. The multiplexed signals are then supplied to recording amplifiers 12A, 12B, respectively, which then supply amplified signals through recording/reproducing mode selector switches 13A, 13B to two-channel magnetic heads 14AB, 15AB, respectively, which are mounted on a rotary drum D at a 180°-spaced angular interval. In a recording mode, the magnetic heads 14AB, 15AB rotate at a speed of 60 revolutions per second, for example, to record, on a magnetic tape T wound around the rotary drum D along a 180° arc, the signals according to a recording pattern (see Figure 4 of the accompanying drawings) with one HDTV frame composed of two channels in four segments (eight tracks) per two revolutions of the rotary drum D. At the same time, the multiplexed digital audio signals are also recorded on the magnetic tape T. More specifically, as shown in Figure 4, an over lap of 4° is provided on each end of each of the tracks, and a 180° angular interval between the opposite overlaps on each track comprises a recording area for 167.5 horizontal periods each corresponding to one horizontal scanning line of the TDM signal. 27 out of these 167.5 horizontal periods, counting from the starting end in the head scanning direction, serve as a recording area for the digital audio signals, and the following 140.5 horizontal periods serve as a recording area for the TDM signal. According to the HDTV format, a maximum of four channels are reserved for the recording of audio signals, and sets of two channels of these four channels may be used independently of each other. The recording area for the digital audio signals includes a recording area for first and second audio signals, and a recording area for third and fourth audio signals. More specifically, one horizontal period, counting from the starting end in the head scanning direction, is reserved as a margin for head switching, and is followed by 9.1 horizontal periods reserved as the recording area for the third and fourth audio signals, including a preamble and a postamble. The recording area for the third and fourth audio signals is followed by 1.7 horizontal periods reversed as a guard for after recording, which guard is in turn followed by 9.1 horizontal periods reserved as the recording area for the first and second audio signals. The recording area for the digital audio signals also includes 2.7 horizontal periods reserved as a recording area for an index signal with a guard of 1.7 horizontal periods interposed between the recording area for the index signal and the recording area for the first and second audio signals. The index signal recording area is followed by a guard of 1.7 horizontal periods. The recording area for the TDM signal includes 4 or 4.5 horizontal periods, counting from the starting end in the head scanning direction, reserved as a recording area for information signals, i.e., a continuous-wave signal for phase locked loop (PLL) synchronisation, a segment synchronising signal, a reference level signal for automatic gain control (AGC), and a ramp signal for linearity correction. The information signal recording area is followed by 135 horizontal periods reserved as a recording area for the TDM signal. The numerals indicated in the TDM signal recording area in Figure 4 represent the horizontal period numbers, and the letters R, B indicate multiplexed chrominance signals. The TDM signal recording area is followed by a margin of 1.5 or 1 horizontal period. The HDTV signal is recorded on the magnetic tape according to the above pattern. In the recording mode, the signals recorded on the magnetic tape T are reproduced by the magnetic heads 14AB, 15AB and supplied through the recording/reproducing mode selector switches 13A, 13B to respective playback amplifiers 16A, 16B. Amplified signals from the playback amplifiers 16A, 16B are supplied to respective frequency demodulators 17A, 17B which supply demodulated signals to analog signal processors 18A, 18B. The processed signals are supplied from the analog signal processors 18A, 18B through low-pass filters 19A, 19B to respective A/D converters 20A, 20B. The A/D converters 20A, 20B supply converted digital signals to a TDM decoder 21. The TDM decoder 21 decodes the supplied digital signals into the luminance signal Y and the chrominance signals P R , P B which are separate from each other, and interpolates the chrominance signals P R , P B . The digital luminance signal Y from the TDM decoder 21 is supplied to a D/A converter 22Y which supplies a converted analog luminance signal Y through a low-pass filter 23Y to an output terminal 24Y. The digital chrominance signals P R , P B from the TDM decoder 21 are supplied to D/A converters 22R, 22B which supply converted analog chrominance signals P R , P B through respective low-pass filters 23R, 23B to output terminals 24R, 24B, respectively. The amplified signals from the playback amplifiers 16A, 16B are also supplied through playback equalizers 25A, 25B to an audio signal playback processor 26. The audio signal playback processor 26 reproduces righthand and lefthand stereophonic audio signals, for example, from the digital audio signals contained in the reproduced signals. The reproduced signals are supplied from the audio signal playback processor 26 to output terminals 27L, 27R. The recorded HDTV signals are reproduced from the magnetic tape in the manner described above. In the above video tape recorder/reproducer, it has been proposed to effect nonlinear emphasis in the vertical direction of the display screen with a view to improving the image quality of the reproduced signal. Such nonlinear emphasis poses no problem with respect to the luminance signal Y as all horizontal scanning lines are recorded and reproduced for the luminance signal Y. However, a problem arises with the chrominance signal P R , P B due to the fact that they are converted into line sequential signals when recorded and they are interpolated when reproduced. The drawback caused by nonlinear emphasis on the chrominance signals P R , P B will now be described in detail. Figure 5 of the accompanying drawings shows a circuit arrangement for effecting vertical nonlinear emphasis. In Figure 5, the luminance signal Y is supplied through a vertical nonlinear emphasis circuit 31Y to the TDM encoder 4. The chrominance signals P R , P B are supplied to respective vertical nonlinear emphasis circuits 31R, 31B. The emphasized signals from the vertical nonlinear emphasis circuits 31R, 31B are then supplied to respective vertical low-pass filters 32R, 32B that remove aliasing distortions caused by the conversion into line sequential signals. The signals from the low-pass filters 32R, 32B are then supplied to the TDM encoder 4. The luminance signal Y decoded by the TDM decoder 21 is supplied to the output terminal through a vertical nonlinear deemphasis circuit 33Y. The chrominance signals P R , P B decoded by the TDM decoder 21 are supplied through respective vertical nonlinear deemphasis circuits 33R, 33B to interpolating filters 34R, 34B, respectively, which interpolate the supplied chrominance signals P R , P B in the vertical direction to compensate for the signal omission caused by the line sequential conversion. The TDM encoder 4 and the TDM decoder 21 shown in Figure 5 are identical to those shown in Figure 1. The vertical low-pass filters 32R, 32B are of a circuit arrangement as shown in Figure 6A of the accompanying drawings, and the interpolating filters 34R, 34B are of a circuit arrangement as shown in Figure 6B of the accompanying drawings. Each of the filters shown in Figures 6A and 6B includes delay lines 41 for one horizontal line, coefficient circuits 42, and an adder 43. The vertical nonlinear emphasis circuits 31R, 31B are of a circuit arrangement as shown in Figure 7A of the accompanying drawings, and the vertical nonlinear deemphasis circuits 33R, 33B are of a circuit arrangement as shown in Figure 7B of the accompanying drawings. The circuit shown in Figure 7A includes a delay line 44 for one horizontal line, a subtracter 45, a level adjuster 47, a coefficient circuit 48, and an adder/subtracter 50. The circuit shown in Figure 7B includes a delay line 44 for one horizontal line, subtracters 45, 46, a level adjuster 47, coefficient circuits 48, 59, and an adder/subtracter 50. In the vertical nonlinear emphasis circuits 31R, 31B shown in Figure 7A, the level adjuster 47 has a characteristic curve as shown in Figure 8A of the accompanying drawings, the coefficient circuit 48 has a coefficient value of 1.5, and the adder/subtracter 50 serves as an adder. In the vertical nonlinear emphasis circuits 33R, 33B shown in Figure 7B, the level adjuster 47 has a characteristic curve as shown in Figure 8B of the accompanying drawings, the coefficient circuits 48, 59 have a coefficient value of 0.6, and the adder/subtracter 50 serves as a subtracter. In the case where the colour of an image changes vertically from green to magenta as shown in Figure 9 of the accompanying drawings, the chrominance signal representative of the image varies as shown in Figure 10A. Small circles in Figures 10A to 10C of the accompanying drawings indicate the positions of horizontal scanning lines. The signals which are omitted in alternate horizontal scanning periods by the line sequential conversion have two phases as shown in Figures 10B and 10C. When the signals omitted with the phases shown in Figures 10B and 10C were recorded and reproduced using the circuit arrangement of Figure 5 which includes the emphasis circuits 31R, 31B and the interpolating filters 34R, 34B in a simulating process, the output signals had waveform distortions as indicated by solid lines a in Figures 11A and 11B of the accompanying drawings. Input signals had waveforms as indicated by solid lines b, and output signals with no emphasis and deemphasis had waveforms as indicated by solid lines c. In the circuit arrangement shown in Figure 5, the emphasis circuits and the deemphasis circuits are combined with the low-pass filters, for removing aliasing distortions, and the interpolating filters respectively. These filters lower the frequency characteristics of the signals, thereby changing their waveforms. As a result, the deemphasized signals suffer waveform distortions, and their original waveforms cannot be reproduced exactly. According to the present invention there is provided a video signal processing apparatus comprising: an encoder for converting a chrominance signal into a line sequential signal and multiplexing the line sequential signal with a luminance signal upon time compression according to time-division multiplexing, thereby producing a time-division-multiplexed signal; a vertical emphasis circuit connected to an input terminal of said encoder, for effecting vertical nonlinear emphasis on said chrominance signal; and a vertical low-pass filter for removing aliasing distortions from said chrominance signal due to the conversion of said chrominance signal into the line sequential signal, wherein the vertical nonlinear emphasis is effected on the chrominance signal after the chrominance signal has been processed by said vertical low-pass filter . Since the vertical nonlinear emphasis is effected on the chrominance signal after it has been processed by the vertical low-pass filter that removes aliasing distortions from the chrominance signal due to the line sequential signal conversion, the signal waveform suffers less distortion, and the chrominance signal can be recorded and reproduced by a relatively simple circuit arrangement. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Figure 1 is a block diagram of a video tape recorder/reproducer. Figures 2A to 2E are diagrams showing luminance and chrominance signals; Figure 3 is a diagram showing a TDM signal; Figure 4 is a diagram illustrative of a recording pattern; Figure 5 is a block diagram of a video signal processing apparatus for effecting vertical nonlinear emphasis; Figures 6A and 6B are block diagrams of filters in the video signal processing apparatus shown in Figure 5. Figures 7A and 7B are block diagrams of emphasis and deemphasis circuits in the video signal processing apparatus shown in Figure 5. Figures 8A and 8B are diagrams showing characteristic curves of level adjusters in the emphasis and deemphasis circuits shown in Figures 7A and 7B. Figure 9 is a diagram of a display screen, showing a colour change of a displayed image; Figures 10A to 10C are diagrams showing signal waveforms; Figures 11A and 11B are diagrams of characteristic curves showing waveform distortion; Figure 12 is a block diagram of a video signal processing apparatus according to one embodiment of the invention; Figures 13A and 13B are diagrams showing characteristic curves of signals produced by the video signal processing apparatus shown in Figure 12; Figure 14 is a block diagram of a video signal processing apparatus according to another embodiment of the invention; Figures 15A and 15B are diagrams showing characteristic curves of signals produced by the video signal processing apparatus shown in Figure 14 and; Figure 16 is a block diagram of a video signal processing apparatus according to still another embodiment of the invention. Figure 12 shows a video signal processing apparatus according to one embodiment of the invention, typically used as a video signal recording/reproducing apparatus in a video tape recorder/reproducer. As shown in Figure 12, a luminance signal Y is supplied through a vertical nonlinear emphasis circuit 31Y to a TDM encoder 4. Chrominance signals P R , P B are supplied to respective vertical low-pass filters 32R, 32B that remove aliasing distortions caused by the conversion into line sequential signals. The signals that have passed through the low-pass filters 32R, 32B are supplied to respective vertical nonlinear emphasis circuits 31R, 31B. The signals from the vertical nonlinear emphasis circuits 31R, 31B are then supplied to the TDM encoder 4. The luminance signal Y decoded by a TDM encoder 21 is supplied to an output terminal through a vertical nonlinear deemphasis circuit 33Y. The chrominance signals P R , P B decoded by the TDM decoder 21 are supplied through respective vertical nonlinear deemphasis circuits 33R, 33B to interpolating filters 34R, 34B, respectively, which interpolate the supplied chrominance signals P R , P B in the vertical direction to compensate for the signal omission caused by the line sequential conversion. The TDM encoder 4 and the TDM encoder 21 shown in Figure 12 are identical to those shown in Figures 1 and 5. When the signals with two phases were recorded and reproduced using the circuit arrangement of Figure 12 in a simulating process, the output signals had waveforms as indicated by solid lines a in Figures 13A and 13B, these output signal waveforms being identical to those of output signals with no emphasis and deemphasis as indicated by solid lines c. Input signals had waveforms as indicated by the solid lines b. In the circuit arrangement of Figure 5, the chrominance signals are limited in bandwidth by the low-pass filters after they have been subjected to vertical emphasis. This signal processing causes large waveform distortions as some signal components are lost after being emphasised. According to the circuit arrangement shown in Figure 12, however, the signals are limited in bandwidth by the low-pass filters before they are subjected to vertical emphasis, so that the signal waveforms will not be varied by the emphasising and deemphasizing processes. In the above simulating process, each of the low-pass filters 32R, 32B and the interpolating filters 34R, 34B is in the form of a 3-tap circuit as shown in Figures 6A and 6B. If these filters comprise ideal circuits, then the input signal waveforms b and the output signal waveforms a may be brought into conformity with each other. With the circuit arrangement shown in Figure 12, the vertical nonlinear emphasis circuits 31R, 31B for nonlinearly emphasising the chrominance signals P R , P B are connected to effect vertical nonlinear emphasis on the chrominance signals P R , P B after they have been processed by the vertical low-pass filters 32R, 32B that remove aliasing distortions caused by the conversion into line sequential signals. Therefore, the signal waveforms suffer less distortion, and the signals can be recorded and reproduced with good characteristics by a circuit arrangement which is relatively simple. Figure 14 shows a video signal processing apparatus according to another embodiment of the invention. The video signal processing apparatus shown in Figure 14 differs from the video signal processing apparatus shown in Figure 12 in that the chrominance signals P R , P B decoded by the TDM decoder 21 are first supplied to the interpolating filters 34R, 34B by which they are interpolated in the vertical direction, and the interpolated chrominance signals P R , P B are supplied to the vertical nonlinear deemphasis circuits 33R, 33B. The signals recorded and reproduced using the circuit arrangement shown in Figure 14 in a simulating process had waveforms as shown in Figures 15A and 15B. With the interpolating filters 34R, 34B comprising ideal circuits, the output signal waveforms a can be identical to the output signal waveforms c with no emphasis and deemphasis effected. Figure 16 shows a video signal processing apparatus according to still another embodiment of the invention, the apparatus including circuits for effecting horizontal nonlinear emphasis and deemphasis. As shown in Figure 16, horizontal nonlinear emphasis circuits 35R, 35B are connected between the vertical low-pass filters 32R, 32B and the vertical nonlinear emphasis circuits 31R, 31B and horizontal nonlinear deemphasis circuits 36R, 36B are connected between the vertical nonlinear deemphasis circuits 33R, 33B and the interpolating filters 34R, 34B. The horizontal nonlinear emphasis circuits 35R, 35B may be connected to input terminals of the vertical low-pass filters 32R, 32B, but should not be connected to output terminals of the vertical nonlinear emphasis circuits 31R, 31B. The horizontal nonlinear deemphasis circuits 36R, 36B may be connected to output terminals of the interpolating filters 34R, 34B, but should not be connected to input terminals of the vertical nonlinear deemphasis circuits 33R, 33B. At least preferred embodiments of the invention provide a video signal processing apparatus of simple circuit arrangement which is capable of effecting vertical emphasis and deemphasis on chrominance signals with low distortion. The present invention may be applied not only to video tape recorder/reproducers for the illustrated HDTV signals, but also to video tape recorder/reproducers for other HDTV signals and conventional television video signals. The principles of the present invention are applicable to the processing of analog signals as well as digital signals.

Claims: A video signal processing apparatus comprising: an encoder (4) for converting a chrominance signal (P R P B ) into a line sequential signal and multiplexing the line sequential signal with a luminance signal (Y) upon time compression according to time-division multiplexing, thereby producing a time-division-multiplexed signal (Figure 3); a vertical emphasis circuit (31R, 31B) connected to an input terminal of said encoder (4), for effecting vertical nonlinear emphasis on said chrominance signal (P R , P B ); and a vertical low-pass filter (32R, 32B) for removing aliasing distortions from said chrominance signal (P R , P B ) due to the conversion of said chrominance signal (P R , P B ) into the line sequential signal, wherein the vertical nonlinear emphasis is effected on the chrominance signal (P R , P B ) after the chrominance signal (P R , P B ) has been processed by said vertical low-pass filter (32R, 32B). Apparatus according to claim 1, including; a decoder (21) for decoding said time-division-multiplexed signal (Figure 3) into the chrominance (P R , P B ) and the luminance (Y) signals; a vertical deemphasis circuit (33R, 33B) for effecting vertical nonlinear deemphasis on said chrominance signal (P R , P B ) decoded by said decoder (21); and an interpolating filter (34R, 34B) for interpolating said chrominance signal (P R , P B ) decoded by said decoder (21), said vertical nonlinear deemphasis circuit (33R, 33B) being connected to an input terminal of said interpolating filter (34R, 34B). Apparatus according to claim 1, including: a decoder (21) for decoding said time-division-multiplexed signal (Figure 3) into the chrominance (P R , P B ) and the luminance (Y) signals; a vertical deemphasis circuit (33R, 33B) for effecting vertical nonlinear deemphasis on said chrominance signal (P R , P B ) decoded by said decoder (21); and an interpolating filter (34R, 34B) for interpolating said chrominance signal (P R , P B ) decoded by said decoder (21), said vertical nonlinear deemphasis circuit (33R, 33B) being connected to an input terminal of said interpolating filter (34R, 34B). Apparatus according to any one of claims 1, 2 and 3 including a horizontal emphasis circuit (35R, 35B) for effecting horizontal emphasis on said chrominance signal, (P R , P B ), said horizontal emphasis circuit (35R, 35B) being connected to an input terminal of said vertical emphasis circuit (31R, 31B). Apparatus according to any one of claims 2 and 3, including a horizontal deemphasis circuit (36R, 36B) for effecting horizontal deemphasis on said chrominance signal (P R , P B ) decoded by said decoder (21), said horizontal deemphasis circuit (36R, 36B) being connected to an output terminal of said vertical deemphasis circuit (33R, 33B). A video tape recorder/reproducer comprising a video signal processing apparatus according to any one of the preceding claims. A video tape recorder/reproducer according to claim 6, comprising means for processing high-definition television signals.

Inventors: SAKAMOTO ETSUROU, TAKASHIMA MASATOSHI, SAKAMOTO, ETSUROU, TAKASHIMA, MASATOSHI, SAKAMOTO, ETSUROU, C/O PATENTS DIVISION, Takashima, Masatoshi, c/o Patents Division
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H04N9
IPC codes: H04N5, H04N9, H04N7