FR2639169A1 - Amplitude modulation and demodulation circuits for recording and reproducing still images - Google Patents

Abstract

The invention relates to image data transmission techniques. In a system for transmitting image data by amplitude modulation, alternate pixel data are modulated so as to correspond respectively to positive and negative half-periods of a carrier signal. The transmission rate and density of recording of the image data are thus doubled by comparison with a conventional system. The amplitude modulator 40 is driven by a carrier signal which is obtained by halving the frequency of the sampling signal applied to a sample-and-hold circuit 12 receiving the input information. Application to the displaying of images on miniature screens.

Description

 The present invention relates to an image data transmission system, and relates more particularly to an amplitude modulation / demodulation circuit, for a fixed video recording / reproduction apparatus.

 A conventional transmission system shown in FIG. 1 has been used to modulate in amplitude and to transmit an analog signal such as a video signal.

 Referring to FIG. 1, it is noted that an input signal S1 having the waveform shown in FIG. 1 is applied to an input terminal 1 and is subjected to a swimming sample operation. biocage by a sample-and-hold circuit 2, with a repetition period T, so as to obtain a signal S2 consisting of sample data a, b, c, ... which are represented in FIG. The signal S2 is then applied to an amplitude modulation circuit 3. A carrier signal Sc having a carrier frequency fc and a period T, which comes from an input terminal 4, is modulated in amplitude by the signal S2. to provide a modulated signal S3, as shown in FIG. 1.In the signal S3, each of the sample values a, b, and c, resulting from the sampling in the sample-and-hold circuit 2, corresponds to each period T of the carrier signal Sc. In other words, each amplitude of half-moon Positive and negative signals of the carrier signal Sc correspond to a sample value.

 The amplitude modulated signal, S3, is applied by a transmission line to a demodulation circuit 5 on the receiver side, and a signal S4 can be obtained, as shown in FIG. 1. The signal S4 is then applied to a pass filter. 6, so as to obtain by demodulation the original signal S1 which is applied to an output terminal 7.

 The classical amplitude modulation is performed as described above. In this case, the sampling frequency of the signal must be less than or equal to the carrier frequency fc. The carrier frequency fc is frequently restricted by the characteristics of signal transmission channels or recording medium at the time of system design. Therefore, when the sampled data is amplitude modulated and transmitted, the transmission rate or the data recording density is limited by the characteristics of the transmission channels and the recording medium. For this reason, when, for example, image data obtained by sampling a video signal is amplitude modulated and recorded on a magnetic tape, the recording time is considerably increased.

 An essential object of the invention is to allow obtaining an improved transmission rate and recording density, equal to twice that of the conventional amplitude modulation system, by using a transmission path and a recording medium having a limited frequency band.

 Another object of the invention is to minimize the signal distortion that occurs when a signal passes through a transmission or recording system.

 Still another object of the invention is to reproduce a still image using an audio recording / reproducing system having a fixed head in a relatively short time.

 Other features and advantages of the invention will be better understood on reading the following description of embodiments and with reference to the appended drawings in which FIG. 1 is a block diagram of an audio transmission system. amplitude modulation of the conventional type FIG. 2 is a block diagram of an amplitude modulation transmission system according to the invention FIG. 3 is a block diagram of circuits intended to correct data in amplitude modulation. Fig. 4 is a block diagram of a recording system of an audio / still image signal; Fig. 5 is a block diagram of a reproduction system; and Fig. 6 is a block diagram showing a modified form of an image memory and a controller used in the case of recording a color still image.

 Figure 2 shows a transmission system that uses an amplitude modulation system according to an embodiment of the invention. In this embodiment, hereinafter will be described a case in which an input signal S1 is a video signal.

 In FIG. 2, the references 10 and 20 (parts surrounded by dashed lines) denote amplitude modulation and demodulation circuits, respectively.

 The video signal S1 which is applied to an input terminal 11 is sampled in a sample-and-hold circuit 12. In this case, a carrier signal Ssam having a frequency (2fc) which is equal to twice a frequency (fc) of a carrier signal Sc, is applied to an input terminal 13. The input signal is sampled in the sample-and-hold circuit 12 with an interval T / 2 (denoting by T the period of the carrier signal Sc) . It is therefore possible to obtain a signal S2 which consists of image data a, b, c, ... corresponding to each pixel. The carrier signal Sc having a carrier frequency fc, which is obtained by division of the carrier signal Ssam by a divider of frequency by two, 15, is modulated in amplitude by the signal S2 in a modulator 14, so as to give a modulated signal S3 which is transmitted to a transmission line via an output terminal 16.

As shown in FIG. 2, in the signal 53 the image data a, b, c, ... correspond to each period T / 2 of the carrier signal Sc; and the amplitude level of each period T / 2 corresponds to the pixel data a, b, c, ... In other words, the pixel data a, c, e, correspond to the positive half-periods of the signal 53, and the pixel data b, d, f, ... correspond to the negative half-periods of the signal S3. The modulator 14 is thus designed so that the input signal S2 is inverted during the negative periods of the carrier signal
Sc, synchronized with the input signal S2. The signal S3 propagates through the transmission line and is applied to an input terminal 21 on the receiver side. Then, the signal S3 is applied to a demodulation circuit 20 which comprises a full-wave rectifier circuit 22. More precisely, the full-wave rectifier circuit 22 provides a signal 54 in which the image data a, b, c , appear with periods T / 2. The signal S4 is then applied to a low-pass filter 23, so as to obtain the original video signal S1 on an output terminal 24.

 In the above system, it can be seen that the transmission rate of the image data a, b, c,... Can be twice that of the conventional system shown in FIG. uses the same carrier frequency fc.

 More specifically, the invention is suitable for an image data transmission system. In general, because the image data of a particular pixel correlates with the image data of pixels that are adjacent to the determined pixels (subsequent pixel data on a horizontal line, pixel data on lines following, or pixel data on subsequent frames or images), the levels V1 and V2 of the data a and b do not differ significantly from one another. Therefore, the use of the modulation system shown in FIG. 2 hardly causes any problem.

 If the levels V1 and V2 of the data a and b differ considerably from each other, the data can be subjected to an equilibrium correction for transmitting a signal having positive and negative levels which are substantially equal to each other, relative to each other. at a central level. Table 1 shows correction values used when performing the aforementioned equilibrium correction.

Table 1: Balance correction

<tb><SEP> b
<tb><SEP> 0 <SEP> 1 <SEP> 2 <SEP> 3 <SEP> 13 <SEP> 14 <SEP> 15
<tb> a
<tb> a
<tb><SEP> O <SEP> 1.5 <SEP> ...... <SEP> 6.5 <SEP> 7 <SEP> 7.5
<tb><SEP> 1 <SEP> ~ <SEP> 2 <SEP> ...... <SEP> 0 <SEP> 7 <SEP> 7.5 <SEP> 8
<tb><SEP> 2 <SEP> 2.5 <SEP> ...... <SEP> 7.5 <SEP> 8 <SEP> 8.5
<tb><SEP> 3 <SEP> 1.5 <SEP> 2 <SEP> 2.5 <SEP> 3 <SEP> ...... <SEP> 8 <SEP> 8.5 <SEP> 9
<tb><SEP>.<SEP>.<SEP>,<SEP>.<SEP>&commat;<SEP> 0
<tb><SEP> 13 <SEP> 6.5 <SEP> 7 <SEP> 7.5 <SEP> B <SEP> ......
<Tb>

<SEP> 14 <SEP> 7 <SEP> 7.5 <SEP> 8 <SEP> 8.5
<tb><SEP> 15 <SEP> 7.5 <SEP> 8 <SEP> 8.5 <SEP> 9
<Tb>
In Table 1, the image data a and b (x and y addresses) are respectively 4-bit data, i.e. each data represents a luminance level out of 16. Each region represented by a oblique line is a region in which a correction is not made, because the difference between the data a and b is small. In addition to these regions, the correction is not performed in regions (not shown) in which the difference between the data a and b is less than or equal to "2". This is for example the case when the ratio a: b (or b: a) is equal to 5: 6, 5: 5, 5: 4, 5: 3, etc. The other regions are correction regions, and the data a and b are the subject of an equilibrium correction which gives them for example a mean value a = b = (a + b) / 2.

 Fig. 3 shows an automatic data balance control circuit 30 and a modulation circuit 40 which are based on a digital signal processing technique.

 Four-bit image data which is digitized at a frequency of 2 fc is applied to an input terminal 31. A carrier signal Sc (fc) is applied to an input terminal 32. input a, b, c, ... which are applied to the input terminal 31 are directly applied to the terminal y of a read-only memory 34. In addition, the data a, b, c, ... are delayed one bit by a network of flip-flops 33 and they are applied to the terminal x of the read-only memory 34.

Consequently, when, for example, the data b is directly applied to the read-only memory 34, the data a is transmitted from the latch network 33 to the read-only memory 34. The read-only memory 34 stores the data of the table of the correction that indicates Table 1.

The correction values are read based on the input data a and b, which are x and y addresses, and corrected data a 'and b' are output. The corrected data that is output is then applied to the modulation circuit 40.

The modulation circuit 40 includes an inverter 41 which is adapted to invert each bit in accordance with the corresponding corrected data and a digital-to-analog converter 42. The inverter 41 inverts each bit of the corresponding input data in the course of alternate half cycles. Therefore, the inverter 41 can transmit the signal S3 of FIG. 2 as a numerical value. The data thus obtained passes through the digital-to-analog converter 42 and a low-pass filter 43, so as to provide on an output terminal 44 an amplitude-modulated equilibrium-corrected signal.

 An embodiment of a system in which still image signals and audio signals are recorded on an audio magnetic tape and reproduced using the amplitude modulation system discussed above will be described below.

 Figure 4 shows an embodiment of a recording system. A still picture signal S1 which corresponds to an image or a frame, which originates from a signal source such as a video recorder, a video camera or a video disc, is applied to a decoder 52 via the intermediary of an input terminal 51. Simultaneously, an audio signal Sa corresponding to the aforesaid image signal, which originates from the signal source, is applied to an input terminal 53, and is transmitted to a head 55 by through an audio recording amplifier 54, so that the signal Sa which is applied is recorded on an audio track of a magnetic tape. In this case, the audio signal Sa is recorded for example on a recording track. the right channel among a pair of stereophonic tracks, i.e. tracks of the left channel and the right channel which are formed in a long tudinal direction of a band 19. The modulated still image signal amplitude is recorded by a head 56 on the track of the left track.

The still image signal which is applied to the input terminal 51 is transmitted to the decoder 52 which demodulates the primary color signals R, G and B. In addition, the input still image signal is applied. a synchronization separation circuit 57, which separates a synchronization signal. The primary color signals R, G and B which are demodulated by the decoder 52 are applied to analog-to-digital converters 58, 59 and 60, and they are converted into digital signals comprising respectively 4, 5 and 3 bits, depending on sampling pulses which originate from a clock generator 61 which operates under the control of the separate synchronization signal. The primary digital color signals R,
G, and B are written to a memory 62 that has a capacity of a video image or a video frame. In this case, the least significant bit of the green signal in the primary color signals is applied to a channel corresponding to blue, in order to simplify the manipulation of the signals, so that each channel has 4 bits. Therefore, R, G 'and B' represent the signals in this state.

 A system controller 63 which operates under the control of the clock generator 61 controls the write and read operations of the memory 62. The primary digital color signals R, G 'and B' which are read in the memory 62 are applied to the automatic data balance control circuit 30.

previously mentioned, and to the modulation circuit 40 of FIG.

 A clock generator 64 applies a clock signal to the system controller 63 so as to sequentially read the signals R, G 'and B' in the memory 62. In this case, a base of The time is converted so that a fixed color image can be transmitted in about 2.8 s. The modulation circuit 40 may provide an amplitude modulated signal having a frequency fc which is, for example, 8.7 kHz. This amplitude modulated signal passes through a switch 65 and a recording amplifier 67, and the head 56 records it on the track of the left channel of the audio band. The switch 65 multiplexes a control signal. A control data generator 66 receives external control data to produce digital control data. The control signal is modulated by a modulation circuit 68, and is multiplexed with the still image signals. In this case, a carrier frequency corresponding to the control signal is less than the carrier frequency of the image data, for example 3 kHz, to increase the signal-to-noise ratio. The control data includes interframe space information, discrimination information for black and white or color data, and discrimination information for a high definition image or a normal image, for example.

 Thus, in the audio band, the audio signal is recorded in the right channel, and the still picture information including the control data is recorded in the left channel.

 Figure 5 is a block diagram of a reproduction device. With regard to the external appearance of this reproduction device having a size that allows it to fit in the hand, a liquid crystal display device is mounted on a stereo magnetic recorder operating with headphones.

 A head 80 for the right channel picks up the audio signal. The captured audio signal is applied to an audio signal processing circuit 85, via a preamplifier 83. If an audio signal is recorded by a left-channel head, 81, the signal is applied to the processing circuit 85 audio signal through a preamplifier 84 and a switch 86, as for the head of the right channel. In this case, stereophonic audio signals are respectively obtained on earphone output terminals 88 and 89, as in a stereophonic player operating on headphones, of conventional type. If necessary, a loudspeaker 87 can be incorporated.

 When the signal that is recorded in the left channel consists of still image data, the switch 86 is switched, and an output signal of the preamplifier 84 is applied to an automatic gain control (AGC) circuit 90. control which is intended to be applied to the switch 86 comes from a terminal 82, for example by a manual operation. Thus, the control data and the image data that. are obtained are applied to a low-pass filter 91, and the image data is demodulated by a demodulation circuit 92.

The demodulation circuit 92 may be identical to the demodulation circuit 20 of FIG. 2 described above. The demodulated signal is applied to an analog to digital converter 93 in the booster stage, and to an AGC detector 97, to obtain an AGC control signal. The AGC control signal that is obtained is applied to the AGC circuit 90.

 The output signal of the low pass filter 91 is also applied to a bandpass filter 98 which has a center frequency of 8.7 kHz. This bandpass filter 98 extracts bearer components, and the extracted components are applied to a clock generator 99. The clock generator 99 produces various clock signals in synchronism with the image data. input, and the various clock signals are applied to the demodulation circuit 92, to the analog-to-digital converter 93, to a control signal decoder 100 and to a system controller 101, as required.

 The analog-to-digital converter 93 converts the demodulated primary color signals R, G 'and B' into 4-bit signals, and the 4-bit signals that result from the conversion are applied to an image memory unit 94. image memory unit 94 includes image memories 95 and 96 which are provided for performing alternately write and read operations. More specifically, the application to the image memory unit 94 of data corresponding to a complete still image requires about 2.8 s, as described above. Therefore, for example, for a period of during which new data is applied to the image memory 95, i.e. during 2.8 s, image data previously recorded in the image memory 96 are read repeatedly under dependence of a synchronization signal, in accordance with a normal television system. A timing generator 102 therefore produces the synchronization signal in accordance with the NTSC color television standard.

 The signals R, G 'and 8' which are read in the image memory unit 94 are returned to the original binary states by operations opposite to those of a recording mode. In other words, the signals R, G 'and B' are converted into data comprising respectively 4, 5 and 3 bits for the signals R, G and B, and these data are applied to respective digital-to-analog converters 103, 104 and 105 The data that is applied is converted into analog signals and the latter is applied to a display control circuit 106 in the company of the synchronization signal.

Therefore, liquid crystal display panel drivers 107 and 108 control a color liquid crystal display panel 109, in response to driving signals that originate from the display control circuit 106, to obtain a still image in color. In one experiment, a color LCD panel with 128 triads was used
RGB x 128 lines, and we could view a still image in color of 4096 pixels at a rate of one image every 3 seconds or so.

You can view a black and white image at a frame rate of one frame per second.

Figure 5 shows an example in which the primary signals
R, G and B are processed sequentially for each frame. Figure 6 shows a memory control unit in which Y, RY, and BY signals are used. As shown in FIG. 6, when the luminance signal Y and the color difference signals RY and
BY are transmitted sequentially for each frame, it is advantageous to improve the compatibility between the black and white mode and the color mode. In the same manner as in the description of FIG. 5, the demodulated still picture data is applied to an input terminal 201. The input data is applied to an analog-to-digital converter 202 and is converted to data. This signal is applied to a switching circuit 203 and is then applied to a switching circuit 208. In this case, in the color mode as in the black-and-white mode, the interlocks 204, 205 and 206 are closed at the time of application of the data which follows a control signal C. The data is written simultaneously in the memories 213, 215 and 217 via switches 209, 210 and 211 in the switching circuit 208.

 Therefore, black and white image data V1, V2, ...

are written simultaneously in the three parts of the image memory unit 212. If the image data is color data, and
If color difference data (RY) is applied immediately after the luminance data Y1, only the switch 204 is open, and the memories 215 and 217 are updated. When the next data (BY) is applied to the input, the switches 204 and 205 are open, and only the memory 217 is updated. Consequently, the data Y1, (RY) 1, and (BY) 1 are respectively recorded in the memories 213, 215 and 217. It is noted that when data corresponding to an image are recorded, the switches 209, 210 and 211 in switching circuit 208 are respectively switched to lower positions, and the following image data is similarly written in memories 214, 216 and 218.

The output signals of the memory groups are applied to OR gates 221, 222 and 223, and to digital-to-analog converters 224, 225 and 226.

 A system controller 220 receives the decoded control signal that is applied to an input terminal 207 so as to perform the memory control operations mentioned above.

As in Fig. 5, a timing generator 227 is enabled to read data in the picture memory unit 212, in dependence on a conventional television sync signal.

 Using the configuration and control system mentioned above, still images can be processed in black-and-white and color without the use of special color and black disc-rim data. and white, in the form of a control signal.

 It goes without saying that many modifications can be made to the device and method described and shown, without departing from the scope of the invention.

Claims (3)

 A still image reproducing and recording apparatus, characterized in that the reproducing assembly comprises a transducer head (81) which is adapted to reproduce an amplitude modulated fixed image information together with a signal control, from a recording track of an audio tape; a demodulator (92) which is connected to the transducer head (81) for recovering original fixed image information; first and second image memories (95, 96) for recording the still image information; and memory control means (101) which is connected to the first and second memories (95, 96) for reading a still picture information which is recorded in one of the memories, while writing a still picture information in the other memory, on the basis of the control signal reproduced by the transducer head (81), and in that the recording assembly for recording a still image information on a magnetic tape of a tape recorder comprises: digitizing means (58, 59, 60) for digitizing an incoming fixed video signal; memory means (62) which is connected to the digitizing means (58, 59, 60) for recording the digitized fixed video information; first amplitude modulation means (40) which is connected to the memory means for amplitude modulating a first signal relating to the digitized fixed video information which is read from the memory (62); digital-to-analog converting means for converting the amplitude modulated and digitized fixed video information to analog fixed amplitude amplitude video information; and means having a magnetic head (56) for recording the amplitude modulated fixed video information on a recording track of an audio tape.  The still image reproducing and recording apparatus according to claim 1, characterized in that each of the first and second memories (95, 96) of the reproduction unit comprises three memory elements for the luminance information. , and a pair of color difference information of the still image information.  The still image reproducing and recording apparatus as claimed in any one of the preceding claims, characterized in that the recording assembly further comprises modulation means (68) for modulating by a control signal. a second carrier signal which has a frequency lower than that of the first carrier signal; signal mixing means (65) which is connected to the first modulation means (40) and the second modulation means (68) for interposing the second modulation signal between successive fixed video information which modulates the first carrier signal; and means (56) for recording on a recording track of a magnetic tape signals which are provided by the signal mixing means (65).