FR2633131A1 - - Google Patents

Abstract

Techniques for transmitting image data are disclosed. In an amplitude modulation image data transmission system, alternate pixel data is modulated to correspond to positive and negative half periods, respectively, of a carrier signal. The transmission rate and the recording density of the image data are thus doubled compared to a conventional system. The amplitude modulator 40 is driven by a carrier signal which is obtained by dividing by two the frequency of the sampling signal which is applied to a sample-and-hold circuit 12 receiving the input information. Application to the display of images on miniature screens.

Description

The present invention relates to a data transmission system

  born of image, and it relates more particularly to a circuit of

  modulation / demodulation of amplitude, for a recording apparatus

  reproduction / reproduction of fixed video images.

  A conventional transmission system shown in FIG. 1 has been used to modulate in amplitude and to transmit a signal

analogue such as a video signal.

  Referring to FIG. 1, it will be noted that an input signal S1 having the waveform shown in FIG.

  to an input terminal 1 and it is subjected to a sampling operation-

  swimming-blocking by a sample-and-carry circuit 2, with a

  repetition period T, so as to obtain an S2 signal

  consisting of sample data a, b, c, -... which are representative of

  1. 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, so as to give a modulated signal

  S3, as shown in FIG. 1. In the signal S3, each of the sample values a, b, and c, resulting from 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

  positive and negative periods of the carrier signal Sc corresponds 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 filter 6, so as to obtain by demodulation the original signal S1 which is applied to a terminal of

exit 7.

  The classical amplitude modulation is done in the way

  described above. In this case, the sampling frequency of the

  the signal must be less than or equal to the carrier frequency fc. The frequency

  the carrier state fc is frequently restricted by the characteristics of signal transmission paths or of a recording medium,

  at the time of system design. Therefore, when

  sampled births are amplitude modulated and transmitted, the

  transmission dence or the density of data recording is

  limited by the characteristics of the transmission flights and the

  record port. For this reason, for example when

  The results obtained by sampling a video signal are modulated in amplitude and recorded on a magnetic tape.

  registration is considerably increased.

  An essential object of the invention is to make it possible to obtain an improved transmission rate and recording density,

  twice that of the classical amplitude modulation system.

  using a transmission vole and recording medium.

  have a limited frequency band.

  Another object of the invention is to minimize the distortion of

  signal that occurs when a signal passes through a transmission system.

sion or registration.

  Yet 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 duration.

  Other features and advantages of the invention will be better

  understood in the following description of the modes of

  and with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of an amplitude modulated audio transmission system of 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 for correcting data in amplitude modulation; Fig. 4 is a block diagram of a recording system of an audio / still image signal; Figure 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 control device used in

  the case of recording a still image in color.

  Figure 2 shows a transmission system that uses a system

  amplitude modulation system according to one embodiment of the invention. In this embodiment, a case will be described below.

  wherein an input signal Sl 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 a

  input terminal 13. The input signal is sampled in the

  sampler-and-hold i2 with an interval T / 2 (denoting by T the period of the carrier signal Sc). We can therefore 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 frequency divider

  this by two, 15, is modulated in amplitude by the signal S2 in one

  dulator 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 S3 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 data

  of pixel a, b, c, ... In other words, the pixel data a, c, e ,.

  correspond to the positive half periods of the signal S3, and the data

  of pixel b, d, f, ... correspond to the negative half-periods of the

  General S3. The modulator 14 is therefore designed so that the signal of

  S2 is reversed 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 circuit

  demodulation circuit 20 which comprises a double-circuit rectifier circuit

  22. More specifically, the rectifier circuit with

  this 22 provides a signal S4 in which the image data a, b, c, ...

  appear with T / 2 periods. The signal S4 is then applied

  to a low pass filter 23, so as to obtain the video signal of origin

S1 on an output terminal 24.

  In the above system, we see that the rate of transmission of the data of the image a, b, c, ... can be equal to twice that of the

  conventional system which is shown in Figure 1, although it is useful

  read the same carrier frequency fc.

  More specifically, the invention is suitable for an image data transmission system. In general, since the image data of a particular pixel correlates with the pixel image data that is adjacent to the determined pixels (following pixel data on a horizontal line, pixel data on pixels), and

  following lines, or pixel data on frames or images

  the V1 and V2 levels of data a and b do not differ

  dreadfully one from the other. Therefore, the use of the

  modulation scheme shown in Figure 2 is not practical.

no problem.

  If the levels V1 and V2 of the data a and b differ considerably

  From each other, the data can be equilibrated to transmit a signal having positive and negative levels that are substantially equal to each other, relative to a central level. Table 1 shows correction values that

  used when performing the aforementioned equilibrium correction.

- -

  Table 1: Balance correction b

X 0 1 2 3 ...... 13 14 15

at

0 1.5 ...... 6.5 7 7.5

I 2. 7 7.5 8

_ _ _ _ _ _ _ _ _ _

2 2.5 ... 7.5 8 8.5

3 1.5 2 2.5 3 ...... 8 8.5 9

13 6.5 7 7.5 8 ......

14 7 7.5 8 8.5 ......

7.5 8 8.5 9 ......

  In Table 1, the image data a and b (addresses x and y)

  are respectively 4-bit data, that is to say that each

  is one luminance level out of 16. Each region represents

  oblique line is a region in which a correction is

  tion is not carried out because the difference between the data

  a and b is weak. In addition to these areas, the correction is not ef-

  in regions (not shown) in which the

  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. Other regions are regions

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  of correction, and the data a and b are the subject of an equilibrium correction which gives them for example an average 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 that is digitized at a frequency of

  2c are applied to an input terminal 31. A signal

  Sc (fc) is applied to an input terminal 32. The input image data a, b, c, ... which are applied to the input terminal 31 are directly applied to the terminal y d a read-only memory 34. In addition,

  the data a, b, c, ... are delayed one bit by a network of

  33 and they are applied to the terminal x of the ROM 34.

  Therefore, when for example data b is directly

  in read-only memory 34, the data are transmitted from the

  flip-flop bucket 33 to read-only memory 34. Read-write memory 34

  ve the data of the table of the correction indicated in Table 1.

  The correction values are read on the basis of the input data a and b, which are x and y addresses, and corrected data.

  and b 'are output. The corrected data that is pre-

  output are then applied to the modulation circuit 40.

  The modulation circuit 40 comprises an inverter 41 which is intended to

  to invert each bit according to the corrected data corresponding to

  and a digital-to-analog converter 42. The inverter 41 invokes

  each bit of the corresponding input data in the half-way

  alternating cycles of the carrier signal Sc. Therefore, the inverter 41 can transmit the signal S3 of FIG. 2 in the form of a value

  digital. The data that is thus obtained passes through the conver-

  digital-to-analog weaver 42 and a low-pass filter 43, so as to provide on an output terminal 44 an amplitude-modulated signal with

balance correction.

  An embodiment of a system in the following will be described below.

  which of the still image signals and audio signals are recorded

  audio tape and are reproduced using the system.

  amplitude modulation scheme considered above.

  FIG. 4 shows an embodiment of a recording system

  tration. A still image 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 disc, is applied to a decoder 52 by means of

  As a result, an audio signal Sa corresponding to the above-mentioned image signal, which originates from the signal source, is applied to an input terminal 53, and is transmitted to a head 55. via an audio recording amplifier 54, so that the applied signal Sa is recorded on an audio track of a magnetic tape. In this case, the audio signal Sa is recorded for example on a track of the right channel among a pair of stereophonic tracks, that is to say tracks of the flight.

  left and right-hand side which are formed in a long direction

  tudinal of a band 19. The amplitude-modulated still image signal

  is recorded by a head 56 on the track of the left flight.

  The still image signal that is applied to the input terminal 51 is

  transmitted to the decoder 52 which demodulates the primal color signals.

  res R, G and B. In addition, the input still image signal is applied to a sync separation circuit 57, which separates a sync 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 are converted into signals

  4, 5 and 3 bits, respectively, under the

  this of sampling pulses that come from a generator of

  clock signal 61 which operates under the control of the sync signal.

  separate chronization. The digital primary color signals R, G, and B are written to a memory 62 which 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 handling of

  signal, so that each channel has 4 bits. We are

  thus presents by R, G 'and B' the signals in this state.

  A system controller 63 which operates under the control of the clock generator 61 controls the operations

  memory write and read 62. The primary color signals

  digital mayors 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

  time base is converted so that a still image in color can

  be transmitted in approximately 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

  record it on the track of the left track of the audio track. Com-

  mutator 65 multlplexes a control signal. A data generator

  command 66 receives external control data so as to pro-

  to obtain numerical control data. The control signal is modulated by a modulation circuit 68, and it is multiplexed with the

  fixed image signals. In this case, a corresponding carrier frequency

  The signal at the control signal is less than the carrier frequency of the image data, for example 3 kHz, to increase the signal-to-noise ratio. Order data includes information

  space between images, discrimination information for

  born in black and white or in color, and discriminatory information

  nation for a high-definition picture or a normal picture, by

example.

  Alnsl, in the audio band, the audio signal is recorded in the right channel, and the still picture information including the data

  command is saved in the left channel.

  FIG. 5 is a block diagram of a reproduction device

  duction. With regard to the external appearance of this

  production with a size that allows him to hold in hand, a

  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 of audio signal 85 through a preamplifier 84 and a switch 86, as for the head of the

  straight track. 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

  classic type. If necessary, a loudspeaker 87 can be incorporated.

  When the signal that is recorded in the left channel consists of still picture data, the switch 86 is switched, and an output signal of the preamplifier 84 is applied to an automatic gain control (AGC) circuit 90. A signal of control that is intended to be applied to the switch 86 comes from a terminal 82, for example

  by a manual operation. Thus, control data and data

  the resulting images 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 Figure 2 previously described. The demodulated signal is

  applied to an analogue-to-digital converter 93 in the following

  to an AGC detector 97, to obtain an AGC control signal. The AGC control signal that is obtained is applied to the AGC control signal.

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 Extracts are Applied to a Generator-Clock Signal

  99. The clock generator 99 produces various clock signals.

  synchronizes with the input image data, and the various clock signals are applied to the demodulation circuit 92,

  digital-to-digital converter 93, to a signal decoder

  100 and to a system controller 101, depending on

needs.

  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. The image memory unit 94 comprises

  image memories 95 and 96 which are provided to perform alternately

  read and write operations. More precisely,

  the application to the image memory unit 94 of corresponding data

  a full still image takes about 2.8 seconds, as described above. Therefore, for example, during a period during which new data is applied to memory

  95, that is to say for 2.8 s, recorded image data.

  previously in the image memory 96 are read in a

  bothered by a synchronization signal, in compliance

  with a normal television system. A synchronization generator

  tion 102 therefore produces the synchronization signal in accordance with

  standard color television NTSC.

  The signals R, G 'and B' which are read in the memory unit

  are fed back to the original binary states by

  inversions of 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 R, G and B signals, and the data is applied to respective digital-to-analog converters 103, 104 and 105. The data which is applied is converted into

  analog signals and these are applied to a communication circuit.

  display 106, along with the synchronization signal.

  Therefore, liquid crystal display panel drivers 107 and 108 control a display panel

  color LCD 109, under the control of

  which come from the display control circuit 106,

  to obtain a still image in color. In one experiment, we used

  a color LCD panel consisting of 128 RGB x 128 line triads, and a still image in color of

  4,096 pixels at a frame rate every 3 seconds or so.

  We can visualize a black and white image at a rate of one

per second.

  Figure 5 shows an example in which the primary signals

  R, G and B are processed sequentially for each frame. The figure

  re 6 shows a memory control unit in which Y, R-Y, and B-Y signals are used. As shown in Figure 6, when the

- 11

  luminance signal Y and the R-Y color difference signals and

  B-Y are transmitted sequentially for each frame, it is possible to

  to improve the compatibility between mode-in black and white

  and the color mode. In the same way as in the description of

  FIG. 5, the demodulated still image data is applied to a

  input terminal.201. Input data is applied to a conver-

  analog-to-digital weaver 202 and they are converted to 4-bit 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 interfer-

  204, -205 and 206 are closed at the time of application of the

  The data is written simultaneously in the memories 213, 215 and 217 via

  switches 209, 210 and 211 in the switching circuit 208.

  Therefore, the image data -in black and white V1, V2, ...

  are written simultaneously in the three parts of the memo-

  212. If the image data is color data, and

  if color difference (R-Y) data are applied immediately

  after the luminance data Y1, only the switch 204 is

  open, and the memories 215 and 217 are updated. When the data

  following (B-Y) are applied to the input, the switches 204

  and 205 are open, and only the memory 217 is updated. By con-

  the data Y1, (R-Y) 1, and (B-Y) 1 are respectively recorded.

  stored in memories 213, 215 and 217. Note that when data corresponding to an image is recorded, switches 209, 210 and 211 in switching circuit 208 are respectively

  switched to the lower positions, and the subsequent image data

  are similarly written in memoirs 214, 216 and 218.

  The output signals of the memory groups are applied to

  OR 221, 222 and 223, and to digital-to-analog converters

* 224, 225 and 226.

  A system controller 220 receives the communication signal

  decoded message which is applied to an input terminal 207, so as to

  perform the memory control operations mentioned above.

  As in FIG. 5, a synchronization generator 227 is incor-

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  poré for reading data in the image memory unit 212, in dependence on a conventional television synchronization signal.

  The use of the configuration and control system men-

  above makes it possible to process still images, both

  black and white only in color, without using discriminatory data.

  particular for color and black and white, in the form of

a control signal.

  It goes without saying that many changes can be made

  to the device and method described and shown, without leaving

of the scope of the invention.

13-

Claims (8)

  A modulation circuit for transmitting on an transmission line an incoming information signal, characterized in that it comprises: sampling means (12) for sampling the incoming information signal at a sampling frequency fs; and amplitude modulation means (14, 40) which are connected to the sampling means (12) for amplitude modulating a carrier signal   having a frequency fc equal to half the sampling frequency   sampling fs, using the incoming information signal sampled.   Modulation circuit according to Claim 1, characterized in that   that the carrier frequency fc is obtained by division by 2 of the frequency sampling frequency fs.   3. Modulation circuit according to claim 1, characterized in that it further comprises amplitude adjustment means (30) which are interposed between the sampling means (12) and the means   of amplitude modulation (40) to restrict to a predetermined value.   the difference between two adjacent data.   A modulation circuit for modulating digitized information, characterized by comprising: data inverting means (41) for inverting one out of two digitized information; digital-to-analog converting means (42) connected to the data inverting means for producing an amplitude modulated signal; and a low-pass filter (43) which is connected to   digital-to-analog conversion means (42).   5. Demodulation circuit for demodulating a modulated signal in terms of   amplitude produced by an amplitude modulator comprising: sampling means (12) for sampling the incoming information signal at a sampling frequency fs, and amplitude modulation means (14) ', are connected to the sampling means (12) for amplitude modulating a carrier signal   having a frequency fc which is equal to half the sampling frequency.   sampling fs, by means of the sampled incoming information signal characterized in that it comprises: a full-wave rectifier circuit (22) which receives the amplitude-modulated signal; and one   filter (23) which is connected to the full wave rectifier circuit.   A still image reproducing apparatus, characterized in that it comprises: a transducer head (81) which is intended to reproduce amplitude modulated image image information together with a control signal, from a recording track of a   audio tape; a demodulator (92) which is connected to the transmission head   driver (81) for recovering original fixed data information; first and second image memories (95, 96) for recording the still image information; and control means   memory (101) connected to the first and second memories.   (95, 96) for reading a fixed information item which is stored in one of the memories, while writing a fixed information item   in the other memory, based on the control signal that is reproduced   duit by the transducer head (81).   The fixed-image reproducing apparatus according to claim 6, characterized in that each of the first and second memories (95,   96) has three memory elements for the luminance information.   this, and a pair of color difference information from the information image image.   8B. A fixed-image recording apparatus for recording still picture information on a magnetic tape of a tape recorder, characterized in that it 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; amplitude modulation means (40) which are connected to the means   memory to modulate in amplitude the digital fixed video   which is read in the memory (62); digital conversion means   analog-to-analog video information which is intended to convert the amplitude modulated and digitized fixed video information into analog fixed amplitude-modulated video information; and means comprising   a magnetic head (56) for recording the fixed video information   amplitude amplitude on a recording track of an audio tape.   9. Apparatus for recording fixed video information, characterized in that it comprises: first modulation means (40) for   modulating a first carrier signal with a fixed video information   trante; second modulating 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   modulate the first carrier signal; and means (56) for recording   tracing on a recording track a magnetic tape signals   which are provided by the signal mixing means (65).