GB2219906A

GB2219906A - Image data transmitting systems

Info

Publication number: GB2219906A
Application number: GB8912862A
Authority: GB
Inventors: Koji Ebisu; Koji Kanbayashi; Kenichi Shibuya
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1988-06-15
Filing date: 1989-06-05
Publication date: 1989-12-20
Also published as: FR2633131A1; KR910002286A; DE3919302A1; GB8912862D0

Description

0 C. n -,, '_1 6 1 IMAGE DATA TRANSMT,TING SYSEMS This invention relates

to systems for trarsmitting image data, and in particular to such systems which may invove amplitude modulation and/or demodulation such as in still video image recording and/or reproducing apparatus.

When an analog signal such as an analog video signal is amplitude modulated and transmitted, a transmission system as shown in Figure 1 of the accompanying drawings has previously been used.

Referring to Figure 1, an input signal S1 having a waveform as shown in Figure 1 and supplied to an input terminal 1 is sampled and held by a sample-hold (S/H) circuit 2 at a repetition period T, so that a signal S2 consisting of sample data a, b, c, (as shown in Figure 1) can be obtained. The signal 52 is then supplied to an amplitude modulation (AM) circuit (MOD) 3. A carrier signal Se having a carrier frequency fe and a period T is supplied from an input terminal 4 and is AM-modulated by the signal S2, so that a modulated signal 53 can be obtained (as shown in Figure 1). In the signal S3, each of the samp.e values a, b and c sampled at the S/H circuit 2 corresponds to each period T of the carrLer signal Se. In other words, the amplitude of each pair of positive and negative half periodis of the carri.er signal Sc corresponds to one sample value.

The AM-modullated signall 53 is supplied th-rough a transmission line to a demodulating circuit (DEMOD) 5 on a receiving sice, and a signal S4 can be obtained (as shown in Figure 1). The signal S4 is then supplied to a low-pass filter (LPF) 6, so that. the original signal 51 is obtained by demodulation and is provided at an output terminal 7.

In the above-described transmission system, the sampling frequency for the signal has to be equal to or lower than the carrier frequency fe. The carrier frequency fc is frequently restricted by the characteristics of signal transmission paths or a recording medium imposed by the design of the system. Therefore, when sampled data is AM- modulated and transmitted, the transmission rate or recording density of the data is limited by the characteristics of the transmission paths and/or recording medium. For this reason, when, for example, image data obtained by sampling a video signal is AM-modulated and recorded on a magnetic tape, the recording time is increased 2 considerably.

According to a first aspect of the present invention there is provided a modulation circuit for transmitting an incoming information signal on to a transmission line, the circuit comprising:

sampling means for sampling said incoming information signall at a sampling frequency; and amplitude modulating means connected to said sampling means for amplitude modulating a carrier signal having a frequency that is half of said sampling frequency by said sampled incoming information signal.

According to a second aspect of the present invention there is provided a demodulating circuit for demodulating an amplitude modulated signal generated by a modulation circuit as set forth above, the demodulating circuit comprising:

full wave rectifier circuit means pupplied with the amplitude modulated signal; and filter means connected to said full wave rectifier circuit means.

A preferred embodiment of the present invention can achieve an improved transmission rate and/or a recording density which are twice -ion system jS-'L-g a those in the previously -proposed AMmodulat transmission path and/or a recording medium of a limited frequency band.

The preferred embodiment can minimise signal distortion arising when a signal passes through a transmission or recording system.

According to a third aspect of the present invention there is provided a modulation circuit for modulating digitised information, the circuit comprising:

data inverting means for inverting every other incoming digitised sample of information; digital to analog converting means connected to said data inverting means for generating an amplitude modulated signal; and low pass filter means connected to said digital to analog converting means.

According to a fourth aspect of the present invention there is provided a still image reproducing apparatus comprising:

a transducer head for reproducing an amplitude modulated still image information signal together with a control signal from a recording track of an audio tape; 3 a demodullator connected to said transc-Lcer head for reccver'.ne the original st-J-,- image information; first and second image memories for storing said stil- image information; and memory control means connected to said first and second memories for reading stored still image information from one of said memories while writing still image information into the other of said memories based on said control signal reproduced by said transducer head.

According to a fifth aspect of the present invention there is provided a still image recording apparatus for recording still video information on a magnetic tape, the apparatus comprising: digitising means for digitising an incoming still video signal; memory means connected to said digitising means for storing the digitised still video information; amplitude modulating means connected to said memory means for amplitude modulating the digitised still video information read out from said memory; isej digital to analog conversion means for converting the dig.1 amplitude modulated still video information into analog amplitude modulated still video information; and magnetic head means for recording said analog amplitude mocu-ated still video information on a recording track of an audio tape.

According to a sixth aspect of the present invention there is provided a still video information recording apparatus comprising:

first modulation means for modulating a first carrier by an incoming still video information signal; second modulation means for modulating a second carrier which has a lower frequency than that of the first carrier by a control signal; signal mixing means connected to said first modulation means and said second modulation means for interposing a modulation signal from the second modulation means between successive still video information signals modulating said first carrier; and means for recording signals derived from said signal mixing means on a recording track of an audio tape. 35 Preferred still image reproducing apparatus can reproduce a still image using an audio record ing/reproducing system of a fixed head within a relatively short period of time.

4 now be described by way of example w The invention wil Ztn reference to the accompanying drawings, in which:

Figure 1 is a block diagram of a previously-proposed AM transmission system; Figure 2 is a block diagram of an AM transmission system according to an embodiment of the present invention; Figure 3 is a block diagram of a circuit for correcting AM data; Figure 4 is a block diagram of a recording system for audio and still image signals; Figure 5 is a block diagram of a reproducing system; and Figure 6 is a block diagram showing a modification of an image memory and a controller when a colour still image is recordec.

Figure 2 shows a transmission system including an AM modulation system according to an embodiment of the present invention. In this embodiment, the case in which an input signal S1 is a video signal will be described. Referring to Figure 2, the transmission system includes an AM modulation circuit 10 anc an AM demodulating circuill 20. The video signal S1 is supplied to an input terminal 11 and is s-ampled at this case, a carrier signal Ssam a samp-le-hold (5/H) circuit 12. In 1.

having a frequency 2fc which is twice a frequency 1Pc of a carrier Sc is supplied to an input terminal 13. The input signal is samD!ed at the 5/H circuit 12 at intervals W2, where T is the period of the carrier Sc. Therefore, a signal S2 consisting of image data a, b, c....... corresponding to each pixel of the image to be displayed can be obtained. In a modulator (MOD) 14, the carrier signal Se having a carrier frequency fe obtained by dividing the carrier Ssam by a 1/2 frequency divider 15 is AM-modulated by the signal 52, so that a modulated signal S3 can be obtained and transmitted to a transmission line through an output terminal 16. As shown in Figure 2, in the signal S3, the image data a, b, c,..... correspond to each hallf period T/2 of the carrier signal Sc, and the amplitude level of each half period T/2 corresponds to the pixel data a, b, c,...... As shown, the pixel data a, c, e. correspond to positive half periods of the sIgnal 53, and the pixel data b, d, f,..... correspond to negative half periods of the signal S3. Therefore, the modollator 14 has an arrangement such that the input signal S2 is inverted during the negative periods of the carrier signal So synchronised with the input signal S2. Tlhe signal S3 passes through the transmission Line and is 21 of a receivi supp.Lied to an input terminal ing side. Then, the signal S3 is supplied to the demodulating circuit 20 which includes a full.

wave rectifier circuit (DET) 22. More specifically, a signal Su in which the image data a, b, c,..... are arranged at half periods T/2 is obtained from the full wave rectifier circuit 22. The signal S4 is then supplied to a low-pass filter (LPF) 23, so that the originall video signal S1 can be obtained at an output terminal 24.

According to the above-described system, it is apparent that the transmission rate of the image data a, b, c,..... can be twice that of the previously-proposed system shown in Figure 1, although the same carrier frequency fc is used.

In particular, the present invention is suitable for application to a system for transmitting image data. In general, since the image data of a given pixel has correlation with image data of adjacent pixels (succeeding pixel data on a horizontal line, pixell data on succeeding lines, or pixel data on succeeding frames or fields), the levels V1 and V2 oil, for example, the data a and b are not significantly different from each other. Therefore, the modulatl system shown in Figure 2 can be used without significant problems occurring.

P 4 -ant' ly If tne 'Levels V' and V2 of the data a and b are signidifferent from each other, the data may be balance- corrected to transmit a signal having positive and negative levels which are substantially similar with respect to a central level. Table I shows typical correction values when such balance correction is performed.

6 Table 1 balance correction 0 1 2 3...... 13 14 is _\a 0 1.5...... 6.5 7 7.5 1 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 a.......

7 7.5 a 8.5......

7.5 1, 8 1 8.5 1 9 1...... 1 In Table the image data aand b (addresses x and y) are eaen 4-bit data, such that each item of data can represent one of lo luminance levels. Each region in the table represented by an oblique line is a region where a correction is not performed because the difference between the data a and b is small. In addition to 1-hese regions, the correction is not performed in regions (not shown) where the difference between the data a and b is 11211 or less. For example, a:b (orb:a) is5:6, 5:5, 5:4, 5:3, or thelike. Other regions are correction regions, and the data a and b are balance- corrected to an average value of a = b = (a + b)/2, for example.

Figure 3 shows an automatic data balance control (ADBC) circuit 30 and a modulation circuit 40 based on a digital signal processing 7 technique.

Four-bit image dalla t4 Lsed at a freouency 2fe is suppLied to an input terminal 311. A carrier signal Sc (at% a frequency fc) is supplied to an input terminal 32. The input image data a, b, c, supplied to the input terminal 31 are directly applied to the y terminal of a ROM 34. In addition, the data a, b, c. are delayed by one bit by a latch 33 and then supplied to the x terminal of the ROM 34. Therefore, for example, when the data b is directly supplied to the ROM 34, the data a is supplied from the latch 33 to the ROM 34.

The ROM 34 stores the data in the correction table in Table 1. The correction values are read out from the ROM 34 based on the input data a and b serving as addresses x and 1, and corrected data a' and b' are read out. The readout corrected data are then supplied to the modulation circuit 40. The modulation circuit 40 includes an inverter (INV) 41 for inverting each bit in accordance with the corresponding corrected data, a digital-analog (D/A) converter 42, and a low-pass filter (LPF) 43. The inverter 41 inverts each bit of the corresponding input data at alternate h,-:,-If cycles of the carrier signal Sc. Therefore, the inverter 41 ca-n provide the signal S3 shown in Figure 2 as a digital value. The resulting data passes through the D/A converter 42 and the L.PF 43, so that a balance-corrected analog AM signal can be obtained at an output terminall 44.

An embodiment of a system in which still image and audio signals are recorded on an audio magnetic tape or other medium and reproduced using the above-mentioned AM modulation system will now be described.

Figure 4 shows an embodiment of a recording system. A still image signal S1 of one fra or one field obtained from a signal source such as a video tape recorder (VTR), camera, or a video disc is supplied to a decoder 52 through an input terminal 51. At the same 'I image signal S1 and time, an audio signal Sa corresponding to the sti, also obtained from the signal source is supplied via an input terminal 53 to a head 55 through an audio recording amplifier 54, so that the audio signal Sa is recorded on an audio track of a magnetic tape. In this case, the audio signal Sa is recorded on, for example, an R-channel track of two stereo tracks, that is L- and R-channel tracks formed in a longitudinal direction on the tape. On the L-channel track, the AM-modulated stil'L image signal is recorded by a head 56.

8 The st-i image signal I T fed to the decoder 52, and red, green and blue pr-mary colour signals -411 image s- R, G and B are demodulated. In addition, the st- igna-' S' is t supplied to a sync separation circuit (SYNC SEP) 57, in which a sync signal is separated. The primary colour signals R, G and B demodulated by the decoder 52 are supplied to A/D converters 58, 59 and 60, and converted into 4-, 5- and 3-bit digital signals in response to respective sampling pulses supplied from a timing signal generator (TIMING GEN) 61 driven in response to the separated sync signal. The digital primary colour signals R, G and B are written into a memory 62 having a capacity of one video frame or one video field. In this case, the least significant bit of the green signal of the primary colour signal's is fed to a blue channel in order to simplify signal handling, so that each channel has 4 bits. Therefore, the signals in this state are represented as R, G' and B'. --- A system controller (SYS CONT) 63 driven by the timing sgnal generator 61 controls writing and reading operations of the memory 62. The digital primary colour signals R, G' and B' read out from the memory 62 are supplied to the above-described ADBC circuit 30 and the modulation circuit 40 (shown in Figure 3).

A timing signal- is supplied from a timing signal generator 64 to the system controller 63, so that the signals R, G' and B' are sequentially read out from the memory 62. In this case, a time base is converted so that one colour still image can be transmitted within about 2.8 see. An AM-modulated wave having a frequency fc of, for example, 8.7 kHz can be obtained from the modulation circuit LO. This AM- modulated wave passes through a switch 65 and a recording amplifier 67, and is recorded on the L-channel track of the audio tape by the head 56. The switch 65 multiplexes a controll signal with the AM- modulated wave. A control data generator (CONT DATA GEN) 66 receives external control data to generate digital control data. The control signal is modulated by a modulation circuit (MOD) 68, and multiplexed with a division point of the still image signals. In this case, a carrier frequency corresponding to the control signal is lower than the carrier frequency of the image data, for example, 3 kHz to increase the signal-to-noise (S/N) ratio. The control data includes space information between images, discrimination information for blackf'white 9 or colour data, and discrimination information for high deflnition or normal image, for example.

Thus, on the audio tape, the audio signal is recorded in the R channel, and the still image information including the control data is recorded in the L-channel.

Figure 5 is a block diagram of a reproducing unit, preferably a palm-sized reproducing unit in which a liquid crystal display (LCD) is mounted on a headphone personal stereo tape recorder.

An R-channel head 80 reproduces the audio signal from a prerecorded magnetic tape. The reproduced audio signal is supplied to an audio signal processing circuit (AUDIO PROCESS) 85 through a pre amplifier 83. If an audio signal is also reproduced by an '--channel head 81, the signal is supplied to the audio signal processing circuit through a pre-amplifier 84 and a switch 86, as with the H-channel head. In this case, stereo audio signals can be respectively obtained at headphone output terminals 88R and 89L, as in a normal headphone stereo player. If required, a speaker 87 may be provided.

When the signal recorded in the L-channe! is still image data, the switch 86 is changed over, and the output from the pre-amplifier 84 is supplied to an automatic gain control (AGC) circuit 90. A control signal to be supplied to the switch 86 is fed from a terminal 82 by, -ing controL for example, manual operation. The result data and image data are supplied to a low-pass filter (LPIF) 9', and the imaze data is demodulated by a demodulating circuit (DEMOD) 92. The demodulat.ng circuit 92 may be the same as the demodulating circuit 20 in Figure 2, as described above. The demodulated signall is supplied to an A/D converter 93 in the next stage and to an AGC detector (AGC DET) 57 to obtain an AGC control signal. The resulting AGC control signal is supplied to the AGC circuit 90.

An output from the LPF 91 is also supplied to a band-pass filter (BPF) 98 having a centre frequency of 8.7 kH2. The BPF 98 extracts carrier components which are supplied to a timing signal generator (T. SIG GEN) 99. The timing signal generator 99 forms various timing -a, and the various signals in synchronism with the input image dat timing signals are supplied to the demodulating circuit 92, the A/D converter 93, a control signal decoder 100, and a system controller (SYS CON) 101, as required.

The AiD converter 93 converts the demodulated primarY col-our signal's R, G' and B' into 4-bit signals, and the convertec --D-t signals are supplied to a frame memory unit 9t. The frame memory unit 94 includes frame memories 95 and 96 for alternately performing writing and reading operations. More specifically, when data of one complete still image is supplied to the frame memory unit 94, it takes about 2.8 see., as described above. Therefore, for example, during a period in which new data is supplied to the frame memory 95, namely 2.8 sec., data of a previously stored image in the frame memory 96 is repeatedly read out in response to a sync signal complying with a normal television system standard. Therefore, a sync generator (SYNC GEN) 102 forms the sync signal, for example, in accordance with the NTSC colour standard.

The signals R, G' and B' read out from the frame memory unit 94 are returned to the original bit states by operations which are the reverse of the recording mode. That is, the signals, R, G' and B' are converted into 4-, 5- and 3-bit data for the signals R, G and B, and supplied to D/A converters 103, 104 and 105, respectively. The resulting data are converted into analog signals, and are supplied to a display control circuit (DISPL CONT) 106 together with tne sync signal. Thus, LCD drive circuits (DISPL DRIVE) 107 and 108 control a colour liquid crystal display (LCD) panel 109 in response to drive signals provided by the display control circuit 106 to obtain a colour still image. In an experiment, a 128 RGB trio x 128 line colour 'Liquid crystal panel was used, and a 4,096 pixel colour display still =age could be displayed at a rate of one image about every 3 see. A black/white image could be displayed at a rate of one image per second.

Figure 5 shows an embodiment wherein the primary signals R, G and B are sequentially processed for each field. Figure 6 shows a memory control unit in which signals Y, R-Y and B-Y are used. As shown in Figure 6, when a luminance signal Y and colour difference signals R-Y and B-Y are sequentially transmitted for each field, compatibility between the black/white and colour modes can be advantageously improved. In the same manner as in the system of Figure 5, the demodulated still image data is supplied to an input terminal 201. The input data is supplied to an A/D converter 202 and converted into 4bit data. The converted signal is supplied to a switch circuit 203, and then to a switch circuit 208. In this case, in wth the co-our anc black/wh-ite modes, when the data fo.:.low-'ng a con'-rol sJgna" ' -'s L - - 1.

- 3 are supplied, switches 204, 205 and 206 in the sw'.-,ch circui. 20 turned on. The data are simultaneously written into memories 213, 2'5 and 217 of a frame memory unit 212 through switches 209, 210 and 211 in the switch circuit 208.

Therefore, black/white data V1, V2. are simultaneously written into three of the memories in the frame memory unit 212. If the image data is colour data, and colour difference data (R-Y)l is supplied immediately after the luminance data Y1, only the switch 204 is turned off, and the memories 215 and 217 are updated. When the succeeding data (B-Y)l is supplied, the switches 204 and 205 are turned off, and only the memory 217 is updated. Thus, the data Y1, (R-Y)l and (B-Y)l are stored in the memories 213, 215 and 217, respectively. Note that when one-frame data are stored, the switches 209, 210 and 211 in the switch circuit 208 are respectively switched to the lower positions, and the next image data are similarly written in the memories 214, 216 and 218. Outputs from the memory groups are supplied to OR gates 221, 222 and 223, and D/A converters 224, 225 and 226.

A system control ler (SYS CONT) 220 receives the decoded control signal supplied to an input terminal 207, so that the above-descr-ibed memory control operations can be performed. As in Figure 5, a sync generator (SYNC GEN) 227 is provided to read out data from the frame memory unit 212 in response to a standard television sync signal.

As a result of using the above-described arrangement and control system, both black/white and colour still images can be processed without the need for any particular colour or black/white discrimination data to act as a control signal.

1 12

Claims

1 A modulation circuit for transmitting an incoming informarlion signal on to a transmission line, the circuit comprising:

sampling means for sampling said incoming information sIgnal at a sampling frequency; and amplitude modulating means connected to said sampling means for amplitude modulating a carrier signal having a frequency that is half of said sampling frequency by said sampled incoming information signal.

2. A modulation circuit according to claim 1, wherein the carrier frequency is generated by dividing said sampling frequency by 2.

3. A modulation circuit according to claim 1 or claim 2, comprising amplitude adjusting means interposed between said sampling means and ween said amplitude modulating means for restricting the difference bet two adjacent data to a predetermined value.

4. A modulation circuit for modulating digitised information, the circuit comprising:

data inverting mreans for inverting every other incoming digitised sample of information; digital to analog converting means connected to said data ated signal; and inverting means for generating an amplitude modu.

low pass filter means connected to said digital to analog converting means.

5. A demodulating circuit for demodulating an amplitude modulated signal generated by a modulation circuit according to claim 1, claim 2 or claim 3, the demodulating circuit comprising: full wave rectifier circuit means supplied with the amplitude modulated signal; and filter means connected to said full wave rectifier circuit means.

6. A still image reproducing apparatus comprising: a transducer head for reproducing an amplitude modulated still image information signal together with a control signall from a 13 recording track of an audio tape; a demodulator connected to said transducer head for recovering the original still image information; first and second image memories for storing said still image information; and memory control means connected to said first and second memories for reading stored still image information from one of said memories while writing still image information into the other of said memories based on said control signal reproduced by said transducer head.

7. A still image reproducing apparatus according to claim 6, wherein each of said first and second memories has three memory elements for luminance information and two kinds of colour difference information of said still image information.

8. A still image recording apparatus for recording still video information on a magnetic tape, the apparatus comprising: digitising means for d-gitising an -incoming still video signal; -oring the memory means connected to said digizising means for st digitised still video information; amplitude modulating means connected to said memory means for -412 video information read out -ing the digitised sll--- amplitude modulat from said memory; digital to analog conversion means for converting the digitised amplitude modulated still video information into analog amplitude modulated still video information; and magnetic head means for recording said analog amplitude modulated still video information on a recording track of an audio tape.

9. A still video information recording apparatus comprising:

first modulation means for modulating a first carrier by an incoming still video information signal; second modulation means for modulating a second carrier which has a lower frequency than that of the first carrier by a control signal; signal mixing means connected to said first modulation means and said second modulation means for interposing a modulation signal from the second modulation means between successive still video information 14 -Jng said first carrier; and signals modullatmeans for recording signals derived from said signal mixing means on a recording track of an audio tape.

10. A modulation circuit substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

11. A modulation circuit substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings. 10

12. A demodulating circuit substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

13. A still image reproducing apparatus substantially as hereinbefore 15 described with reference to Figure 5 of the accompanying drawings.

ially as hereinbefore

14. A still image reproducing apparatus substant described with reference to Figure 6 of the accompanying drawings.

image recording apparatus or a still video recording

15. A stM apparatus substantially as hereinbefore described with refference to Figure 4 of the accompanying drawings.

Publishe,-41989 a, TiepatertOLice.SLatr-T-13-ase.66 71 HigIHoIborz.L:r. donWC1R4TP Further copies maybe obtained Lrctin The Patent Office. SaJes Branch. St Mary Cray. Orpington. Kcn,. BR5 3RD Printed by Miltiplex techniques Itd. S-, MazT Cray. He-i. Con 1.87