DE3919302A1 - DEVICE FOR TRANSMITTING IMAGE INFORMATION - Google Patents

Abstract

A system for transmitting image data by amplitude modulation in which alternate pixel data a, b, c..... are modulated in a modulator 14 so as to correspond to positive and negative half periods of a carrier signal Sc. The modulated data are then demodulated by a demodulating circuit 20. As a result of this technique, the transmission rate and the recording density of the image data can be doubled as compared with a system in which data is modulated over full periods of the carrier signal. The system may be used in the recording of still images on a portable audio cassette recorder with the provision of suitable frame memories for colour or black and white image signals. Using the technique a single still frame takes about 2.8 seconds to reproduce. Sound and vision signals may be recorded one in each of two stereo tracks available. <IMAGE>

Description

The invention relates to circuits for modulating, for transmitting and for demodulating data. The invention also relates to the application of such circuits in a device for how given by still pictures.

The background of the invention is explained in more detail below with reference to FIG. 6. It relates to a transmission system in which an analog signal, such as a video signal, is amplitude modulated, transmitted and received.

An input signal S 1 with the form shown in FIG. 1 is fed to an input 1 and sampled and held by a sample / hold circuit (A / H) 2 at predetermined time intervals T. This forms a signal S 2 which has sampling data a , b , c , ... This signal S 2 is fed to an amplitude modulator (MOD) 3 , which is supplied from an input 4 with a carrier signal Sc of the carrier frequency fc corresponding to the period T mentioned above. The amplitude modulator outputs a modulated signal S 3 . In this, each of the sample data values a , b and c corresponds to a full period T of the carrier signal Sc , as shown in FIG. 1.

The amplitude-modulated signal S 3 is fed via a transmission line to a demodulator (DEMOD) 5 on the receiver side. The signal S 4 shown in FIG. 1 is obtained there. This is fed to a low-pass filter (TPF) 6 , as a result of which the original signal S 1 is generated again after the filtering and is tapped at an output 7 .

In this conventional amplitude modulation, the sampling frequency must be the same as or small as the carrier frequency fc . The possible amount of the latter is usually limited by the transmission properties of the transmission line or a receiving medium, depending on the design of the system. Accordingly, when sampled data is amplitude modulated and transmitted, the transmission speed or recording density of the data is limited by the properties of the transmission path and / or the recording medium. In particular when recording data on a magnetic tape, this leads to relatively high recording times.

The invention has for its object circuits for Modu lier, transmit and demodulate in connection with ampli tude-modulated signals indicate which circuits are high Allow transmission speeds. The invention lies further based on the object of a device for generating of still images using such circuits.

All circuits according to the independent claims are common sam that they concern circuits that he sampled signals testify or take advantage of each other only over a half Extend period of a carrier oscillation. While at the booth technology a sampled signal through the entirety of a positive and a negative half wave was shown below distinguish the circuits according to the invention between positive and negative half-waves and order each half-wave in the modu a single sampled signal. This allows double the transmission speed. When demodulating it is considered that data with twice the carrier frequency successive. In a device for playing back Still pictures can be color and with such circuits Process black and white images equally easily.

According to an advantageous development of the invention, the Modulation made an equalization if the levels were adjacent ter sampled data is more than a predetermined value differentiate.  

The invention is explained in more detail below with reference to exemplary embodiments illustrated in FIGS. 1-5. Fig. 6 to the state of the art has already been described. Show it:

Fig. 1 is a block diagram of a transmission system with respect to the carrier frequency-doubled sampling frequency;

Fig. 2 is a block diagram of a level correction circuit;

Fig. 3 is a block diagram of a video system still picture recording system;

Fig. 4 is a block diagram of a playback system;

Fig. 5 is a block diagram of a control device for recording a still picture and a diagram of the contents of an image memory; and

Fig. 6 is a block diagram of a conventional transmission system for transmitting an amplitude-modulated audio signal.

For describing the transmission system according to Fig. 1, it should be taken that the power supplied to the system input signal is a video signal S 1. The system has an amplitude modulation circuit 10 and a demodulation circuit 20 (each with a dashed border).

The video signal S 1 is fed to an input 11 and sampled by a sample / hold circuit (A / H) 12 . At an input 13 , a scanning signal Ssam is supplied, the frequency (2 fc ) of which corresponds to twice the frequency ( fc ) of a carrier signal Sc . The input signal is accordingly sampled by the sample / hold circuit 12 with an interval T / 2 which corresponds to half the period T of the carrier signal Sc . For each pixel of the transmitted image, image data a , b , c . . ., Which together form a signal S 2 . In a modulator (MOD) 14 , the carrier signal Sc is amplitude modulated by the signal S 2 . The carrier signal was previously generated in a frequency divider 15 from the scanning signal Ssam . The amplitude modulated signal S 3 is supplied to an output 16 and sent from there via a transmission line.

As shown in Fig. 2, in the signal S 3, the amplitude of each half-wave of the period P / 2 of the carrier signal Sc corresponds to an image point value a , b , c ,. . . The pixel data a , c , e,. . . positive half-waves, while the pixel data b , d , f,. . . correspond to negative half-waves in the signal S 3 . The modulator 14 is accordingly constructed so that it inverts the input signal S 2 during negative half-waves of the carrier signal Sc .

The signal S 3 reaches an input 21 on the receiver side via the transmission line. From there, the signal S 3 reaches a demodulating circuit 20 , which has a full-wave rectifier 22 . This outputs a signal S 4 in which the image data a , b , c,. . . half of the period T / 2 all positive levels. From this signal S 4 , the original video signal S 1 is formed in a low pass filter (TPF) 23 , which is given to an output terminal 24 .

From the above explanation it follows that the pixel data a , b , c at the same carrier frequency fc as in the conventional system can be transmitted twice as fast compared to the transmission speed there.

The system described is particularly suitable for the transmission of image data. This is because, in the case of image data, there are generally no large deviations in the values for adjacent data, that is to say adjacent along a column, a row, or in relation to successive images or fields. The like data can also be processed with the simple modulator circuit 10 according to FIG. 1.

However, if the levels of consecutive data are high differ from each other, they are advantageously so corrected in the level that successive positive and nega tive levels are substantially the same. Table 1 shows one Example of such a level correction.

Table 1

Level correction

In the example case, the pixel data a and b (addresses x and y ) are each 4-bit data, ie data which each indicate one of 16 brightness levels. Each box with an oblique line corresponds to a pixel combination for which no correction is necessary, since the difference in the levels of the data values a and b is small. No correction is made even where the difference is "2" or less, for example, a : b (or b : a ) is 5: 6, 5: 5, 5: 4, 5: 3 or the like. Corrections are made for other value pairs, for example according to the equation a = b = ( a + b ) / 2.

Fig. 2 shows an automatic level correction circuit 30 and a modulation circuit 40, the signals processed digitally. Digitized 4-bit pixel data with the frequency 2 fc are fed to an input 31 . At an input 32 is the carrier signal Sc of frequency fc . The pixel data a , b , c,. . . go directly from the input 31 to the y connection of a ROM 34 . In addition, after a delay of one bit each, this data arrives at the x connection of the ROM 34 . The deceleration takes place in a delay element 33 . For example, if the data d is written directly into the ROM 34 , the delayed data a is written at the same time. The ROM 34 stores the data in a correction table that corresponds to the table shown. Corrected data values are then read out, the relationship illustrated in Table 1 being between the data to be corrected and the addresses. The corrected data are fed to the modulation circuit 40 . This has an inverter (INV) 41 , a D / A converter 42 and a low-pass filter (TPF) 43 . The inverter 41 inverts each bit of the associated input data to alternate half-waves of the carrier signal Sc . Accordingly, it outputs the signal S 3 according to FIG. 1 as a digital signal. After analog conversion and Ver work in the low-pass filter 43 , a pe gel-corrected amplitude-modulated signal is available at an output 44 .

In the following, a system is explained in which audio signals and signals for a still picture are recorded on an audio magnetic tape net and reproduced, each using of the modulation method explained above.

Fig. 3 is an example of a recording system. A still image signal S 1 for a frame or field, which signal is obtained from a video camera or a video disc, is supplied to a decoder 52 via an input 51 . At the same time, another input 53 is supplied with an audio signal Sa , from where it arrives at a recording head 55 via an audio amplifier 54 , so that the audio signal Sa can be recorded on an audio track of a magnetic tape. This audio signal Sa is recorded in one of two stereo tracks, for example in the track for the R channel. Two tracks, namely for the L and R channels run along a band. An amplitude-modulated still image signal is recorded on the track for the L channel by a head 56 .

The still image signal supplied to the input 51 is supplied to the decoder 52 and primary color signals R , G and B are demodulated. In addition, the still image signal goes to a synchronizing separating circuit 57 which separates a synchronizing signal. The primary color signals R , G and B demodulated by the decoder 52 are fed to A / D converters 58 , 59 and 60 and converted into 4, 5 and 3 bit digital signals depending on sampling pulses. The sampling pulses are generated by a clock generator 61 which is synchronized by the signal from the synchronizing separation circuit 57 . The digital primary color signals are written into a memory 62 , the capacity of which corresponds to the number of pixels in a video frame or field. The least significant bit for the green signal within the primary signals is fed to the blue channel to simplify signal processing, so that four bits are available in each channel. The signals in this state are referred to as R, G 'and B ', as shown in Fig. 3 below.

A system controller 63 , which is clocked by the clock generator 61 , controls the write and read operations of the memory 62 . The digital primary color signals R , G 'and B ' read from it are fed to the automatic level correction circuit 30 , which was explained above with reference to FIG. 2.

The system controller 63 is also supplied with a clock signal from a further clock signal generator 64 , with the aid of which the primary color signals R , G 'and B ' are read out from the memory 62 one after the other. The time base is changed so that a still image can be read out every 2.8 seconds. A modulation circuit 40 generates an amplitude-modulated signal with a frequency fc of 8.7 kHz from the level-corrected signal, in the example case. This amplitude-modulated signal passes through a switch 65 to a recording amplifier 67 and is then recorded in the track for the L channel on the recording tape by a head 56 . Switch 56 multiplexes a control signal. To generate this, it holds a control data generator control data that are modulated in a modulator 68 and then multiplexed with a fraction of the still image signal. In this case, the carrier frequency corresponding to the control signal is lower than that of the image signal, for example only 3 kHz, in order to increase the signal / noise ratio. The control data include distance information between images, discrimination information for black / white or color data and, for example, discrimination information for high or normal resolution.

So the audio signal is on the audio tape in the track for the R channel and still picture information including tax data recorded in the track for the L channel.  

The signal thus recorded can be played back with the playback circuit according to the block diagram of FIG. 4. The circuit can be accommodated in a hand-sized stereo headphone tape device with a liquid crystal display.

In the circuit, the audio signal is picked up by an R-channel head 80 and sent to an audio signal processing circuit 85 via a preamplifier 83 . An L-channel head 81 scans the associated tape track. If an audio signal is recorded there, it arrives via a preamplifier 84 and a switch 86 at the processing circuit 85 . The circuit then works as a normal processing circuit for stereo audio signals. These are put on headphone connections 88 and 89 . A loudspeaker 87 can also be present.

If, on the other hand, data for a still image are recorded in the L channel, the switch 86 is switched, as a result of which the signal from the preamplifier 84 reaches an automatic gain control (AGC) 90 . The switchover signal to the switch 86 is input via a connection 82 , for example by manual operation. The image and control data from the L channel are fed to a low pass filter 91 and the image data are demodulated by a demodulator 92 . The demodulator 92 can be constructed like the demodulator 20 described with reference to FIG. 1. The demodulated signal is fed to an A / D converter 93 and a detector for automatic gain control (AGC DET) 97 in order to obtain a control signal for the automatic gain control 90 .

The output signal from the low-pass filter 91 is also supplied to a bandpass filter 98 with a frequency of 8.7 kHz as the center frequency. This bandpass filter 98 filters out the carrier components and feeds them to a clock signal generator 99 . This forms various clock signals in synchronism with the input image data, which are fed to the demodulator 92 , the A / D converter 93 , a control signal decoder 100 and a system controller 101 .

The A / D converter 93 converts the demodulated primary color signals R , G 'and B ' into 4-bit signals, which are fed to a memory unit 94 with frame memories 95 and 96 , which serve to alternately carry out write and read operations. When a complete set of still image data is supplied to the storage unit 94 , it takes about 2.8 seconds as described above. While new data is being written into the memory 95 , ie in a period of 2.8 seconds, data previously stored in the frame memory 96 are read out in response to a synchronizing signal which corresponds to a conventional television signal. A synchronization signal generator (SYNCH GEN) 102 accordingly forms a synchronization signal according to the NTSC color standard.

The signals R , G 'and B ' read out from the memory unit 94 are converted back into the original bit form, which he does by undoing the processes during recording. That is, the signals R , G 'and B ' are converted back into 4, 5 and 3-bit data, that is, into the original signals R , G and B , and these become D / A converters 103 , 104 , and 105 fed. The analog output data, together with the synchronization signal, reach a display controller 106 . Driver circuits 107 and 108 control a liquid crystal display device 109 depending on driver signals from the display controller 106 , which then displays a color still image. In a practical embodiment, a device with 128 lines and 128 RGB triples was used. A color still image with 4096 pixels could be displayed with a frame rate of approximately one image every 3 seconds. Black and white images can be displayed at a rate of approximately one image per second.

FIG. 4 explained above relates to an embodiment in which the primary color signals R , G and B are processed in succession for each field. Fig. 5 shows contrast, via a memory controller for Y, RY and BY signals. If the luminance signal Y and the color difference signals RY and BY are successively transmitted for each field, there is compatibility between the black / white and color mode, which can be used advantageously. Corresponding to the procedure explained with reference to FIG. 4, the demodulated data for the still picture are fed to an input terminal 201 . From there, they arrive at an A / D converter 202 , where they are converted into 4-bit data. This signal reaches a frame memory 212 via two switches 203 and 208 . Individual switches 204 , 205 and 206 are present in switch 203 , for passing the three signals mentioned. These switches are closed for both color and black / white display. The data are simultaneously written into individual memories 213 , 215 and 217 via individual switches 209-211 in switch 208 .

Black and white data V 1 , V 2,. . . are therefore simultaneously written into a triple of the frame memory 212 . If it is color data and color difference data ( RY ) are sent directly after luminance data Y 1 , only the individual switch 204 is opened, so that only the individual memories 215 and 217 are brought up to date. On the other hand, when the next difference data value ( BY ) is input, the switches 204 and 205 are opened, so that only the content of the individual memory 217 is updated. Thus, the data Y 1 , ( RY ) 1 and ( BY ) 1 are stored in the individual memories 213 , 215 and 217 , respectively. When all the data for one frame have been stored, the individual switches 209-211 are set down in the second switch 208 so that the data for the next image are written accordingly into other individual memories 214 , 216 and 218 . Output signals from the individual memories who the OR gates 211-223 and subsequent D / A converters 224-226 fed.

A system controller (SYS CONT) 220 receives control signals decoded via an input 207 in order to perform the above-mentioned memory control as a function thereof. As in the TIC shown in FIG. 4 is a synchronizing signal generator 227 before hands to read data from the frame memory 212 to be read according to a television standard.

Will the above arrangement with the control mentioned both black and white and color still images can be used data are processed without special distinctive data.

Claims (14)

1. Modulation circuit for modulating digital data, with

• a D / A converter for generating an amplitude-modulated signal, and
• a low-pass filter that contains the converted data,

marked by

• - An inverter for alternately inverting the incoming the digital data and to output the data to the Converter.

2. Transmission circuit for outputting a signal on a transmission line, with

• a sampling device ( 12 ) for sampling the incoming signal at a sampling frequency,

marked by

• - An amplitude modulator ( 14 ) for amplitude modulation of a carrier signal with the aid of the sampled data, the carrier signal having the holding frequency of the scanning signal.

3. A circuit according to claim 1, characterized by a frequency divider ( 15 ) for dividing the sampling frequency by two for winning the carrier frequency. 4. Circuit according to one of claims 1 or 2, characterized by a level correction circuit ( 30 ) between the sampling circuit ( 12 ) and the amplitude modulator ( 14 ) to compensate for level differences between successive data values to a predetermined value. 5. Demodulation circuit for demodulating an amplitude-modulated signal, with

• - A sampling device for sampling an incoming signal with a sampling frequency, and
• - a filter ( 23 ),

marked by

• - An amplitude modulator which amplitude modulates a carrier signal with the aid of the sampled signal, the carrier signal frequency being half the sampling frequency, and
• - A full rectifier ( 22 ) which receives the amplitude-modulated signal.

6. Still picture display device with

• - A read head ( 81 ) for reading amplitude-modulated still image signals together with control signals from the recording track of an audio tape,
• - a demodulator ( 92 ) for recovering the original still image,

marked by

• - First and second image memories ( 95 , 96 ) for storing the still image information, and
• - A memory controller ( 101 ) for reading out the information from one of the memories as long as information is written into the other memory.

7. The device according to claim 6, characterized in that each of the two memories ( 95 , 96 ) has three memory elements, namely for luminance information and twice for color difference information. 8. Still image recording device for recording still image information on an audio magnetic tape

• - a magnetic head ( 56 ) for recording still information on a recording track of the tape,

marked by

• a digitizing device ( 58-60 ) for digitizing the still image information,
• - a memory ( 62 ) for storing the digital information,
• - An amplitude modulator ( 40 ) for generating amplitude modulated data using the digital still information, as it is read from the memory, and
• - A device for converting the digital amplitude modulated still picture information into amplitude-modulated still picture information, which is fed to the recording head.

9. The device according to claim 8, characterized by

• a first modulation device for modulating a first carrier by incoming still image information,
• a second modulation device for modulating a second carrier with a frequency lower than that of the first carrier using a control signal,
• - A signal mixing device ( 65 ), which is connected to the two modulation devices in order to classify the second modulation signal between successive still information which modulate the first carrier, and
• - A device ( 67 , 56 ) for recording the signals from the signal mixer on the recording track of an audio tape.