DE2419279A1 - Television system transmits black and white pictures - uses PAL or NTSC coded colour pictures and binary logic signals - Google Patents

Abstract

Additional television digital signals are transmitted in the horizontal blanking intervals during the blank patch. This additional signal pulse frequency corresponds to that of the auxiliary colour carrier. The burst required for the colour t.v. signal decoding is recovered in the receiver from the auxiliary colour carrier frequency pulses of the additional signal. This signal consists of pulses whose amplitudes, including the "logic O" signal value is above the black level, and the maximum digital value corresponds to the white level.

Description

Television system The invention relates to a television system for broadcasting of black and white TV pictures and PAL or NTSC coded color TV pictures, in which additional information is transmitted in the horizontal blanking areas.

Such a system is for example in the magazine EBU-Review No. 128, August 1971, page 145 ff. With this system will be additional information, e.g. sound signals, in the horizontal blanking areas during the duration of the back porch, in digital form as PCM signals.

During the period the back porch is used in systems with PAL or NTSC coded color television pictures a so-called color reference signal, also known as burst, transmitted at the frequency of the color subcarrier.

In the publication mentioned, the PCM-coded additional Signals a pulse frequency which corresponds to that of the color reference signal.

On the receiving side it must be ensured that from the pulse train except for the additional information contained therein also the burst error-free can be recovered, otherwise there will be color errors in the image.

How to use any pattern of a digital, encoded Can see pulse train, the information "logic zero" occurs frequently. at In the known method mentioned, the code information "logic zero" is the value of the reference level, i.e. assigned to the black level. Since the color reference signal with the frequency of the color subcarrier oscillates around the reference level is inevitably absent this oscillation when the code sign "logic zero" occurs.

This lack can occur in the recovery of the recipient Color reference signal and thus cause interference in color image reception.

The object of the invention is now to provide such a system Specify initially mentioned type in which an error-free evaluation of the color reference signal is guaranteed.

According to the present invention, this object is achieved by that the digitally transmitted, additional information consists of pulses, whose Amplitude, including the information logic zero "one of the reference level (black level) has different value.

Further advantages and details of the invention can be found in the following Description of the accompanying drawings and the claims can be found.

Fig. 1 shows schematically the signal course during the horizontal blanking area, Fig. 2 shows the reduction made within the horizontal blanking range of the time relationships, FIG. 3 shows the changed signal profile in the horizontal blanking area with the additional information and FIG. 4 shows a block circuit design the transmitting and receiving arrangement.

The normal signal curve of the horizontal blanking area begins with the end of the visible image line BI and the signal level drops to the value the front porch FP. This is followed by a further level reduction which is retained over a certain period of time and as a line or horizontal sync pulse StIN is evaluated in the receiver.

The rear black shoulder BPN lasts from the end of the horizontal sync pulse SHN to the beginning of the visible part BI of the next line.

In the case of color television broadcasts, the back porch is used for the duration BPN the color reference signal FRS oscillating with the frequency of the color subcarrier transfer. The duration of the color reference signal, also commonly known as the burst, is about 8-12 periods of the frequency of the color subcarrier.

The division of the horizontal blanking area shown in FIG. 1 corresponds the television arm applicable in most countries.

For the transmission of additional information in the horizontal blanking area one has, as for example with the known method described at the beginning, the temporal Division of the horizontal blanking area changed. As Fig. 2 clearly shows, is made this change in such a way that this duration of the horizontal sync pulse is shortened, so that instead of the standardized pulse SHN now the shortened Pulse SHS is transmitted. This creates an elongated back porch BPL instead of the standardized BPN according to FIG. 1.

Fig. 3 shows that represented in a ternary code, for example digital, additional information. The three different pulse heights of the code have the values CI, CIS and CRZ and a repetition frequency which corresponds to the frequency of the Color reference signal. This is shown in FIG. 3 by the period duration shown Tsc indicated. Every pulse value, including the information "logic zero", for example assigned pulse value CRZ has one of the reference value, i.e. the black level of the rear Black shoulder BPL different value. This occurs during the duration of the information transfer a continuous pulse train with the frequency of the color subcarrier from which the Burst can be derived directly or indirectly on the receiver side.

The entire range of the reference level is used to generate the pulses "Black" to the reference level "White", which results in a gradation that is easy to evaluate can achieve.

In Fig. 4 is a block diagram of both the transmitter lo and the Receiver 20 shown.

It is assumed that the image source 11 is, for example, a standard Color television signal, the so-called FBAS signal, emits, as indicated in Fig. 1 became. This FBAS signal arrives at a standard converter 12, which converts the FBAS signal into converts such a composite signal, the essential conversion being shown in FIG is.

At 13 is the source for the additional information to be transmitted shown. The source 13 can for example be a sound source. The sound signals are converted into digital values in an analog-to-digital converter 14 and in a subsequent encoder 15 is coded in the manner as shown in Fig. 3, for example.

The standard-converted FBAS 'signals and the coded additional information supplied in such a way that the digital information appears at the predetermined point of the rear porch BPL according to FIG. 3. The signal composed in this way is transmitted via the transmitter 17.

It goes without saying that the consisting of parts 13, 14 and 15 Arrangement a second or more can be connected in parallel if taken care of is that the information is fed to the adder 16 in a correspondingly ordered manner.

The receiver 20 has the usual high-frequency part at its input 21. The output signal of a thick HF / IF part 21 becomes common a demodulator 22 is supplied.

The received, demudulated signal is converted into a decoder 24 the e.g. PCf4-coded additional information is obtained, whereby the decoder 24 has the necessary clock signals are fed to an input 27. From demodulator 22 the total signal is also fed to a time selection circuit 23. From the The time range of the rear black shoulder BPL selected in this way becomes the existing one Pulse train for the recovery of the color reference signal of a limiter and amplifier stage fed. The burst is brought to the standard length and that too FJ1S 'signal obtained in the time selection circuit 23 in the adder 26 added. The output signal of the adder 26 can then not be shown here Way can be converted back into the standard composite composite signal.

2 claims, 2 sheets of drawings, 4 figs.

Claims (2)

Patent claims: 1. Television system for the transmission of black and white television images and PAL or NTSC coded color television pictures in which in the horizontal blanking areas additional information in digital form during the duration of the rear black shoulder, in which the digitally transmitted, additional information has a pulse frequency corresponding to the frequency of the color subcarrier and at the color reference signal required in the context of decoding the color television signals (Burst) at the receiving location by evaluating the with the frequency of the color subcarrier transmitted pulses of the additional information is recovered, characterized in that that the digitally transmitted, additional information consists of pulses, whose Amplitude, including the information "logic zero" one of the reference level (black level) has different value. 2. Television system according to claim 1, characterized in that the The digital value of the information "logic zero" is above the reference level and the maximum digital value corresponds to the white value.