WO-A-9003082 (Article 54.3 EPC) describes a transmission system for a high-bandwidth high-resolution image signal in time and space for transmission over two lower-bandwidth transmission channels, with a first transmission channel transmitting a lower-local and higher-resolution first standard image signal and a second transmission channel transmitting a locally high-resolution low-resolution image signal in time.
A transmission system and a receiver for a high-definition television signal shall be specified, which, in the case of existing band-limited transmission channels on the receiver side, allows the reconstruction of image information even when receiving only one channel.
On the transmitter side, a high-local and time resolution HDTV signal is split into two signals, the first of which has a low local but high time resolution and can be converted into a standard TV signal, e.g. PAL, Secam, NTSC or D2-MAC, or digitally with or without data reduction, by coding, and transmitted over a first band-limited channel.
The second signal has a high local but low temporal resolution. This can be achieved, for example, by omitting images, preferably every second image. By means of a corresponding coder, it can be converted, for example, into an HD-MAC signal or also be transmitted directly digitally with or without data reduction over a second band-limited channel.
The first channel allows a complete local low and high-resolution image signal to be received on the receiver side.
The second channel shall be capable of receiving a complete time-dependent and locally high-resolution image signal, as compared with the state of the art, from which an adequate locally high-resolution image signal, hereinafter referred to as the HD signal, can be reconstructed by appropriate decoding and image regeneration measures.
The purpose of the regeneration measures is to reconstruct to the greatest extent possible the information lost by the receiver by omission of images, especially in moving sequences.
To establish a complete HDTV signal, both channels must be evaluated on the receiver side, using the high-resolution image information of the first channel in time-reconstruction, particularly for dynamic image content.
This creates a HDTV transmission system compatible with conventional transmission systems, with the first channel providing a picture signal with a resolution corresponding to today's television standard and the second channel providing a full high local resolution picture signal.
The present invention is intended to enable a HDTV-like transmission to be made over the second transmission channel, which has at least the high local resolution of the HDTV image.This task is solved by the features given in claim 1 and by the advantages of further training in the invention given in the subclaims.
An alternative solution is claimed in independent claim 2.
It is known from WO-A-9003082 that the code detects and transmits motion vectors, but because of the limited channel capacity, the motion vectors cannot be transmitted with any accuracy or only with a limited amount, but in an improved receiver more precise motion vectors can be formed, preferably using the transmitted motion vectors.
When the receiver combines the signals of the first transmission channel with the signals of the second transmission channel, the signals must be compatible. If the signals are transmitted over two different channels, in particular, their level and phase position must be adapted.
In order to save the user the input or programming of two channels each for the reproduction of an HDTV programme, the first channel or the second channel or both channels may contain additional information enabling the receiver to identify and receive the other channel required independently.
If, in a corresponding future television system, both channels are used as digital channels for the transmission of HDTV signals at a time position of the images of the first channel between the images of the second channel, a corresponding receiver, which necessarily contains image storage, can achieve better use of the image storage or a reduction in the number of images stored by eliminating an image regeneration circuit and by switching between images.
Two examples of implementation are described in detail in the following drawings.Fig. 1Block diagram of an HD decoder with improved motion vector calculationFig. 2Known two-channel HDTV transmission system with one analogue and one digital channelFig. 3Block diagram of a known image generatorFig. 4Known two-channel HDTV transmission system with two digital channels according to the invention
Fig. 1 shows an HD decoder 7 with a buffer memory and video multiplexer, improved over the corresponding HD decoder 7 from W090/03082, 15 each output from the buffer memory 15 leads to a decoder 16 and a motion vector decoder 21. An output from the decoder 16 leads via an inverse weight 17, an inverse scanner 18 and an inverse discrete cosine transformer 19 to a block reconstruction circuit 20. The output from the block reconstruction circuit 20 leads to an underexposed image regeneration circuit and a first input of an image storage device 22. The output from the motion vector decoder 21 leads first to a motion vector corrector 211 and a second input of the image storage device 22.
In decoder 16, transmitted addresses and coefficients are decoded back to their original form before transmission. The motion vector decoder 21 performs the same for the motion vectors. However, because only a limited data rate is available for the transmission of the motion vectors, the motion vectors also have only a limited accuracy or amount.
Figure 2 shows the two-channel HDTV transmission system proposed in WO-A-9003082. An HDTV signal generated from a source is fed to a first transmission line consisting of a transcoder 1 and a TV encoder 2 in the transmitter and a TV decoder 3 and a transcoder 4 in the receiver, and a second transmission line consisting of an image suppression circuit 5 and an HD encoder 6 in the transmitter and an HD decoder 7 and an image regeneration circuit 8 in the receiver.
The transcoder 1 of the first transmission line reduces the horizontal resolution of the image by 2:1 and the vertical resolution by 3:2 by filtering it accordingly. In addition, the HDTV signal present in the progressive scan is converted into a signal with a line jump, while maintaining the temporal resolution. The output signal of the transcoder 1 is fed to the TV encoder 2 which generates a standard TV signal, e.g. in PAL, Secam, NTSC or D2-MAC, and its output is connected to a first transmission channel.
In the first transmission channel, the incoming standard TV signal is decoded in the TV decoder 3 and the standard TV signal is then picked up at the output of the TV decoder 3.
The HDTV signal fed to the second transmission line is subjected to image omission to adapt to a band-limited second transmission channel. With the help of the image suppression circuit 5, for example, only every second image is transmitted. The output signal of the image suppression circuit 5 is transmitted via the HD encoder 6 to a second transmission channel.
The output of the HD decoder 7 is connected to the image regeneration circuit 8 which, using transmitted motion vectors, performs a reconstruction of the images omitted from the receiver side. At the output of the image regeneration circuit 8, an HD signal with high local resolution and original temporal resolution is then detectable, but with possible errors in the range of moving image contents.
To minimize these errors in the moving image range and thus achieve the original high temporal resolution of the source HDTV signal, the standard TV input signal in the transcoder 4 is used to reverse the function of the transcoder 1.
Fig. 3 shows the image regenerator 8 described in WO-A-9003082. The output signal of the HD decoder 7 is fed to a first image storage 38 An output from the first image storage 38 leads to an image interpolation circuit 37 Another output to a second image storage 39 and a multiplexer 40 Further inputs of the image interpolation circuit 37 receive further data from the HD decoder 7, e.g. the motion vectors 53 and the coder modulation 54, i.e. information on inter- or intraframe coding respectively.
If a future HDTV transmission system also transmits digital information over the analogue channel, this may save image storage in the corresponding HDTV receivers.
Fig. 4 shows a corresponding HDTV transmission system for two digital channels. An HDTV signal generated from a source with, for example, 50 Hz frame rate and progressive scanning is split into odd and even images in a separation circuit 41. The odd images are encoded in a first HD encoder 42 and the even images in a second HD encoder 43.
A transmission system according to WO-A-9003082 contains three image storage units (22, 38, 399). However, the transmission system according to Fig. 4 contains only two image storage units (22 in HD decoder 44 and 22 in HD decoder 45). The first 44 and second 45 HD decoders include, for example, an HD decoder according to Fig. 1.Since the first HD decoder 44 and the second HD decoder 45 require one image storage 22 each, but do not require two images storage 38 and 39, the two-channel HDTV transmission system with two digital channels saves at least one image storage in total compared to the two-channel HDTV transmission system according to WO-A-9003082.