Picture Signals Research Articles

Picture Signal Improvement in Coloyr TV Receivers

Picture Signal Improvement in Coloyr TV Receivers

An automatic transversal‐type ghost canceller

AbstractA system study has been conducted on an adaptive transversal filter Ghost Canceller to achieve system optimization, and prototype ghost cancellers have been conducted on a trial basis. The results of tests showed that: (1) a Ghost Canceller for picture signals using an LSI CCD transversal filter could improve the quality of TV pictures by more than one grade in a five‐grade subjective evaluation against multiple ghost images of up to a 12‐μs delay time; and (2) a non‐CCD and totally digitalized Ghost Canceller for Teletext signals has shown a significant improvement in reducing strong short‐delay time ghost echoes and equalizing waveform distortion. This paper clarifies the system structure and the design method for both of the cancellers and shows the practical usefulness of the Ghost Cancellers.

A conditional access system for direct broadcasting by satellite

This paper outlines the main features of a proposed Conditional Access television system, especially for DBS and suitable for large numbers of subscribers. The system includes a computer with a data-base in which all subscriber-related data are stored and processed and which outputs Validation Codes, scrambling-control and key signals for transmission control. A detachable induction-coupled sub-system carrying a unique Address and Distribution Key is provided for each receiver. Payments for a service result in the over-air delivery of new Validation Codes, which, in combination with the Distribution Code, determine the Authorization Key needed for decrypting the signals which control descrambling of the picture and sound signals.

Theoretical Comparison Between DPCM and Transform Coding Regarding the Robustness of Coding Performance for Variation of Picture Statistics

Since DPCM and transform coding are two fundamental approaches to high-efficiency (bit reduction) coding, it is important to clarify the basic coding characteristics of these approaches and the differences between them in order to utilize the high-efficiency coding method effectively. It is important to compare them not only from the standpoint of coding performance as optimized coding schemes based on the statistics of the input picture signal, but also from that of the robustness of coding performance for the variation of picture statistics to be coded. This paper theoretically compares the robustness of the coding performance of DPCM having a two-dimensional predictor with that of a two-dimensional Hadamard transform coding in an intrafield coding method of the NTSC composite signal. The comparison provides theoretical evidence that transform coding is more stable than DPCM, and this tendency is marked at lower bit rates such as 1 or 2 bits/pel, while DPCM has a higher coding performance for pictures with high autocorrelation.

Significance of group delay functions in signal reconstruction from spectral magnitude or phase

In this paper we discuss the problem of signal reconstruction from spectral magnitude or phase using group delay functions. We define two separate group delay functions for a signal, one is derived from the magnitude and the other from the phase of the Fourier transform of the signal. The group delay functions offer insight into the problem of signal reconstruction and suggest methods for reconstructing signals from partial information such as spectral magnitude or phase. We examine the problem of signal reconstruction from spectral magnitude or phase on the basis of these two group delay functions and derive the conditions for signal reconstruction. Based on existing iterative and noniterative algorithms for signal reconstruction, we propose new algorithms for some special classes of signals. The algorithms are illustrated with several examples. Our study shows that the relative importance of spectral magnitude and phase depends on the nature of signals. Speech signals are used to illustrate the importance of spectral magnitude and picture signals are used to illustrate the importance of phase in signal reconstruction problems. Using the group delay functions, we explain the convergence behavior of the existing iterative algorithms for signal reconstruction.

Optical Fibre Communication Systems for Voice and Video Signals—State-of-the Art

The optical fibre communication systems have a tremendous potential of carrying a large number of voice and video signals. Many fibre systems have already been installed and many more are planned and are under development. They are useful for all kinds of applications, such as submarine communications, intercity long haul communications, metropolitan trunking systems, subscriber loops and military communications in a telecommunication network. These applications and some of the new customer services which can be provided by fibre optic systems are reviewed. Current trends in the development of the components such as the optical sources, detectors and fibres are presented. Sources and detectors at long wavelengths, 1300 and 1600 nm range, where the fibre attenuation and dispersion are minimum, and the single-mode fibres are in advanced stages of development. Far greater repeater spacings than possible with metallic cables, would be achieved by using them in optical fibre systems. The ever-growing demand on telecommunication services can be met by a two-prong approach: (i) exploiting new wideband media like optical fibres and (ii) compression of bandwidths of the voice and the video signals at the source. Techniques of bandwidth reduction and progress made in generation of digital speech and picture signals at low bit rates are reviewed. Multiplexing methods and various line codes used in baseband transmission systems arc summarized.

Reversible predictive coding of continuous‐tone picture signals using block adaptive variable‐length codes — A scheme of reversible coding for picture data base

AbstractIn the picture data base the allowable distortion is dependent on the various uses for each picture signal. an efficient reversible coding for continuous‐tone picture signals, which does not increase the distortions of PCM original picture signals, is necessary to construct the picture data base efficiently. In most of the former proposed reversible coding schemes, the compression characteristic deteriorates remarkably as the number of picture signal gradations is increased. In this paper, a scheme of reversible predictive coding using block adaptive variable‐length codes is proposed for 8 bit/6 bit PCM continuous‐tone picture signals. A simple method of selecting the appropriate variable‐length code in every block based upon threshold logic, which is designed by means of numerical calculation, is shown to be able to achieve almost the same efficiency as in the optimum selection scheme. Besides, a method of adapting its block size is introduced to cope with the block size dependency of the compression characteristic. This coding scheme yields a performance advantage of approximately 0.2 ‐ 0.4 bit/pel for 8 bit PCM picture signals and 0.11 ‐ 0.17 bit/pel for 6 bit PCM picture signals over Rice Machine 1.

Arithmetically symmetrical digital bandpass and band‐elimination filter design by frequency transformation

AbstractIn transmission systems of modulated data or picture signals, bandpass filters are required with symmetrical amplitude and delay characteristics around their own center frequencies on an arithmetic frequency scale. In variable attenuation equalizers, etc., band‐elimination filters are required with arithmetically symmetrical stopband amplitude characteristics around the center frequency. This paper proposes frequency transformations to make an analog bandpass filter and a band‐elimination filter (with geometrically symmetrical amplitude characteristics around the center frequencies that are obtained through reactance frequency transformation from analog lowpass filters) into a digital bandpass filter and a band‐elimination filter with arithmetically symmetrical amplitude characteristics. This transformation maps the positive imaginary axis and the negative real axis of analog frequency S to the real axis and the upper half of the unit circle on the z‐plane. the interval on the unit circle of the z‐plane mapping of the positive imaginary axis of the S‐plane is designed to cover the specified frequency region. This is done by controlling the locations of geometrically symmetrical two frequency points around the center frequency of bandpass (band‐elimination) filter by adjusting the parameters of lowpass‐bandpass (band‐elimination) transformation. Some design examples are also shown.

New SECAM Composite SAW IF Filter Separating the Sound and Picture Signals

A new Surface Acoustic Wave (SAW) filter for the French L/SECAM system has been developed. It has two input transducers and two output transducers which are constructed on 128°Y-XLiNbO3 and it separates the input signal into sound and picture signals for use in the L/SECAN system which uniquely utilizes an AM sound signal. The size is the same as that of the conventional SAW IF filter, and it is sealed in a TO-8 can package. Compared with previous models, this new SAW filter enables the TV IF circuit to lower the sound-picture crossbeat interference (the beat noise in speakers) by 3.4 dB and reduces the number of electrical parts.

New Color TV Receiver With Composite SAW IF Filter Separating the Sound and Picture Signals

Numerous researches and developments of Surface Acoustic Wave (SAW) TV IF filter have been performed for cost reduction and improvement of reliability of TV circuit. Under these circumstances we reported in 1978 that we had established the design and the fabrication techniques of the SAW IF filter-low noise amplifier system in massproduction size, and put it into the market. This year we have completed a high performance TV IF circuit for sound multiplexing broadcasting, which consists of a more advanced SAW filter. The signal detections are individually performed by the interearrier signal in IF without any external signal. This paper describes the design techniques of newly developed composite SAW IF filter, which is the key device to realize the new circuit and the sound-picture-color crossbeat interferences to picture and sound quality in color TV sets.

A 1-Bit/Pel Digital Encoder for Achromatic Pictures

The paper describes a scheme for producing and digitizing a low-resolution (256 × 256 pels) achromatic picture signals. Using the technique of time expansion at the transmitter, it is possible to send a higher quality picture at a lower bit rate. A DM-encoded picture at 8 MHz is transmitted at 4 Mb/s in the channel achieving a band compression by four. Suitable interpolation at the receiver improves the quality of the picture.

High-Speed Transmission of Sequential Freeze-Pictures by Extracting Changed Areas

A very high-speed freeze-picture transmission system via telephone lines is realized by sending only the changed areas from the previous picture. Transmission speed is improved in reverse proportion to the changed areas compared with conventional systems. Increase in circuit size is nominal. The new system is also much simpler than interframe codecs because it does not employ complicated coding mode controls, addressing, or buffering. Block size of the changed areas is selected to satisfy both fast transmission speed and circuit simplicity. High-speed transmission compatible with high picture quality is achieved by extraction of changed blocks using both the average value of the picture signal difference in each block and the maximum value. Protection of picture data against transmission errors is achieved using two synchronizing data groups among tripled addressing data groups. Reduction of impairments due to errors in DPCM picture data using backward decoding is also proposed and adopted.

Analysis of the simultaneous transmission system for a picture and narrowband signals

AbstractSystematic investigation is made on the noise generated in an FM transmission system for the simultaneous transmission of wideband picture signals and narrowband voice and data facsimile signals. In thermal noise analysis, tradeoffs are carried out between the noise characteristics resulting due to the methods of modulation and multiplexing of narrowband signals. Methods of handling the cross noise and distortion noise, caused by narrowband signals are described. As far as the methods of modulation of the subcarrier wave which corresponds to the narrowband signal are concerned, AM, FM and PSK are considered. The FM and PSK are taken as the focus of present discussion. As far as the distorition noise is concerned, besides the noise of narrowband signal, it is necessary to account for the noise that drops into the picture signal band. The reason for the former is considered mainly to be the differential gain (DG), and the reason for the latter varies depending on the dropping frequency of the noise. The computed values agree very well with the experimental characteristics.For the medium of transmission of multiple signals that include wideband picture signals, the frequency modulation formula has an advantage and the probability of its future development is large.

Theoretical analysis of distortion of simultaneous transmission systems for picture and narrowband signals

AbstractThis paper presents formulas for calculation of the distortion noise in picture and subcarrier FM transmission. The distortion is calculated from the transmission channel characteristics at the sideband of the FM wave which is expanded in Bessel function. FM and PSK are considered as the subcarrier modulation. The spectral models for the picture brightness signals and color signals are approximated by e‐aΔ at frequency Δ.The main results include: (1) the calculation of the distortion due to the differential gain (DG); (2) the calculation of 16 different kinds of distortions; and (3) the application to TV‐speech multibroadcasting, two‐picture simultaneous transmission, and picture‐telephone simultaneous transmission.

Optimized interpolation of discrete picture signals

AbstractThis paper describes the optimization of linear interpolation of picture elements in terms of least mean square error for pictures of a square array of elements. Two kinds of models are assumed for autocorrelation function m, n which is defined as the correlation of two elements separated m picture elements in a horizontal direction and n picture elements in a vertical direction. One is a homogeneous model in which m, n is given by the equation m, nIn the interpolation of the picture element at the point not sampled, the optimum interpolation can be achieved by the linear combination of the four picture elements nearest to the point to be interpolated. This is strictly true in the case of an inhomogeneous correlation function and approximately true in the case of a homogeneous correlation function. On the other hand, in the interpolation of the picture element at the sampling point, the interpolation can be optimized by the linear combination of eight picture elements around the point to be interpolated. This is strictly true in the case of an inhomogeneous correlation function and approximately true in the case of a homogeneous correlation function.Using the above results, interpolation techniques in “standard conversion in broadcasting television signals” and “system conversion from video phone signal to broadcasting television signal” are reviewed, and the pictures processed with the interpolation techniques are evaluated.

Multistage selective dpcm

AbstractThe DPCM, a representative prediction encoding system of picture signals, produces two conflicting noises‐overload and granular. This paper describes the selective DPCM that separates picture signals into edge and slant components, and an optimum encoding is applied for each component to consider the two noises. First, statistical analyses on picture signals conclude that they are composed of the edge component and slant component. Second, the edge component, which shows frames of pictures, is approximated by step waves and the slant component, which shows the smoothness of pictures, is approximated by delta modulation. A new method is proposed here: a statistic adaptation in each block and a constant speed scanning are applied for input picture signals. Finally, it is demonstrated that computer simulations prove the usefulness of the method.

Digital Frame Memory for Still Picture Television Receivers — PASS Encoding System and Application

A new form of television broadcasting is proposed. It consists of the transmission of a series of color still pictures accompanied by their individual sound complements. To this effect, the still picture receiver must incorporate a frame memory for the storage and repeated readout of a given program picture until a new picture signal is received. Single-chip 64K-bit CCD memories are now commercially available (among other memory devices) and may provide for a quite economical frame memory of small size, well suited for the purpose. Phase Alternating Sub-Nyquist Sampling (PASS) is used for the digital recording of NTSC video signals. This reduces the bit rate and the amount of memory required. The principles of PASS encoding are explained. Three types of interpolation filters, needed for the suppression of aliasing, have been investigated. A two-dimensional analysis of PASS encoding is discussed in the paper. Three PASS encoding methods are described in detail: (1) field alternation; (2) one-line alternation; and (3) two-line alternation. An outline of the practical design of an experimental digital frame memory for a still picture television receiver is given. With this design, actual picture signals appeared good. Vectorscope color bar displays before and after processing by the frame memory showed good coincidence.

Digital Television Transmission with 34 Mbit/s

Digital modulation methods for TV satellite transmission can offer advantages in satellite transmission power and bandwidth if the bit rate can be reduced to 34 Mbit/s (to 34.368 Mbit/s, the bit rate for 480-channel PCM systems). A very efficient coding technique, differential pulse code modulation (DPCM), is described, and its application for TV transmission is shown. A test system for demonstrating the feasibility of digital TV transmission is described in detail. In this system the composite TV signal is split into its luminance and chrominance components. Tests via directional radio and satellite line have been carried out using a modem with 4-PSK (phase-shift-keying) as interface. After DPCM encoding these picture signals and accompanying sound signals are multiplexed and transmitted together with a code word for synchronization. On the receive side the signals are demultiplexed and after decoding are provided as analog signals. An example of digitally transmitted pictures is given to show that good picture quality has been achieved.

Predictors for intraframe encoding of Pal picture signals

A predictor based on three previous ‘pels’ along a scan line is examined for d.p.c.m. encoding of composite Pal signals. The predictor coefficients are described in terms of the ratio of sampling frequency fs to colour subcarrier fsc. Predictions based on p.e.l.s on the second previous and previous lines are derived for the case of fs/fsc = 2.5. Simple 2-dimensional predictors are then formed and used in the d.p.c.m. encoding of a Pal colour-bar signal.

Picture coding: A review

This paper presents a review of techniques used for digital encoding of picture material. Statistical models of picture signals and elements of psychophysics relevant to picture coding are covered first, followed by a description of the coding techniques. Detailed examples of three typical systems, which combine some of the coding principles, are given. A bright future for new systems is forecasted based on emerging new concepts, technology of integrated circuits and the need to digitize in a variety of contexts.