EP0250532A1 - Procede de transmission d'un signal video sous forme echantillonnee - Google Patents

Procede de transmission d'un signal video sous forme echantillonnee

Info

Publication number
EP0250532A1
EP0250532A1 EP19870900233 EP87900233A EP0250532A1 EP 0250532 A1 EP0250532 A1 EP 0250532A1 EP 19870900233 EP19870900233 EP 19870900233 EP 87900233 A EP87900233 A EP 87900233A EP 0250532 A1 EP0250532 A1 EP 0250532A1
Authority
EP
European Patent Office
Prior art keywords
sample
transmitted
samples
video signal
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19870900233
Other languages
German (de)
English (en)
Inventor
Nicholas Dominic Wells
Michael James Knee
Charles Peter Sandbank
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Broadcasting Corp
Original Assignee
British Broadcasting Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Broadcasting Corp filed Critical British Broadcasting Corp
Publication of EP0250532A1 publication Critical patent/EP0250532A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/12—Systems in which the television signal is transmitted via one channel or a plurality of parallel channels, the bandwidth of each channel being less than the bandwidth of the television signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/015—High-definition television systems
    • H04N7/0152—High-definition television systems using spatial or temporal subsampling

Definitions

  • HDTV high-definition television
  • a video signal is coded by transmitting only selected samples, the samples to be transmitted being selected by determining whether omission of that sample and transmission of the next sample would cause any regenerated samples to differ from the corresponding actual input sample by more than a threshold value.
  • the values transmitted may not be the actual values of the corresponding input samples but are preferably values defining the ends of "best-fit" straight lines chosen to minimise the mean square error.
  • the threshold may be adaptively dependent upon picture content.
  • the video signal is particularly suitable for transmission in analogue form, with an indication of the positions of the transmitted samples being transmitted digitally in the signal multiplex.
  • Figure 1 is a waveform diagram illustrating the principle of operation of a system embodying the invention
  • Figure 2 is a waveform diagram illustrating the sample selection process
  • Figure 3 is a waveform diagram illustrating a modification using "best-fit" straight lines
  • Figure 4 illustrates the lower bound for the signalling rate plotted against the proportion of samples transmitted for two types of bit rate reduction coding of the SPI signal
  • Figure 5 illustrates the variation of the threshold T upon mean signal level and slope
  • Figure 6 is an enlarged diagram based on Figure 3 illustrating the use of "best-fit" straight lines
  • FIG. 7 is a block circuit diagram of a slope coder embodying the invention.
  • Figure 8 is a block circuit diagram of a best-fit slope parameter generator used in the slope coder of Figure 7.
  • the coder operates on a sampled picture signal. It selects some of the samples using a method which is described below. The selected samples are transmitted, together with a sample-position indicator (SPI) signal which indicates where in the picture the transmitted samples have come from.
  • SPI sample-position indicator
  • the decoder calculates values for each missing sample by linear interpolation between the last sample transmitted and the next to be transmitted, in the current line of the picture, as illustrated in Figure 1.
  • the straight lines in the diagram illustrate the interpolation process and do not show the exact shape of the decoded analogue waveform.
  • the input signal is coverted into digital form at a high enough sampling rate to give a full-resolution picture.
  • Adaptive subsampling is then carried out by the coder on the digital signal. This process gives rise to an auxiliary data signal which, possibly following a bit-rate reduction process, is transmitted to the decoder.
  • the samples resulting from the adaptive subsampling process will emerge at an irregular rate. They are, therefore, written into a buffer store so that they can be read out at a regular rate for conversion back into analogue form for transmission.
  • a feedback control path is normally necessary between the buffer store and the subsampling process to prevent buffer overflow or underflow.
  • the coder uses the following method to select which samples to transmit. It transmits the first sample in each line. The samples following it are considered in turn. A sample is only transmitted If a decision not to do so, and to transmit the next sample instead, would result in one or more of the decoder's reconstructed sample values differing from the corresponding input sample value by more than a certain threshold, T, see Figure 2. Thus, the process ensures that the decoded sample values never differ from the input by more than T.
  • each new input sample is considered in turn as a potential transmitted sample. If the resulting Interpolated signal, between the previously transmitted sample and the current sample, fails to meet the threshold criterion, the sample immediately before the current sample is transmitted and the process begins again.
  • the value of T is controlled by feedback from the coder's buffer store.
  • the SPI signal requires an additional data rate corresponding to about 0.5 bits (or fewer) per input sample.
  • the coder ' has to calculate for each transmitted field a suitable value of T to produce the required sample rate. This value will vary with the source material.
  • One approach to this problem is to use a transmission buffer and to control the value of T by feedback based on the buffer occupancy. Another is to base the value for the current field on that used in the previous field, code the current field, and then remove a few samples from, or add a few samples to, the coded signal to produce the correct sample rate.
  • the technique also has possibilities for hybrid systems In which the samples are converted to analogue form for transmission and the SPI signal sent in digital form.
  • a sample rate reduction factor of 4 should enable an analogue HDTV signal, for example, to be transmitted in one 27 MHz fm channel, leaving capacity for a small signalling overhead which could be used for the SPI signal if its data rate requirement could be made sufficiently small.
  • slope coding One of the main advantages of slope coding is that the decoder can be very simple, particularly if one bit per input sample is available for the SPI signal. Another advantage particularly important in an all-digital implementation, is that, provided the SPI signal is rugged, the effect of transmission errors is very limited in extent. POSSIBLE REFINEMENTS AND VARIATIONS
  • the coder could instead use the mean, or even the accumulated, energy of the error between the input and decoded picture signal.
  • the digital data rate required to indicate the positions of the transmitted samples is rather high.
  • the basic data rate is equivalent to one bit per input sample. The value of each bit is 1 if and only if the corresponding sample (or an approximation to the corresponding sample) Is transmitted.
  • the SPI signal could be transmitted in this form, as a fixed-rate signal multiplexed together with the transmitted samples.
  • bit-rate-reduced version of the SPI signal can be carried out in several ways, of which the following are examples: Method 1 Entropy coding
  • the SPI signal is divided into blocks of M consecutive bits.
  • the non-uniform probability distribution of each of the 2 possible bit-patterns is exploited by assigning to the patterns a variable-length binary code, so that short codes are assigned to highly probable patterns and longer codes to less probable patterns.
  • This can be done by a variety of well-known techniques such as that described by Huffman in "A method for the construction of minimum- redundancy codes", Proc. IRE, September 1952, pp. 1098-1101. Both the complexity and efficiency of this method will increase with M; it is suggested that a value of M approximately equal to the average bandwidth reduction factor would be a reasonable compromise.
  • a transmission buffer will be required to smooth out the data rate.
  • the SPI signal can be considered as a series of runs of (possibly zero) O's followed by a 1.
  • the length of each run forms a new signal which can take any value between 0 and some maximum run-length.
  • This new signal can be entropy coded as in Method 1.
  • the degree of bit-rate reduction that can be achieved is about the same in each method.
  • This run-length signal can be entropy coded, but with one of several different variable-length codes being used on each occasion, the choice being determined by the SPI signal in the previous field or line. For example, there might be one variable-length code for each possible length of the run occupied by the sample immediately above (or above and to the right of) the first sample in the run being coded. Thus, the correlation between run-lengths on adjacent field-lines is exploited.
  • Method 4 Run-length coding using fixed-length codes
  • This method is the same as Method 2 except that a fixed-length code of M hits is used to describe the length of each run.
  • This will not be as efficient as Method 2, but it has one advantage over all the ' methods involving variable-length coding.
  • the chosen value of M limits the maximum run-length and this may bring about- a slight penalty in the degree of bandwidth compression that can be achieved.
  • a significant further sample rate saving can be achieved by adapting 'the threshold value according to the size of the interpolated slope (which serves as a measure of picture activity) and also according to the mean level of the picture signal in the area being coded.
  • the average transmitted sample rate for a given subjective picture quality can be improved by about 12% by increasing the value of the threshold T according to some measure of picture activity and according to the mean signal level. This can be done because quantization noise is less visible in active areas and also in dark or bright areas of the picture.
  • An effective and readily available measure of activity is the magnitude of the interpolated slope. *
  • Figure 5 shows how, in one example, the value of T depends on the slope magnitude and mean level.
  • the function defined in Figure 5 at zero slope values has high points at black B and white W and a minimum at a mid-grey G.
  • the function with slope from this grey point is to increase up to a maximum M.
  • the maximum of these two functions is selected at any point.
  • each straight line segment is independent of those on either side and, in general, two samples are transmitted for each line segment.
  • the first strategy is as follows: If the best-fit straight line through samples y n > n + ] _ an d v n +2 deviates from the input signal by more than the threshold T, then sample y n is transmitted and the slope coding process begins afresh with sample y n+ ⁇ • ⁇ e second strategy is to disallow such single- sample segments, as follows: If the best-fit line through , y n+ n and y n+ 2 deviates from the Input by more than T, then samples y n and y n+ ; j _ are transmitted and the process begins afresh with y n+2 .
  • the second strategy is less efficient than the first but has the advantage that the benefits of Method 4 above still apply, the only difference being that each package consists of two samples and M SPI bits.
  • the slope coding technique can be used in the vertical or the temporal dimension instead of in the horizontal dimension as described above. That is, instead of comparing with preceding samples on the same line, the comparison may be with corresponding lines on preceding lines on fields respectively.
  • coding in the temporal dimension produces decoded pictures that are superior to those resulting from coding in the horizontal dimension, particularly in respect of behaviour in the presence of noise on the source.
  • the colour difference (Cr and Cb) component signals can each be slope-coded independently of the luminance. However, this is expensive in channel capacity. One problem is that, with slope coding, there is little to be gained from an initial 2:1 horizontal subsampling of the colour difference components. However, three other methods of reducing the channel capacity occupied by the colour difference signals can be considered: (i) The Cr and Cb signals could each be vertically filtered, 2:1 subsampled and transmitted on alternate lines.
  • the colour difference signals will occupy an analogue transmission channel capacity equal to half of that occupied by the luminance signal, and will add nothing to the digital ' data rate.
  • Figure 6 gives a block diagram of one possible Implementation of a slope coder, for the particular technique described above.
  • the incoming signal, Y is written into a shift register containing N elements, where N is the maximum line-segment length.
  • N is the maximum line-segment length.
  • a line segment n samples long is being tested to see if the "best-fit" estimate obeys the threshold criterion.
  • the "best-fit" estimate v- of the samples y. contained in the shift register are derived, via coefficients c-(n), from the mean value and gradient parameter which are calculated from the input samples in the generator of best-fit slope parameters.
  • the resulting error values e are provided, via coefficients c-(n), from the mean value and gradient parameter which are calculated from the input samples in the generator of best-fit slope parameters.
  • the generator of best-fit slope parameters also provides the SPI signal, which may then go through a bit-rate reduction process as described above and the transmitted samples corresponding to the start and end of each best-fit line segment.
  • a block diagram of the generator of best-fit slope parameters is given in Figure 7.
  • the decoder is much simpler than the coder. There is no loop and no need to calculate the best-fit slope parameters.
  • a slope coding system like any other technique involving adaptive subsampling, requires buffer stores and associated feedback control circuits.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

On code un signal vidéo en transmettant uniquement des échantillons sélectionnés; on sélectionne les échantillons à transmettre en déterminant si l'omission d'un échantillon donné et la transmission de l'échantillon suivant entraînerait des différences supérieures à une valeur de seuil entre des échantillons reconstitués et l'échantillon entré effectif correspondant. Dans la négative, l'échantillon est omis. Les valeurs effectivement transmises peuvent définir les extrémités de lignes droites "le mieux ajustées". Le seuil peut être adapté en fonction du contenu de l'image. On peut ainsi obtenir une réduction de la largeur de la bande de transmission.
EP19870900233 1985-12-24 1986-12-23 Procede de transmission d'un signal video sous forme echantillonnee Withdrawn EP0250532A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8531778 1985-12-24
GB8531778 1985-12-24

Publications (1)

Publication Number Publication Date
EP0250532A1 true EP0250532A1 (fr) 1988-01-07

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EP19870900233 Withdrawn EP0250532A1 (fr) 1985-12-24 1986-12-23 Procede de transmission d'un signal video sous forme echantillonnee

Country Status (2)

Country Link
EP (1) EP0250532A1 (fr)
WO (1) WO1987004032A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9100225A (nl) * 1991-02-08 1992-09-01 Oce Nederland Bv Werkwijze en inrichting voor het coderen van digitale beeldgegevens.
JP3038143B2 (ja) * 1994-12-29 2000-05-08 現代電子産業株式会社 映像機器の物体別形状情報の減縮装置及びその減縮方法並びに多角近似化方法
KR100212552B1 (ko) * 1996-12-23 1999-08-02 전주범 이산적 사인 변환을 이용한 윤곽선 영상 신호 부호화 방법 및 그 장치
US7006097B2 (en) * 2000-11-23 2006-02-28 Samsung Electronic Co., Ltd. Method and apparatus for compression and reconstruction of animation path using linear approximation

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3824590A (en) * 1973-03-26 1974-07-16 Bell Telephone Labor Inc Adaptive interpolating video encoder

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8704032A1 *

Also Published As

Publication number Publication date
WO1987004032A1 (fr) 1987-07-02

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Inventor name: SANDBANK, CHARLES, PETER