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WO1999030507A1 - Traitement de signal video - Google Patents

Traitement de signal video Download PDF

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Publication number
WO1999030507A1
WO1999030507A1 PCT/GB1998/003693 GB9803693W WO9930507A1 WO 1999030507 A1 WO1999030507 A1 WO 1999030507A1 GB 9803693 W GB9803693 W GB 9803693W WO 9930507 A1 WO9930507 A1 WO 9930507A1
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WO
WIPO (PCT)
Prior art keywords
filter
pixels
signal
products
separation
Prior art date
Application number
PCT/GB1998/003693
Other languages
English (en)
Inventor
Martin Weston
William Beningfield Collis
Original Assignee
Snell & Wilcox Limited
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 Snell & Wilcox Limited filed Critical Snell & Wilcox Limited
Priority to AU14963/99A priority Critical patent/AU1496399A/en
Publication of WO1999030507A1 publication Critical patent/WO1999030507A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/77—Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase
    • H04N9/78—Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase for separating the brightness signal or the chrominance signal from the colour television signal, e.g. using comb filter

Definitions

  • This invention relates principally to the decoding of composite video signals into components.
  • the technology of line and field combs for decoding is well known.
  • the present invention consists in one aspect in a composite video decoder having a separation filter serving to separate luminance and chrominance information, the filter taking weighted sums of pixels in a filter aperture; characterised in that the filter incorporates weighted sums of products of pixels.
  • the filter incorporates weighted sums of products of triplets of pixels.
  • the filter comprises weighted sums of pixels and products of triplets of pixels.
  • the separation filter operates on a demodulated signal, an output of the separation filter being remodulated.
  • first and second different filters are provided for operation on respective adjacent video fields.
  • the present invention consists in a method of decoding a composite video signal to components, comprising training and decoding modes, wherein in a training mode a luminance/chrominance separation filter taking weighted sums of products of pixels in a filter aperture is fed a composite signal at least one constituent component of which is known, and the filter weightings are optimised to minimise an error between said known component and an output of the filter; and wherein in a decoding mode the luminance/chrominance separation filter with optimised parameters operates on a composite signal.
  • the present invention consists in a composite video decoder for use with a film-originating composite video signal having a first video field and a second video field derived from each film frame, the decoder having two separation filters operating to separate luminance and chrominance information, the filters taking weighted sums of pixels in respective different filter apertures; one of the said separation filters operating on said first video fields and the other operating on said second video fields.
  • Figure 1 is a diagram illustrating a four tap, third order polynomial filter
  • Figure 2 is a block diagram of a decoder according to this invention. - 3 -
  • Figure 3 is a diagram illustrating a training process according to this invention.
  • Figure 4 is a diagram illustrating a 5 field filter aperture
  • Figure 5 is a diagram illustrating an intra-frame aperture.
  • the currently accepted approach to the complex problem of decoding a generalised composite signal is to make decoders data adaptive, that is to say switching between linear filters in a given set of filters, based on an appropriate function of the data.
  • the major difficulty in designing a data adaptive filter is in choosing the adaptation parameters; that is, knowing when to switch to a different filter.
  • an alternative approach is taken based on a non-linear filter in which polynomial combinations of pixel values in the aperture are formed.
  • a general polynomial filter of infinite order is capable of modelling a large range of nonlinear functions, but to design a realisable polynomial filter it is necessary to truncate at some arbitrary order. In the example discussed here, for reasons to be discussed, this is chosen to be done at the third order. This produces a relatively smooth non-linear function, as it will contain only functions of straight lines, quadratics and cubics, and as such is capable of modelling mild non-linearities.
  • Such a non-linear filter can remain continuously in service, in the sense that that there is no need for adaption according to the video input.
  • a polynomial non-linear filter in addition to the linear terms, includes the sum of filter coefficients multiplied by products of pairs of pixel values, triplets of pixel values, and so on.
  • a four tap polynomial filter will contain four filter coefficients that are multiplied by single pixel values, ten filter coefficients that are multiplied by products of pixel values, twenty filter coefficients that are multiplied by triplets of pixel values, and so on.
  • the polynomial series must be truncated at some point.
  • a filter truncated at the third order is convenient and there is shown diagrammatically in Figure 1 a four tap third order filter. This is illustrated graphically as the combination of a linear filter 100, a quadratic filter 102 and a cubic filter 103.
  • the linear filter utilises three delay elements 104 to generate four taps from the input signal. Each tap is multiplied by a coefficient in a respective multiplier 105 and a weighted sum generated in summing device 106.
  • Similar delay elements 114 provide four taps from the input video signal and ten multipliers 115 generate all ten possible products, again weighted by respective coefficients.
  • a sum is formed in summing device 116.
  • the cubic filter has twenty multipliers 125 operating on the taps from delay elements 124 to generate all possible combinations of triplets of taps and a weighted sum is formed in summing device 126. Although the delay elements 104, 114 and 124 have been shown separately in the three filters, one set of delay elements would usually suffice.
  • a single processing element will receive the four taps and with appropriate multipliers, coefficient stores and one or more summing devices, output directly the sum of the linear, quadratic and cubic filters.
  • the filter output will contain linear, quadratic and cubic terms, it is able to model systems which contain both quadratic and cubic non-linear elements. These generate both skewed and symmetric distortions of the probability density function. Higher order models can be used and should give improved results, but the size of the filter and the computation required in its estimation rise exponentially and there are rapidly diminishing returns.
  • the fifth order six tap filter contains over five times as many parameters as the third order six tap filter.
  • the high frequency signal is then demodulated in demodulator 204, to produce a demodulated chrominance signal that will contain cross colour. This is passed to a four tap third order polynomial filter 206 which performs the function illustrated in Figure 1.
  • the input signal is also passed through a complementary low pass filter 208 to generate a low frequency luminance signal.
  • the polynomial filter 206 separates the chrominance from the cross colour.
  • the chrominance C is output directly.
  • the cross colour is passed to remodulator 208 and added in adder 210 to the low frequency luminance (which is passed through a suitable compensating delay 212) to give wide band luminance Y.
  • a chrominance output from the separation filter could alternatively be remodulated for subtraction from a full bandwidth composite signal to derive luminance.
  • linear filter takes weighted sums of horizontally, vertically, and/or temporarily displaced pixels of the contaminated chrominance to form an estimate of the pure chrominance.
  • More advanced decoders use adaptive techniques, i.e. they allow different combinations of filter taps to be used in different areas of the picture.
  • the new decoder described here utilises a filter based on the weighted sum of a polynomial expansion of sums of horizontally, vertically and temporally displaced pixels.
  • a typical high quality linear decoder may contain 9 such filter weights the value of which can be calculated by empirical means.
  • An equivalent cubic, non-linear filter would contain 220 parameters.
  • a further aspect of the present invention provides an automated method of calculating the filter weights.
  • a training sequence in the form of a component digital video signal is provided to a conventional encoder 300.
  • the composite output from this encoder provides the input x to the decoder 302 according to the present invention. Attention is focussed on the chrominance output z of the decoder and this is compared in block 304 with the desired chrominance output y, which is simply the chrominance signal of the training sequence input.
  • the output of block 304 is the difference between the actual filter output y and the desired output d and the optimisation process generates optimal filter coefficients for the decoder 302 to minimise the square of this difference.
  • the desired signal y is the chrominance signal uncontaminated by cross colour. This is obtained from the encoder by taking the modulated and bandpass filtered chrominance before the luminance is added to it and then demodulating and lowpass filtering. This will result in a chrominance signal with no cross colour.
  • the input to the decoder contains the chrominance signal which has been encoded with the luminance and so will contain cross colour.
  • the objective is to design a filter that minimises the mean squared error between its output and the desired signal. This should force the output of the decoder towards the pure chrominance signal.
  • Such a scheme will create a set of filter coefficients that produce the optimum decoder, in the sense of least mean square error, for that particular sequence.
  • the mean squared error is just one example, others include, mean fourth error, just noticeable difference, etc.
  • a major advantage of using the mean squared error is that it generates a quadratic error function that can be solved by a simple closed form solution. Other possible error functions will require some form of iterative solution that will be far more complex and require much more computational power.
  • the object is to design an N point digital finite impulse response filter, h, to modify the input, x(n), in such a way as to minimise the mean square error, e(n), between the filter output z(n) and the desired signal, y(n).
  • h N point digital finite impulse response filter
  • x(n) is the demodulated, band pass filtered chrominance, contaminated with cross colour
  • z(n) is the output of the decoder
  • y(n) is the desired signal, i.e. the pure chrominance signal with no cross colour.
  • X T X and X T Y are usually much smaller than X. Hence, it is much more efficient to compute X T X and X T Y directly from x(n) and y(n) rather than to form X.
  • the optimal filter in the least squares sense, can then be estimated by computing (X T X) "1 X T y-
  • the filter will contain three separate components, the DC term, the standard linear coefficients which should be multiplied by single pixel values, and the quadratic coefficients which will be multiplied by products of pixel values.
  • This approach will produce a decoder that will provide the optimally decoded output for the particular sequence used to calculate the filter coefficients. It is found that if a relatively long sequence is used (that is to say L is very large), with that sequence containing a wide variety of picture material, a decoder is produced with provides results which are superior to the prior art over a wide range of inputs.
  • An alternative to using a single long input sequence is to use a number of shorter sequences, each exemplifying a different category of picture material, and to combine the respective auto correlation matrices X T X and the respective cross correlation matrices X ⁇ y, before generating the filter coefficients h according to:
  • a decoder for use with film-originating material be provided with different filters for the respective fields associated with a single film frame.
  • a 50Hz television signal derived from 24 frames per second film two filters will suffice.
  • a 60Hz signal derived from film using the 3:2 pull down process more thyan two filters will be required.
  • the two filters for a 50Hz decoder are generated in a training process, they will tend to take most information from - in one case - the preceding field, and - in the other case - the succeeding field.
  • the combined effect will be to give precedence to picture information from the film frame associated with the current video field.
  • this bias towards the film frame can be in-built.
  • Figures 4 and 5 Two particularly preferred apertures are shown in Figures 4 and 5.
  • the filters for both field 1 and field 2 are shown.
  • Figure 4 shows a 5 field aperture with two additional horizontal filter taps. This has been found to perform extremely well although it produces a filter with a large number of parameters.
  • An 11 tap third order polynomial filter will have 363 parameters.
  • the pixels in the outer two fields reduce the cross colour significantly but unlike its linear counterpart the non-linear filter is able to adapt to reduce trailing dots caused by chroma smear. It will be seen that the taps are the same for the two fields although thew coefficients will differ.
  • Figure 5 shows is a slightly smaller aperture which is confined to a single frame.
  • the taps are different for the two fields, one looking forward, the other backward.
  • This aperture does not have quite such a dramatic effect on cross colour but the reduced number of temporal taps allows a slightly larger horizontal component in order to help with horizontal dots.
  • a polynomial non-linear filter could be implemented using a very large number of multipliers and adders or more simply as a lookup table. Although large, its structure is very simple and repetitive and so it may be easier to implement in silicon than an adaptive architecture.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Processing Of Color Television Signals (AREA)

Abstract

La présente invention concerne un décodeur de signal vidéo composite comportant un filtre de séparation servant à séparer le signal luminance du signal chrominance. Le filtre utilise les sommes pondérées des pixels et les produits de triplets de pixels et restitue un comportement non linéaire sans adaptation. L'invention concerne également un procédé de calcul des coefficients des filtres.
PCT/GB1998/003693 1997-12-10 1998-12-10 Traitement de signal video WO1999030507A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU14963/99A AU1496399A (en) 1997-12-10 1998-12-10 Video signal processing

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9726134A GB2332324A (en) 1997-12-10 1997-12-10 Luminance and chrominance separation filter for composite video decoder
GB9726134.1 1997-12-10

Publications (1)

Publication Number Publication Date
WO1999030507A1 true WO1999030507A1 (fr) 1999-06-17

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PCT/GB1998/003693 WO1999030507A1 (fr) 1997-12-10 1998-12-10 Traitement de signal video

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AU (1) AU1496399A (fr)
GB (1) GB2332324A (fr)
WO (1) WO1999030507A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2008472B1 (fr) 2006-04-07 2015-06-03 ATI Technologies Inc. Séparation luminance/chrominance en vidéo

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6096979A (ja) * 1983-10-31 1985-05-30 Sony Corp カラーデコード方法
EP0298613A1 (fr) * 1987-06-10 1989-01-11 Questech Limited Dispositif de décodage de télévision en couleur
WO1997039589A1 (fr) * 1996-04-12 1997-10-23 Snell & Wilcox Limited Procede et appareil de decodage de signaux video composites

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6096979A (ja) * 1983-10-31 1985-05-30 Sony Corp カラーデコード方法
EP0298613A1 (fr) * 1987-06-10 1989-01-11 Questech Limited Dispositif de décodage de télévision en couleur
WO1997039589A1 (fr) * 1996-04-12 1997-10-23 Snell & Wilcox Limited Procede et appareil de decodage de signaux video composites

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 009, no. 248 (E - 347) 4 October 1985 (1985-10-04) *

Also Published As

Publication number Publication date
GB9726134D0 (en) 1998-02-11
AU1496399A (en) 1999-06-28
GB2332324A (en) 1999-06-16
GB2332324A9 (en)

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