Separable diamond shaped multidimensional filters for composite video endocing/decoding applications

=:~ BACKGROUND OE' THE INVENTION zo~5~37 Eield of the invention This invention relates to an apparatus for encoding~decoding a composite color video signal and more particularly, to a mult;flimon~ A1 filter for the separation of the luminance and chrominance components of NTSC, PAL and ATV color television signals.

The present invention also relates to a method for designing several classes of diamond shaped filter.

Description of the Prior Art ;,, u~ During the past few years, there has been an increasing use of vertical delay line comb filters for improving the horizontal separation of the luminance and chrominance composents in a composite ~V signal Several separable filters respectively in the horizontal and vertical domains have been implemented with analog or digital techniques as disclosed in U.S.

Patents Nos.

4,345,268j 4,500,912 and 4,524.400.

However, this class of filters yield a resolution loss of diagonal hi~h frequency luminance information.

Therefore, some adaptation and/or compensation techniques were suggested such as disclosed in U.S.

Patent Nos. 4,040,084 and 4,240,105.

However adaptation artifacts can be introduced in the viewed image.

Recently there was introduced the diamond shaped spectrum of the chrominance components in an NTSC encoded ~ignal, and U.S.

Patent No. 4,829,367 teaches the use of non-separable horizontal vertical diamond shaped filters for NTSC encoding and decoding. - ~hese non-separable filters are generally complex and the luminance bandstop filter performance is not ideal alon~ the horizontal and vertical requency domain axes.

_ z _ ::~ 20~5~37 In the vertical temporal domain, U.S.

Patent No. 4,683,490 describes the use of diamond shaped filters implements with odd and even field delays and suitable lowpass and highpass filter coefficients.

However, the proposed twelve field filter yields a limit of 15 dB for component separation along the zero axes.

The inventors have also suggested the use of frame sampled filters which are simply rectangular shaped bandpass or bandstop filters in the vertical temporal frequency domain.

In the case of encoding/decoding a PAL video signal, the situation is quite similar.

In an article by J.O.

Drewery, entitled "The Filtering of Luminance and Chrominance Signals to Avoid Cross - Colour in a PAL Colour System", BBC Engineering, 8-39, Sept. 19~6, there is - proposed some (separable~ rectangular or ~non-separable) circular shaped filters in the spatial frequency domain.

The choice of circular shaped region remains intuitive and yields a relativeLy simple filter calculation.

In the vertical-temporal domain.

Drewery and C.K.P.

Clar:ke, in an article entitled "PAL Decoding:

~ultidimensional Filter Design for Chrominance - Luminance Separation", B3C Research Department Report no BBC-RD 1988~11, have suggested also tbe use of odd and even field delays for diamond shaped filter implementation. ~he filter performance is similar to that of filter performance of U.S.

Patent No. 4,683,490, in the case of NTSC signal.

Finally, it is noted that all existinS proposed filters have the diamond shaped region in either the horizontal-vertical or vertical-temporal domain.

, ~.--,i -- 3 - -- - . . . .~=d _ 201558~ 8UMMARY OF T~IE lNV~ N -, It is a feature o~ the present invention to provide a general 3ephrable 3D diamond shaped filter in both horizontal-vertical and vertical-temporal domains for encodinq/decoding an NlmSC video signal The filter includes a matching delay, an adder and the cascades connection of seven unidimensional fiLters working individually in their own zero or oblique frequency axis.

Another feature of the present invention i8 to provide ~ n~ l versions of diamond shaped filters in only one of the above-mentioned domains. ~~~ A further feature of the present invention is to provide diamond shaped filters obtained by , ~n~n~ ~eparable and simple ~In~ ci^n:~l filters.

A still further feature of the present invention i8 7 to provide a class of NTSC encoding/decoding filters capable of preserving the luminance information along the three zero ' axis in frequency domain.

Another feature of the present invention is to provide a diamond shaped filter in the spatial fre~uency ~domain for encoding/decoding a PAL video signal.

A still urther feature of the present invention is -to provide several 3D diamond shaped filters allowing the use - of the Fukinuki hole for ATV applications.

These filters are ~e~ci in the article of Fukinuki, E~irano, entitled "Extended Definition TV Fully Compatible with Existing :

8tandard", IEEE Trans. on f', i~ations, vol. COM32, No. 8, fAugust 1986, pp. 948-953. , ~ ; n~J to a broad aspect of the present ~ invention, there is provided a diamond shaped mul~ r cion~l filter circuit for decoding composite video signals.

The diamond shaped filter circuit is comprised of a -series configuration o~ separable filters.

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20~L~5~7 connected at an input to the composition video signals. A matching delay circuit is connected to the input and provides a delayed output signal matching the delay of the resulting signal of the series of separable filters.

The series configuration produce a chrominance signal at an output thereof.

An adder circuit is provided and has a positive and a negative input.

The negative input is connected to the chrominance output to receive the chrominance signal.

The delayed output signal is connected to the positive input of the adder whereby the adder will yield a bandstop luminous signal at an output thereof.

According to a still iurther broad aspect o the present invention, there is provided a diamond shaped multi~lim~ns~nnRl filter circuit for encoding composite video signals.

The diamond shaped filter circuit comprises two series configuration of separable unidimensional lowpass filters connected respectively to two chrominance input signals and producing two lowpass chromin~nce output signals. A chroma quadrature modulator is connected to the lowpass chrominance output signals and provides a modulated chroma output signal~ A separable diamond shaped bandpass filter is connected to a luminance input signal and produces a bandstop luminance output signal. A matching delay circuit is connected to the bandstop luminance output signal and provides ~ delayed luminance output ~slgnal matching the delay of the modulated chroma output signal.

An adder is connected to the delayed luminance output signal and the modulated chroma output signal and produces at the output thereof a composite video signal.

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~. ~0~37 ~ ccordinq to a still further broad aspect of the present invention, there is provided a diamond shaped multidimensional filter circuit for encoding composite video signals, The circuit comprises a chroma c;uadrature modulator conhected to chrominance input signals. A matching delay circuit is connected to a luminance input siqnal~ The chroma quadrature modulator has an output connected to a negative input of a first adder circuit.

The first adder circuit has a positive input connected to the luminance input signal.

The adder circuit yields an output signal which is fed to a bandpass filter formed of a series connection of separsble filters.

The output of the bandpass filter is connected to a negative input of a second adder circuit.

The delayed luminance output signal is fed to a posltive input of the second adder circuit whereby the second adder circuit yields a composite video output siqnal.

According to a still further broad aspect of the present invention, there is provided a method o~ decading composite video siqnals by the use of a diamond shaped multidimensional filter circuit.

The method comprises feeding the composite video signals to an input of the series configuration of separable filters.

The composite video signals are also fed to a matching delay circuit.

The matching delay circuit produces a delayed video output signal which is matched to the delay caused by the series o~ separable filters, ~ chrominance signal is produce at an output of a series of separable filters to produce an output chrominance signal.

The output of . -, the separable filters is fed to an adder circuit negative -- 6 -~ _.

~' ~ 201~587 input.

The delayed video output signal is fed to a positive input of the adder whereoy the adder will produce a bandstop ' n~n~e signal at an output thereof .

According to a still further broad aspect of the present invention, there is provided a method of encoding composlte video signals by the use of a diamond shaped mult jA~ ;~n=l filter circult.

The method comprises ~eeding chrominance input signals to two series configuration of separable lln;Ai lonal lowpasa filters to produce lowpass chrominance output signals.

The lowpass chrominance output signalG are modulated to produce a modulated chrominance signal . A 1 ; n=noe input signal is fed to a aeries configuration of separable unidimensional filters to produce a bandpass luminance output 3ignal and to a matching delay circuit to provide a delayed 1 ; n~n.-e output signal matching the delay of the separable series connected f ilters .

The delayed luminance output signal and the bandpass luminance output signal are fed to a positive input and neg2tive input, respectively, of an adder circuit to provide a bandstop n=n, e output signal.

The ~andstop luminance output signal is delay-matched to produce a delayed bandstop luminance output signal having the same delay as the mo~9ulator chroma output signal.

The modulated chroma output slgnal and the delayed bandstop luminance output signal are fed to an adder circuit to produce at an output thereof a composite video signal.

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~ 2015~87 BRIEF DESCRIPTION OF T~E DRAWINGS :

A preferr~d embodiment of the present invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a block diagram o~ the proposed interfYame 3D diamond shaped separable bandpass-bandstop ;;

filter for NTSC encoding/decoding; ~ ~ FIGURE 2 is a block diagram of the proposed , spatial diamond shaped separable bandpass-bandstop filter with an optional temporal bandpass filter for NTSC - encoding/decoding;

FIGURE 3 is a block diagram of the proposed __ NTSC interframe diamond shaped separable bandpass-bandstop f ilter; r ~ FIGURE 4 is a block diagram of the proposed NTSC interfield diamond shaped separable bandpass-bandstop filter for both chroma and Fukinuki hole informations;

FIGURE SA is a block diagram of chroma encoding . lowpass filter associated with Figures. 1, 2, 3, and 4;

FIGURE SB is a block diagram of luminance :- ~ chrominance non-complementary encoding filter using the = circuit of Figures. 1, 2, 3, 4, and S. ::

FIGURE SC is a block diagram of a luminance --~ chrominance complementary encoding filter with the .

proposed bandpass filters shown in Figures 1, '', 3, and 4; ` FIGURE 6 is a block diagram of a FIR lD filter ~-r which may be used in the circuit of Figures 1, 2, 3, 4, and S; ~ F~GURE 7 is a perspective view of a general =_ spatial-temporal spectrum form of the filter o Figure l;

FIGURE 8 is a perspective view o a gener~l spatial-temporal spectrum form of the filters of Figure 2, ~ -;

3, and 4;

8 - . .

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~ 20~ ~5~7 FIGURP' 9 is a block diagram of the proposed PAL spatial diamond shaped separable bandpass-bandstop filter with an optional temporal bandpass filter;

FIGVRES 10A, B, and C illustrate as example, the spectral result of the lH+2P and lH-2P lowpass filters in series, and FIGVRES llA, B, C, and D are perspe~tive views and graphs illustrating as exemple, spectral characteristics of the spatial diamond shaped filter of Figure. 2.

DESCRIPTION OF THE PREFERRED EMBODIDqENTS Referring now to the dra~ings, and more particularly to Figure 1, there is illustrated the proposed interframe 3D diamond shaped bandpass-bandstop filter of the invention for NTSC encoding and decoding.

It consists generally of a matching delay 112, and adder 114 and a separable 3D diamond shaped bandpass filter.

The proposed bandpass filter i5 composed of seven small filters in series, namely: temporal bandpass filter 103, 526 H lowpass filter 104, 524 H lowpass filter 105, vertical highpass filter L06, lH+2P lowpass filter 107, lH-2P lowpass filter 108 ana finally horizontal bandpass or highpass filter 109.

The filter position ordering is not an important factor for the system' s functionality.

However, in order to minimize the matching delay 112, the filter which produces the longest delay will be placed at the begining of the sequence.

In the present case, there are three possible candidates. the temporal bandpass filter 103, and the 526 H or 524 H lowpass filters 104, 105, respectively.

These three filters form the temporal-vertical bandpass filter 102.

The other filters form a horizontal-vertical diamond shaped filter.

~, _ g _ ~01~ The video input lOL, orthogonally sampled at ~ _ four times the color subcarrier frequency, is supplied to --the first filter input. ~he approprlate delayed input 111 _~ produced by the first filter is sent, in turn, to the matching delay 112.

The bandpass output 110 i5 sent together with the matching delay output 113, respectively to the negative and positive inputs of the adder 114 which yields the bandstop luminance output 115.

In the decoding case, the bandpass output 110 corresponds to the modulated chroma output.

Considering now, in detail, the seven filters - which form the desired separable diamond shaped 3D bandpass filter.

The5e filters are simply FIR unidimensional filters working individually in their own and appropriate. dimensions. ~igure 6 illustrates a finite impulse response lD filter and the associated delay to various types of filter The transfer functions of the seven filters in Erlgure 1 are respectively:

The temporal band filter: c, + 2 ~i c~ cos 2n~, '1 n=~ The SZo H lolYpass fil~er:

c, + 2 ~ c, cos n~2~, + c~,) (2) n=l The 524 H lo~qpass fill:er:

c. + 2 ~ Cn cos n(-241, + Q ,~ (3 n=l -- 10 - .J, ' ` ~ , A ~ , :

?~Oi~587 ..

The verti ca1 ~li ghpass fi 1 eer:

,, cO + 2 ~ c~ cos n~ (4) n = 1 The lH+2P lowpass filter: .

cO ~ 2 ~ c, cos n(2O~, + fl),) t5 n--1 The 111-2P l~wpass filter:

c, + 2 ~: c. cos n(-2QS~ + fJ,) (6) ,",~G The horizontal bandpass filter:

.,~ cO + 2 ~ CA cf~S 2nQI~ (7) n _ 1 , ` In these above expressions, H denotes l line delay, P is l pixel delay.

The normalized frequencies ~ ~2 ' ~3 ~ respectively to the horizontal, verti.cal and temporal frequencies are .defined as follows: f"j = 2 J~ fi / f8i (8~ in which i = l, 2, 3 an~ he corresponding sampling =-- ~requencies f8f~.are ..

f5, = 4 f5~ = 14.32 MHz (9) f~z - 262.,5 c/ph or cycle / picture height (10) ~ f5,= !;9-94 ~z (11) ",~ The pair of filters 104 and lO~ yields diamond shaped in the vertical-temporaI domain In similar 4 '' manner, the filters 107 and 108 form diamond regions in the horizontal-vertical doriain.

~ 201~587 ~v- It i8 worthwhile to note that similar filters with the sampling frequency f81 = 13.5 MHz can be used.

However, it is neces~ary to take some precaution in filter design about the offset between 13.5 MHz/4 and the color g~hC~rriPr frequency.

Figure 7 illu~trates a portion of spatial-temporal spectra form of the resulting filter in Figure 1.

It is pointe~ out that in the horizontal-temporal frequency domain the f ilter shape i8 not a diamond .

This consideration is based on the true spectrum of various image sequences.

Moreover, by using the frame delay, the resulting b~ndpass-bandstop filters in Figure 1 are ~uitable for both chroma and Fukinuki hole informations.

Various filter nooff~n~pnts for the configuration in Figure 1 are given in Table 1.

There i~ a filter with 16 fields.

It i~ noted that the filter coPff~r~nts are simple and the cnpffi~ipnt multiplications can be implemented using ~dd-r~.

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~ 2~15587 TABLE FILTER COEPFICIE~TS FOR FIGURE 1 ~ -:

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FILTER WITH 16 FIELDS FILTER 103 104 106 107 10~ 105 108 Co 4a/128 200/128 150/512 200/128 C, -32/128 -36/128 -112/512 -36/128 :

C2 8/128 48/512 C, -15/512 C~ . 5/512 Cs -1/512 Referring now to Figure 2 which illustrates the ~ 1 simplest version of the previous filter, it i5 a separable :_ diamond shaped filter working essentially in the .~ .,~.

intrafield spatial domain.

The proposed bandpass filter _= consists of five small filters in series: optional temporal bandpass filter 203, vertic~l highpass filter ~204, lH+2P lowpass ~ilter 205, IH-2P lowpass filter 205 - =,.

and hori20ntal bandpass filter 207. Y: - ~ The transfer functions of these filters are ~-.

given respectively in equations (1), ~4), (5), (6~ and (7) .

Figure 8 represents a portion of ..

spatial-temporal spectra form of the resulting filter of _~.

Figure 2 The diamond shaped characterir~tic is only in - 13 - r :. ~,,;: ~ ~ 2~ 8~ ~ the horizontal-vertical fre~uency domain.

The optional bandpass 203 limits the filter spread in the temporal f requency domain .

As an exarnple, the coefficients of a filter ~ith 12 lines are given in ~rable II.

The optional temporal ,_ bandpass filter coefficients are also given for ~,~ completeness.

An eight field filte~ yields good result. ~ of course, di~ferent filters can be obtained according to -desired specifications. ~ ' , :, TABLE rI FILTER COEPFICIENTS FOR FIGURE 2 .

FILTER WITH 12 LINES ~ AND 8 OPTI ONAL Fl ELDS F~LTER OPTIONAL 204 205 , Z03207 206 C~80/128 48/128 100/128 C,-32/128 -32/128 32/128 C2-8/128 8/128 - 8/128 ,~ Figure LlA to llD represent the spatial spectral characteristics of the filter defined by the given \ coefficients.

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-- 1 4 -- = t- 201~87 Referring now to Figure 3, there i~ illustrated : ~ -the proposed interirame separable bandpass-bandstop filter for NTSC encoding decoding.

It is a simplified version of _= the filter cf Figure 1.

The bandpass filter is composed ~, of five small filters in series: temporal bandpass filter 303, 526 H lowpass filter 304, 524 H lowpass filter 305, ` vertical highpass filter 306, horizontal bandpass filter _~ 307.

The transfer functions of these filters are given respectively in equations ~l), (2), (3), (4) and ~ -~ (7).

Figure 8 illustrates the 3D spectral ,~." characteristics of the filter of Plgure l In this case, the diamond shaped characteristic is in the :~, temporal-vertical frequency domain.

Table III shows the 14 field filteP coefficients as an example. ~ - '' ~'''.

TABLE III : ~ FILTER COEFFICIENTS FOR FIGURE 3 . ..

FI LTER Wl TH 14 Fl ELDS Fl LT,ER 303 304 307 306 305 C64/1 28 1 60/1 28 64/1 28 C,-32/128 -16/128 -37~128 ~ C, 5/128 ~_ -- 15 - .~_,._ . r ~ ' ~ 2015587 , . = Referring now to Pigure 4 there is illustrated ~ ~,",.-..

the proposed NTSC interfield separable bandpass-bandstop -filter for both chroma and Fukinuki hole informations.

The 3D bandpass filter is composed of seven filters 403, 408, 409, 416, 417, 418, 419 and an adder 307.

The video .. = signal 401 is applied to the lnput of the temporal - .

bandpass filter 403.

The filter output 404 is sent, in ~ parallel, to both filters 416, 418 followed respectively .

by the fiIters 417, 419.

The respective outputs 405, 406 ~ of the above filters are combined together to the adder =~ 407 followed, in series, by the vertical highpass filter 408 and the horizontal bandpass filter 409 The resulting signal 410 is the 3D bandpass filter output.

The transfer functions of the filters 403, 408 ~,f and 409 are described respectively by equations (1), (4) and (7) -~ The 263 ~I filters 416 and 418 have the following , -~ expression as transfer function:

c, + 2 ~ c. cos n(~, + '~7 n=1 ~12) Finally for the 262}~ filters 417 and 419:

. ., cO + 2 ~ c~ cos n(~, + '~,) 113) n=l -:, The diamond shaped filter region, similar to that of the previous interframe ~ilter, is in the temporal-vertical frequency domain as illustrated by Figure 8 -- 16 - . _ . . _ . _ -- . z,., ~ ', 201SS87 Erom an encoding point of view, the Figures 1, 2, 3, and 4 are suitable only for the luminance component.

Figure SA illustrates the associated lowpass fllter chroma encoding.

In the complete case corresponding to Figure 1, the proposed chroma lowpass filter includes the cascade connection of seven uni~ q;~nAl lowpass filters 502, 503, 504, 505, 506, 507, and 508.

The transfer functions of the filters 502, 503, 504, 505, 506, and 507 are given respectively by equations ( 1 ), ( 12 ), ( 13 ), ( 4 ), ( 5 ), and 6).

For the horizontal lowpass filter 508, the transfer function is described as follows:

c, + 2 ~ c, cos n~, n=1 (14) Associated with Eigure 2, the encoding chroma ,. . .

lowpass filter illustrated in ~igure SA contains only five filters 502 (optional), 505, 506, 507, and 508 in series.

As. for the case of Pigures 3 and 4, the corresponding chroma lowpass filter is Gomposed of 502, 503, 504, 505, and soa.

The above described filters can be used fDr ~TSC encoding as shown in Figures 5 and 6.

It consists of }wo ~ proposed separable diamond shaped lowpass f~lters 520, 521, respectively for the two chroma components I and 9, a chroma quadrature modulator 522, a proposed separable - ~ diamond shaped bandstop filter 523 for the luminance =, ,,'D component Y, a matching delay 524, and an adder 525.

Referring now to Pigure SC, there is shown a -complementary filter for both luminance-chrominance encoding. Since this configuration is well known, it is i ~ ~- ,, -- 1 7 -- , , ,~ ~ , . ~ .

' : ~O~SS8'7 sufficient to mentlon that the bandpass filte~ 514 is nowone of the previously descrlbed bandpass filter in Figures 1, 2, 3, and 4.

Having described the preferred embodiments ~r , ,~ concerniny NTSC encoding/decoding, we now consider the PAL video signal.

Only the spatial diamond shaped filter for PAL will be described.

Referring now to Figure 9 there is shown the ;~ proposed configuration, of the PAL bandpass filter which :

-a=:r,is composed of four ~ilters 904, 905, 906, 907 and an 14 optional temporal bandpass ~ilter 903.

The video input ~ ~ 901, quasi-orthoganally sampled at 4f L5 applied to the ~ -~ filter input.

The transfer functions of the five filters in ~igure 9 are given respectively as follows: The temporal bandpass filter 903:

c. + 2 ~ Cn C05 n2QI~ (15) n=1 rhe vertical bandpass filter 904:

c, + 2 ~ c, cos n2Q, 16 n=1 ( ) The 2H ~ 2P lowpass filter 905:

c, + 2 ~ c, cos n2(c~, + ~2) (17 n=l The 2H - 2P lowpass filter 90~ c, + 2 ~ c, cos n2(~ ,) (18) n=1 . ~ ; ~.

-- 18 - 201~87 The normalized frequencies ~, ~2, a)D respect;vely to the horizontal, vertical and temporal frequerc;es are defined as follows:

~j = 2 ~ fi I fsi i = 1, 2, 3 (l9) in which the corresponding sampling frequencies are ~ f 8i 4 f~c = 17.73 MH2 (20) fc2 = 3125 clph (21) fs3 = 50 H~ (22) It is pointed our that according to desired specifications, various filter coefficients can be obtained.

Various diamond shaped filters are herein proposed ~or encoding/decoding the N~SC, PAL and ATV video signals.

These filters are separable and, therefore, implemented by introducing various oblique frequency axes = such as (2~Dl +u)2, 2uJl ~ 4)2 ) for NTSC, PAL spatial filters, ~ (2u'3 +~V2, 2~V3 - ~)2)for interframe fil,ter, (W3 + ~ ~2,W 3 ~ ~2) for interfield filter and ( 2u~l+ 2~z~ 2~ - 2~V2)for PA1 spatial filter This can be explained briefIy as follows.

Lets consider~ for example, the pair of lX+2P and lX-2P lowpass filters.

Referring to Figure lOA there 15 represented the spatial data array of a video signal. ~he enclosed dots correspond l:o sampled data stored in these ~ -- filters for a given central pixel.

The cascade connection of these t~o lowpass filters results in three pass bands in the spatial frequency domain, as illustrated by Figure -- -lOB.

In order to obtain only the desired band shown in Pigure lOC, it is necessary to use a palr of horizontal ~ ~ bandpass and vertical highpass filters in series.

The two ~= last filters provide at a same time two main benefits for -~ controlling the diamon~ shape dimensions and the desired ~-~ system periormance 2long the zero axes. = ~ .

- 19 .. = _ .. , . . _