DE2822668A1 - DEVICE FOR SEPARATING THE LUMINANCE COMPONENT OF A COMPOSITE PAL INPUT COLOR TELEVISION SIGNAL - Google Patents

Description

Pofentonwäli · Re-zr / 9078

Ür.-Ing. Wilhelm ßeichel ~ ⁵ ~
DipWng. Y / olirang Reichel

6 Frankfurt a. M. 1
Paiksirasse 13

BRITISH BROADCASTING CORPORATION, a British. Body Corporate, of Broadcasting House, London W1A 1AA, England

Means for separating out the luminance component of a composite PAL input color television signal

The invention relates to a device for separating out the luminance component of a composite PAL input color television signal or a PAL television signal processing circuit.

The invention relates in particular to the separation of the luminance and chrominance information of a PAL signal, as is done, for example, in a PAL decoder, but the invention is also applicable to PAL encoders applicable.

With the PAL color television signal, which also applies to other color television systems, the color information (chrominance) as a modulated subcarrier which is part of the luminance spectrum, which luminance subtleties contains. The decoder has the task of removing the chrominance signal from the luminance signal without any significant mode * fication in terms of frequency and phase responsiveness occurs. This is generally done using a bandstop filter brought about with a jagged or edge characteristic that a compromise between the loss of luminance fineness and the subcarrier pattern. The decoder also prevents the generation of false or undesired Color information through synchronous demodulation, although this is not suppressed in relation to the fineness patterns which precisely doubles the PAL subcarrier phase relationships.

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British Broadcasting Corp. Re-zr / 9078

Segment filtering is a technique used with the National Television System Committee (N.T.S.C.) is applied, but the properties peculiar to the PAL coding method preclude its use a simple filter with the PAL system. In the N.T.S.C. system certain colors are represented by the same phase with respect to a reference color phase in each line, that is, there is an intercarrier-to-line relationship that is an offset of half a cycle between adjacent ones Lines ensures. A segment or comb filter can be obtained simply by adding a delay a line length is applied and an addition circuit adds the input and output of the delay circuit. With such a filter, the chrominance information is deleted, while the luminance range or the luminance sensitivity is retained, albeit in a discontinuous form.

This simple phase relationship cannot be used with the PAL method. After each line this will be Coding method changed, resulting in a chrominance phase that is not the same as that of the previous one Row. Likewise, the intercarrier-line relationship in the PAL method is more complex, causing an offset between the lines by a quarter of a period. For these two reasons, a simple comb filter will not work.

In a precise representation, the equations that define the PAL signal are written as follows: _{Ε η} = E ' _y + E' _u cos 2iTf _sc t + E ' _v sin 2Tf _sc t (1)

^E 'n + 1 ^{= E} ' y ^{+ E} 'u ^{cos 2} ^ sC * ~ ^E ' v ^{sin 2Tf} sc ^{t (2)} and f _sc = (284 - \) f _H + 25 Hz (3);

therein mean: E '_n; ^E ' _n + i aie coded voltage signals

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consecutive lines; E ¹ the luminance voltage signal; E ¹ ; E ' _v the two color difference voltage waveforms; f is the subcarrier frequency; and £ " the line repetition rate.

The conventional phase relationship of the N.T.S.C. system occurs only in every other line in the PAL system, and so a comb filter of the type described can be made are used / when a two-step delay is used. However, it has been shown that systems which such Use a comb filter, only achieve a low level of effectiveness. The main reason for this is that a comb filter is its effectiveness loses when the color information is above the delay element changes. The probability of a substantial change over two lines in a television field is relatively large.

The object of the invention is to provide a PAL chrominance modification device to create that is an effective comb filter that has considerable advantages in comparison to the conventional edge filters without having their disadvantages or significantly reducing these disadvantages.

This object is achieved according to the invention in that devices for each current line of an input signal generate a modified signal line derived from the chrominance frequency band of one or both lines which are adjacent to the current line modified by reversing the phase of the vertical component, and that a subtraction circuit is present, which the current signal and the modified signal or one derived therefrom Signals with the same instantaneous color subtracting phase are subtracted from each other to give an output luminance signal form.

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British Broadcasting Corp. Re-zr / 9078

The modification procedure is in the article of Dr.W. Break in the Telefunken-Zeitung, Volume 37 (1964), No. 2, Pages 115 to 135, to which reference is made. As a result of the modification, two modified color signals of the following form are obtained:

^E 'n ^{= E} ' y ^{+ E} 'u ^{cos 2} ^ SC * " ^E ' v ^sin

^E 'n + 1 ^{= E} ' y ^{+ E} 'u ^{cos 2} ^ SC * ^{+ E} ' v ^sin ^ c

It can be seen that the sign of the E ^! Terms in each of equations (4) and (5) with respect to the original equations (1) and (2). Dr. Bruch's described technique for making such a modification involves two steps, first modulating the chrominance signal on a carrier whose frequency is twice the PAL color subcarrier frequency (2 f), and secondly selecting the lower sideband of the resulting signal which is centered with respect to the value f.

In an embodiment of the invention, this relates to a device for removing the components from a PAL input luminance signal, which can cause overlapping colors, whereby the facility is characterized by that for each current line of an input signal a modified signal is generated which is derived from the chrominance frequency frequency band of one or both of the lines adjacent to the current line by reversing the phase of the components that correspond to the vertical component, and that a subtraction circuit is the current signal and the modified signal or a signal derived therefrom with a phase equal to the instantaneous color subcarrier phase of each other subtracted to get an output.

The invention is of particular use when used in a PAL decoder for the line delay, as in

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for example the chrominance band pass filter is used and the delay line present in the decoder can also be used for the formation of the modified signal can, the only essential, necessary addition being the modification circuit itself.

The invention also makes it possible to remove those components in a PAL luminance signal, which may cause incorrect color information, known as crossover colors, after demodulation of a composite PAL signal derived from the luminance signal is formed. This has proven to be useful when used in a PAL encoder.

With the invention, a signal can be subtracted from the modified signal by combining it with the unmodified chrominance frequency band of the current line can be derived, the amplitudes of the combined Signals essentially correspond to the ratio £ C: (1-Ot).

The further embodiment of the invention relates to a PAL television signal processing circuit with delay circuits, connected to the input to delay the input signal by an integer number of line periods, which is characterized in that a PAL modification device with the output of a delay circuit for the modification of the applied signal by reversing the phase of the vertical component or any one representing it Component is connected that a bandpass circuit between the input terminal and the modification device for the selection of the chrominance frequency band of the signal is that a subtraction circuit with its first input to the input terminal and to its second Input connected to the output of the modification device and provides an output signal, and that the signals fed into the subtraction circuit have the same instantaneous subcarrier phase exhibit.

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The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawings. Show it:

Figure 1 is a block diagram of a PAL decoder according to the invention;

FIG. 2 - a block diagram of a modified decoder for broadcast use;

Figure 3 - a block diagram of a filter according to the invention for filtering a luminance signal its feeding into a PAL encoder; and

Figure 4 is a block diagram of an improved filter according to the invention.

A PAL decoder 1o in FIG. 1 corresponds essentially a PAL decoder with a delay line Construction modified in accordance with the invention to provide improved filtering in the luminaire channel to obtain. The usual PAL decoder elements of the delay line are within the dash-dotted lines Device 12 is shown and includes a chrominance band pass filter 14, a delay circuit 16 and two summing circuits 18, 2o. The circuit 18 operates as an addition circuit to add the delayed and non-delayed ones To add signals, and the circuit 2o works as a subtracting circuit for the same signals. the Chrominance signal components U and V are tapped at the outputs 22, 24.

In a conventional circuit, the PAL signal fed to an input terminal 26 and passed to a notch filter which completely removes the portion of the frequency band, which is centered around the color subcarrier frequency f _ in order to generate a luminance signal. This gives a very rough separation insofar as the luminance subtleties are at the same time in this frequency band are removed, while some of the chrominance information is outside the removed Frequency band remain in the luminance signal.

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In order to improve this, the device or circuit shown in FIG. 1 contains a PAL chrominance modification device 3o, which is connected to the output of the delay circuit 16. The modification device comprises essentially a modulator 32 and a bandpass filter 34, which has f__ as the center frequency. The modulator

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receives a carrier signal from a 2 f _sc oscillator 36 and the modifying means provides an output signal from the bandpass filter 34 to the inverter input of a subtraction circuit 38. The subtraction circuit 38 also receives the PAL signal from the input terminal 26 and provides an output 4o which the represents decoded luminance signal.

If the current line n + 1 is present on the input terminal 26 at any point in time, it is assumed that the applied signal corresponds to the above equation (2), while that at the output of the delay circuit 16 output signal of equation (1) is sufficient. Both signals contain luminance components present in the frequency band transmitted by the filter 14. Afterward the modification means 3o changes the delay output signal to the modified signal given by equation (4), and this has the same form as that signal present at the input. The mode of operation in which the modifier works is detailed in the article by Dr. Fraction, which is mentioned above, it should only be pointed out that it is for the 2 f carrier is important to have a fixed phase relationship to the chrominance signal. This can be done by using an oscillator blocking the color sync signal or the chrominance signal to control the 2 f "oscillator.

SC

be enough.

Between the two inputs of the subtraction circuit An exact phase relationship is desired for the chrominance components fed in. Because of this, it differs

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the delay time introduced by the delay circuit 16 changes of an exact line period H by a small amount «which is the quarter line offset in the Compensated for inter-carrier-line relationship. In the case of a conventional 625/50 signal where H is 64 pS, oT is equal to 56 nS,

The output of the subtraction circuit 38 does not contain any signal components for which this phase relationship is valid this also includes all chrominance signals, sidebands and any other components of the luminance signal E one that may appear to simulate the chrominance signals. For other luminance signals, the subtraction process can attenuate or boost the signal, depending on the inherent precise phase relationship “If the luminance relationships are purely random, then the entire integrated Zero yield change that gives an overall sensitivity that appears flat in an imaged image.

Since the delay period of the delay circuit 16 is not exactly one line, outside of the Bandes equalization or transient processes occur with actual vertical luminance transitions. However, this is true more for electronically generated test waveforms than for actual images, which do not have strictly vertical transitions prevalence. In any case, these transients are much smaller than those that occur with a conventional one Notch filters are generated.

Furthermore, the circuit does not completely remove the subcarrier components from the luminance signal im Area of color transitions in the horizontal direction. If this is perceived as annoying, a further notch filter can be connected after the subtraction circuit 38. This filter does not have to meet the very strict requirements that are required in a conventional decoder and can reduce this chrominance breakthrough while it is

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still maintains sufficient luminance sensitivity. The sensitivity of the notch filter can rely on active control over the level of the chrominance band signal which is determined at the output of the subtraction circuit 38.

A comparison with a conventional decoder which uses a notch filter in the luminance channel alone shows the following advantages:

(a) There is very little residual color between carrier band in the luminance signal.

(b) The color subcarrier sidebands are determined by the luminance signal, that is in the area of the vertical color transitions, removed.

(c) The luminance information remains in the range of chrominance signal frequencies obtained, which improves the subtleties in the displayed image.

(d) The phase sensitivity (group delay characteristics) of the luminance channel are improved.

The modifications required for the PAL decoder are of relatively minor nature and are particularly demanding no additional delay elements.

However, it is possible to improve the mode of operation by adding further delay elements. In Figure 2, a circuit or a device is shown, which is more professional for broadcasting Quality is built.

A decoder 5o shown in FIG. 2 corresponds essentially to that according to FIG. 1 and has the same components are identified by the same reference numbers and are no longer described in detail below.

Additional components that are used in the circuit of Figure 2 are a second delay circuit

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device 52, an addition circuit 54, and a third delay circuit 56. Both delay circuits 52 and 56 have the same delay period as the delay circuit 16. The delay circuit 52 is in series connected to the delay circuit 16 so that its output receives a signal delayed by two lines compared to the input signal. The PAL input signal is delayed by one line in the delay circuit 56. The input signal and the signal delayed by two lines, both after filtering by the filter 14 are added and halved in an addition circuit 54 to form a signal containing the mean of the chrominance components of the signals that preceded the line and the line supplies to the normal input of the subtraction circuit 38 after the line under consideration. It thus becomes the output signal the addition circuit 54 of the modification device 3o supplied. It is also common to have this signal in place of a non-delayed signal in the line delay decoder, and it is therefore also used by the summing circuits 18 and 2o forwarded.

Thus, the introduction of a second delay circuit 52 enables averaging prior to modification of the two signals on either side of the line used as the luminance output. With an input signal of the form according to equation (2), the input signals to the addition circuit 54 will also be of this type, as will the input to the modification device 3o _t Equation (1) subtracted.

Using the information of the lines on either side of the current luminance output line gives for the decoder a greater tolerance for changes in the color information in the vertical direction. Likewise, the chrominance axis separation via the same two-line opening or

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Width and the chrominance output is spatially coherent with the luminance. Although this from a certain one This latter improvement occurs as a side effect to the primary improvement in the luminance signal.

Figure 3 shows the use of a filter 60 according to the invention for removing the components that a Color crossing of a luminance signal before the PAL coding. As far as the circuit components are identical are with the corresponding components of the circuit according to Figure 1, they are marked with the same reference numerals and are not described again in detail.

In this circuit, a delay unit 62 connects the output of the filter 14 to the modification device 3o. This delay unit can, for example cause a delay of a line, as shown in FIG. In this case the delay circuit is 56, which is shown in dashed lines, is not required. Optionally, the delay unit 62 can also be a substantially Introduce two-line delay, with an averaging circuit connected to the input and output of the delay unit is connected, as can be seen from the circuits 16, 52 shown in FIG. In this case the delay circuit 56 is provided for one line. In theory, the delay unit 62 can optionally either be arranged before the filter 14 or after the modification circuit 3o, but the position shown in Figure 3 is preferred.

The circuit operates in an exactly analogous manner to the circuits of Figures 1 and 2, which were previously have been described. In a conventional manner, the oscillator 36 is powered by the subcarrier frequency source of the encoder and a frequency doubler.

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The modified filter shown in FIG. 4 is based on the filter 60 according to FIG. 3 and has the same parts are identified by the same reference numbers and will not be described again.

With reference to filter 60 of Figure 3, the signal path is from input port 26 to the luminance output 4o of the filter explained as follows:

(1) Frequency components within the chrominance bandwidth that have no relation to the color subcarrier frequency are modulated in terms of amplitude and phase. The amplitude modulation takes place in such a way that these output components oscillate from zero amplitude to twice the value of their input amplitude.

(2) Within the chrominance bandwidth, the output contains portions of the two input lines that are currently under consideration Line and the line preceding it are not subject to a delay. The rush of these two Lines results in a loss of quality of 3 dB in the chrominance signal-to-noise output ratio.

In the improved filter of Figure 4, the output of the bandpass filter 34 is in the modification device 3o not directly connected to the subtraction circuit 38, but via a weighting addition circuit 72 in a summing stage 74. The output of the bandpass filter 14 is furthermore connected to the other input of the addition circuit 72 via a phase shifter 76. The addition circuit combines the modified output with the chrominance component of the current line suitably out of phase with respect to the two coefficients OC and ß>, with β = 1 - Oc, that is, with others Words the sum of the two coefficients is equal to 1. The resultant is fed to the inverter input of the circuit. The phase shifter 76 cancels any phase difference between the input and output of filter 14 at the color subcarrier frequency.

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The coefficients Oc and / 5> for example, both can be equal to 1/2. The adverse amplitude modulation effect, which is described in (1) above now reveals that the frequency components which have no relation to the chrominance signal stand, oscillate between the amplitude zero and their input amplitude. This arises because of the proportion from the modification device 3o to the output signal was halved.

The noise voltage from the modification channel is is also halved, and the noise voltage from subtraction circuit 38 is determined by the coherent signal from the / t> input of the addition circuit 74 is half cleared. The total output noise in the chrominance band is therefore 3 dB lower than at the filter input.

The modified filter according to FIG. 4 thus results in a noise improvement and does not cause an output double amplitude high frequency components appear while it continues to remove PAL chrominance components. Of further transients appear outside the band, caused by strictly vertical transitions in the filter according to FIG 1 occur, not with the filter according to FIG. 4. For certain applications, other values for the coefficients Ot and β can be chosen.

The improvements in the embodiment according to Figure 4 can be used when the delay unit 62 results in a two-line delay, the delay circuit 56 is included and is connected to the normal input of the subtraction circuit 38 and the input to phase shifter 76 delayed by (H- «iJ) is. This can be done using the output of the delay circuit 16. The improvement is the same for PAL decoders as shown in FIGS. 1 and 2 are applicable.

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It goes without saying that the addition circuit 72 and subtraction circuit 38 in Figure 4, if desired, to a suinialization circuit of three Inputs can be combined. The terms "addition" and "subtraction" should then be used accordingly must be taken into account.

Although only the processing of analog signals has been described, the invention applies to processing as well suitable for digital signals.

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Claims (12)

German engineer VVÜüfilm oak oil iOv WuitHüti'j Mehel May 22, 1978 6 Frcmkiuri a. Ul 1 _, ««., « P 13 Re-zr / 9078 BRITISH BROADCASTING CORPORATION, a British Body Corporate, of Broadcasting House, London W1A 1AA, England Claims ( Λ J means for separating out the luminance component of a composite PAL input color television signal, characterized in that means (12, 3o) generate for each current line of an input signal a modified signal line which is derived from the chrominance frequency band of one or both lines, that of the current line Line are adjacent, modified by reversing the phase of the vertical component, and in that a subtraction circuit (38) is present which subtracts the current signal and the modified signal or a signal derived therefrom with the same instantaneous color subcarrier phase to produce an output luminance signal to build. 2. Means for removing the components from a PAL input luminance signal, which can cause overlapping colors, characterized in that devices (12, 3o) have one for each current line Input signal generate a modified signal that is derived from the chrominance frequency band of one or both of the lines that the current line are derived by reversing the phase of the components corresponding to the vertical component is, and that a subtraction circuit (38) the current signal and the modified signal or a signal derived therefrom with a phase equal to the current color 809848/0978 British Broadcasting Corp. Re-zr / 9078 Subcarrier phase subtracted from each other to produce an output signal to obtain. 3. Device according to claim 1 or 2, characterized in that the devices (12, 3o) comprise a single-stage delay circuit (16) whose output signal is converted will. 4. Device according to claim 1 or 2, characterized in that the devices (12, 3o) have a two-stage delay circuit (16, 52), the input and output signals of which are averaged in an addition circuit (54), to get a signal that is converted. 5. Device according to claim 1, 2, 3 or 4, characterized in that the means (12, 3o) for modifying the signal a modulator (32) which receives a carrier signal of twice the subcarrier frequency and that a Bandpass filter (34) is connected to the output of the modulator (32). 6. Device according to each of claims 1 to 5, characterized in that that the output of the devices (12, 3o) via an addition circuit (72) is connected to one input of a subtraction circuit (38), the other input of which is the phase-shifted Receives chrominance frequency band of the input signal (see FIG. 4). 7. PAL television signal processing circuit having delay circuits connected to the input for the input signal to delay an integer number of line periods, 809848/0978 British Broadcasting Corp "Re-zr / 9078 characterized in that a PAL modification device (3o) with the output a delay circuit for the modification of the applied signal by reversing the phase of the vertical component or each component representing it is connected by a bandpass circuit (14) between the input terminal (26) and the modification device (3o) for the selection of the chrominance frequency band of the signal is connected that a subtraction circuit (38) with its first input the input connection (26) and its second input is connected to the output of the modification device (3o) and provides an output signal and that the signals fed to the subtraction circuit (38) have the same instantaneous subcarrier phase exhibit. 8. PAL television signal processing circuit according to claim 7, characterized in that the delay circuit consists of a single-stage delay circuit (16), which is connected between the input terminal (26) and the modification device (3o) is. 9. PAL television signal processing circuit according to claim 7, characterized in that the delay circuit is a two-stage delay circuit (16, 52), which are connected to the input connection (26) is connected that an addition circuit (54) for averaging has two inputs connected to the input and the output of the delay circuit (16, 52) are connected and further an output which is connected to the modification means (3o) is connected, and that a single-stage delay circuit (56) between the input terminal (26) and the first input of the subtraction circuit (38) is connected. 10. PAL television signal processing circuit according to claims 7, 8 or 9, 809848/0973 British Broadcasting Corp. Re-zr / 9078 characterized in that an addition circuit (72) feeds the output of the modification device (3o) receives and its output is connected to the second input of the subtraction circuit (38), and that the addition circuit (72) is connected to the output of a bandpass filter (14) via a phase shifter (76) which is connected to the input terminal (26) and selects the chrominance frequency band. 11. Method for separating the brightness component of a composite PAL color television signal, characterized in that for each current line of the input signal one modified Signal line is generated from the chrominance frequency quenzband of one or both of the lines adjacent to the current line is obtained, which is obtained by reversing the phase of the Vertical component are modified, and that the current signal and the modified signal or one of them with the signal derived from the same instantaneous color subcarrier phase are subtracted from one another to produce an output luminance signal to obtain. 12. Method of removing PAL input luminance signal components, which can cause an overlap of colors, characterized in that for each current line of the input signal a modified Signal is generated from the chrominance frequency band of a line or both adjacent to the current line Lines is derived by reversing the phase of those components that correspond to the vertical component, and that the current signal and the modified signal or one thereof having a phase equal to the instantaneous color subcarrier phase derived signal are subtracted from each other to obtain an output signal. 809848/0978