Non-sharp cut filters for assembling and splitting in Weston Clean PAL
AssigneeBritish Broadcasting Corporation
InventorsJohn O. Drewery, Nicholas D. Wells
Life of this patent
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Abstract
An assembler and splitter of a Weston PAL (W-PAL) video signal has filter functions F.sub.1, F.sub.2 at the assembler for the luminance and chrominance components and corresponding functions F.sub.3, F.sub.4 at the splitter. The transfer functions are defined as F.sub.1 =(L.sub.2 +L.sub.1)/2+(L.sub.2 -L.sub.1)z-.sup.1 /2, F.sub.2 =-(H.sub.1 -H.sub.2)/2+(H.sub.1 +H.sub.2)z.sup.-1 /2, F.sub.3 =(L2-L.sub.1)/2+(L.sub.2 +L.sub.1)z.sup.-1 /2, F.sub.4 =(H.sub.1 +H2)/2-(H.sub.1 -H.sub.2)z.sup.-1 /2 and wherein H.sub.1 (f)=L.sub.2 (2fsc-f) and H.sub.2 (f)=L.sub.1 (2fsc-f). Thus the filters are non-sharp cut and are compatible with normal PAL.
Claims18
A system for transmitting and receiving a Weston Clean PAL (W-PAL) video signal in which a luminance signal Y is sampled at twice a color sub-carrier frequency f and chrominance components U, V are sampled at the color sub-carrier frequency and carried as sum (U+V) and difference (U-V) signals on alternate video lines, comprising, at a transmitter:
- an assembler for assembling co-phased or quadrature 2fsc luminance signals and fsc chrominance signals to form a W-PAL signal for transmission and having:
- a first filter means (F.sub.1) for filtering the 2fsc luminance signal;
- and
- a second filter means (F.sub.2) for filtering the fsc chrominance signals;
- and at a receiver
- a third filter means (F.sub.3) for filtering a received 2fsc luminance signal;
- and
- a fourth filter means (F.sub.4) for filtering received fsc chominance signals;
- wherein:
- the fourth filter means (F.sub.4) is a shifted mirror of the first filter means (F.sub.1), the third filter means (F.sub.3) is a shifted mirror of the second filter means (F.sub.2) and the product F.sub.1 F.sub.3 of the first and third filter means and the product F.sub.2 F.sub.4 of the second and fourth filter means are Nyquist filters N.sub.y, N.sub.c.
An assembler for a Weston Clean PAL (W-PAL) video signal comprising:
- first filter means for filtering a luminance signal sampled at twice a subcarrier frequency;
- second filter means for filtering sum and difference chrominance signals sampled at the subcarrier frequency;
- and
- means for adding filtered luminance and chrominance signals from n said first and second filter means for transmission in a PAL channel having a high pass link filter;
- a splitter having third and fourth filter means, the first and second filter means being chosen in conjunction with the third and fourth filter means in the splitter such that
- the amplitudes of the fourth and third filter means are shifted mirrors of the amplitudes of the first and second filter means, respectively, and the product of the first and third filter means and the second and fourth filter means are Nyquist filters N.sub.y, N.sub.c.
A splitter for a Weston Clean PAL (W-PAL) transmitted video signal having luminance and chrominance components, comprising
- third filter means for filtering a received W-PAL transmitted video signal to form a luminance signal for display or recording;
- fourth filter means for filtering a received W-PAL transmitted video signal to form a chrominance signal for display or recording;
- and
- means for demodulating the received W-PAL transmitted video signal;
- wherein the luminance and chominance components thereof are filtered prior to transmission by first and second filter means, respectively, and
- the amplitude of the fourth and third filter means are shifted mirrors of the first and second filter means, respectively, and
- the product of the first and third filter means and of the second and fourth filter means are Nyquist filters N.sub.y, N.sub.c.
Apparatus for generating a Weston Clean PAL (W-PAL) video signal for transmission in which a 2fsc luminance signal Y is sampled at twice a color sub-carrier frequency f and fsc chrominance components U, V are sampled at the color subcarrier frequency and carried as sum (U+V) and difference (U-V) signals on alternate video lines, comprising:
- an assembler for assembling co-phased or quadrature 2fsc luminance signals and fsc chrominance components to form a PAL signal for transmission and having;
- first filter means for filtering the 2fsc luminance signal;
- second filter means for filtering the fsc chrominance components;
- and
- means for adding the filtered 2fsc luminance signal and fsc chrominance components to form a PAL video signal;
- wherein
- the first filter means has a transfer function F.sub.1 =(L.sub.2 +L.sub.1)/2+(L.sub.2 -L.sub.1) z-.sup.1 /2 and the second filter means has a transfer function F.sub.2 =-(H.sub.1 +H.sub.2)/2+(H.sub.1 +H.sub.2) z-.sup.1 /2
- where L.sub.1, .sub.L 2 are transfer functions of first and second low pass filters and H.sub.1, H.sub.2 are transfer functions of first and second high pass filters and z-.sup.1 is the transfer function of a video delay line;
- and wherein
- H.sub.1 (f)=L.sub.2 (2fsc-f)
- and
- H.sub.2 (f)=L.sub.1 (2fsc-f).
An assembler for a Weston Clean PAL (W-PAL) video signal comprising:
- first filter means for filtering a luminance signal sampled at twice a subcarrier frequency f;
- second filter means for filtering sum (U+V) and difference (U-V) chrominance signals sampled at the subcarrier frequency;
- and
- means for adding the filtered luminance and chrominance signals for transmission in a PAL channel;
- wherein the first filter means F.sub.1 =(L.sub.2 +L.sub.1)/2+(L.sub.2 -L.sub.1) z-.sup.1 /2 and the second filter means has a transfer function
- F.sub.2 =-(H.sub.1 -H.sub.2)/2+(H.sub.1 +H.sub.2)z-.sup.1 /2
- where L.sub.1, L.sub.2 are transfer functions of first and second low pass filters;
- H.sub.1, H.sub.2 are transfer functions of first and second high pass filters, z-.sup.1 is the transfer function of a video line delay, and wherein
- H.sub.1 (f)=L.sub.2 (2fsc-f)
- and
- H.sub.2 (f)=L.sub.1 (2fsc-f).
A Weston Clean PAL (W-PAL) video signal system in which a luminance signal is sampled at twice a color sub-carrier frequency f and chrominance components U, V are sampled at the subcarrier frequency and carried as sum (U+V) and difference (U+V) signals, comprising at a transmitter;
- an assembler for assembling a co-phased or quadrature luminance signal and co-phased or quadrature chrominance components to form a PAL signal for transmission and having;
- first filter means for filtering the luminance signal;
- second filter means for filtering the chrominance components;
- and
- means for adding the outputs of the first and second filter means to form a W-Pal signal having a luminance component and a chrominance output for transmission;
- first filter means for filtering the luminance signal;
- second filter means for filtering the chrominance components;
- and
- means for adding the outputs of the first and second filter means to form a W-PAL signal having a luminance component and a chrominance output for transmission;
- and at a receiver:
- a splitter for splitting a received W-PAL signal to form baseband luminance and chrominance signals for storage of display and having;
- third filter means for filtering the received luminance component for the W-PAL signal;
- fourth filter means for filtering the received chrominance component for the W-PAL signal;
- and
- demodulation means for demodulating the outputs of the third and fourth filter means in co-phase or quadrature;
- wherein the first to fourth filter means have transfer functions F.sub.1 to F4 defined by
- F.sub.1 =(L.sub.2 +L.sub.1)/2+(L.sub.2 -L.sub.1)z-.sup.1 /2
- F.sub.2 =-(H.sub.1 -H.sub.2)/2+(H.sub.1 +H.sub.2)z-.sup.1 /2
- F.sub.3 =(L.sub.2 -L.sub.1)/2+(L.sub.2 +L.sub.1)z-.sup.1 /2
- F.sub.4 =(H.sub.1 +H.sub.2)/2-(H.sub.1 -H.sub.2)z-.sup.1 /2
- and wherein
- H.sub.1 (f)=L.sub.2 (2fsc-f)
- and
- H.sub.2 (f)=L.sub.1 (2fsc-f)
- where L.sub.1, L.sub.2 are transfer functions of first and second low pass filters, H.sub.1, H.sub.2 are transfer functions of high pass filters and z-.sup.1 is the transfer function of a video line delay.
Dependencies are inferred from the claim text.