Facsimile and static presentation processing – Facsimile – Recording apparatus
Patent
1985-11-06
1988-08-23
Richardson, Robert L.
Facsimile and static presentation processing
Facsimile
Recording apparatus
360 141, H04N 576
Patent
active
047665017
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method in the so-called cutting of recorded color television signals for editing purposes, and in particular signals according to PAL and SECAM standards.
In order to comprehend the present invention, it is necessary to have some knowledge of the aforesaid signal transmission and recording systems, upon which much has been written. A brief disclosure will now be made of the nature of the problem which the invention is meant to solve. The invention will be primarily described with a starting point from the PAL-system, although it will be understood that a similar problem also exists in the SECAM-system, this problem also being solved by the invention, and in the NTSC-system.
It is known that a conventional TV-signal reproduces 25 frames per second, each divided into two fields each of which sweeps interdigitally 3121/2 lines, or together 625 lines. The color information exists in the form of a luminance signal, which is compatible with black and white reception, and a chrominance signal, which exists as a sideband of a suppressed carrier wave at a frequency spacing of approximately 4.43 MHz from the luminance signal. In the PAL-system the chrominance signal, from which two scalar color signals shall be taken in order to calculate together with the amplitude of the luminance signal the three color signals, is transmitted in phase quadrature wherewith the chrominance signal is displaced in phase through 180.degree. for each alternate line, in order to compensate for phase errors when de-coding. In the SECAM-system the one component is instead transmitted in each alternate line and the second component in each other line, wherewith calculation of the three color signals is effected with the aid of the one component directly and the other component taken from a preceding line, collected from a delay line.
Thus, a fundamental principle of both the PAL and the SECAM systems is that the information is not similarly coded in two mutually sequential lines, but that said lines have opposite chrominance coding and must each be decoded in a manner peculiar thereto. Now, if the number of lines in a TV-frame (two fields, 625 lines) had been an even number, then the problem solved by the invention would never have existed. It has not been possible, however, to avoid an uneven number of lines, because of the problem of interlacing between the fields.
Decoding of the chrominance signal in the PAL-system is effected by means of a reference signal (color carrier wave f.sub.o) obtained from an oscillator which is normally crystal controlled and which is phase locked to a series of short carrier-wave transmissions, which take place over horizontal and vertical retrace periods, or blanking intervals. During these burst phases, the transmitted carrier-wave frequency is phase-displaced alternately through +135.degree. and alternately through -135.degree. in relation to the ideal oscillator frequency. The task of signal "cutting", in which a series of frames with relevant control signals are placed one after the other in immediate sequence on, for example, a video tape (or during transmission) can be beset with certain problems since the periodicity of the control signals does not coincide exactly with the frequency of the frames.
For example, in the case of the PAL-system the periodicity is equally divisible by a period corresponding to four frames (eight fields), at least if the horizontal synchronizing (sync) signals f.sub.H and the color carrier-wave f.sub.o originate from one and the same oscillator frequency according to the formula ##EQU1## which is recommended by CCITT. This equation can be written as ##EQU2## It will be seen immediately that the denominator and the numerator lack common integer factors (the denominator is an odd number and does not end in 0 or 5), and that the two frequencies are equally divided after 4 . 625 periods for f.sub.H, corresponding accordingly to four frames. Thus, in this respect four types of frames can suitably be discerned, and can be designated I, II, III and IV.
REFERENCES:
patent: 4052733 (1977-10-01), Devenbecker, Jr.
E.B.U. Review #172, pp. 265-281, Dec. 1978.
Heinermark Tommy
Hjelm Anders
AB Film-Teknik
Richardson Robert L.
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