Television – Flutter or jitter correction
Reexamination Certificate
1998-03-04
2001-12-18
Lee, Michael (Department: 2614)
Television
Flutter or jitter correction
Reexamination Certificate
active
06331875
ABSTRACT:
The invention relates to a method and a device for arranging digitized image signals or data, which do not necessarily have a constant time base, in orthogonal rows and columns with a constant time base.
BACKGROUND OF THE INVENTION
Television receivers are increasingly making use of digital signal processing, for example for 100 Hz or 120 Hz reproduction. For this purpose, the analogue video signals are digitized using an A/D converter, digitally processed and thereafter reconverted, using a D/A converter, into analogue signals which are represented on a picture screen.
Present-day television receivers use a line-coupled clock system as clock for the A/D and D/A converters, since this produces an orthogonal pixel array for signal processing on the picture screen. The disadvantage of such a clock grid resides in its problematical generation, in particular whenever video recorders are used as signal source, because they emit unstable or non-standard signals.
SUMMARY OF THE INVENTION
The object of the invention is to specify a method for an arrangement or representation of image signals or data which is essentially on a constant time base and in which such clock problems are avoided. This object is achieved by means of the method specified herein.
It is further the object of the invention to specify a device for applying the method according to the invention. This object is achieved by means of the device specified herein.
It is further the object of the invention to specify a television receiver for applying the method according to the invention. This object is achieved by means of the television receiver specified in herein.
According to the invention, video signals which are unstable, at least as to their time base, in particular video signals which originate from a video recorder or comparable sources of image signals, are digitized by means of a free-wheeling clock from a quartz oscillator in the A/D converter(s) at the input end. The free-wheeling clock represents the system clock by means of which, or in a fashion derived from which, the digital signal processing which then follows is also operated, including possible D/A conversion at the image signal, sound signal, data and/or address or deflecting outputs of the digital signal processing system.
Video signals which are standard or stable as to their time base can, however, also be processed using this method. It is, however, advantageous for the video signals governed by this system clock likewise to be present in an orthogonal, line-coupled array. The horizontal deflection of the television receiver can also advantageously be synchronized with the system clock or the corresponding clock derived therefrom, with the result that, for example, 1152 system clock pulses (in the case of an 18 MHz system clock)always supply 1152 pixels in each of the lines. The associated pixels of an imaginary input signal pixel column are then situated exactly one below another when represented on the display.
However, in general a frequency deviation occurs between the horizontal frequency of the video signal from the video recorder and the horizontal frequency of the television receiver. Nevertheless, the horizontal deflection of the television receiver must no longer be synchronized with the input signal. The horizontal deflection of the television receiver should, certainly, run synchronously with the corresponding internal clock, but the picture-tube deflection or display addressing and the system clock must in principle no longer be synchronous relative to the television receiver input signal.
In order not to have to use theoretically infinitely large buffer memories, the vertical deflection or vertical addressing is synchronized with the input signal. The contradiction thereby arising that, on the one hand, the deflection or display addressing should be asynchronous relative to the input signal but, on the other hand, should be synchronous on average relative thereto is eliminated according to the invention by operating the picture tube or the display with a variable picture frequency or vertical frequency, but with an invariable line frequency. The horizontal frequency no longer has a fixed relationship to that of the input signal; the vertical frequency, however, follows that of the television receiver input signal.
The standard fixed relationship between the vertical and horizontal frequency or deflection in the television receiver is no longer continuously present. The number of lines reproduced per field can fluctuate and will also do so in the case of video recorder signals.
A distinction must be drawn between the number of lines per time unit (corresponds to the line frequency) and the number of lines per field or per frame. The line frequency, that is to say the line duration of 64 &mgr;s (active line duration 52 &mgr;s) in the case of a 625 line/50 Hz television signal standard, is preferably constant in the invention, while the number of lines per field or per frame is dynamically matched.
Experiments have shown that at least some television receivers on the market (for example those manufactured by Thomson) are best suited for this operation using variable line numbers, by contrast with, for example, studio monitors.
The great advantage of this invention results in that it is no longer necessary for the many phase-locked loops of a television receiver (for example as used in synchronization pulse separation and the conditioning, in the generation of line pulses or in deflection, in the PLL for clock pulse generation) also to be designed for satisfactory operation of the television receiver with a video recorder, or to design them for input signals which are variable as to the time base. This renders it possible to develop new, more highly integrated television receiver chassis, which can therefore be produced more cost effectively.
In principle, the method according to the invention serves the purpose of arranging digitized image signals or data, which contain parts suitable for synchronization and do not necessarily have a constant time base, in orthogonal rows and columns, the number of lines per field or frame and/or of pixels per line that is used for an arrangement or representation of the image signals or data on an essentially constant time base being matched to the corresponding original number of image signals or data so as in each case to produce within a limited time interval a synchronization of the image signals or data provided for the representation with the original image signals or original data.
Advantageous developments of the method according to the invention follow from the associated dependent claims.
In principle, the device according to the invention serves the purpose of arranging digitized image signals or data, which contain parts suitable for synchronization and do not necessarily have a constant time base, in orthogonal rows and columns with an essentially constant time base, and is provided with:
first means which compare the synchronization parts with a first clock, which can be based on a system clock and which can also be the system clock;
second means, which arrange or represent the image signals or data with an essentially constant time base by means of a second clock, which is based on the system clock and can also be the system clock, specifically with a number of lines per field or frame and/or of pixels per line which is such, by comparison with the corresponding original number of image signals or data, that the image signals or data provided for the representation are synchronized with the original image signals or image data by means of the comparison in the first means inside a limited time interval in each case.
In principle, the television receiver according to the invention arranges digitized image signals, which do not necessarily have a constant time base, in orthogonal rows and columns with an essentially constant time base, and is provided with:
first means, which compare the synchronization signals contained in the image signals with a first clock, which can be based on a
Hirtz Gangolf
Hollmann Thomas
Rothermel Albrecht
Schweer Rainer
Deutsch Thomson-Brandt GmbH
Lee Michael
Shedd R. D.
Shoneman D. T.
Tripoli J. S.
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