Television – Format – Specified color signal format
Reexamination Certificate
2000-03-29
2001-11-20
Lee, Michael (Department: 2614)
Television
Format
Specified color signal format
C348S607000, C348S613000, C348S619000, C382S265000
Reexamination Certificate
active
06320622
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates, in general, to a de-emphasis filter for SECAM-coded picture signals. Such filters are used in SECAM decoders for television or video equipment.
The SECAM Standard provides for the color information of an image to be transmitted with half as large a spatial resolution as the brightness information. In effect, color information is transmitted only with each second picture line. Since a complete item of color information includes two different types of color information in addition to the brightness, only one of the two items of information is modulated onto the signal of the relevant line, the other being transmitted with the line following thereupon. In order to be able to distinguish the two different items of color information at the receiver, two different carrier frequencies f
r
and f
b
are used for the two types of information. The lines thus modulated are denoted correspondingly as D
r
lines and D
b
lines, respectively.
The incoming color information signals are mixed in the receiver with a frequency of f
0
=4.286 MHz. This yields base frequency signals with a constant offset that corresponds in each case to the difference between the respective color carrier frequency and the mixed frequency:
f
r
−f
0
and f
b
−f
0
,
respectively. These frequencies must be very constant in order to avoid errors in the color rendition. The transmitter therefore transmits, in the burst gate period of the signal, identification pulses that are intended to permit the detection of a line as a D
r
line or D
b
line and to permit the adjustment of the mixed frequency f
0
.
A special circuit must be provided in each SECAM decoder for the purpose of evaluating these pulses and forming a mean value over a plurality of rows (the achromatic value).
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a de-emphasis filter for a SECAM decoder which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type in such a way that a special circuit for evaluating the identification pulses transmitted in the burst gate period need not be provided for the SECAM decoder.
The invention is based on the finding that this special circuit is always active only during a fraction of the picture signal periods, specifically during the blanking interval, in which the burst signal is transmitted. A further obligatory component of each SECAM decoder is a de-emphasis filter. The de-emphasis filter serves the purpose of once again damping radio-frequency components of the picture signal that are transmitted by the transmitter with a gain (with pre-emphasis) relative to the low frequency components in order to achieve a linear response characteristic with a constant signal-to-noise ratio. This de-emphasis filter is active only during the transmission of the picture line signal.
With the foregoing and other objects in view there is provided, in accordance with the invention, a digital de-emphasis filter that can be become active during the blanking interval for the purpose of determining the achromatic value.
The digital de-emphasis filter includes a recursion register for storing an auxiliary value obtained from an input image data value, and an arithmetic circuit configured to use the auxiliary value and a new image data value to generate a new auxiliary value and a filtered image data value. A device is provided for storing and outputting a value representative of an estimated value of an achromatic value of a SECAM signal. A first switch is provided for applying the value output by the device into the recursion register to obtain a registered value at the beginning of each burst gate period of the SECAM signal. The arithmetic circuit is configured to use the registered value and at least one value of the burst signal of the SECAM signal to output an estimated value that is updated using the value of the burst signal.
When the filter is being operated as a de-emphasis filter, the recursion register receives and stores an auxiliary value that can be an intermediate value that occurs during the determination of the output value of the filter, or can be the output value itself, and that subsequently features in the processing of a subsequent line signal value input into the filter. The strength of this influence or of the recursivity is determined by components of the arithmetic circuit such as, for example, multipliers. At the start of the burst gate period, the contents of the recursion register are replaced by an estimated value with the aid of a device for outputting a signal representative of an estimated value of the achromatic value and with the aid of a first switch. During the burst gate period, the filter processes at least one value of the burst signal with the aid of the estimated value, in order to obtain an improved estimated value. This can be performed, in particular, by the filter generating and outputting a mean value of the estimated value and of the burst signal value.
In accordance with an added feature of the invention, there is provided a device for outputting an estimated value that includes a register in which a value representative of an achromatic value measured in the course of an earlier burst gate period is stored. It is particularly advantageous for this purpose for the filter to include a second switch which, at the end of each burst gate period, applies the output value of the recursion register to an input of the device for outputting an estimated value for the purpose of storing the output value therein.
In accordance with an additional feature of the invention, the device for outputting an estimated value expediently includes two registers in order to be able to handle two different estimated values, one for D
r
lines and the other for D
b
lines. A particularly simple management of the registers results when the latter are not assigned to one type of line, but are connected in series so that each register alternately stores D
b
estimated values and D
r
estimated values.
In accordance with another feature of the invention, there is provided at least one multiplier with a variable multiplication factor. Differences in the processing of line signal data and burst signal data can be accomplished, for example, with the aid of such a multiplier with a variable multiplication factor. Alternatively, or in combination therewith, a different response of the filter, in the case of an unchanged transfer function, can be simulated by virtue of the fact that the filter operates with a different clock-pulse rate during the picture line signal than during the burst signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a de-emphasis filter with integrated determination of achromatic values, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 3863264 (1975-01-01), Nelson et al.
patent: 4135201 (1979-01-01), Dickie et al.
patent: 4499427 (1985-02-01), Demmer et al.
patent: 4571613 (1986-02-01), Fukuda et al.
patent: 4646153 (1987-02-01), Fukuda et al.
patent: 281 073 A1 (1990-07-01), None
patent: 294 152 A5 (1991-09-01), None
patent: 0 335 371 A2 (1989-10-01), None
“Digitale PAL-SECAM-Videosignalverarbeitung” (Digital PAL-SECAM-video signal processing), Electronics, vol. 12, Berlin 1988, pp. 751-757.
Patent Abstracts of Japan No. 59-128890 (Teruo), dated Jul. 25, 1984.
Greenberg Laurence A.
Infineon - Technologies AG
Lee Michael
Lerner Herbert L.
Stemer Werner H.
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