Television – Image signal processing circuitry specific to television – Special effects
Reexamination Certificate
1998-08-27
2001-10-30
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
Special effects
C348S584000, C348S585000, C348S586000, C348S625000, C348S497000, C348S512000, C382S100000, C382S130000
Reexamination Certificate
active
06310658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video system for mixing a video signal, and more particularly, to a video signal mixing apparatus and method for mixing two video signals while minimizing jitter.
2. Description of the Related Art
FIG. 1
shows a displayed image mixed by a conventional video signal mixing method. Here, the X-axis represents pixels in the horizontal direction, and the Y-axis represents horizontal lines in the vertical directions.
FIG. 1
shows a partial screen having 50 pixels×100 horizontal lines.
A mixed image displayed in a video system includes a main screen
12
and a sub-screen
14
. It is assumed that a video signal (or an internal video signal) on the main screen
12
is generated by a system A and a video signal (or external video signal) on the sub-screen
14
is generated by a system B.
Here, the internal video signal and external video signal are synchronized with each other based on a video synchronous signal. The video synchronous signal means a horizontal synchronous signal and a vertical synchronous signal. However, the internal and external video signals are not processed using the same system clock signal. That is, the internal video signal is synchronized with a system clock signal (or internal clock signal) of the system A while the external video signal is synchronized with a system clock signal (or external clock signal) of the system B.
When the system A mixes the internal and external video signals in response to a digital selection signal synchronized with the external clock signal, timing jitter occurs in the mixed video signal. This is because a digital selection signal is input to the system A after being delayed by 1 period of the internal clock signal or advanced by 1 period of the internal clock signal, so the point in time that the system A recognizes the digital selection signal has an error of about 1 period of the internal clock signal.
For example, assuming that one period of the internal clock signal is 100 ns, the timing jitter of about 100 ns occurs. That is, whenever the digital selection signal is input to the system A within 1 period of the internal clock signal, timing jitter of 100 ns occurs in the resultant mixed video image.
In a video system having a picture in picture (PIP) function, the above-described timing jitter appears as dot crawl at a vertical boundary
10
by 1 period of the internal clock signal, shown in FIG.
1
.
Therefore, a need exists to provide a video signal mixing apparatus capable of minimizing timing jitter caused when digitally mixing video signals which have not been synchronized with each other.
SUMMARY OF THE INVENTION
There is provided a video signal mixing apparatus for digitally mixing a first video signal which is not synchronized with a clock signal and a second video signal which is synchronized with the clock signal, in response to a digital selection signal which is not synchronized with the clock signal, and for outputting the mixed result as a mixed video signal; the apparatus comprising: a signal subtractor for subtracting the second video signal from the first video signal; a weighted value extractor for dividing one period of the clock signal into N intervals for detecting the interval wherein the digital selection signal is generated, and outputting a predetermined value (where 0≦predetermined value≦1) allocated to the detected interval as a weighted value; a multiplier for multiplying the weighted value by the output of the signal subtractor, and outputting the multiplication result; and a signal mixer for mixing the multiplication result with the second video signal and outputting the mixed result as the mixed video signal.
There is also provided a video signal mixing method for digitally mixing a first video signal which is not synchronized with a clock signal and a second video signal which is synchronized with the clock signal, in response to a digital selection signal which is not synchronized with the clock signal, and outputting the mixed signal as a mixed video signal, the method comprising the steps of: (a) dividing one period of the clock signal into N intervals; (b) allocating a predetermined value (0≦predetermined value≦1) to the respective N divided intervals; (c) detecting the interval where the digital selection signal is generated, among the N divided intervals; (d) subtracting the second video signal from the first video signal; (e) multiplying the subtraction result by the predetermined value allocated to the detected interval; and (f) mixing the multiplication result with the second video signal to generate the mixed video signal.
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Kang Bong-soon
Kwak Mal-seob
Eisenzopf Reinhard J.
F. Chau & Associates LLP
Natnael Paulos
Samsung Electronics Co,. Ltd.
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