JPH0591412A - Key signal generator - Google Patents

Abstract

PURPOSE:To provide a high quality key signal that never causes any comb- shaped jaggies on the boundary between the screens when two video signals are wiped in the horizontal direction by resetting a frequency divider with a horizontal reset signal. CONSTITUTION:A key signal generator is provided with a frequency divider 4 which divides a signal having its frequency of (n) times as high as the color subcarrier frequency, a horizontal key start position counter 5 and 8 vertical key start position counter 6 which count the output of the divider 4 and are reset by the horizontal and vertical reset signals, and a vertical key position counter which counts the horizontal reset signals and is reset by a vertical blanking signal. Furthermore a control means 9 is added to produce a key signal from the outputs of both counters 5 and 6. The divider 4 is reset by the horizontal reset signals that reset both counters 5 and 6. In such a constitution, no error is produced between the horizontal key position signals on the lines contiguous to each other in each horizontal period or between the fields. Then the comb-shaped jaggies are never caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key signal generator used in a device for generating special effects for television images.

[0002]

2. Description of the Prior Art In a manner such that a portion of a television image provided by one video signal is replaced by a television image provided by another video signal.
Various special effect generators have been proposed which generate wipes by combining two video signals. An example of such a conventional technique is shown in FIG. In the figure, 1 is a terminal to which an n-fold color subcarrier synchronized with a horizontal synchronizing signal (hereinafter referred to as fsc) is input, 2 is a terminal to which a horizontal reset signal made from the half-etch rejected horizontal synchronizing signal is input, and 3 Is a terminal to which a vertical blanking signal is input. Further, 4 is a frequency divider for dividing the nfsc,
Numerals 5 and 6 count the output of the frequency divider 4 and are reset by the horizontal reset signal. A horizontal key start position counter and a horizontal key end position counter (hereinafter referred to as the horizontal key start position counter 5 and the horizontal key end position counter 6). Collectively referred to as a horizontal key position counter), 7 and 8 are a vertical key start position counter and a vertical key end position counter which count the horizontal reset signal and are reset by the vertical blanking signal. Each of these counters 5, 6, 7, and 8 has a load terminal that can be preset to any count state. Depending on the load value, the counter 5 is used for the horizontal key start position and the counter 6 is used for the horizontal key end position. , The counter 7 is set for the vertical key start position, and the counter 8 is set for the vertical key end position. The value to be loaded may be set by the CPU. 9 more
Is a control means for generating a key signal using the signals output from the four counters 5, 6, 7, and 8 and supplying it to an image switch for switching two video signals (not shown), and 10 is a key signal Is a terminal for outputting. However, in this conventional technique, when two video signals are wiped in the horizontal direction, a comb-shaped jaggy occurs at the boundary of the screen.
The clock input to the horizontal key start position counter 5 is f
FIG. 3 shows a screen example in which this phenomenon occurs at the time of sc. The reason why this phenomenon occurs will be described below. Now, assuming that each horizontal key position counter 5 and 6 is composed of an 8-bit counter, in order to be able to freely set the key position from the left end to the right end of the screen, the number of clocks (that is, minute count) to be input is input. It is necessary to set the output of the frequency divider 4) to a value close to 256 in one horizontal period. However, n times fsc
Is divided by a frequency divider having a simple structure such that the frequency division ratio is represented by an integer, the output becomes a non-integer within one horizontal period. For example, if the output clock of the frequency divider is 4 /
If it is 3 fsc, the clock count number in one horizontal period is 303.3, and if the same clock is fsc, the clock count number is 227.5, which is a non-integer. Of course, it is possible to make the number of clock counts in one horizontal period an integer by increasing the number of bits and clock frequency of each horizontal key position counter 5, 6, but this is not realistic because the circuit scale becomes very large. .. Now, a timing chart of such a conventional technique is shown in FIG. This figure shows the cause of the comb-shaped jaggies when the number of clocks in one horizontal period of the horizontal key position counter is a non-integer. The output clock of the frequency divider 4 (a in FIG. 3) is fsc.
Is an example of the case. Here, as described above, the number of clock counts in one horizontal period of the horizontal key position counter is 2
27.5, and the reset signal (b in FIG. 3) of the horizontal key position counter and the phase of the clock signal are different in the horizontal period before and after as shown in FIG. As a result, the phase of the horizontal key position counter output (c in FIG. 3) with respect to the horizontal reset signal is 1
It will shift every horizontal period. In this example, the horizontal key position signals of adjacent lines between fields are about 140
It is shifted by ns, and this shift becomes a comb-shaped jaggy.
Similarly, when the output clock of the frequency divider 4 is 4/3 fsc, a shift of about 140 ns also occurs, but in this case, the relationship of the phase shift between adjacent lines between fields is not constant and the comb-shaped jaggies are shown in FIG. As shown.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the conventional technique. When two video signals are horizontally wiped,
(EN) A key signal generator which can obtain a high-quality key signal in which no comb-shaped jaggies are generated at the boundary of a screen and which has an extremely simple structure.

[0004]

SUMMARY OF THE INVENTION Therefore, according to the present invention, a signal having a frequency N times as high as the color subcarrier frequency is divided, and a frequency is reset by a horizontal reset signal generated from a half-etch rejected horizontal synchronizing signal. Key, a horizontal key position counter that counts the output of the frequency divider and is reset by the horizontal reset signal, a vertical key position counter that counts the horizontal reset signal and is reset by a vertical blanking signal, and the horizontal , And a control means for generating a key signal by using a vertical counter output.

[0005]

Since the frequency divider of the present invention is reset by the horizontal reset signal, even if the clock count number in one horizontal period of the horizontal key position counter is a non-integer, the horizontal reset signal and the output of the frequency divider are output. The phase with the clock always matches.

[0006]

FIG. 1 shows an embodiment of the present invention. A timing chart of the embodiment is shown in FIG. FIG. 6 shows that the comb-shaped jaggies do not occur even if the number of clocks in one horizontal period of the horizontal key position counter is a non-integer. As in FIG. 4, the clock (a in FIG. 6) is designated as fsc. This is an example of the case. Further, in FIG. 1, the same components as those of the conventional technique are designated by the same reference numerals, and the description thereof will be omitted. Figure 1
As shown in (1), the feature of the present invention resides in that the frequency divider 3 is reset by a horizontal reset signal generated from a half-etch rejected horizontal synchronizing signal.
As a result, as shown in FIG. 6, even if the number of clock counts in one horizontal period of the horizontal key position counter is a non-integer, the phase of the reset signal (b in FIG. 6) and the clock signal of the horizontal key position counter is the frequency divider. It always matches regardless of the division ratio of 3. That is, the horizontal key position signal does not shift between adjacent lines every horizontal period or between fields,
The comb-shaped jaggies do not occur.

[0007]

As described above, according to the present invention, it is possible to inexpensively obtain a high-quality key signal which does not cause comb-shaped jaggies at the boundary between screens when two video signals are horizontally wiped.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is an example of a screen in which comb-shaped jaggies occur at the boundary between two wiped screens.

FIG. 4 is a timing chart for explaining the operation of the conventional example.

FIG. 5 is another screen example in which comb-shaped jaggies are generated at the boundary between two wiped screens.

FIG. 6 is a timing chart for explaining the operation of the present invention.

[Explanation of symbols]

 4 ... Frequency divider 5, 6 Horizontal key position counter 7, 8 Vertical key position counter 9 ... Control means

Claims (1)

[Claims] 1. A frequency divider which divides a signal having a frequency n times the color subcarrier frequency and is reset by a horizontal reset signal made from a half-etch rejected horizontal synchronizing signal, and an output of the frequency divider. And a horizontal key position counter that is reset by the horizontal reset signal, a vertical key position counter that counts the horizontal reset signal and is reset by a vertical blanking signal, and a key signal using the horizontal and vertical counter outputs. A key signal generator comprising a control means for creating