JP2000050158A - Video compositing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To process level adjustment when an analog first video signal and a digital second video signal are analog-compositing without operating it manually operation. SOLUTION: A clamping circuit 3 clamps the black level of a first video signal V1 to a voltage equal to the output voltage of a D/A conversion part 1 which corresponds to the minimum level of a second video signal V2. A level setting part 4 sets the level of the video signal from the clamping circuit 3. The output signal of the level setting part 4 is wave-detected by a detection part 6. A video level from the detection part 6 is compared with a voltage equal to the output voltage of the D/A conversion part 1 which corresponds to the maximum level of the second video signal V2 by a comparison part 7. Setting control data So by which two levels become the same in the comparison are stored in a memory part 9 based on the comparison result signal from the comparison part 7. A control part 8 sets the level setting part 4 based on the data of the memory part 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video synthesizing apparatus, and more particularly, to an analog first video signal (for example, a personal computer signal) and a digital second video signal (for example, a television video signal). It relates to level adjustment when performing synthesis processing.

[0002]

2. Description of the Related Art FIG. 3A shows an analog first video signal.
FIG. 11 is a main block diagram showing an example of a conventional video synthesizing apparatus that synthesizes V1 and a digital second video signal V2. The first video signal V1 is a RGB signal from a personal computer (PC).
The second video signal V2 is a general RGB video signal such as a television video. Since the second video signal V2 is a digital signal, the digital signal is converted to a D / A converter.
The signal is converted into an analog signal at 12, and the converted analog video signal and the first video signal V1 are switched by a switching circuit 13 in accordance with a switching control signal S11 to output a composite video signal Vo.
FIG. 3B shows an example of the mode of the composite video when the composite video signal Vo is displayed. FIG. 2 shows an example in which a second video signal V2 is inserted at substantially the center of the first video signal V1. In the synthesis, the level of the first video signal V1 and the output level of the D / A converter 12 are not always the same due to variations and the like. Therefore, when the composite video signal Vo is displayed, the brightness of both signals may be unbalanced. Therefore, D / A
A gain control 11 is provided in a stage preceding the conversion unit 12, and the D / A
The level of the gain control 11 is manually adjusted so that the output level of the conversion unit 12 becomes equal to the level of the first video signal V1.

[0003]

However, in the case of the level adjustment shown in FIG. 3, there is a drawback that the dynamic range of the D / A converter 12 is not always fully used. That is, even when the level of the first video signal V1 is large, the level of the second video signal V2 can be adjusted. It is necessary to leave a part of the 12 dynamic range as a margin without using it fully. Therefore, the first
When the level of the video signal V1 is low, the D / A converter 12
Of the output signal becomes insufficient. Therefore, the D / A converter
It would be desirable to have a strategy that makes full use of the 12 dynamic ranges and allows for level matching of both signals. An object of the present invention is to provide a video synthesizing device made from such a viewpoint.

[0004]

According to the present invention, an analog first video signal and a digital second video signal are input, and the second video signal is converted into an analog video signal by a D / A converter. In the video synthesizing device for synthesizing the converted video signal and the first video signal, the first video signal to be synthesized and the analog output of the D / A conversion unit have the same level. It is an object of the present invention to provide a video synthesizing apparatus provided with level setting means for performing level setting processing on a video signal.

The level setting means clamps the black level of the first video signal to the same voltage as the output voltage of the D / A converter corresponding to the minimum level of the second video signal. A level setting unit for setting a level with respect to a video signal from the clamp circuit, a detection unit for detecting an output signal of the level setting unit, and a video level in a detection signal from the detection unit, the second A comparison unit that compares the output voltage of the D / A conversion unit corresponding to the maximum level of the video signal with the same voltage and outputs a comparison result signal, and based on the comparison result signal from the comparison unit, And a control unit for setting and controlling the level setting unit so that the levels are the same.

The level setting section includes an amplifier circuit and an attenuation circuit. Further, the detection unit may detect only the video period based on the input horizontal synchronization signal and output a detection signal.

[0007] Further, a memory unit for storing setting control data for setting both levels in the comparison to be the same level is provided under the control unit, and after the storage, the level setting unit stores the same in the stored setting control data. To set.

The video signal used for level setting by the level setting means is a video signal in which the horizontal blanking period is a black level and the video period is 100% white.

[0009]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 is a main block diagram showing an embodiment of a video synthesizing apparatus according to the present invention.
FIG. 2 is a video signal waveform diagram for explaining FIG. In FIG. 1, V1 is a first video signal, which is a personal computer (PC).
Are analog RGB signals. V2 is a second video signal, which is a general digital RGB video signal such as a television video. The second video signal V2 is D / A
The converter 1 converts a digital signal into an analog signal. This D / A converter 1 receives Vl from the reference voltage generator 2.
Two kinds of reference voltages Vh are supplied. Reference voltage Vl
Is the analog output voltage corresponding to the minimum level (black level) of the second video signal V2, and the reference voltage Vh
Is an analog output voltage corresponding to the maximum level (white level) of the second video signal V2. Reference voltage Vl,
The analog video signal D / A converted based on Vh is sent to the switching circuit 5.

On the other hand, the first video signal V1 is
Enter When setting the level, the first video signal V1
Is used as the signal shown in FIG. As shown, the video period tv is a 100% white signal, the horizontal blanking period tb is at the black level, and there is no horizontal synchronization signal. The clamp circuit 3 clamps the black level (horizontal blanking period) of the first video signal V1 to the reference voltage Vl from the reference voltage generator 2. The output signal of the clamp circuit 3 is sent to the switching circuit 5 and the detection unit 6 via the level setting unit 4. The detection section 6 receives the input horizontal synchronizing signal.
Based on Sh, a 100% white video component (FIG. 2) is detected and output. The detected 100% white video component is compared with the reference voltage Vh from the reference voltage generator 2 in the comparator 7, and the comparison result signal Sc is sent to the controller 8.

When the comparison result signal Sc has a higher video level than the reference voltage Vh, the control section 8 controls the output level of the level setting section 4 to decrease. The output video signal based on this control is detected again by the detector 6 and compared with the reference voltage Vh by the comparator 7. This comparison result signal Sc is fed back to the control unit 8. As described above, the level setting unit 4 is balanced by the feedback circuit of the level setting unit 4 → the detection unit 6 → the comparison unit 7 → the control unit 8 → the level setting unit 4 so that the video level becomes the same level as the reference voltage Vh. .
On the other hand, when the comparison result signal Sc has a smaller video level than the reference voltage Vh, the control unit 8 controls the output level of the level setting unit 4 to increase. The control result is fed back to the control unit 8 in the same manner as described above, and ultimately is balanced with the video level being the same as the reference voltage Vh as described above. The level setting section 4 is provided with an attenuating function (attenuating circuit) together with an amplifying function (amplifying circuit) so that the output level can be increased or decreased.

The setting control data So for setting the video level to the same level as the reference voltage Vh is stored in the memory unit 9. Thereafter, during normal operation, the control unit 8 sets the output level of the level setting unit 4 based on the setting control data So stored in the memory unit 9. As a result, the level of the analog output of the D / A conversion unit 1 matches the output level of the level setting unit 4. Level setting unit 4 and D / A conversion unit 1
Are output to the switching circuit 5 and are switched according to the switching control signal S1 in the same manner as in FIG. 3A, and the video signal Vo related to the composite video as illustrated in FIG. 3B is output.

[0013]

As described above, according to the present invention, an analog first video signal and a digital second video signal are input, and the second video signal is converted by the D / A converter into an analog signal. When the signal converted to the video signal and the first video signal are combined, the levels of both signals can be automatically set to the same level. On the other hand, the level setting in the related art (FIG. 3) is manually performed. This level setting is performed on the analog first video signal side. Therefore, the dynamic range of the D / A conversion unit can be fully used in comparison with the configuration in which the dynamic range of the D / A conversion unit is changed as in the related art (FIG. 3), and the synthesis due to the lack of the dynamic range can be performed. The problem of insufficient video gradation on the second video signal side does not occur. From the above, it can be said that the present invention can contribute to improving the performance of the video synthesizing apparatus.

[Brief description of the drawings]

FIG. 1 is a main block diagram showing an embodiment of a video synthesizing apparatus according to the present invention.

FIG. 2 is a video signal waveform diagram for explaining FIG. 1;

FIG. 3 is a main block diagram showing an example of a conventional video synthesizing apparatus.

[Explanation of symbols]

 V1 First video signal V2 Second video signal 1 D / A conversion unit 2 Reference voltage generation unit 3 Clamp circuit 4 Level setting unit 5 Switching circuit 6 Detection unit 7 Comparison unit 8 Control unit 9 Memory unit 11 Gain control 12 D / A converter 13 Switching circuit Vo Composite video output signal

Claims (6)

[Claims] An analog first video signal and a digital second video signal are input, and the second video signal is converted into an analog video signal by a D / A conversion unit, and the first video signal is converted to an analog video signal. In a video synthesizing apparatus for synthesizing a video signal, a level setting process is performed on the first video signal to be synthesized and the analog output of the D / A conversion unit so that the levels of the analog video output become the same. A video synthesizing apparatus characterized by comprising a level setting means for setting. 2. The clamp for clamping the black level of the first video signal to the same voltage as the output voltage of the D / A converter corresponding to the minimum level of the second video signal. A level setting unit for setting a level with respect to a video signal from the clamp circuit, a detection unit for detecting an output signal of the level setting unit, and a video level in a detection signal from the detection unit, the second A comparison unit that compares the output voltage of the D / A conversion unit corresponding to the maximum level of the video signal with the same voltage and outputs a comparison result signal, and based on the comparison result signal from the comparison unit, 2. The video synthesizing apparatus according to claim 1, further comprising: a control unit configured to set and control the level setting unit so that the levels are the same. 3. The video synthesizing apparatus according to claim 2, wherein said level setting section includes an amplification circuit and an attenuation circuit. 4. The video synthesizing apparatus according to claim 2, wherein said detection unit detects only an image period based on an input horizontal synchronization signal and outputs a detection signal. 5. A memory unit for storing setting control data for setting both levels in the comparison at the same level is provided under the control unit, and after the storing, the level setting unit stores the setting control data in the same storage. 3. The video synthesizing device according to claim 2, wherein the setting is performed. 6. The video signal used for level setting by said level setting means is a video signal in which a horizontal blanking period is a black level and a video period is 100% white. Item 3. The video synthesizing device according to Item 2.