JPH01233899A - Color video signal level adjustment circuit - Google Patents

Abstract

PURPOSE:To adjust a picture level with high accuracy and simple constitution by driving each DA conversion circuit by a common DC voltage so as to vary the DC voltage. CONSTITUTION:When the video signal level is desired to be varied, a variable resistor 6 is varied, then the DC voltage V fed to each DA conversion circuit is changed entirely by the same ratio and as a result, the level of an obtained analog output signal level is changed by the same ratio with the DC voltage V. Thus, R, G, B signals being outputs of a matrix circuit 3 are varied by the same ratio without distorting the color balance and the level is changed while keeping the accurate color reproducibility. Thus, the circuit constitution is very simple and the level is adjusted accurately without distorting the color balance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color video signal level adjustment circuit.

[Conventional technology]

Generally, color video file devices etc. have a frame memory, and information from this frame memory is transferred to the DA.
Red, green, blue (R, G,
B,) are designed to create primary color signals. However, it is necessary to adjust the image level due to level differences due to differences in input sensitivity for each CRT display and differences in point conditions at the time of image capture. In this case, to adjust the level of the video signal, variable resistors that are variable in conjunction with each other are inserted into the video amplification stage for each of the R, G, and B signals.
Adjusting the gain.

[Problem that the invention seeks to solve]

However, if the gains of the R, G, and B video amplification stages are varied at the same ratio, the circuit would be complicated, and the precision of the components would need to be high. Since a resistor is inserted, there are drawbacks such as deterioration of frequency characteristics.

An object of the present invention is to accurately adjust the image level with a simple configuration.

[Means for solving problems]

The color video signal level adjustment circuit according to the present invention is a video signal circuit that converts a plurality of digitized signals constituting an image signal into DA conversion circuits using a plurality of DA conversion circuits to create a color signal. It is characterized in that the circuits are driven by a common DC voltage and that the DC voltage is made variable.

[Effect]

According to the above configuration, the analog output of each DA converter changes at the same ratio according to the DC voltage, so it is possible to adjust the video level without disturbing the color balance.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an example of a color video level adjustment circuit according to the present invention.

In the figure, three DA transformations DAI of DA transformation l,
DA2. DA3 has a luminance signal of Y, and Y
The J digital information of the signal, R-Y signal, and B-Y signal is added, and the analog conversion output of these is obtained at the output terminal, and a predetermined band limit is applied to each by the filter 2.
It is added to the matrix circuit 3. In the matrix circuit 3, these Y, RY, and B-Y signals become R, G, and B signals and are applied to the video amplifier 4. The above DA converter DAI,
DA2. Each power supply terminal Vl, V2, v3 of DA3
, a DC power supply 6 is connected by a voltage dividing circuit using a variable resistor 5.
The output voltage of is adjusted and applied.

Since Figures 2 to 4 can be used as the above-mentioned DA converter, they each have a combination of a resistor network, a switch circuit, and an amplifier circuit, and all of these are connected to the DC current applied to the power supply terminal ■. Supply voltage V, input PCM
Adjustment is made according to each bit of the signal, and these are switched and added according to the on/off state of each focus to perform DA conversion.

In the embodiment of FIG. 1, each DA converter DA1, DA
2. It is assumed that DA3 has the same configuration.

In the above configuration, the variable resistor 5 is set at a specific position (as in the conventional case, the input digital signal is
The signal is converted into R, G, and B signals by the conversion matrix circuit 3. Next, if you want to change the video signal level,
Change the variable resistor 5. Then, the DC voltage V applied to each DA converter changes at exactly the same ratio, and as a result, the level of the obtained analog output signal also changes at the same ratio as this DC voltage V. The output R, G, and B signals also change at the same ratio without disturbing the color balance, and the levels can be changed while maintaining accurate color reproducibility. The above explanation is for the case where Y, RY, and BY signals are used, but it can also be used when, for example, [ and Q signals are used. Furthermore, if the input digital information directly represents R, G, and B signals, the matrix circuit may be omitted.

〔Effect of the invention〕

As described above, according to the present invention, the level of the color signal output is changed by changing the DC voltage of the DA converter, so the circuit configuration is extremely simple, and the accuracy can be improved without destroying the color balance. You can easily adjust the level. Furthermore, since there is no need to insert a variable resistor into each of the R, G, and B signal circuits after analog conversion, frequency characteristics are not impaired.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
FIGS. 3 and 4 are circuit diagrams showing typical examples of DA converters that can be used in the present invention. 1...DA converter 2...Low pass filter 3...Matrix circuit 4...Video amplifier patent applicant Nippon Columbia Co., Ltd. +1. t'
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Claims (1)

[Claims] In a video signal circuit in which a plurality of digitized signals constituting an image signal are DA-converted by a plurality of DA-conversion circuits to create a color signal, each of the DA-conversion circuits is driven by a common DC voltage, and A color video signal level adjustment circuit characterized in that the DC voltage is made variable.