JPH0573318B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a color video signal processing circuit for a display device, which converts an external composite color video signal and three input primary color signals into video signals of the same type (for example, a luminance signal and The present invention relates to a color video signal processing circuit for a display device, which converts the signal into a color difference signal or three primary color signals, and selectively outputs one of the two.

2. Prior Art FIG. 2 shows a block diagram of a part of a color video signal processing circuit of a conventional display device. In the figure, a composite color video signal entering an input terminal 1 is supplied to a C/Y separation circuit 2 and separated into a luminance signal and a carrier color signal. This luminance signal is supplied to the gain control circuit 3, while the carrier color signal is demodulated by the color demodulation circuit 4 to produce color difference signals R-Y,
G-Y and B-Y, and are supplied to the matrix circuit 5.

Further, the Revill shift circuit 6, the comparison circuit 7, the capacitor C ₁ and resistor R ₁ for setting the DC regeneration rate, the capacitor C ₂ for peak hold, and the variable resistor R ₂ for bright control constitute a DC regeneration circuit 8 .

The comparator circuit 7 uses a clamp pulse supplied from the terminal 9 to compare the output signal level of the level shift circuit 6 and the DC voltage E P set by the bright control variable resistor R ₂ only during the back porch period, and compares the output signal level with the DC voltage E _P set by the bright control variable resistor R 2 . A signal corresponding to the level difference is output to the level shift circuit 6. The level shift circuit 6 level-shifts the output luminance signal of the gain control circuit 3 according to the output signal of the comparison circuit 7. In this way, the pedestal level of the output luminance signal of the gain control circuit 3 is clamped to the DC voltage _EP .

In this way, the pedestally clamped luminance signal Y is supplied to the matrix circuit 5 and the reverse blanking circuit 10, respectively.

The reverse blanking circuit 10 constitutes a black level correction circuit 12 together with a black peak detection circuit 11, a reference voltage setting variable resistor _R3 , and a peak hold capacitor _C3 . Here, the reverse blanking circuit 10 adds a blanking pulse from a terminal 13 to make the black blanking part white when it is higher than the black level of the incoming luminance signal Y, and outputs it to the black peak detection circuit 11. do.

The black peak detection circuit 11 is connected to the reference voltage E _R set by the variable resistor R ₃ and the reverse blanking circuit 1
The output brightness signal is compared with the output brightness signal of 0, and the darkest part in the output brightness signal is detected, and the obtained detection signal is output to the gain control circuit 3. The gain control circuit 3 has its gain varied in accordance with the detection signal, and is thereby controlled so that the black peak level of the luminance signal Y substantially matches the reference voltage _ER .

Next, the matrix circuit 5 generates R, G, Three primary color signals of B are generated and output to the high speed switch circuit 14.

On the other hand, the three primary color signals of R, G, and B supplied from the outside via terminals 15, 16, and 17 are supplied to the clamp circuit 18 via capacitors _C4 , _C5 , and _C6, respectively. The clamp circuit 18 clamps the incoming three primary color signals at a predetermined level and outputs the clamped signals to the gain control circuit 19, for example, in order to ensure the dynamic range of an integrated circuit (IC). The gain control circuit 19 amplifies the three primary color signals output from the clamp circuit 18 based on the gain set by the RGB contrast control variable resistor R ₄ and outputs the amplified signals to the clamp circuit 20 . The clamp circuit 20 includes hold capacitors C ₇ , C ₈ , C ₉ and
By clamping the incoming three primary color signals at a level set by the RGB bright control variable resistor _R5 , the brightness is adjusted and output to the high speed switch circuit 14.

The high-speed switch circuit 14 selects one of the three primary color signals from the matrix circuit 5 or the clamp circuit 20 in response to a switching signal from the terminal 21 and outputs it to output terminals 22, 23, and 24.

Here, when displaying a CRT screen using the three primary color signals output from the high speed switch 14, one screen may be displayed using either the composite color video signal or the input three primary color signals, or one screen may be displayed using only the composite color video signal or the input three primary color signals. The high speed switch circuit 14 may be switched so as to display a combination of the video signal and the input three primary color signals.

By the way, in general, in order to perform faithful color reproduction in a color television receiver, it is necessary to transmit 100% of the DC component of the color video signal in order to define the relative potential between the color signal and the luminance signal. in this case,
The DC transmission in the luminance signal processing is carried out in the form of DC reproduction by clamping the pedestal portion of the luminance signal by the DC component regeneration circuit 8. However, in order to optimally reproduce an image, a DC reproduction rate of 100% is required as an optical output rather than an electrical signal. At this time, the DC regeneration rate of the electrical signal is 100
It does not necessarily mean that it is %.

The reason is that the CRT drive conditions for obtaining optical output are determined by the relative potential between the cathode and each grid, but this relative potential usually varies depending on the value of the CRT's average beam current, and generally This is because when the average beam current is increased, the cathode voltage of the CRT decreases, and the relative potential changes in the direction of increasing the black level (in other words, in the direction of white).

This equivalently corresponds to the DC regeneration rate exceeding 100%. Therefore, to stabilize the optical output, the DC regeneration rate of the luminance signal must be 100%.
You need to lower it below to find a balance. In the case of ordinary color television receivers, this DC reproduction rate is often set at about 70 to 80%.

In addition, in order to improve gradation reproducibility, black level correction (the black level correction circuit 1
2) and luminance signal processing, the apparent gradation is corrected to a preferable one through non-linear processing such as white level compression and black level expansion. There is.

Problems to be Solved by the Invention However, in the color video signal processing circuit of the conventional display device described above, when the DC component is changed in the form of three primary color signals, not only the luminance gradation but also the color gradation changes to R, G, B varies depending on the amount of each component separately, while the CRT bias condition depends on the average beam current of all three electron guns with a certain time constant (for example, a time constant of one vertical scanning period or more). As a result, the hue changes depending on the content of the picture. For this reason, there was a problem in that the three primary color signal processing could only perform 100% direct current reproduction as an electrical signal.

Furthermore, since the color saturation and hue vary depending on the magnitude of the signal amplitude, performing non-linear processing on the three primary color signals is undesirable because color reproduction deteriorates. In this way, conventionally, DC reproduction rate setting and black level correction are performed for optimal gradation reproduction for externally input composite color video signals, whereas externally input 3 Since signal processing for optimal gradation reproduction cannot be performed on the primary color signals as described above, the input three primary color signals are inferior to the input composite color video signal in terms of gradation reproduction, so it is difficult to improve image quality. The problem was that I couldn't do it.

Therefore, the present invention performs DC reproduction and black level correction on either the luminance signal in the external composite color video signal or the luminance signal generated from the external input three primary color signals.
It is an object of the present invention to provide a color video signal processing circuit for a display device that solves the above problems.

Means for Solving the Problems A color video signal processing circuit for a display device according to the present invention includes a matrix circuit that generates a first luminance signal and a first color difference signal from input three primary color signals supplied from the outside; It is comprised of separation means for separating and outputting a carrier color signal and a second luminance signal from a composite color video signal supplied from the outside, a switching means, a correction means for direct current reproduction and black level correction, and a selection means.

Function: The switching means is supplied with the first and second luminance signals from the matrix circuit and the separation means, respectively, and performs correction by switching either one of the first or second luminance signals in response to an external switching signal. Output to means. The correction means performs DC reproduction and black level correction on the output luminance signal of the switching means. On the other hand, the selection means selects either the first color difference signal or the second color difference signal obtained by demodulating the carrier color signal in response to the switching signal.

In this way, the correction means and selection means respectively output a luminance signal and a color difference signal according to the switching signal.

Embodiment FIG. 1 shows a block system diagram of an embodiment of a color video signal processing circuit for a display device according to the present invention. In the figure, the same components as those in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted. This embodiment is characterized in that a switch circuit 25 is inserted and connected between the C/Y separation circuit 2 and the gain control circuit 3.

Here, the matrix circuit 26 generates a luminance signal and color difference signals R-Y, G-Y, B-Y from the output three primary color signals of the gain control circuit 19, respectively, and outputs the luminance signal to the terminal 25a of the switch circuit 25. On the other hand, the color difference signals R-Y, G-Y, and B-Y are output to the high-speed switch circuit 27. The high-speed switch circuit 27 is also supplied with color difference signals R-Y, G-Y, and B-Y from the color signal demodulation circuit 4.
Further, a luminance signal is supplied from the C/Y separation circuit 2 to a terminal 25b of the switch circuit 25.

The above switch circuit 25 and high speed switch circuit 2
7 are both switched in response to a switching signal supplied from a terminal 28. In other words, the switching signal causes input 3 to
When selectively outputting a primary color signal, the switch circuit 25 is switched to the terminal 25a side, and the output luminance signal of the matrix circuit 26 is sent to the gain control circuit 3, DC component regeneration circuit 8, and black level correction circuit 12 to adjust its pedestal level and The black peak level is controlled to match the DC voltage _EP and the reference voltage _ER , respectively, and then outputted to the output terminal 29. At the same time, the high-speed switch circuit 27 selects the output color difference signal of the matrix circuit 26 from among the two input color difference signals, and selects the output color difference signal from the matrix circuit 26 and
Output to 2 respectively.

Next, when selectively outputting the composite color video signal using the switching signal, the switch circuit 25 is connected to the terminal 2.
5b side, and the output luminance signal of the C/Y separation circuit 2 is output after being controlled so that its pedestal level and black peak level match the DC voltage E _P and reference voltage E _R , respectively, in the same manner as described above. It is output to terminal 29. At the same time, the high-speed switch circuit 27 selects the output color difference signal of the color signal demodulation circuit 4 from among the two input color difference signals, and selects the output color difference signal from the output terminal 3.
0, 31, and 32, respectively.

In this way, the same processing for improving gradation reproducibility as for the composite color video signal is performed on the externally input three primary color signals.

Note that the configurations of the gain control circuit 3, DC component regeneration circuit 8, and black level correction circuit 12 for correcting the pedestal level and black peak level with respect to the luminance signal are not limited to this embodiment, and other configurations may be used. It may also be configured as follows. Also, depending on the type of CRT drive circuit connected to the latter stage of the circuit of the present invention, a matrix circuit may be newly provided.
The luminance signal Y and color difference signals R-Y, G-Y, B-Y output to the terminals 29 and 30, 31, and 32 are converted into three primary color signals of R, G, and B by the above matrix circuit and then output to the above CRT. Of course, it may be configured to output to the drive circuit.

Effects of the Invention As described above, according to the present invention, the luminance signal in the external composite color video signal and the external input 3
Since DC reproduction and black level correction are performed on either one of the luminance signals generated from the primary color signals, DC reproduction and black level correction are performed on the input three primary color signals as well as on the composite color video signal. Therefore, it is possible to improve the image quality of the input three primary color signals, and the processing circuit for DC reproduction and black level correction can be shared by the input three primary color signals and the composite color video signal. It has features such as a simple circuit configuration and the ability to realize an inexpensive color video signal processing circuit for display equipment.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing an embodiment of a color video signal processing circuit of a display device according to the present invention, and FIG. 2 is a block system diagram showing an example of a color video signal processing circuit of a conventional display device. DESCRIPTION OF SYMBOLS 1... Composite color video signal input terminal, 8... DC component regeneration circuit, 12... Black level correction circuit, 25... Switch circuit, 26... Matrix circuit, 27... High speed switch circuit, 28... Switching signal input terminal, 29... Luminance signal Output terminal.

Claims (1)

[Claims] 1 The first of the three input primary color signals supplied from the outside
a matrix circuit that generates a luminance signal and a first color difference signal, respectively; a separation means that separates and outputs a carrier color signal and a second luminance signal from a composite color video signal supplied from the outside; a switching means for switching and outputting one of the first and second luminance signals according to a switching signal to be outputted; and a correction means for performing DC reproduction and black level correction on the output luminance signal of the switching means. and a selection means for selecting either one of the first color difference signal and a second color difference signal obtained by demodulating the carrier color signal in accordance with the switching signal, the correction means and the selection means. A color video signal processing circuit for a display device, characterized in that the circuit outputs a luminance signal and a color difference signal according to the switching signal from the means.