JPS6361836B2 - - Google Patents

Description

[Detailed Description of the Invention] In order to achieve both faithful color reproduction and the beauty of white color at white peak in a color television receiver, it is necessary to
It is necessary to change the reference white color of the picture tube depending on whether the brightness level of the video signal is low or high. For example, at a level lower than the skin tone level, it is 9300〓+
It is desirable to maintain a color temperature of 8MPCD, and at the white peak level, the color temperature should be 14000 + 8MPCD.

As a method for controlling the color temperature of a picture tube in this manner, the method shown in FIG. 1 has been proposed.

That is, the red, green, and blue primary color signal voltages obtained from the color decoder 10 are applied to the cathodes K _R , K _G , K _B of the picture tube 30 through the video output circuit 20 and the cathode resistors R _R , R _G , R _{B .} However, this method connects a series circuit of Zener diodes Z _G , Z _B and resistors r _{G , r B in} parallel with green and blue cathode resistors R _G , R _B . Therefore, when the cathode current increases, the Zener diodes Z _G , Z _B conduct and the green and blue cathode feedback resistors R _G , R _B to R _G
Green by decreasing r _G and R _B r _B respectively,
The amount of blue feedback decreases, the green and blue drive currents increase, and the color temperature increases.

However, in this case, the feedback resistance is actually the sum of the output impedance of the video output circuit and the above-mentioned resistance. Therefore, R _G , R _B to R _G r _G , R _B r _B
The change in feedback resistance is small even if the Therefore, the change in color temperature is small, and it is difficult to achieve the desired color temperature at the white peak level as shown by the solid line 1 in FIG. 2, and the color temperature becomes insufficient as shown by the broken line 2. Furthermore, if the color temperature is changed by changing the feedback resistance at lower brightness levels, the desired color temperature can be achieved at the white peak level as shown by broken line 3, but in order to achieve faithful color reproduction, As mentioned above, it is necessary to maintain a low color temperature up to the skin color level, so this is not preferable.

Another method is to change the values of the resistors R _R , R _G , R _B themselves without connecting the series circuit of the Zener diodes Z _G , Z _B and the resistors r _G , r _B as shown in Fig. 1.
In other words, there is also a method of making the relationship R _R > R _G > R _B.

However, this method also has the same drawbacks as the above-mentioned method. Furthermore, it is not preferable to set the resistors R _G and R _B to small values in order to protect the video output circuit 20 from discharge in the picture tube 30 . Furthermore, the resistances R _R , R _G ,
If the difference between R _{and B} is large, the frequency characteristics will no longer match among red, green, and blue, resulting in the disadvantage that the pulse characteristics will deteriorate and color smear will occur.

Therefore, the applicant of the present application has proposed the following device that can control the color temperature to a desired characteristic without causing such inconveniences.

FIG. 3 shows an example of the basic configuration, in which the primary color signal voltages of red, green, and blue obtained from the color decoder 10 are transmitted through the video output circuit 20 to the cathode resistors R _R , R _G ,
It is applied to the cathodes K _R , K _G , K _B of the picture tube 30 through R _B , and non-linear or linear circuits 40 R, 40 G, 40 are provided between the decoder 10 and the video output circuit 20.
Insert B.

Circuit 40B inserted into the blue primary color signal voltage line
is a linear circuit, that is, as shown by straight line 5B in FIG. 5, the output/input is set to a constant value G _O regardless of the input level. The circuit 40G inserted into the green primary color signal voltage line is a non-linear circuit, and as shown by the polygonal line 5G in Figure 5, when the output/input is lower than a certain level V _O of the input level, it becomes G _O , When the level is higher than V _O , the value G _L is set to be smaller than G _O. The circuit 40R inserted into the red primary color signal voltage line is also a nonlinear circuit, and as shown by the polygonal line 5R in Figure 5, when the input level of the output/input is lower than the level V _O , it becomes G _O , and the level When the value is higher than _VO , the value G _LL is set to be even smaller than _GL .

Therefore, the red and green primary color signal voltages are at the level
When it becomes higher than V _O , the red and green primary color signal voltages are compressed, the blue primary color signal voltage is relatively expanded, the blue drive current increases, and the color temperature becomes high. By selecting the level V _O , at a level lower than the skin tone level, 9300〓+
Color temperature kept at 8MPCD, above mentioned values G _L and G _LL
By selecting , it is possible to achieve a color temperature of 14000 + 8 MPCD at the white peak level.

The video output circuit 20 is configured with an SEPP circuit or the like to have a low output impedance of several hundred ohms or less, so that the output is linear.

FIG. 4 shows a specific example of the configuration shown in FIG. 3, and a circuit 40 is a combination of the above-mentioned circuits 40R, 40G, and 40B. The red, green, and blue primary color signal voltages from _the color decoder 10 are passed through resistors _{R XR} , R _XG , _{and R DR} , _RDG ,
It is applied to the video output circuit 20 via _RDB . The bases of transistors Q _R and Q _G are resistors R _YR and
It is connected to the emitter of the transistor Q _O through a series circuit of R _YG and diodes D _R and _DG , and a voltage V _O is applied to the base of the transistor Q _O.

Therefore, the red and green primary color signal voltages are at the level
When the voltage becomes higher than V _O , the diodes D _R and D _G become conductive, and the red and green primary color signal voltages are compressed by the ratios of R _YR /R _XR + R _YR and R _YG /R _XG + R _YG , respectively. The blue primary color signal voltage is expanded.

The circuit for the blue primary color signal voltage is a linear circuit as shown by the straight line 6B in FIG. 6, and the circuit for the green and red primary color signal voltages is a non-linear circuit with output/output as shown by the polygonal lines 6G and 6R in FIG. The input may be switched to a plurality of stages to perform curve approximation when the input level is higher than the level V _O. Such characteristics can be realized by providing a plurality of circuits corresponding to the transistor Q _O in FIG. 4.

In addition, the circuit for the red primary color signal voltage is a linear circuit, and as shown by the straight line 7R in Figure 7, the output/input is a constant value G _O regardless of the input level, and the circuit for the green primary color signal voltage is a nonlinear circuit. In the circuit, as shown by line 7G in Figure 7, when the input level is lower than the level V _O , the output/input becomes G _O , and when it is higher than the level V _O , it becomes G _H , which is larger than G _O , and the blue The circuit for the primary color signal voltage is also a nonlinear circuit, as shown by line 7B in Figure 7, when the output/input is lower than the level V _O , the output/input is G _O , and when it is higher than the level V _O , it is G _H. may also be set to an even larger value _GHH .

Note that in order to increase the color temperature, it is sufficient to increase the blue drive current, so the circuit for the green primary color signal voltage may have the same characteristics as the circuit for the red primary color signal voltage.

According to this device, color temperature can be controlled to desired characteristics. Moreover, since the cathode resistance does not need to be of a small value, there is no problem in terms of countermeasures against discharge of the picture tube. Furthermore, since the cathode resistances can be made equal, there is no possibility that the frequency characteristics of red, green, and blue will not match and the pulse characteristics will deteriorate.

However, with this device, for example, if the white peak level is adjusted to the desired color temperature at the maximum video signal level, but if the video signal level in the received signal becomes low, the video signal will reach the white peak in this state. Even as the color temperature increases, the color temperature does not rise sufficiently, making it impossible to obtain a good white color.

Furthermore, if the video is only blue instead of white, and the video signal level increases, only the blue will be raised to a higher level than necessary, resulting in an extremely unnatural video.

In view of these points, the present invention is designed to eliminate the above-mentioned drawbacks with a simple configuration.
That is, the present invention includes a circuit in the front stage of the video output circuit in which the output/input of the blue primary color signal voltage is larger than the output/input of the red primary color signal voltage when the input level is closer to the white level than a predetermined level. The color temperature control device of the inserted picture tube detects at least the absolute value of the color difference signal, and changes the output/input magnitude of the blue or red primary color signal of the inserted circuit according to this detection level. This is what I did. still,
The absolute value of the color difference signal referred to here is, for example, √(-) ² +(-) ² in the case of biaxial compound tone, and this value is ultimately the same as the absolute value of the carrier color signal.

Further, this value also corresponds to the distance from the white peak (point a) on the chromaticity diagram (FIG. 8) to be described later, that is, the size of the color difference vector. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 8 shows a chromaticity diagram. If the white peak shown at point a in the figure is moved, for example, in the cyan direction shown at point b, the white color becomes beautiful as described above. However, in the above example, such movement is not performed when the video signal level is low for gray, and even when the level of only one or two of the three primary color signals is high and outside the white area indicated by the broken line c. When the video signal level was high, the above-mentioned movement occurred and the color changed.

Therefore, if it is determined that the video signal is inside the above-mentioned broken line c and the movement is performed at this time, good color temperature control can always be performed.

FIG. 9 shows an example of a circuit for this purpose. The figure shows an example in which the circuit is applied to a circuit that obtains characteristics similar to those shown in FIG.

In the figure, a color decoder 10 is supplied with a pigment signal C-Y and a luminance signal Y, and is supplied with three primary color signals.
RGB is demodulated. These signals RGB are supplied to the video output circuit 20, and the edge and blue primary color signals GB are added to the original signals by adder circuits 42G and 42B through amplifiers 41G and 41B, respectively, to increase the level of these signals. It will be done.

Further, the color difference signal C-Y is supplied to the absolute value calculation circuit 51 to form a signal |C-Y|, and this signal and the low-frequency signal Y _L of the luminance signal supplied to the low-pass filter 52 are calculated. The signal is supplied to the circuit 53 to form a signal |Y _L /C−Y|. The gains of amplifiers 41G and 41B are controlled according to the level of this signal.

In this circuit, the absolute value of the color difference signal CY corresponds to the distance from the white point a on the chromaticity diagram,
The value increases as the distance increases. However, if this is done alone, the absolute value will be small when the level of the luminance signal Y is low, so normalization is performed using the low frequency component Y _L of the luminance signal, and gain control is performed using this normalized signal.

Then, the arithmetic circuit 53 outputs a signal that is approximately equal to 0 outside the area c and approximately 1 inside the area c, and this signal is transmitted to the amplifiers 41G and 4.
1B, the blue and green primary color signals are intensified inside region c, and the color temperature of white is increased.

In this way, the color temperature of white is raised, but according to the present invention, the area close to white on the chromaticity diagram is determined and control is performed when the signal is inside the area, so the video signal level is increased. Good control is achieved even when the level is low, and there is no unnatural enhancement when the level of only one or two colors is high.

Note that as the absolute value calculation circuit 51, a method such as detecting the color difference signal with a diode or the like and then smoothing it with a low-pass filter or the like can be considered.

Further, the gain control of the primary color signal may be performed by changing the bias of a nonlinear element such as a diode, or by switching.

Further, the signal for controlling the gain of the amplifiers 41G and 41B may be |Y _L |-|C-Y| or |
CY| may be used directly.

Note that the present invention can be similarly applied to circuits having the characteristics shown in FIGS. 5 and 6 described above.

[Brief explanation of drawings]

Figure 1 is a connection diagram of an example of a conventional device, Figure 2 is an explanatory diagram, Figure 3 is a system diagram of an example of the basic configuration of the previously proposed device, and Figure 4 is a specific example thereof. 5 to 7 are diagrams showing characteristics in various cases, FIG. 8 is a diagram for explaining the present invention, and FIG. 9 is a system diagram of an example. 20 is a video output circuit, 30 is a picture tube, 51,5
2 is an arithmetic circuit.

Claims (1)

[Claims] 1. A nonlinear circuit is provided in any two of the red, green, and blue signal lines that connect the video output circuit and the color decoder, and the nonlinear circuit is configured to:
A color temperature control device for a picture tube, wherein the blue signal level supplied to the video output circuit is made higher than the red and green signal levels when the input level is closer to the white level than a predetermined level, It has means for detecting the absolute value of the color difference signal input to the color decoder, and forms a control signal based on the signal detected by the means, and when the detected signal exceeds a predetermined value. A color temperature control device for a picture tube, wherein: the control signal changes an input/output ratio of the nonlinear circuit.