JPH0479693A - White balance correcting device - Google Patents

Abstract

PURPOSE:To maintain the tonal characteristic of luminance by driving each electron gun by means of driving signals outputted from each phosphor which produces the driving signals based on of inputted luminance signals. CONSTITUTION:Matrix circuits 5 and 6 drive a red and green projection tubes 9 and 10 by outputting red and green primary color signals after forming the signals by synthesizing (adding) luminance signals and color difference signals and control the intensities of the red light and green light emitted from the tubes 9 and 10. On the other hand, luminance signals (gamma-corrected Y signals) which are obtained by correcting the amplitude of luminance signals inputted from a terminal 1 by means of a reverse gamma correction circuit 8 and blue color difference signals (B-Y signals) are inputted to a blue (B) matrix circuit 7. The B matrix circuit 7 synthesizes the gamma-corrected Y signals and B-Y signals, drives a blue projection tube 11 with blue primary color signals, and controls the intensity of blue light emitted from the tube 11. Therefore, the tonal characteristics of luminance can be maintained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a white balance correction device that achieves white reproducibility (white balance) on the screen in a color image display device configured using a cathode ray tube or the like. It is something.

[Conventional technology]

When a black-and-white image is reproduced on a color receiver, it must be achromatic at various brightness levels, from bright to dark, and the electrode voltage and drive of the picture tube must be adjusted to produce such a screen. Adjusting the voltage is called white balance correction, and if this is not done properly, correct color reproduction will not be possible even if you try to display a color image.

Various white balance correction devices are already known for realizing such white balance, and the one described in Japanese Patent Publication No. 60-2251 will be taken as an example and explained below.

FIG. 6 is a circuit diagram showing a conventional example of such a white balance correction device.

In the figure, a brightness signal Y is applied to a terminal 101,
Transistor 10 through transistor 102 and resistors 105, 109, 113 that constitute an emitter follower.
A luminance signal is applied to the emitter terminals of 4, 108 and 112. Terminals 103, 107, 111 have (R-
Y), (G-Y), (B-Y) color difference signals are applied,
Transistors 104, 108, and 112 each generate a difference signal between a color difference signal applied to a base terminal and a luminance signal applied to an emitter terminal, amplify this signal, and send primary color signals R, G, and B to their respective collector terminals. occurs. Resistors 106, 110, and 114 are load resistances. The parts up to this point are generally called the output circuit.

The primary color signal B generated at the collector terminal of the transistor 112 is connected to the resistor 119, 121 and the Zener diode 12.
0 and is applied to the cathode electrode 124 of the blue electron gun of the color picture tube 125 to modulate the blue electron beam. Similarly, the primary color signal G generated at the collector terminal of the transistor 108 is applied to the cathode electrode 123 of the green electron gun via a circuit network composed of resistors 116, 118 and a Zener diode 117 to modulate the green electron beam.

Further, the primary color signal R generated at the collector terminal of the transistor 104 is applied to the cathode electrode 122 of the red electron gun via the resistor 115 to modulate the red electron beam. The amount of beam current flowing through the electron gun is determined by the difference between the voltage applied to the cathode electrode and the voltage applied to the first grid electrode (not shown).

Now, if we focus on the red electron gun assuming that the first grids of the red, green, and blue electron guns are kept at zero potential, when the voltage at the collector terminal of the transistor 104 decreases, the voltage at the cathode electrode 122 also decreases. However, the red electron beam will increase, but since the beam current will flow through the resistor 115,
A voltage proportional to the amount of beam current is generated across the resistor 115.

Since this voltage is generated in a direction that cancels the voltage change occurring at the collector terminal, the beam current is difficult to flow. It has the effect of performing an operation closer to linearity.The nonlinear characteristic of an electron gun is generally called gamma.That is, the resistor 115 has the effect of controlling gamma, and the larger the resistor 115, the greater the amount of negative feedback. The gamma will be smaller and more linear.

The Zener diodes 117 and 120 have a dark value voltage (Zener voltage), and are turned off when the voltage between the terminals is less than the Zener voltage, and turned on when the voltage is equal to or higher than the Zener voltage. If the beam current flowing through the green electron gun and the blue electron gun is small, the voltage generated across the resistors 116 and 119 is smaller than the Zener voltage, and the Zener diode 1
17°120 is off.

At this time, if resistor 106+resistor 115=resistor 110+resistor 116=resistor 114+resistor 119, the red, green, and blue electron guns operate with equal gamma, and white balance can be achieved.

Next, the beam current flowing through the green and blue electron guns increases,
When the voltage between the terminals of the resistors 116 and 119 exceeds the Zener voltage, the Zener diodes 117 and 120 are turned on, and the resistor inserted into the cathode circuit of the green electron gun is the resistor 11.
6 and 118 in parallel, and the resistor inserted in the cathode circuit of the blue electron gun is the parallel composite value of resistors 119 and 121. At this time, [Resistance 114+Resistance 119//Resistance 121)<(Resistance 1
If the values of the resistors 118 and 121 are set so that the following condition is satisfied: 10+resistance 116//resistance 118)<[resistance 106+resistance 115], the gamma of the blue electron gun will be the largest, and the gamma of the red electron gun will be the largest. The gamma of the green electron gun is approximately halfway between that of red and blue.

In this way, at the luminance signal level above the threshold value, the blue beam current is the largest, and the green beam current and red beam current become smaller in turn. Above the luminance signal level, an image in which the color temperature gradually increases, that is, a white balance is reproduced.

[Problem to be solved by the invention] A color image display device using a cathode ray tube, especially red, green,
In projection displays, in which images from separate small blue cathode ray tubes are enlarged and projected onto a screen and then synthesized, the images are being made to have higher brightness and resolution in order to improve the image quality.

However, to increase the brightness, it is necessary to increase the electron beam current of the cathode ray tube, and to increase the resolution, it is necessary to reduce the diameter of the electron beam spot. The power density applied to each phosphor is increasing, and as a result, the brightness saturation tendency of the phosphor is increasing.

The luminance saturation of the phosphor mentioned here means that the rate of increase in the luminance of the phosphor relative to the electron beam current is saturated at a large current. This brightness saturation of the phosphor is particularly remarkable in the blue phosphor compared to the red and green phosphors.

If the beam current is Ib and the luminance of the phosphor is P, then generally, P=Kp(Ib)γ' ・Old...
(1) Kp: There is a proportionality constant relationship, and Tp varies depending on the beam current for red, green, and blue phosphors, but each varies from 1.0° to 1.0.
It is about 0.9, 0.7 to 0.6.

By the way, when the drive voltage in an electron gun is Ed and the anode current (beam current) is Ib, it is known that there is a relationship between the two: Ib = KEdγ (where K is a constant), and this is This is what is called a gamma characteristic.

Therefore, if the value of gamma (γ) in the electron gun is, for example, about 2.5, the blue light output will have a gamma of 1.8 to 1.5 with respect to the drive voltage that drives the cathode ray tube. value. Because P (blue) = Kp(
I b) O・7~0.6=Kp(KEd")O・fu-"ocEd'・'~1. This is because S.

This blue gamma value (1.8 to 1.5) improves the balance between the three colors of red, green, and blue because the blue phosphor is saturated while the red and green phosphors are not saturated. You can see that it has to be larger than red and green in order to capture the color.

By the way, in the case of an ordinary direct-view television receiver in which the three colors red, blue, and green are projected onto a single cathode ray tube, the relationship between the voltage applied to the grid of the picture tube and the light output is, of course, linear. There is no proportional relationship, and the optical output is said to be approximately proportional to the 2.2 power of the signal voltage applied to the grid. Therefore, in order to return this to a linear proportional relationship, before applying the signal voltage (luminance signal) to the picture tube, the voltage of the output signal must be approximately 0.45 of the voltage of the input signal (2,, the reciprocal of 2). ), it can be corrected by passing it through a correction circuit that is multiplied by
In the case of video signals based on this system, the TV station multiplies the video signals to the above 0.45 power in advance and outputs them, so there is no need to provide a correction circuit like the above on each TV receiver. It has become.

For a normal direct-view TV set, this will give good picture quality, but as mentioned earlier, red, blue,
In the case of a projection type display that uses a small, independent green cathode ray tube, higher brightness is required compared to a direct-view TV receiver, so the blue color, which was not a problem in a direct-view TV receiver, is Saturation of the phosphor becomes a problem.

In other words, in video signals based on the NTSC' system, red, blue, and green signals are multiplied to the 0.45th power and output from the television station, but saturation of the blue phosphor becomes a problem. It is understood that, compared to red and green, which do not have the problem of saturation, it is not possible to obtain good, balanced image quality for blue signals unless the gamma value is set to a value sufficient to compensate for saturation. There will be.

This kind of technical situation has arisen as the brightness of screens has increased, whereas the above-mentioned conventional technology described above is capable of relaxing the gamma characteristic, but it is not possible to increase the gamma characteristic. The problem is that it can't be done. In addition, by applying the above conventional technology to the red and green drive circuits, the overall result was 1.8
It is conceivable to maintain the white balance according to the nearby gamma, but in this case, the original gradation characteristics cannot be achieved with respect to the luminance signal, that is, the brightness, resulting in a problem of deterioration of image quality.

The purpose of the present invention is to perform accurate gamma correction and reduce the gamma value even for image display devices whose gamma values are no longer appropriate as a whole due to saturation of specific phosphors due to increased brightness and resolution. An object of the present invention is to provide a white balance correction device that can maintain white balance from brightness to high brightness and maintain gradation characteristics of brightness.

[Means to solve the problem]

In order to achieve the above object, the present invention is provided with a circuit that performs gamma correction on the drive voltage of the cathode ray tube in the direction opposite to that of conventional correction means in accordance with the input luminance signal.

For example, in the case of an NTSC television receiver, for boat fishing, the video chroma signal processing circuit:
Luminance signal (Y) and color difference signal (R to Y, G-Y, B-Y)
In this method, a matrix circuit that outputs and drives a cathode ray tube adds the luminance signal and color difference signal to create a primary color signal, which drives the cathode terminal of the cathode ray tube.

Therefore, the luminance signal input to the matrix circuit that drives the cathode ray tube is corrected for backward gamma correction. That is, depending on the gamma characteristic (Tρ) of the corresponding phosphor,
When the input of the correction circuit is (e,) and the output is (eo), the characteristics are eo = (es>X...
...(2) However, if x = 2.2 /γ·γp, the purpose can be achieved.

However, γ is the gamma value of the cathode ray tube (the above-mentioned electron gun).

The circuit that performs the above-mentioned correction needs to have a large gain with respect to the input signal ei because X≧1. In order to configure this with a simple circuit, for example, in a common collector amplifier circuit, the required number of resistors are connected in parallel to the emitter resistor RE corresponding to the gain of the common collector amplifier circuit, depending on the input signal level range. By doing so, a gain corresponding to the range of the input signal level is realized, and the characteristic of the above equation (2) is approximately realized by a combination of 0 straight lines (the number determined depending on how the range of the input signal level is determined).

[Effect]

In the correction circuit, as the input signal e increases, e
When l reaches a certain voltage level Vn, a diode Dn prepared corresponding to Vn turns on,
Since the resistor Rn corresponding to Vn is connected in parallel to the emitter resistor RE, the collector current of the common emitter amplifier circuit increases, and as a result, the gain increases due to an increase in e. I can do it. Therefore, by using n elements in parallel, the on-voltage V of each diode Dn
By changing n and resistance Rn step by step,
In the near future, the characteristic of equation (2) above can be realized. Thereby, for example, red, green at low brightness.

Based on the blue emission intensity, at high brightness, a higher drive voltage than the drive voltage of the red and green projection tubes is required to reduce the reduction in emission intensity due to saturation for the blue phosphor. By applying this, the light emission intensity can be raised to the same level as that of red and green. That is, the luminance characteristics for red, green, and blue input voltages can be set to the same condition, and the white balance can always be kept constant.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 1st
The figure is a block diagram showing an example in which the present invention is implemented in a projection television device.

The configuration of this embodiment is that the luminance signal input terminal 1 is red.

Green, blue difference signal input terminals 2, 3, 4, red, green, blue matrix circuits 5, 6, 7, inverse gamma correction circuit 8, red, green, blue projection tubes 9, 10, 11, projection lens 12. 13,14
, a reflecting mirror 15, and a screen 16.

Next, the operation will be explained. Red (R) and green (G) matrix circuits 5 and 6 receive a luminance signal (hereinafter referred to as Y) from terminal 1.
The red difference signal (R- signal) is output from terminal 2.3, respectively.
Y signal) and a green signal (G-Y signal) are input. The matrix circuits 5 and 6 combine (add) the luminance signal and the color difference signal to form and output primary color signals of red and green, thereby driving the red and green projection tubes 9 and 10. , 10 to control the intensity of red and green light emitted from them.

On the other hand, the blue (B) matrix circuit 7 receives a luminance signal (T-corrected Y signal) obtained by correcting the amplitude of the luminance signal input from the terminal 1 by the inverse gamma correction circuit 8, and a blue difference signal (B-Y signal). is input. The B matrix circuit 7 synthesizes the T-corrected Y signal and the B-Y signal, and outputs the blue projection tube 1 with the blue primary color signal.
1 to control the intensity of blue light emitted from the blue projection tube 11.

The light emitted from the tube surfaces of the red, green, and blue projection tubes 9 to 11 is enlarged and projected onto the screen 16 via the reflecting mirror 15 by the red, green, and blue projection lenses 12 to 14, respectively. At the same time, red, green, and blue light are combined. Red on screen 16 in this case.

Fig. 4 shows the luminance characteristics of green and blue.

FIG. 4 is a logarithmic diagram showing an example of the characteristic of the brightness Is on the screen 16 with respect to the Y signal amplitude v7 input from the terminal 1. In the figure, the brightness characteristics of red and green are shown by lines 61 and 60, respectively. Further, the luminance characteristics of blue color when the inverse gamma correction circuit 8 is not used and when it is used are shown by a line 622 and a dotted line 63, respectively.

For the brightness characteristics of red, green, and blue, when an NTSC signal is input as the brightness signal, the slopes of the characteristic curves 60 to 62 are approximately 2.2 and all three are equal, that is, l5ocvY2°2... ... (3) is desirable in terms of white balance.

However, in reality, due to differences in the characteristics of the phosphors and electron guns used in the projection tubes 9 to 11, the brightness characteristics of blue in particular and the slope of the characteristic curve 62 may vary due to the saturation characteristics of the phosphors. This value is smaller than the characteristic curve 60.61. Therefore,
By correcting the luminance signal amplitude v7 by the inverse gamma correction circuit 8 of FIG. 1 so that the slope of the characteristic curve 62 becomes the characteristic curve 63 (the slope is the same as that of the characteristic curves 60 and 61),
The white balance can always be kept constant despite changes in brightness.

As an example, if the slope of the line 60.61 is equal to 2.2 and the slope of the line 62 is 1.6, then the relationship between the input signal (V'/in) and the output signal (Vyout) of the inverse gamma correction circuit 8 is , 1'-(Vyout) L=, (VYin)"'
If it is possible to do """ (5), it is possible.

FIG. 2 is a circuit diagram showing a specific example of the configuration of the inverse gamma correction circuit shown in FIG. 1. In the same configuration example, the voltage source 20. Resistance 22-31. Transistors 40-44. Output terminal 21
It consists of

Next, the operation will be explained with reference to FIG. Third
The figure is a characteristic diagram showing the output voltage amplitude characteristics with respect to the input of the inverse gamma correction circuit 8.

In FIG. 3, a dotted line 50 is a curve expressed by the above equation (5), and solid lines 51 to 53 indicate characteristic curves realized by the correction circuit 8. Also, points 54 and 55 correspond to solid lines 51 and 52, respectively. Solid lines 52 and 53 represent the inflection points.

In FIG. 2, a transistor (hereinafter referred to as Tr) 4
3 and a resistor (hereinafter referred to as R) 22 to create a constant current (11)
At the same time as configuring the circuit, the emitter voltage VE of Tr43
I is kept at a constant voltage.

A luminance signal (vYin) is applied to the base of Tr 40, but the polarity of the signal is in reverse phase. The change in voltage at the emitter of Tr40 is the change in current at R23 (Δ1tfi
), and the voltage change of R26 (R26(+, -Jftn
)), and is output as an output signal to the terminal 21 through an emitter follower formed by Tr44 and R31.

Therefore, the gain G1 at a small amplitude of the luminance signal input from the terminal 1 is determined by the following equation, which is shown by the solid line 51 in FIG.

When V□7 increases and the emitter voltage of Tr40 becomes lower than the emitter voltage set by Tr42, Tr42 becomes conductive, and the gain G2 at the medium amplitude of the luminance signal input from terminal 1 is determined by R23 and R25. Since it is connected in parallel, . This is shown by the solid line 52 in FIG. Point 5 in Figure 3
4 is the boundary of the voltage at which the Tr 42 becomes conductive in FIG.

Furthermore, when the amplitude of v7□4 (luminance signal input from terminal 1) increases, Tr41 also increases at any set voltage.
becomes conductive, and R24 is further added in parallel. The gain G3 when the input luminance signal has a large amplitude is thus obtained. A point 55 in FIG. 3 is the operating voltage of the Tr 41, and a solid line 53 corresponds to the gain in equation (8) above.

The circuit configuration shown in FIG. 2 uses three straight lines 51 to 53 for approximation in order to obtain the correction curve 50 shown in FIG.
This is sufficient to obtain the characteristic curve 63 shown in the figure.

FIG. 5 is a circuit diagram showing another example of the configuration of the inverse gamma correction circuit 8 in FIG. 1. The differences in configuration and operation compared to the example shown in FIG. 2 will be explained below.

Resistors R27 to R30 constitute a constant voltage source. From the voltage of this constant voltage source and the emitter of Tr40 to R35 and R
34, and R33, R32, Tr41. Tr4
The base voltage of 2 is divided and set.

Since a signal in phase with the input signal is generated at the emitter of Tr40, Tr41. The threshold voltage at which the Tr 42 switches from off to on changes relatively depending on the input signal. Therefore, in the amplitude characteristic between input and output, the gain changes gradually and gently near the refraction points 54 and 55 shown in FIG. 3, making it possible to approximate the ideal waveform 50 more closely.

In this embodiment, a method has been described in which the characteristics realized by the inverse gamma correction circuit 8 are approximated by three straight lines, but the number of approximated straight lines can be increased by adding transistors and resistors. I can do it.

In addition, it can be applied not only to the brightness characteristics of the blue projection tube, but also to red, green, and blue as necessary, and it goes without saying that it is effective and can be used to correct the brightness characteristics of all projection tubes. stomach.

Further, in this embodiment, an example of application to a signal processing method having a color difference signal and a luminance signal, which is most commonly used, is shown on the premise that the method is used in a television receiver. In display devices used in general computer terminal devices, signal processing is performed using only primary color signals, but even in such cases, the inverse gamma correction circuit shown in this example is applied to the primary color signals. By applying it, you can obtain exactly the same correction effect.

As explained above, according to this embodiment, red.

Gamma characteristics can be corrected so that the luminance of green and blue is the same, even if the luminance of blue becomes weaker than other colors due to saturation, so white always remains constant with respect to the luminance signal. Can maintain balance. In addition, in particular, as can be seen from the characteristics shown in Figure 3, at low luminance levels where the input luminance signal is at a low level, the amplification gain is relatively lowered to suppress blue coloring, so it is difficult to visually see. This has the effect of improving the contrast.

[Effects of the Invention] According to the present invention, the ratio of the red, green, and blue luminance to the luminance signal can be adjusted even when the luminance of the blue phosphor is lower than that of other color phosphors due to saturation. Since it can be kept constant, a constant white balance can always be maintained from low brightness to high brightness.

In addition, when adjusting white balance, conventionally, it was necessary to repeatedly adjust the low brightness side and the high brightness side, without displaying grayscale etc., and then balancing low, medium, and high brightness. However, due to the effect of the correction circuit of the present invention, the white balance of medium brightness can also be adjusted by adjusting only low and high brightness, making it possible to adjust the white balance of medium brightness. Another advantage is that adjustment time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the white balance correction device according to the present invention, FIG. 2 is a circuit diagram showing a specific configuration example of the inverse gamma correction circuit in FIG. 1, and FIG.
Characteristic diagram showing the relationship between input and output of the circuit shown in the figure, No. 4
The figure is a characteristic diagram showing the rate of change in brightness of the brown feel with respect to the brightness signal, Figure 5 is a circuit diagram showing another specific configuration example of the inverse gamma correction circuit in Figure 1, and Figure 6 is a conventional white balance correction device. FIG. 3 is a circuit diagram showing an example. Explanation of symbols 5 to 7...R, G, B matrix circuit, 8... Inverse gamma correction circuit, 9 to 11... R, G, B projection tube, 12
~14...Projection lens, 15...Reflector, 16...
・Screen No. 1 Agent Patent Attorney Akio Namiki No. 2 Fig. 8 Hata Genmaneyama 'Correct turn B incense m Fig. 1 F1-I^ No. j 艮中ll Llψ (Relative I direct) No. 3 Figs. 51-53 -・LZ of the present invention, 6 sleeves, special features, 1 sho 1/'Y
inp＾Power Electric E (W之・Ia) E5 Figure

Claims (1)

[Claims] 1. Red, green, and blue phosphors, and each electron gun that projects an electron beam onto each of the phosphors to cause them to emit light, each of which receives a luminance signal and generates a drive signal based on the luminance signal. and each drive circuit that controls the electron beam emitted from each electron gun by directing and driving the electron beam to each of the electron guns, wherein one or more of the drive circuits When the input signal is Ei and the output signal is Eo, a correction circuit with input/output characteristics as follows is connected to the luminance signal input side of the object, and the luminance input to the drive circuit is A white balance correction device that achieves white balance on a screen by adding correction to a signal. 2. The white balance correction device according to claim 1, wherein the correction circuit is connected only to the luminance signal input side of the drive circuit corresponding to the blue phosphor. 3. The white balance correction device according to claim 1 or 2, wherein the correction circuit has an input/output characteristic Eo=Ei.
A white balance correction device comprising an approximation correction circuit that approximately realizes a curve of ^γ using n polygonal lines. 4. The white balance correction device according to claim 3, wherein the approximation correction circuit comprises: a collector grounded plane amplification circuit for input signals comprising a first resistor (23) and a first transistor (40); When the voltage reaches a certain first level range, the second resistor (24) is connected in parallel to the first resistor (23) and the gain of the amplifier circuit is changed from the gain up to that point. A first switch element (41) that changes the gain to a first gain, and a first resistor (2) that turns on when the input signal further reaches a second level range.
3) and a second switch element (42) which connects a third resistor (25) in parallel to change the gain of the amplifier circuit from the first gain to the second gain; A white balance comprising a desired number of switch elements configured in the same manner according to the set number of ranges, and an emitter follower output circuit (44, 31) that takes out the output of the amplifier circuit as an output signal. correction device. 5. In the white balance correction device according to claim 4, in each switch element constituting the approximation correction circuit, a constant voltage source supplying a constant voltage to the base side of each switch element and the first transistor ( A voltage dividing resistor (32, 33: 34, 35) is connected between the emitter of the voltage dividing resistor (32, 33: 34, 35), and the voltage divided by the voltage dividing resistor is replaced with the constant voltage from the constant voltage source. A white balance correction device characterized in that it is supplied to the base side.