JPH03151786A - Projection picture display device - Google Patents

Abstract

PURPOSE:To reduce color unevenness of a projection type display device by modulating a voltage of a 1st grid or a 2nd grid in response to a luminance level. CONSTITUTION:A correction wave generating circuit 12 generates a correction waveform at a full white level with a high luminance. An output of the correction wave generating circuit 12 and a primary color video signal 13 are multiplied at a multiplier circuit 14. The output of the multiplier circuit 14 is fed to a 1st grid G1. For example, an output of the correction wave generating circuit 12 is A and a waveform of the primary color video signal 13 is B. In this case, the multiplier circuit 14 multiplies A by B. Then an output of the multiplier circuit 14 is C. When a level of a video signal is large, the signal C is corrected but when the level of the video signal is small, the signal C is not almost corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to means for correcting color unevenness in an image on a screen in a projection image display device.

[Conventional technology]

In order to make the image brighter, projection type image display equipment has conventionally used cathode ray tube images in the five primary colors of red, green, and blue, as described in Japanese Patent Application Laid-Open No. 61-95689.
The structure is such that the images are magnified using a lens and then composited on a screen. This configuration itself is one of the causes of so-called color unevenness in the image on the screen (the image appears weakly red or blue depending on its position on the screen).

[Problem to be solved by the invention]

In the above conventional technology, the 5yA color plows/tubes of red, green, and blue are arranged side by side in the left and right direction of the screen.

Therefore, the images of each color have different projection angles with respect to the screen, and also have different brightness distributions on the screen. The result is an image with a weak red or blue tinge, depending on its position on the screen. There has been a problem in that such so-called color unevenness occurs.

This color unevenness will be specifically explained below.

FIG. 5 is a horizontal development view of the conventional projection optical system, in which IR, 1G, and IB are cathode ray tubes for each of the primary colors of red, green, and blue, and 2R, 2G, and 2B are lenses.

6 is a screen.

Figure 6 shows the horizontal brightness distribution at the center of the screen, where the horizontal axis is the horizontal coordinate and the vertical axis is the relative brightness of red, green, and blue, 6R, 6G, 6, with the brightness at the center of the screen being 1.
It shows B.

A cathode ray tube with the three primary colors of red, green, and blue is shown in Figure 5.
They are arranged side by side on the left and right sides of the screen. The axis of the green cathode ray tube 1G is perpendicular to the center of the screen. Therefore, the brightness distribution is symmetrical as shown by the solid line 6G in FIG. In contrast, the red cathode ray tube 1R is tilted toward the left of the screen. Therefore, the brightness distribution is the 6th
As shown in the figure, the chain +w6R is asymmetrical. As a result, the relative brightness of red is higher than green on the left side of the screen.

On the right, the relative brightness of red is lower than that of green. The difference in relative brightness between red and green increases as the distance from the center of the screen increases. Also, regarding blue, it is the opposite of red.

From the above, the image becomes reddish on the left side of the screen (particularly on the left edge), and the image becomes realistic on the right side of the screen (especially on the right edge).

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection image display device that is equipped with means for equalizing the relative brightness distributions of red, green, and blue to reduce color unevenness on the screen.

[Means to solve the problem]

In order to achieve the above object, the present invention is based on a red.

The first grid of Fraun tubes for each color of green and blue, or
The voltage of the second grid is modulated according to the brightness level.

[Effect]

When a white image is displayed on the entire screen, red,
Make the relative brightness distributions of green and blue equal.

Therefore, the voltage of the first grid or the second grid is modulated by 8 for each color. FIG. 7 shows the relationship between the luminance and the potential difference between the first grid and the grid. The horizontal axis is the potential difference obtained by subtracting the cathode potential from the first grid potential. As the video signal becomes larger, the potential difference between the first lid and the cathode becomes larger.

FIG. 8 shows the relationship between luminance, second grid voltage, and primary color signals.

As the video signal increases, the brightness of the cathode ray tube increases.

Hereinafter, "1st grid or g2 grid" will be referred to as "1st (
2) "grid". As the voltage on the first (second) grid increases, the brightness of the cathode ray tube increases. Therefore, where the relative brightness of red and blue is lower than that of green,
Increase the voltage of the first (2) grid. Where the relative brightness is high, the voltage of the first (2) grid is lowered. the result,
The relative brightness distributions of red, green, and blue become equal.

By the way, when the viewing pressure of the first (second) grid is changed, the cutoff of the fluoroun tube (the level of the video signal at which it starts to shine) changes.

This is because the first (second) grid lj:Km is used for each color, so the cutoff is different for each color.

Therefore, when the image g1100 is small, the modulation level of the first (2) grid voltage is reduced, and the cutoff 1 of each color is
Reduce the impact on pressure.

Furthermore, when the screen is dark, the color unevenness is not noticeable, and when the screen is bright, the color unevenness is noticeable. Therefore, when the screen is dark,
(2) Reduce the modulation level of the grid voltage. Then, as the screen becomes brighter, the modulation level of the first (second) grid voltage is increased.

In consideration of the above points, a method is used in which the brightness modulation level is changed depending on the brightness level. Specifically, a waveform obtained by multiplying the video signal of each primary color by a brightness modulation signal is added to the first (2) grid.As a result, color unevenness can be corrected and the problem when the screen is dark is also solved.

5.

An embodiment of the present invention will be described below with reference to FIG. 1 and FIG.

In this embodiment, the solder pressure of the first grid is modulated.

FIG. 1 is a block diagram showing a cathode ray tube 11 and its brightness modulation circuit as an embodiment of the present invention. * Red, green, and blue colors have the same configuration, but one of the colors is shown. In this figure, reference numeral 12 denotes a correction waveform generation circuit, which generates a correction waveform when the screen is completely white with high brightness (a white image is displayed on the entire screen).

The output of the correction waveform generation circuit 12 and the primary color video signal 13 are multiplied by a multiplication circuit 14. The output of the multiplication circuit 14 is added to the first grid G1.

The operation will be further explained with reference to FIG. For example, the output of the correction waveform generation circuit 12 is A. The waveform of the primary color video signal 15 is B. At that time, the multiplication circuit 14 multiplies A and B.

Therefore, the output of the multiplication circuit 14 is C. Ct indicates that when the video signal is large, correction is performed, but when the video signal is small, correction is rarely performed.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 4. In this embodiment, the voltage of the second grid is modulated.

FIG. 6 shows a cathode ray tube 1 as a second embodiment of the present invention.
FIG. 2 is a block diagram showing a brightness modulation circuit thereof.

The output of the correction waveform generation circuit 12 and the primary color video signal 15 are input to the screen voltage modulation circuit 15 to generate a modulated screen voltage and applied to the second grid G2. Next, circuit example 8 of the screen voltage modulation circuit 15 @ Shown in Figure 4. This circuit uses a constant voltage Vo based on the reference voltage V.
The zero screen voltage at which ut is output is typically generated from the flyback nodal during deflection. In FIG. 4, seven rhino clock pulses are input from the input terminal IN by means not shown, and are rectified by a diode D1 and a capacitor C1 to generate a screen voltage. Resistors R2 and R3 are the output soldering pressure Vout
An error signal is generated by comparing the magnitude of 0 that divides the voltage. This one-difference signal changes the voltage drop across R1, and TR1 controls the error. As a result, Vout is the reference voltage V
The soldering pressure is constant based on . Vout is applied to the second grid as the screen voltage 60. Since the screen voltage is normally DC, the reference voltage V is DC. However, in this embodiment, the reference voltage V is modulated to create a modulated screen voltage. Modulation of the reference voltage V is performed by multiplying the output A of the correction waveform generation circuit 12 and the waveform B of the primary color video signal 13 in a multiplication circuit 20, and then using an addition circuit 21.
This is done by adding a constant DC voltage VDC.

In the above embodiments, color unevenness can be reduced by modulating either the first grid or the second grid.

In addition, in the first and second embodiments, if you want to increase the amount of light around the screen, increase the amount of light around the screen (Cheng, @
1 (2) It is possible to increase the grid voltage.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

By modulating the voltage of the first grid or the second grid according to the brightness level, color unevenness in a projection display device can be reduced.

As a result, color reproduction equivalent to that of a conventional color TV using a color frucne tube is possible.

In addition, as another method for reducing color unevenness, red,
There is a structure in which clap plates of different shapes are provided for each color of green and blue. This method of providing a clap board has the disadvantage that the screen becomes dark and color unevenness in details cannot be reduced.

In comparison, the present invention is a little more expensive and complicated, but it reduces color unevenness in details and makes the screen look bluer without darkening it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram showing the output of the multiplication circuit in FIG. 1, and FIG. 3 is a block diagram showing a second embodiment. 4 is a circuit diagram showing specific examples of the screen voltage modulation circuit shown in FIG. 5, FIG. 5 is a horizontal development view of the optical system of a projection display device, and FIG. 6 is a diagram of a conventional projection display device. Fig. 7 is a characteristic diagram showing the relationship between the luminance of the fluoroun tube and the first grid-cando potential difference, and Fig. 748 is a diagram showing the relationship between the luminance of the fluoroun tube and the voltage of the second grid. It is a video signal characteristic diagram. Explanation of symbols IR, IG, IB, 1... Braun tubes 2R, 2G, 2
B...Lens 5...Screen 6R,, 6G, 6B...Relative brightness 12...Correction waveform generation circuit 15...Primary color projection II! Signal 14.20...Multiplication circuit 15...Screen voltage modulation circuit G1...First grid G2...Second grid...
11 ・ Punishment Figure 2 Closed Figure 2 De 4 Figure 5 Closed Figure 6 Iwa Figure Porridge '6 Figure ? Deli F color L

Claims (1)

[Scope of Claims] 1. A projection type image display device that displays red, green, and blue images in color by projecting them onto a screen using corresponding projection tubes, comprising: A reducing means for controlling the brightness of the color by modulating the voltage of the grid or the second grid according to the color of the image projected from the projection tube to reduce color unevenness of the projected image on the screen surface. A projection type image display device comprising: 2. In the projection image display device according to claim 1, the reduction means applies a signal obtained by multiplying a primary color video signal and a high brightness correction waveform signal corresponding to the primary color to the first output of each projection tube. Projection type image display device, characterized in that it comprises means for modulating the voltage of the grid or the second grid.