JPS6129198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a projection type that uses a high-intensity cathode ray tube (hereinafter abbreviated as CRT) as a light source and projects an image onto a screen via a magnifying lens or Schmitt optical system. Regarding the improvement of television equipment, the light source is three CRTs that emit light of different colors, such as the three primary colors, capable of reproducing color images, and the light is projected onto the screen via a magnifying projection lens or a magnifying optical system such as a Schmidt optical system. The purpose is to make the color balance constant at each point on the screen by applying brightness modulation to the circuit system of the CRT when projecting a color image onto the screen and synthesizing and reproducing a color image.

In this type of projection color television apparatus, it is inevitable that the brightness distribution of the image on the screen will be non-uniform due to the limited aperture of the optical system, the loss of obliquely incident light, and the like.

For this reason, when the light sources for each color image are placed at different positions, such as in a so-called three-tube projection type color television system, this causes an essential defect of lack of color balance in the color images on the screen. becomes.

As a countermeasure, it is possible to make the optical system compatible with each CRT extremely bright, such as the so-called Schmitt optical system, or to arrange each CRT in a △ arrangement, thereby reducing the opening angle of the light beam and inevitably increasing the optical path length. The method of using a special screen with a long length, shape (concave surface), and material is used to reduce uneven brightness distribution of each color image and improve color balance as much as possible. This has not resulted in a practically satisfactory solution.

That is, all of these methods leave non-uniform brightness in each color image on the screen, causing color unevenness, and it is difficult to obtain high-quality images, and the equipment becomes larger, which is a bottleneck for lowering costs. Ta.

The present invention focuses on the fact that the color unevenness on the screen is due to the intervention of the optical system, and the brightness distribution on each CRT screen that is a light source is the opposite of the brightness distribution of each color image on the screen due to the optical system. As a characteristic, it attempts to equalize the color balance of color images on the screen by applying brightness modulation to the video input signal of each CRT.

The following explanation will be made regarding a magnifying optical system using a lens, but it goes without saying that the essence of the Schmitt optical system using a concave mirror or the like remains unchanged and generality is not lost.

The details of the present invention will be explained below with reference to the drawings. Figures 1 and 2 basically represent individual CRTs.
A schematic diagram of an optical projection system for considering brightness unevenness due to projection on a screen is shown divided into horizontal and vertical directions.In both drawings,
Figure number 1 is a high-brightness CRT, 2 is a magnifying lens with focal length f, 3 is a screen, 4 is the optical axis of the optical system,
5 and 6 respectively indicate light rays coming out from the edge of the CRT screen and heading toward the edge of the screen.

In order to simplify the explanation below, a case where a thin single lens is used as the lens 2 will be described first.

In each figure, the definition of each symbol is as follows.

W...Half-width length of the CRT1 screen in the horizontal direction, ξ...Angle between ray 5 and optical axis 4, mw...Half-width length of the screen in the horizontal direction, m...Magnifying lens Magnification, P...Aspect ratio of the cathode ray tube, Pw...Half width length of the cathode ray tube screen in the vertical (vertical) direction, η...Angle between ray 6 and optical axis 4, Pmw...Half width length of the screen in the vertical direction, The brightness at the image point of light obliquely incident on a thin single lens follows the well-known cosine fourth law. That is, when the brightness of the light source point is E ₀ and the brightness of the image point is E, it is given by E=E ₀ cos ⁴ θ (1). Here, θ is the angle between the light source and the optical axis. Applying this to the rays 5 and 6 in Figures 1 and 2, E ₁ = E ₁₀ cos ⁴ ξ (2) E ₂ = E ₂₀ cos ⁴ η (3) However, E ₁₀ and E ₂₀ are the rays, respectively. 5 and 6, the brightness of the light spot on the cathode ray tube surface, E ₁ and E ₂ are the brightness on the screen. However, θ in equation (1) is the angle between the actual ray and the optical axis, and ξ and η in equations (2) and (3) are the angles that the projection of the actual ray in each cross section makes with the optical axis. be. Therefore, the meanings of equation (1), (2), and (3) are different.

In reality, the light emission on a CRT screen is made up of horizontal and vertical scanning of electron beams, so to correct the brightness on the CRT screen in accordance with equation (1), (1) It is necessary to be able to resolve cos θ in the equation into directional cosines to two orthogonal planes containing the optical axis, as shown in FIG. In Figure 3, 7 is
This is a CRT screen, and the optical axis is the Z-axis, and the coordinate axes x' and y' are perpendicular to this. Said screen 7
Assume that a light ray 8 emerging from a point P above and passing through the principal point F (located on the optical axis) of the lens forms an image on a point Q on the screen. Coordinate axes x, y on screen 3
are parallel to the x' and y' axes, respectively, and point 0 is the center of the screen and the coordinate origin. Drop a perpendicular line 9 from Q to the X axis, let its foot be R, and let the straight line FR be 10. Now, as shown in the figure, the angle between the ray 8 and the optical axis 4 is α, the angle between the straight line 10 and the optical axis 4 is β, the angle between the ray 8 and the straight line 10 is γ, and the brightness of point P is
Letting the EP and Q points be EQ, as in equation (1), EQ=EPcos ⁴ α (4) However, since cosα=/ and cosβ=/cosγ=/, cosα=cosβ・cosγ (5) Therefore, EQ=EPcos ⁴ β・cos ⁴ γ (6) It can be seen that equations (6) to (4) can be decomposed into components in the x′-axis and y′-axis directions on the CRT screen. and
The light emitted from the end of the CRT screen 7 on the x' axis forms an image on the end of the screen 3 on the x axis, which is the first
Corresponds to ray 5 in the figure. The same applies to the y' axis, which corresponds to ray 6 in FIG. From the basic formula for lenses, cosξ=(m+1)/
√() ² + (+1) ^{2 2} (7) cosη=(m+1)/
It is clear that √() ² + (+1) ^{2 2} (8).

Taking all the above into account, in order to make the brightness uniform on the screen, in principle, the brightness of each point on the CRT screen (7) should be adjusted in the horizontal (horizontal) direction and the vertical (vertical) direction, respectively. The brightness is modulated in proportion to 1/cos ⁴ β and 1/cos ⁴ γ, and the brightness distribution of the light spot with respect to the scanning time T is It turns out that it is sufficient to configure it so that.

Here, I _0y and I _0x represent the brightness in the y' and x' directions, respectively, when unmodulated, and T _y and T _x represent the beam scanning times in the y' and x' directions, respectively.

4 and 5 show the raster luminance distribution in the x'-axis direction and the y'-axis direction on the CTR screen 7 subjected to such luminance modulation (correction). T in the figure
_y and T _x are horizontal and vertical scanning times, respectively, and w _y and w _x are given by the following equations.

The above explanation is about a thin single lens; actual systems often use a combination of lenses, and in this case, the aperture efficiency comes into play and the peripheral area of the screen is much darker than the above. However, correction in this case is also extremely easy.
In other words, as shown in equation (6), since the correction only needs to be made separately in the vertical and horizontal directions, first of all,
Scanning is performed on the x' axis to measure the brightness distribution on the x axis of the screen, and the reciprocal of this distribution curve is used as a correction curve. The same applies to the vertical direction.

Although it is relatively difficult to accurately obtain the above distribution curve, in the example, the brightness of the light sources 5 and 6 in FIGS. 1 and 2 was measured, and (7),
The ratio in equation (8) is set as k and k', and the correction is made by increasing the amplitude of the parabolic waveform. Even with such a simple correction, the brightness distribution on the screen is ±5%.
It was confirmed that it was uniform within the range of .

FIG. 6 shows an explanatory diagram of the optical system of the projection color television apparatus according to the present invention, with 101, 10
2 and 103 each indicate a CRT serving as a light source,
Both are on a plane parallel to the surface of the screen 107,
The center axis of the screen is on the same straight line (this is the y-axis)
It is installed so that the 104,105,10
Reference numerals 6 designate projection lenses, which all have the same characteristics; however, for convenience of explanation, it is assumed that a single thin lens is used. Therefore, each principal plane is a plane passing through the center of the lens,
Its principal point is the center 111 of the screen 107 and each
It lies on a straight line connecting the centers 108, 109, and 110 of the CRT.

Below, we will discuss the geometry of these optical systems and explain the conditions for eliminating color unevenness on the screen. FIG. 7 is a three-dimensional perspective view of the target optical system. In the same figure, 113, 114 and 115 respectively represent CRTs 101, 102 and 103 in FIG.
116, 117 and 118 indicate the principal points of magnifying lenses 104, 105 and 106, respectively.

Now, if the legs of the perpendicular line drawn from the principal point 116 to the screen 107 and the screen 113 of the CRT 101 are respectively 121 and 119, each point 119,
A straight line 123 connecting 116 and 121 becomes the optical axis of the lens 104 parallel to the Z axis.

Similarly, for CRTs 102 and 103, corresponding points 111, 109 and 122, 120 and optical axis 1
12,124 are defined. Next, set the coordinate axes on each CRT screen to x ₁ ′, x 2 ′, and x ₂ ′ in the vertical scanning direction, respectively.
x ₃ ', y' in the horizontal scanning direction, and the screen 107
Let the corresponding coordinate axes x and y be the above. Said CRT1
For 02, from equation 9, the luminance distribution after correction on the screen is: however, I ₂ is the brightness at the point 109, I _2x and I _2y are the brightness of the CRT screen 114 in the x ₂ ' and y' directions, respectively, and T
_x and T _y are scanning times of the electron beam in the x ₂ ' and y' directions, respectively.

From the above considerations, it is possible to consider brightness modulation correction for the screens of CRTs 101 and 103 separately in the x'-axis and y'-axis directions. It is clear that for the in-line arrangement in the x'-axis direction, the brightness modulation correction in the x'-axis direction is given by an equation of exactly the same form. Also, screen 11 of CRT101
Assuming that the brightness correction curve in the x ₁ ' axis direction on 3 is I _1x , the difference between I _1x and I _2x is only the geometric difference in the center point of consideration, and the center point of the screen 113 is It becomes 119. Now, the brightness of point 119 is
If I ₁ , becomes. However, w _1x = w _2x Therefore, in order to balance the three primary colors on the screen 107, the center point 111 of the screen 107 should be
The brightness on the screen 107 of light reaching
The ratio of the brightness on the screen of the light coming out from the center 109 of the CRT screen 114 and reaching the center point 111 on the screen is the ratio of the brightness on the screen of the light coming out from the center 109 of the CRT screen 114 and reaching the center point 111 on the screen from any point 125 on the CRT screen to the point 126 on the screen 107.
The brightness of the light focused on and the point 12 on the CRT screen 114 corresponding to the point 125 on the CRT screen 113.
9 and the said point 126 on the screen 107
is required to be equal to the ratio of the brightness of the light focused on the image.

However, as mentioned above, the brightness of any point is
It can be considered separately into components in the x'-axis and y'-axis directions, and the brightness curve about the _x1' -axis is given by equation (15), and each lens 104, 105 is exactly the same and is a thin single lens. As a result, if we take into account that the cosine fourth law holds true for oblique rays and that the optical system is centrally symmetric with respect to its optical axis, then for both CRTs at point 111 on screen 107, It can be seen that it is sufficient to correct the distribution curve in the y'-axis direction so that the brightnesses are equalized and the brightness is uniform on the y-axis. However, if the brightness at point 119 is _I1 , then the brightness at point 121 is _I1 . Then, if the end points of 113 on the y′ axis are respectively 130 and 131, and their luminances are respectively I ₁ ′ and I ₁ ″, then the corresponding point 13
The brightness I ₁ y′, I ₁ y″ at 2,133 is I _1y ″=I ₁ ″{b ⁴ / [b ² + (mw-mw/m+1)
² 〕 ² } (17) Now, equations (1) and (2) are conditions under which the brightness distribution due to the projection light from the CRT 101 on the screen 107 is uniform. Therefore, (16), (1
6) Both expressions must be equal to I ₁ , and the cosine fourth law holds between them, and
The CRT's scanning time in the y′ direction is all the same, and 1
19 is shifted from the center point 108, the corrected brightness distribution curve I _1y on the CRT screen 113
must be expressed in the form:

I _1y = I ₁ /cos ^4w _1y (t-T _y /2-T ₁ ) (18) And at t=0, I _1y = I ₁ ', and at t=T _y , I _1y =
I ₁ ″ than Similarly, I ₁ /b ⁴ [b ² + (m/m+1w+mw) ² ] ² = I ₁ /
cos ^4w _1y (T _y /2 ^{- T1} ) (20) From these T ₁ =mw−(mw/m+1)/2mwT _y (22) That is, by providing the brightness distribution given by equations (18), (21), and (22), a uniform distribution on the screen 107 can be achieved. can be realized. Considering that the CRT screen 115 is completely symmetrical, I _3y = I ₃ /cos ⁴ w ₃ y (t-T _y /2 + T ₁ ) (23) However, And it is sufficient. By determining the ratio of I ₁ , I ₂ , and I ₃ so as to achieve white balance, it is possible to achieve perfect color balance on the screen 107. FIG. 8 shows an example of a brightness distribution curve in the y-axis direction. In the figure, A, B, and C are screen 11 respectively.
This is the distribution on 3,114,115. In addition, T
_y is one horizontal scanning time, T ₁ is from the center of the CRT screen,
This is the scanning time up to point 119 or point 120. The above is a CRT as shown in Figure 7 (or Figure 6).
Although the case where 101, 102, and 103 are on a straight line has been considered, it goes without saying that the present invention can be applied to general cases by simply changing the constants.

Next, an example of simultaneously correcting the luminance balance and color balance will be described with reference to FIG. 9 showing a circuit block diagram of the main part of the apparatus of the present invention.

The circuit block diagram is roughly divided into a vertical correction circuit ( V ) and a horizontal correction circuit ( H ). The vertical correction circuit ( V ) includes a buffer circuit 34, a waveform conversion circuit 35 that receives the sawtooth wave output and converts it into a pseudo-parabolic waveform, and an amplifier circuit 36.
An example of the waveform conversion circuit 35 is shown in the corresponding block, and the details will be described later together with the circuit operation.

As mentioned above, the vertical correction modulation waveform is
Therefore, it is sufficient to distribute the output of the amplification circuit.

The horizontal correction circuit ( H ) has a different configuration between the circuit for the central cathode ray tube and the circuit for the cathode ray tubes on both sides. 37 is an integrating circuit that integrates the horizontal deflection switching current applied to the input terminal 50 and converts it into a sawtooth wave, and includes horizontal correction circuits for each cathode ray tube, that is, first, second, and third horizontal correction circuits.
Commonly provided for H ₁ , H ₂ and H ₃ . Each horizontal correction circuit includes first, second, and third resonant circuits 38, 39, and 40 corresponding to each other, each receiving the output of the integrating circuit 37 as an input. The second resonant circuit 39 resonates with the horizontal scanning frequency, receives the sawtooth wave as shown in FIG. 10A, and outputs a symmetrical pseudo-parabolic waveform with the valley in the center as shown in FIG. 10B. . The resonant frequency of the third resonant circuit 40 is slightly lower than the horizontal resonant frequency, so that the valley of the output pseudo-parabolic waveform is located at the point 120 on the screen of the third CRT, as shown by the solid line in FIG. selected.

The delay circuit 42 eliminates causes of new unevenness in brightness so that the peak of the output of the third resonant circuit 40 comes to the scanning end, that is, it does not appear on the screen.

The resonant frequency of the first resonant circuit 38 is selected to be slightly larger than the horizontal resonant frequency so that the valley of the output pseudo-parabolic waveform is located at a position corresponding to point 119 on the screen of the first CRT. Delay circuit 41
The purpose of is the same as that of the third horizontal correction circuit 42.

With this circuit configuration, the vertical deflection current applied to the input terminal 33 is applied to the waveform conversion circuit 35 via the buffer circuit 34. The upper half of the applied sawtooth wave flows into the reactance transformer 22 due to the conduction of the diode 21, is integrated to form the second half of the Palvola waveform, and simultaneously charges the capacitor 23. Next, during the half cycle in which the diode 21 is non-conductive, the discharge of the capacitor 23 causes a current in the first half of the parabolic waveform to be generated in the reactance transformer 22, and both the first half and the second half combine to complete a parabolic current. On the other hand, the horizontal drive current applied to the input terminal 50 is converted into a sawtooth wave in the integrating circuit 37, and then the 138th and 239th
and the 340th resonant circuit, and in the second resonant circuit 39, the parabolic waveform approximated by the 14th equation (see the dotted line in FIG. In the formula, the third
In the resonant circuit 40 and the third delay circuit 42,
Parabolic waveforms each approximated by Equation 23 are generated.

The outputs of the first and third delay circuits 41, 42 and the second resonant circuit 39 are amplified by corresponding amplification circuits 43, 44 and 45 and their levels are adjusted, and then the outputs of the first and third delay circuits 41, 42 and the second resonant circuit 39 are amplified and their levels are adjusted. 1, second and third adder circuits 46, 47 and 48, it is superimposed on the vertical correction signal which is the output of the amplification circuit 36,
applied to each corresponding CRT control grid to modulate the brightness signal. Figure 11 shows the horizontal correction circuit ( H )
This represents another embodiment of .

In this embodiment, the second horizontal correction circuit (H ₂ )
No changes will be made to the 1st and 3rd
The configurations of the horizontal correction circuits (H ₁ ) and (H ₃ ) are further simplified. Note that the same parts as in the embodiment shown in FIG. 9 are given the same reference numerals, and the description thereof will be omitted.

The first horizontal correction circuit (H ₁ ) has a configuration in which the output of a buffer circuit 51 that adjusts the output level of the integration circuit 37 and the output of the second resonance circuit 39 are superimposed in an adder circuit 52 to obtain a pseudo-parabolic waveform. , the position of the trough of the waveform is determined by the volume 53 of the buffer circuit.

The third horizontal correction circuit (H ₃ ) receives the output of the buffer circuit 54, which also includes a phase inversion circuit that inverts the output of the integration circuit and converts it into a forward downward sawtooth wave, and the output of the second resonance circuit 39. is superimposed by an adder circuit 55 to obtain a pseudo-parabolic waveform that approximates Equation 23. The position of the trough of the waveform can be freely set by changing the level of the sawtooth wave using the volume 56.

The above description has been made assuming that the projection lens is a single thin lens, but in reality, a combination of lenses is often used.

In such a case, in addition to the above-mentioned cosine-fourth law, there will be unevenness in the brightness distribution due to the aperture efficiency of the lens, but since all of these are centrally symmetrical distributions, each of the amplifying circuits 43 and 44 described above By adjusting the gain of 45 or 36, it can be corrected to the extent that it cannot be clearly seen. Furthermore, if the uneven brightness on the screen can be ignored, that is, if only the color balance needs to be maintained, the circuit configuration will be simpler. That is, in such a case, the vertical correction circuit ( V ) and the second horizontal correction circuit ( _H2 ) can be completely omitted. Then,
Only the gains of the amplifier circuits 43 and 48 are adjusted, and the first,
It is sufficient to balance the colors on the screen by the third CRTs 101 and 103.

Since the present invention has the above-described configuration, in a projection type color television device, the brightness distribution and color unevenness of the image on the screen, which are caused by the aperture limit of the optical system, the loss of obliquely incident light, etc., can be corrected by using a special screen. This projection type is capable of reproducing projected images with high image quality, excellent contrast, and no color unevenness or brightness unevenness in clear vision, since it can be corrected without using methods or increasing the light intensity more than necessary. A color television device can be realized.

[Brief explanation of the drawing]

The drawings all relate to the apparatus of the present invention, and FIG. 1 is a horizontal schematic diagram of the basic projection optical system, FIG. 2 is a vertical schematic diagram, FIG. 3 is a perspective schematic diagram, and FIG. Figures 5 and 5 are waveform explanatory diagrams, respectively.
The figure is a schematic diagram of the three-color projection optical system, Figure 7 is a schematic perspective view, Figure 8 is a waveform explanatory diagram, and Figure 9 is
Main part circuit block diagram of one embodiment, 1st
0 is a waveform explanatory diagram, and FIG. 11 is a main circuit block diagram of another embodiment. 101...1st CRT, 102...2nd CRT, 103
...Third CRT, 104...First projection lens, 105...
Second projection lens, 106...Third projection lens, ( V )
...Vertical correction circuit, ( H )...Horizontal correction circuit.

Claims (1)

[Scope of Claims] 1. A projection-type color television that projects and synthesizes the information lights of three cathode ray tubes corresponding to the three emission colors constituting a color image onto a screen using corresponding magnifying projection lenses with the same characteristics. In the camera, a line connecting the image plane of each cathode ray tube and the center of each lens on the same plane as the screen, and connecting the center of the image plane of each cathode ray tube and the principal point of the corresponding lens is on the screen. The horizontal brightness distribution curve of the screen is I ₁ y = I ₁ / cos ⁴ on one of the three cathode ray tubes on both sides. w ₁ y (t-Ty/2-T ₁ ) On the other hand, the brightness distribution curve in the horizontal direction of the screen is I ₃ y=I ₃ /cos ⁴ w ₃ y (t-Ty/2+T ₁ ) However, T ₁ = mw-(mw/m+1)/2mwTy I ₁ , I ₃ ...Brightness at the center of the image plane (screen) Ty...One horizontal scanning time m...Magnification of the magnifying lens w...Horizontal half-width length f of the screen ...a projection television apparatus configured such that color unevenness of the projected image on the screen can be ignored in clear vision by applying brightness modulation to match the focal length.