JPH04114590A - Shading correction circuit - Google Patents

Abstract

PURPOSE:To attain excellent shading correction over the entire face of a screen automatically by making a brightness level at left and right ends of the screen based on a detection signal constant. CONSTITUTION:Photodetectors 19a, 19b detect respectively a luminance level at the left and right side of a screen 4 and output a brightness detection signal to a level difference comparison section 20. The level difference comparison section 20 compares the levels of the brightness detection signals to output the result of comparison based on a brightness level difference at the left and right of the screen 4 to shading control sections 23, 24. The shading control sections 23, 24 adjust the amplitude of a correction wave from a correction wave generating section 21 so that the level difference between the brightness detection signals is zero and output the result to shading correction sections 8,10. The shading correction sections 8,10 superimpose the correction wave onto the video signal to implement shading correction. Thus, uneven brightness and color on the screen 4 are corrected.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Field of Application) The present invention relates to a shading correction device, and in particular, a shading device suitable for correcting uneven brightness and color on a screen of a rear projection type projection display device. The present invention relates to a correction device.

(Prior art) In a projection display device,
Image lights of three primary colors, R, G, and H, are projected onto a screen and combined on the screen to project a color image. Due to this, uneven brightness and color may occur depending on the relative arrangement of each projection tube with respect to the screen, the condition of the surface of the screen, etc. Therefore, conventionally, a shading correction device has been employed to correct the uneven brightness and color.

FIG. 4 is an explanatory diagram showing the configuration of a projection display device.

The projection tubes 1, 2.3 are equipped with optical lenses (not shown), and project R, G, and B image lights onto the screen 4, respectively. The projection tubes 1, 2.3 are arranged in a line on a horizontal plane substantially parallel to the surface of the screen 4, and the projection tube 2 is arranged on the central axis of the screen 4. placed on the left and right.

The orientation of each projection tube 1.2.3 is set so that the image lights are combined on the screen 4.

FIG. 5 is a graph for explaining luminance unevenness, with the horizontal axis of the screen 4 plotted on the horizontal axis and the luminance plotted on the vertical axis. The solid line shows the characteristics of the projection tube 3, and the broken line shows the characteristics of the projection tube 1.

The distance of the projection tube 1 to the right edge of the screen 4 is longer than the distance to the left edge, and the distance of the projection tube 3 to the left edge of the screen 4 is longer than the distance to the right edge. The amount of image light produced by the projection tube 1 is greater at the left end of the screen 4 than at the right end, and as shown by the broken line in FIG. Similarly, as shown by the solid line in FIG. 5, the brightness of the projection tube 3 on the screen 4 is higher at the right end of the screen 4 than at the left end. As described above, since the brightness distribution on the screen 4 due to the image light emitted from the projection tubes 1 and 3 is different, uneven brightness and color unevenness occur on the screen 4.

Therefore, conventionally, the image light from the projection tubes 1 and 3 is given the characteristics shown in the explanatory diagram of FIG. The solid line in FIG. 6 indicates the characteristics imparted to the projection tube 3, and the broken line in FIG.
It shows the characteristics imparted to

That is, for the projection tube 1, the right end of the screen 4 (
The amount of emitted light corresponding to point B in FIG. 6 is increased compared to the left end of the screen 4 (point A in FIG. 6). Also, the projection tube 3
In this case, as shown by the solid line in Fig. 6, the screen 4
The amount of emitted light corresponding to the left end of the screen 4 is increased compared to the right side of the screen 4. In this way, by modulating the amount of light emitted from the projection tubes 1 and 3 into a sawtooth waveform or a parabolic waveform, the amount of light on the screen 4 due to the difference in distance from each projection tube 1 and 3 to the screen 4 is canceled out. This is to prevent uneven brightness and color from occurring.

FIG. 7 is a block diagram showing a conventional shading correction device that performs such correction.

A video signal input via the input terminal 5 is given to a video processing section 9. The video processing unit 9 performs contrast adjustment and image quality adjustment of the video signal.

The video signal from the video processing section 9 is given to the video amplification section 12, and is also given to the video amplification sections 11 and 13 via the shading correction sections 8 and 10, respectively.

The video amplification unit 11.12.13 performs DC component reproduction and video amplification of the input video signal.
2 and 13 supply R, G, and B video signals to the projection tubes 1.2.3, respectively. Here, in order to correct uneven brightness and color, the video signals input to the left and right projection tubes 1.3 are given characteristics shown by the broken lines and solid lines in FIG. 6, respectively, by the shading correction section 8.10. It is now possible to do so.

That is, a horizontal synchronization signal and the like are input to the input terminal 6 in order to generate a correction wave for shading correction.

The correction wave generation section 7 generates a sawtooth wave or a parabolic wave from the horizontal synchronization signal etc. inputted through the input terminal 6, and supplies it to the shading correction section 810. The shading correction sections 8 and 10 superimpose a vertical sawtooth wave or a parabolic wave on the video signals supplied to the projection tubes 1 and 3 to impart the characteristics shown by the broken lines and solid lines in FIG. 6. Note that the shading correction amount is adjusted by adjusting the control volume 14 and changing the control voltage applied to the shading correction section 8.10.

By the way, when performing shading correction, the control volume 14 is adjusted while viewing the image projected on the screen 4.

Since the adjustment is done by visual inspection, the amount of correction varies depending on the adjuster, making it impossible to perform reliable shading correction. Moreover, since the screen 4 is a relatively large screen, in order to make complete adjustments over the entire screen, it is necessary to view the image from a relatively far distance from the screen 4. In addition to the above, a person was required to visually check the screen 4 and give instructions, and two people were required to make adjustments.

(Problems to be Solved by the Invention) As described above, in the conventional shading correction device described above, since the adjuster performs the adjustment by visual inspection, it is difficult to perform accurate adjustment, and the screen is large. Therefore, there was a problem in that two people were required to make complete adjustments over the entire screen.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a shading correction device that can automatically perform good shading correction over the entire screen by detecting the brightness at the left and right ends of the screen and controlling the amplitude of a correction wave.

[Structure of the Invention] (Means for Solving the Problems) A shading correction device according to the present invention corrects shading of a projection display device that projects a color image by forming image lights from a plurality of projection tubes on a screen. In a shading correction device that corrects
detection signal superimposition means for supplying to the projection tube a video signal on which a detection signal for detecting a brightness level is superimposed in place of the video signal corresponding to the overscan portion of the screen;
a light detection means that detects the brightness level of the left and right overscan portions of the screen and outputs a brightness detection signal, and compares the brightness levels of the left and right overscan portions of the screen using the brightness detection signal and outputs a comparison result. a control means for controlling the amplitude of a correction wave for correcting uneven brightness and color on the screen based on the comparison result; and a control means for superimposing the correction wave from the control means on the video signal. and correction means for applying a correction to the projection tube.

(Function) In the present invention, the detection signal is superimposed on the overscan portion of the video signal by the detection signal superimposition means. Image light based on this detection signal is projected onto the overscan portion of the screen. The light detection means detects the brightness level of this overscan portion and outputs a brightness detection signal to the comparison means. On the other hand, the correction means superimposes a correction wave for correcting uneven brightness and color on the screen on the video signal, and the control means adjusts the amplitude of the correction wave based on the comparison result of the comparison means. give to That is, the control means adjusts the amplitude of the correction wave so that the comparison result becomes 0, and the brightness level of the left and right overscan portions of the screen becomes constant. In this way, good shading correction is automatically performed over the entire screen.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing an embodiment of a shading correction device according to the present invention. Components in FIG. 1 that are the same as those in FIG. 7 are given the same reference numerals.

A video signal input via the input terminal 5 is given to a video processing section 9. The video processing section 9 performs contrast adjustment and image quality adjustment on this video signal and outputs it to the video amplification section 12, as well as the shading correction section 8,
10, respectively, to video amplification units 16 and 17.

The video amplification units 16.12.17 reproduce the DC component of the video signal and amplify the video signal, and supply the projection tubes 1, 2.3 with R, .
It is designed to output G and B video signals. Projection tube 1
．． ．． 2.3 is designed to project R, G, and B image lights onto a screen 4 and form an image on the screen 4, thereby projecting a color image.

In this embodiment, the video amplification units 16 and 17 insert a detection signal, which will be described later, in place of the video signal at the timing of a timing signal, which will be described later. The timing signal indicates the timing of the overscan portion, and the detection signal is inserted into the overscan portion of the video signal by the video amplifiers 16 and 17. That is,
Overscan portion 18a, 1 on screen 4
Image light based on a detection signal is projected from the projection tube 1.degree. 3 onto 8b.

Overscan portion 18a on screen 4.

18b is provided with photodetectors 19a and 19b, respectively, and the photodetectors 19a and 19b detect the brightness level of the image light irradiated onto the overscan portions 18a and 18b, and output a brightness detection signal. This brightness detection signal is given to the level difference comparison section 20. Level difference comparison section 2
0 is the shading correction section 8 based on the brightness detection signal.
, 10 to output a control signal for adjusting the correction amount.

On the other hand, a horizontal synchronization signal and the like are input to the input terminal 6 in order to generate a correction wave for shading correction. These horizontal synchronization signals and the like are given to the correction wave generation section 21 and also to the detection signal and timing signal generation section 22. The correction wave generation unit 21 generates and outputs a vertical sawtooth wave, a parabolic wave, and the like. The detection signal and timing signal generation unit 22 generates a detection signal to be superimposed on the video signal, and also generates a timing signal indicating the timing at which this detection signal is superimposed on the video signal, and generates the detection signal to be superimposed on the video signal.
It is designed to be output on 6th and 17th. Note that the detection signal and the timing signal are switched and outputted at arbitrary timing. Furthermore, the video signal to be subjected to shading correction is time-divisionally switched every predetermined number of frames by a timing signal that provides the timing for superimposing the detection signal on the video signal.

The shading control units 23 and 24 include the correction wave generation unit 21
A vertical sawtooth wave, a parabolic wave, or the like is given from , the amplitude of which is adjusted based on a control signal from the level difference comparison section 20, and output to the shading correction section 8.10. The shading correction section 8.10 is configured to superimpose the correction waves from the shading control sections 23 and 24 on the video signal and output the same.

FIG. 2 is a circuit diagram showing a specific configuration of the photodetectors 19a and 19b, the level difference comparison section 20, the shading control sections 23 and 24, and the shading correction sections 8 and 10. In FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted.

The photodetectors 19a and 19b are constituted by phototransistors Ql and Q2, respectively. The projected light from the left and right overscan portions 18a and 18b of the screen 4 is converted into current by phototransistors Q1 and Q2, respectively, and is further converted into a current by a resistor R1 connected between the emitters of photo transistors Q1 and Q2 and a reference potential point. , R2 into a DC potential.

In this way, the overscan portion 1 on the left and right sides of the screen 4
Brightness detection signal based on the brightness levels of 8a and 18b (
DC potential) is connected to the operational amplifier Q via resistors R3 and R4, respectively.
It is applied to the inverting input terminal and non-inverting input terminal of No. 3. A level difference comparing section 20 is constituted by the operational amplifier Q3, and a comparison result based on the level difference between the luminance detection signals from the transistors Q1 and Q2 is provided from the output terminal of the operational amplifier Q3 to the shading control sections 23 and 24.

The shading control sections 23 and 24 have a sample and hold circuit 31. The sample and hold circuit 31 includes a switch 33 that is controlled on and off by a timing signal input through a terminal 32, a capacitor C1, and a voltage follower operational amplifier Q4. When the switch 33 is turned on by the timing signal, the capacitor C1 is charged until it has the same potential as the comparison result (DC potential) from the level difference comparator 20, and the comparison result is outputted via the operational amplifier Q4. operational amplifier Q
4 has a high input impedance, and the terminal voltage of the capacitor C1 hardly decreases, so the capacitor C1 holds the comparison result until the comparison result is input by the next timing signal. The timing signal input via the input terminal 32 is synchronized with the timing at which the detection signal is superimposed on the video signal, and enables the sample and hold circuit 31 to switch the video signal on which shading correction is to be performed.

The DC potential held in the sample hold circuit 31 is 2
Transistor Q5 of the double-balanced differential amplifier.

It is input to the base of Q8. Transistor Q5.

Q6 and transistors Q7 and Q8 each form a differential pair, and the bases of transistors Q7 and Q8 each have a resistor R5.
, R6, a reference potential Vr is applied thereto. on the other hand,
A correction wave from the correction wave generation section 21 is input to the input terminal 34 . Transistor Q5.

The common emitter of Q6 is l, the collector of transistor Q9,
The common emitters of transistors Q7 and Q8 are connected to the reference potential point via the collector-emitter path of transistor Q10 and the current source 35. A correction wave is supplied to the bases of these transistors Q9 and QIO.

For example, when the comparison result (DC potential) from the level difference comparison section 20 is higher than the reference potential Vr, a current proportional to the correction wave from the input terminal 34 flows to the collector of the transistor Q8. Conversely, when the reference potential Vr is higher than the DC potential as a result of the comparison, a current proportional to the opposite phase of the correction wave flows to the collector of the transistor Q6. Therefore, an amplitude and polarity correction wave based on the comparison result appears at the common collector of transistors Q6 and Q8.

Correction waves from the shading control sections 23 and 24 are given to the shading correction sections 8 and 10.

A positive-polarity video signal is input from the video processing unit 9 to the input terminals 36 of the shading correction units 8 and 10, and a positive-polarity luminance pulse is input to the input terminal 37.

The apparatus shown in FIG. 2 is configured to control the amount of correction so that the amount of shading correction remains constant even when the APL (average brightness level) and brightness information of the video signal change. That is, the video signal input through the input terminal 36 is transmitted to the transistor Q11. The black level is clamped by a clamp circuit constituted by Q12 and the like. The transistor Q11 is turned on at the timing of the brightness pulse inputted through the input terminal 37, and the black level of the video signal from the input terminal 36 is clamped to the DC potential set by the transistor Q12, the diode D1, and the volume VR. It is. Note that the black level of the video signal is adjusted by the volume VR.

In this case, the DC potential set by the transistor Q12, the volume VR, and the diode D1, which adjusts the black level without modulation, is applied to the base of the transistor Q18 of the double-balanced differential amplifier.

The double balanced differential amplifier that modulates the video signal with a correction wave is 1
- Consisting of transistors Q13 to Q18. Transistor Q13. Q14 and transistor Q1
5. Q16 forms a differential pair, and transistors Q14 .
A correction wave is applied to the base of Q15 via a capacitor c2. Transistor Q13. The common emitter of transistor Q14 is connected to the reference potential point via the collector-emitter path of transistor Q17 and resistor R7.
A video signal is applied to the base of 17 from an input terminal 36 via a capacitor C3. Also, transistor Q15
．． The common emitter of Q16 is connected to a reference potential point via the collector-emitter path of transistor Q18 and resistor R8.

The video signal input to the base of transistor Q17 is
Transistor Q14. It is modulated by the correction wave applied to the base of Q15, and the video signal on which the correction wave is superimposed is outputted to the output terminal 38 from the common collector of transistors Q14 and Q16.

The output from the output terminal 38 is provided to video amplification sections 16 and 17.

Next, the operation of the shading correction apparatus configured as described above will be explained with reference to timing charts 1 to 1 in FIG. 3. 3(a) shows the video signal from the video processing section 9, FIG. 3(b) shows the detection signal, and FIG.
c) shows the correction wave from the correction wave generation section 21, and FIG.
d) shows how the video amplifier units 16 and 17 come out.

A video signal input via the input terminal 5 is given to a video processing section 9. The video processing section 9 performs contrast adjustment, image quality adjustment, etc., and outputs the video signal shown in FIG. 3(a) to the video amplification section 12 and the shading correction sections 8 and 1o. A video amplifying section 12 supplies a video signal to a projection tube 2 arranged on the central axis of the screen 4. The shading correction units 8.10 and shading control units 23.
A correction wave (solid line and broken line in FIG. 3(c)) is applied from 24, and this correction wave is superimposed on the video signal between AJ9 and AJ9 in FIG. 3 and output to the video amplifying section 16.17.

The video amplification sections 16 and 17 insert the detection signal shown in FIG. 3(b) in place of the video signal at the timing of the detection signal and the timing signal from the timing signal generation section 22. As a result, the video amplifying section 16 and 17 transmits the signal as shown in FIG.
Video signals shown in solid lines and broken lines in d) are applied to the projection tubes 1 and 3. In this way, the image light from the projection tube 1.3 is subjected to shading correction.

The shading-corrected image light of period A is projected within the effective screen range on the screen 4 and combined to display a color image. On the other hand, the overscan portion of the image light from the projection tube 13 is based on the detection signal and the detection signal from the timing signal generator 22.

That is, before and after the horizontal scanning period, image light of a predetermined brightness level is emitted. Photodetectors 19a, t9b detect the brightness level in overscan portions 18a, 18b on screen 4.

In the overscan portions 18a and 18b, image light based on the detection signal from the projection tube 1.3 is projected, and correction may be performed so that the brightness levels detected by the photodetectors 19 and 19b are the same. .

The photodetectors 19a and 19b detect the brightness levels on the left and right sides of the screen 4, respectively, and output brightness detection signals to the level difference comparison section 20. By comparing the levels of the brightness detection signals, the level difference comparison unit 20 transmits the comparison result based on the brightness level difference between the left and right sides of the screen 4 to the shading control unit 20.
．． Output to 24. Note that the level difference comparison section 20 performs the comparison operation at the timing of the timing signal. The shading control unit 2324 determines that the level difference of the brightness detection signals is 0.
The amplitude of the correction wave from the correction wave generation section 21 is adjusted so that the amplitude of the correction wave is outputted to the shading correction sections 8 and 10. The shading correction units 8 and 10 perform shading correction by superimposing this correction wave on the video signal. In this way, brightness unevenness and color unevenness on the screen 4 are corrected.

As described above, in this embodiment, a detection signal is inserted in place of the video signal of the period corresponding to the overscan portions 18a and 18b of the screen 4, and the video light based on this detection signal is transmitted to the left and right projection tubes 1. Photodetectors 19a are projected onto the screen 4 from .3 and placed in the overscan sections 18a and 18b, respectively.

Since the amplitude of the correction wave is adjusted and superimposed on the video signal so that the brightness level detected by 19b is the same, manual adjustment work is not required, and various shading corrections can be performed regardless of the screen size. It is possible. Furthermore, since a constant amount of shading correction is obtained regardless of the picture pattern of the video signal, a high-quality image without brightness unevenness or color unevenness can be obtained over the entire screen.

Note that the present invention is not limited to the above embodiments,
For example, a correction wave such as a horizontal parabolic wave may be superimposed on the video signal supplied to the central projection tube.Also, although horizontal shading correction was explained in the above embodiment, a vertical sawtooth wave or By superimposing a vertical parabolic wave on a video signal, it is also possible to correct shading in the vertical direction of the screen. In this case, uniform shading correction can be performed over the entire screen.

[Effects of the Invention] As explained above, according to the present invention, since the brightness level at the left and right edges of the screen is made constant based on the detection signal, good shading correction can be automatically performed over the entire screen. It has the effect that it can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a shading correction device according to the present invention, and FIG. 2 shows a photodetector 1 in FIG.
9a, 19b, level difference comparison section 2o, shading control section 23.24, and shading correction section 8, 10
FIG. 3 is a timing chart for explaining the operation of the embodiment; FIG. 4 is an explanatory diagram showing the configuration of the projection display device;
FIG. 5 is a graph for explaining luminance unevenness on a screen, FIG. 6 is an explanatory diagram for explaining shading correction, and FIG. 7 is a block diagram showing a conventional shading correction device. 1.2.3... Projection tube, 4... Screen, 8.1
0...shading correction section, 12, 16.17...
- Video amplification section, 19a, 19b... photodetector,
20... Level difference comparison section, correction wave generation section, 22... Detection signal and timing signal generation section, shading control section. Figure 3

Claims (1)

[Scope of Claims] A shading correction device that performs shading correction of a projection display device that images image light from a plurality of projection tubes on a screen to project a color image, the shading correction device corresponding to an overscan portion of the screen. a detection signal superimposing means for supplying the projection tube with a video signal on which a detection signal for detecting a brightness level is superimposed in place of the video signal; a light detection means for outputting a brightness level, a comparison means for comparing brightness levels of left and right overscan portions of the screen using the brightness detection signal and outputting a comparison result, and detecting brightness unevenness and color on the screen based on the comparison result. Shading correction characterized by comprising a control means for controlling the amplitude of a correction wave for correcting unevenness, and a correction means for superimposing the correction wave from the control means on the video signal and applying it to the projection tube. Device.