JPH06217239A - Liquid crytal projector with gamma correcting function - Google Patents

Abstract

PURPOSE:To provide the liquid crystal projector with the gamma correcting function on which an operator can correct an image over an actual look at the image by measuring applied voltage transmissivity characteristics while an LCD panel is mounted and making gamma corrections according to correction data based upon the measurement result. CONSTITUTION:This projector is equipped with a luminance meter 34 which measures the luminance of the image, an adjustment controller 17 which generates the correction data for the gamma corrections according to the applied voltage to transmissivity characteristrics of the liquid crystal display panel 36 or by manual operation, a memory 21 for correction which is stored with the correction data, a nonvolatile memory 39 for storage, and 1st, 2nd, and 3rd selectors 16, 28, and 30 which display a video signal input 13 on the liquid crystal display panel 36 in 1st mode, write the correction data in the correction memory 21 in 2nd mode, and transfer data between the correction memory 21 and storage memory 39 with each other in 3rd mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector, and more particularly to a liquid crystal projector having a gamma correction function.

[0002]

2. Description of the Related Art A liquid crystal projector is a device for projecting an image displayed on a liquid crystal display panel onto a screen through a lens by a projection lamp and displaying the image without using an expensive, large and heavy large CRT. Used for the purpose of responding to the needs of consumers in recent years who want to listen to a television screen on a large screen relatively inexpensively, or for the purpose of projecting a video tape in a relatively small movie theater called a mini theater. To be done.

By the way, the characteristic of the transmittance of the projected light with respect to the applied voltage of the liquid crystal display panel (hereinafter referred to as LCD panel) used in the liquid crystal projector (hereinafter referred to as applied voltage-transmittance characteristic) has a linear characteristic range. Because of the narrowness, when a video signal is actually input and an image is projected, a strong nonlinear characteristic may be exhibited on the black side or the white side. For this reason, there is a possibility that an image lacking contrast may be projected because the gradation of black or white is not sufficiently expressed by the liquid crystal projector.

In order to avoid insufficient gradation that occurs when displaying a video signal on such an LCD panel and obtain good gradation and contrast, a non-linear process generally called gamma correction is performed. Done. If the characteristic of this gamma correction is G (v), the characteristic function of applied voltage-transmittance is D (v), and the voltage of the input video signal is v, the transfer characteristic is expressed by the following equation.

D (v) * G (v) = k * v where k is a constant

In reality, the ideal correction represented by the above equation is difficult, and it is often approximated by a broken line circuit of several points. FIG. 2 is a block diagram showing an example of such a gamma correction circuit according to a conventional analog method. In FIG. 2, reference numeral 1 is a video signal input, 2 is a preamplifier, 3 to 5 are first to third video amplifiers, 6 is a combining circuit, and 7 is an LCD panel.

The video signal input 1 is input to the preamplifier 2 and amplified to an appropriate level, and then the video amplifier 3
Input to ~ 5. These video amplifiers 3 to 5 have different operation regions, and proper gains corresponding to the respective operation regions are set. Then, the video signals amplified by the video amplifiers 3 to 5 are reproduced by the synthesizing circuit 6 as a signal having a polygonal line characteristic, amplified to an appropriate level, and input to the LCD panel 7.

However, in the case of such a conventional analog circuit, for example, in the example shown in FIG. 2, each of the video amplifiers 3 to 5 has a region on the black side of the video signal,
Although it is set to handle the white area and its intermediate area, it is necessary to prepare a larger number of video amplifiers in order to obtain more detailed characteristics, so the circuit scale expands and there are variations in parts. It also requires adjustment of the gain, which requires a great deal of effort.

Under these circumstances, digital gamma correction circuits as shown in the block diagram of FIG. 3 are also used today. In FIG. 3, reference numeral 8
Is a video signal input, 9 is an A / D converter, 10 is a gamma ROM in which conversion data based on the transfer characteristics shown in the above equation is stored, 11 is a D / A converter, 12 Shows LCD panels respectively.

The video signal input 8 is converted by the A / D converter 9 into
It is / D converted and once converted to a digital value, and output as the address of the gamma ROM 10. The gamma ROM 10 uses the input digital value as an address, and outputs the data stored in advance corresponding to this address. Therefore, the output from the gamma ROM 10 becomes a digital value converted according to a certain rule according to the conversion data based on the transfer characteristics shown in the above equation. Since the digital value output from this gamma ROM 10 is returned to an analog signal by the D / A converter 11, the video signal input 8 is eventually gamma-corrected and
Given to CD panel 12.

According to such a digital type conventional gamma correction circuit, fine characteristics can be obtained by increasing the resolution of the A / D converter and the D / A converter and the capacity of the gamma ROM 10. At the same time, no adjustment is required, so that the problem in the case of the analog method as described above is solved.

[0012]

However, in reality, the LCD
The applied voltage-transmittance characteristic of the panel depends on the birefringence of the liquid crystal or the thickness of the liquid crystal layer.
With a high-definition LCD panel with over 1 million pixels,
The number that can be obtained in a single step in manufacturing the LCD panel is small, so that the quality variation of individual LCD panels becomes large. Therefore, there is a possibility that the circuit in which the conversion data is fixed as shown in FIG. 3 cannot be used.

The applied voltage-transmittance characteristic also depends on the wavelength of the light source for projection, and is composed of a lamp light source or a reflecting plate corresponding to a high definition, that is, a large LCD panel, and an LCD panel of three primary colors. In a liquid crystal projector, the dichroic mirror that separates and combines colors also has manufacturing variations due to its size.
It seems better to perform gamma correction according to individual characteristics with the D panel mounted.

The present invention has been made in view of the above circumstances, in which an applied voltage-transmittance characteristic is measured in a state where an LCD panel is mounted, and gamma correction is performed according to correction data based on the result. Therefore, it is another object of the present invention to provide a liquid crystal projector having a gamma correction function that allows an operator to actually perform correction while viewing an image.

[0015]

According to the present invention, a liquid crystal display panel for displaying a video signal as an image, a projection means for projecting an image displayed on the liquid crystal display panel on a screen, and a liquid crystal display panel for displaying the image should be displayed. A / D conversion means for converting a video signal into digital data, and the digital data obtained by this A / D conversion means are input as an address signal, and the gamma correction data stored in advance according to the applied voltage-transmittance characteristic is stored. Correction data storage means for outputting data corresponding to the input address signal in the above, and D / A conversion means for converting the data output from the correction data storage means into an analog signal and outputting the analog signal to the liquid crystal display panel. In a liquid crystal projector with a built-in gamma correction function, a DC signal that changes at a predetermined voltage interval is applied to the liquid crystal display panel as a video signal. Signal generating means, brightness measuring means for measuring the brightness of the image displayed on the liquid crystal display panel or the image projected on the screen, and brightness measuring means when a DC signal is applied to the liquid crystal display panel from the DC signal generating means According to the measurement result of the
A characteristic detecting means for detecting the transmittance characteristic, a correction data generating means for generating correction data for gamma correction according to the applied voltage-transmittance characteristic detected by the characteristic detecting means or by manual operation, and if necessary. And a non-volatile storage means for storing the storage content transferred from the correction data storage means, and for transferring the storage content of itself to the correction data storage means for storage, and a first display for displaying a video signal on the liquid crystal display panel. In the mode, the output of the A / D conversion means is input to the correction data storage means as an address signal, and in the second mode in which the gamma correction is adjusted, the output of the correction data generation means is input to the correction data storage means as the address signal. In the third mode in which the correction data is transferred between the correction data storage means and the non-volatile storage means, the correction data storage means is not connected to the correction data storage means. The first selector for connecting the volatile storage means and the data output from the correction data storage means in the first mode are output to the D / A conversion means, and the second selector
In the mode, the correction data generated by the correction data generating means is input to the correction data storage means, and in the third mode, the second selector connecting the correction data storage means and the non-volatile storage means, and the first selector. DC in mode
And a third selector for inputting the signal output from the signal generating means to the liquid crystal display panel and, in the second mode, inputting the DC signal output from the DC signal generating means to the liquid crystal display panel. Characterize.

[0016]

In the liquid crystal projector having the gamma correction function of the present invention, in the second mode, the gamma correction data automatically obtained according to the measurement result by the luminance measuring means, or the correction set by the operator by manual adjustment if necessary. The data is written in the correction data storage means, and thereafter, in the first mode, the input video signal is displayed on the liquid crystal display panel as in a normal liquid crystal projector. At that time, the correction data storage is performed in the second mode. Gamma correction is performed according to the correction data written in the means. Also, the third
In this mode, the data stored in the correction data storage means is transferred to and stored in the non-volatile storage means, and conversely, the correction data stored in the non-volatile storage means is transferred to and written in the correction data storage means. .

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments thereof.

FIG. 1 is a block diagram showing the configuration of a liquid crystal projector having a gamma correction function according to the present invention. Although a liquid crystal projector which is normally composed of an LCD panel of three primary colors is provided with the same circuit for each of the three primary colors, FIG. 1 shows only one circuit out of a total of three circuits.

Further, in FIG. 1, the area surrounded by the one-dot chain line is a basic circuit as a liquid crystal projector, and the adjustment control device 17 and the luminance meter 34 are added thereto. Furthermore, in FIG. 1, the solid line shows a control signal or an analog video signal, and the double line shows digital data.

In FIG. 1, reference numeral 13 indicates a video signal input, which is input to a preamplifier 14 and amplified to an appropriate level. The output of the preamplifier 14 is input to the A / D converter 15 and converted into a digital value, and is input as the address signal 22 to the correction memory 21 via the first selector 16. The output of the correction memory 21 is the second data signal 23.
It is input to the D / A converter 29 via the selector 28 and converted into an analog signal. The analog signal output from the D / A converter 29 is given to the buffer 32 via the third selector 30, and further input to the LCD panel 36 to be displayed as an image. LC
The image displayed on the D panel 36 is projected by the light source 35, enlarged by the projection lens 37, and projected on the screen 38.

The first selector 16 selects not only the A / D converter 15 described above but also the output of the adjustment controller 17 or a memory control circuit 26 described later to correct the correction memory 21.
Address signal 22. Also, the second selector
28 not only outputs the digital signal output from the correction memory 21 described above to the D / A converter 29 as the data signal 23, but also outputs the digital data output from the adjustment control device 17 or the memory control circuit 26 to the data signal 23. Is selected as one of the operations to be input to the correction memory 21.

Further, the third selector 30 is the above-mentioned D / A converter.
Either the analog video signal from 29 or the DC level voltage signal 31 output from the adjustment control device 17 is selected and output to the buffer 32. Each of these selectors 16, 28 and
Which operation the 30 selects is controlled by the mode switching signal 20 output from the system controller 19 and given to each.

The system controller 19 controls each of the selectors 16, 28 and 30 as described above, and the control is performed according to the system control signal 18 given from the adjustment controller 17. The adjustment controller 17 is composed of, for example, a personal computer or the like, and is connected with a luminance meter 34.
The luminance meter 34 measures the luminance of the image on the screen 38 and inputs the measurement data 33 to the adjustment control device 17.

The system control signal 18 is sent from the adjustment control device 17 to the system controller 19 and the memory control circuit 26.
The first memory control signal 25 is output to the correction memory 21, the store signal 24 is output to the memory control circuit 26, the DC level voltage signal 31 is output to the third selector 30, and the first selector 16 and the second selector 28 are output. Digital data as described below is output.

The correction memory 21 has a first memory control signal 25 supplied from the adjustment controller 17 or the memory control circuit 26.
Accordingly, according to the address signal 22 input from the adjustment control device 17 or the memory control circuit 26 via the first selector 16, the data signal 23 input from the adjustment control device 17 or the memory control circuit 26 via the second selector 28. Is stored or the stored converted data is output as the data signal 23 according to the address signal 22 input from the A / D converter 15 via the first selector 16. Further, the memory control circuit 26 can exchange data with the non-volatile storage memory 39, and the second memory control signal 27 is sent from the memory control circuit 26 to the storage memory 39.
Data can be written in the storage memory 39, and conversely, the data stored in the storage memory 39 can be read.

The operation of the liquid crystal projector having the gamma correction function of the present invention as described above is as follows. First, the characteristics of the LCD panel 36 are measured. Specifically, the DC level voltage signal 31 from the adjustment control device 17 is sent to the third selector 30.
Is output to the system controller 19, and a system control signal 18 is output to the system controller 19 to instruct the mode switching signal 20 to be changed. As a result, the third selector 30 selects the DC level voltage signal 31 according to the mode switching signal 20 provided from the system controller 19 and outputs it as a video signal to the LCD panel 36 via the buffer 32.

Then, the adjustment control device 17 changes the voltage of the DC level voltage signal 31 in a predetermined procedure while measuring the brightness of the screen projected on the screen 38 at each voltage with a luminance meter.
34 is measured, and the resulting measurement data 33 is received. Further, the adjustment control device 17 multiplies the received measurement data 33 by the gamma coefficient peculiar to the LCD panel 36 to obtain the applied voltage-transmittance characteristic of the LCD panel 36. The third selector 30 outputs the output from the D / A converter 29, which will be described later, as a video signal to the LCD panel 36 via the buffer 32, except for the characteristics measurement of the LCD panel 36, according to the mode switching signal 20 described above. To work.

The actual adjustment is performed as follows.
The adjustment control device 17 creates correction data of the output data for the input data such that the video signal is gamma-corrected corresponding to the measurement data 33 obtained from the luminance meter 34, and outputs the input data to the first selector 16 to the correction data. Is output to the second selector 28. As the correction data, for example, the value obtained by A / D converting the video signal input 13 is n, and if correction is to be performed so as to be converted to m, the value n is set to the address n of the correction memory 21. It suffices if the data of is written.

During the adjustment work, the first selector
16 and the second selector 28 are both system controllers
A mode switching signal 20 given from 19 controls to connect the correction memory 21 and the adjustment control device 17.
Then, the first selector 16 inputs the signal of the input data output from the adjustment control device 17 into the correction memory 21 as the address signal 22, and the second selector 28 outputs the signal of the correction data output from the adjustment control device 17. The data signal 23 is input to the correction memory 21. The address signal 22 and the data signal 23 are written in the correction memory 21 according to the first memory control signal 25 output from the adjustment control device 17 to the correction memory 21.

When the writing of the correction data corresponding to each address in the correction memory 21 is completed in this way, the adjustment control device 17 outputs the system control signal 18 to change the mode switching signal 20 to the system controller 19. The second selector 28 outputs the data signal output from the correction memory 21 so that the first selector 16 inputs the digital value output from the A / D converter 15 into the correction memory 21 as the address signal 22. Control 23 to be input to D / A converter 29.

The video signal input 13 is amplified to a proper level by the preamplifier 14 and then converted into a digital value by the A / D converter 15 and is then converted into an address signal via the first selector 16.
It is input to the correction memory 21 as 22. With such an operation, the video signal input 13 is converted according to the correction data written in the correction memory 21 and then converted into an analog signal by the D / A converter 29, and input to the LCD panel 36 via the buffer 32. To represent the image. And this LCD panel
The image displayed on 36 is enlarged by the projection light from the light source 35 via the projection lens 37 and projected on the screen 38.

Here, for example, when the operator thinks that the correction state needs to be corrected by looking at the image projected on the screen 38 or the image of the LCD panel 36 observed by a waveform measuring instrument such as an oscilloscope, the adjustment is performed. After the controller 17 is operated to correct the correction data, the correction data may be written in the correction memory 21 in the same procedure as described above. Then, if the above-mentioned procedure is repeated until it seems that no correction is necessary, accurate gamma correction will be performed.

When the data adjustment work is completed, the adjustment control device 17 outputs the system control signal 18 indicating the completion of the adjustment, and the system controller 19 receives the mode switching signal 20.
Is instructed to change. As a result, the first selector 16 uses the memory control circuit 26 as the address signal 22 of the correction memory 21.
So that the address signal output from
The selector 28 is a data signal output from the correction memory 21.
23 operates as input to the memory control circuit 26. Further, the store signal 24 is output from the adjustment control device 17 to the memory control circuit 26. The memory control circuit 26 is supplied with the store signal 24 to supply the address signal to the correction memory 21 to read the correction data and to store the address signal and the second memory control signal 27 in the storage memory 39.
To write the correction data to the storage memory 39. As a result, the final correction data stored in the correction memory 21 is transferred to and stored in the storage memory 39.

The storage memory 39 uses a non-volatile memory, and the correction data is retained in the storage memory 39 even when the power of the entire liquid crystal projector is cut off. When the power of the liquid crystal projector is turned on again, the system controller 19 first sends the mode switching signal.
The second selector 28 outputs 20 so that the first selector 16 receives the address signal from the memory control circuit 26 as the address signal 22 of the correction memory 21.
The data signal 23 is operated so that the data signal from the memory control circuit 26 is input. Then, the memory control circuit 26 outputs the address signal to the correction memory 21 via the first selector 16 and also to the storage memory 39,
The first memory control signal 25 is applied to the correction memory 21 and the second memory control signal 27 is applied to the storage memory 39. As a result, the correction data stored in the storage memory 39 is read from the storage memory 39 according to the address and the second
It is transferred to the correction memory 21 via the selector 28 and written in the correction memory 21 according to the address.

When this transfer operation is completed, the memory control circuit 26 gives a system control signal 18 indicating the end of transfer to the system controller 19. As a result, the system controller 19 outputs the mode switching signal 20, so that the first selector 16 receives the address signal from the A / D converter 15 as the address signal 22 of the correction memory 21. 28 is a data signal 23 output from the correction memory 21
Output to the D / A converter 29. As a result, the video signal input 13 is converted and output according to the correction data stored in the correction memory 21, converted into an analog video signal by the D / A converter 29, and input to the LCD panel 36. This is received by the light emitted from the light source 35, magnified by the projection lens 37, and a correctly gamma-corrected image is projected on the screen 38.

After that, the above operation is repeated each time the liquid crystal projector is powered on.

In the above embodiment, the nonvolatile storage memory 39 in the liquid crystal projector is used as a means for storing the final correction data after the data adjustment is completed. After the adjustment work is completed, the correction data is stored in the external memory, the correction data is transferred to the writing device and written to the non-volatile memory, and the non-volatile memory is replaced with the storage memory 39 and mounted on the device. However, in this case the storage memory
39 and the memory control circuit 26 can be omitted.

[0038]

As described in detail above, according to the present invention,
Compared to the analog method, finer corrections are possible, and even if there are variations in the LCD panel due to manufacturing, it is possible to deal with it.In addition, it is possible to improve the effects of variations in optical components such as dichroic mirrors in the mounted state. Not only the correction data can be created according to the characteristics of, but also the correction can be made while actually confirming the correction state on the screen, and more accurate gamma correction can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a liquid crystal projector having a gamma correction function according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional analog method of a gamma correction circuit.

FIG. 3 is a block diagram showing an example of a conventional digital method of a gamma correction circuit.

[Explanation of symbols]

 13 Video signal input 15 A / D converter 16 First selector 17 Adjustment controller 19 System controller 21 Correction memory 22 Address signal 23 Data signal 28 Second selector 29 D / A converter 30 Third selector 34 Luminance meter 36 LCD Panel 38 screen

Claims (1)

[Claims] 1. A liquid crystal display panel for displaying a video signal as an image, projection means for projecting an image displayed on the liquid crystal display panel onto a screen, and a video signal to be displayed on the liquid crystal display panel converted to digital data. A / D conversion means for inputting the digital data obtained by the A / D conversion means as an address signal, and the input address signal of the gamma correction data stored in advance according to the applied voltage-transmittance characteristic. And a D / A conversion unit for converting the data output from the correction data storage unit into an analog signal and outputting the analog signal to the liquid crystal display panel. In a liquid crystal projector having, a DC signal generating means for applying a DC signal changing at a predetermined voltage interval to the liquid crystal display panel as a video signal, Luminance measuring means for measuring the luminance of the image displayed on the liquid crystal display panel or the image projected on the screen, and the luminance measurement when the DC signal is applied to the liquid crystal display panel from the DC signal generating means. Characteristic detection means for detecting the applied voltage-transmittance characteristic of the liquid crystal display panel according to the measurement result of the means, and for the gamma correction according to the applied voltage-transmittance characteristic detected by the characteristic detecting means or by manual operation. A correction data generating means for generating correction data; and a non-volatile memory for storing the storage content transferred from the correction data storage means, if necessary, and transferring the storage content of itself to the correction data storage means for storage. In the first mode of displaying the memory means and the video signal on the liquid crystal display panel, the output of the A / D conversion means is used as an address signal. In the second mode of adjusting the gamma correction, the output of the correction data generating means is input as an address signal to the correction data storing means, and the correction data storing means and the nonvolatile memory are stored. A first selector that connects the correction data storage unit and the non-volatile storage unit in a third mode in which correction data is transferred to and from the storage unit, and the correction data storage unit in the first mode. The data output from the means is output to the D / A conversion means, the correction data generated by the correction data generation means is input to the correction data storage means in the second mode, and the correction data storage means is input in the third mode. Is a second selector that connects the correction data storage means and the non-volatile storage means, and in the first mode, the DC signal generation A third selector for inputting the signal output from the stage to the liquid crystal display panel and inputting the DC signal output from the DC signal generating means to the liquid crystal display panel in the second mode. A liquid crystal projector having a gamma correction function.