JPS61270993A - Device for improving picture quality of television - Google Patents

Abstract

PURPOSE:To remove a flare component of a screen with a small scale type and to emphasize an outline in parallel by providing in parallel an outline correcting signal forming circuit and a flare correcting signal forming circuit respectively in a horizontal and a vertical directions. CONSTITUTION:A digital signal input is initially inputted to a compensating delay device 25, and signals to which prescribed delay quantity is applied from a tap are respectively fed to signal lines l1, l2, m1, m2. The signals from the signal lines l1, l2 are respectively applied to vertical and horizontal outline correcting FIR filters 21, 22, outline-corrected and fed to a composite circuit 28a. The signals from the signal lines m1, m2 are respectively applied to vertical and horizontal flare correcting composite IIR filters 23, 24, flare-corrected and synthesized in a synthesizing circuit 28b. The respective outputs of the synthesizing circuits 28a, 28b are synthesized in a synthesizing circuit 26 through core ring circuits 27a, 27b and outputted as the corrected signals.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a color television receiver, particularly a so-called projection type receiver that obtains an image by projecting three primary color image lights onto a large screen from a projection tube. Regarding.

[Conventional technology]

Currently, CRTs with large image planes have a manufacturing limit of about 40 inches. Beyond that, a method using a projection tube is currently practical. In the case of a high-quality large screen, high quality cannot be obtained simply by making the screen larger.
As the number of scans increases, requirements regarding image quality become stricter. In particular, in the projection type, the current density of the beam of the projection tube is about 5 to 10 times that of the direct view type, so the beam becomes thicker and the resolution decreases due to the influence of the lens.
Flare caused by high-brightness projection tubes, lenses, etc. was a cause of deterioration in image quality.

Perhaps because large-screen projection receivers are still in the development stage,
The flare correction/contour correction means described above have not yet been established as completely definitive techniques. As a flare correction means that has been proposed for high-definition televisions, there is a paper in "Improvement of Image Quality of Projection Displays for High-Definition Televisions - Removal of Flare Interference by 3AW Filter", Television Society of Japan 1982 National Annual Conference 5PI-14, Safe etc. There is a method using an analog filter in which a video signal is once AM-modulated, passed through a SAW filter, and demodulated again. This method attenuates the modulated signal wave at ±IMHz near the modulated carrier frequency, thereby attenuating the low frequency component for flare correction. However, this method requires the use of a high frequency modulation carrier frequency of 100 MHz or higher,
Furthermore, even if it is possible to remove the flare component in the horizontal direction of the screen, applying it to the vertical component requires a large number of highly accurate one-line delay lines, which is difficult to implement.

The most common method for contour correction is to extract the contour components of the image and add them to the original signal, but most of the methods only emphasize the horizontal direction of the screen, and the vertical direction is emphasized using some method of line delay. There are few examples because it requires creating a

By the way, in order to prevent resolution degradation, contour correction that emphasizes contours and flare correction that suppresses flare are two methods.The former emphasizes high-frequency components including differentials, and the latter emphasizes that a screen with a lot of flare has a low MTF (resolution characteristic). Since it has a shape that is lifted in the range, it gives attenuation characteristics to the low frequency components. Therefore, although contour correction and flare correction can be performed in parallel in terms of frequency, it is difficult to achieve this by mixing digital and analog methods, or by unifying one method. There is no example in which both types of correction processing were performed.

[Problem that the invention seeks to solve]

As mentioned above, regarding large screen projection receivers,
We have not yet reached the stage where we can fully adopt the necessary flare correction and contour correction means and obtain high-quality images. Here, "completely" means that contour/flare correction can be performed for both vertical and horizontal components. In the analog method,
In particular, there are problems such as uniformity of filter characteristics and temperature-related fluctuations in delay lines, and in a large-scale system, it is difficult to adjust the timing of all devices. In principle, a digital system can sufficiently deal with the above problems and is highly flexible in terms of design. However, there are difficulties as the scale increases. The problem lies in how to implement the digital correction device.

In view of the above-mentioned circumstances, an object of the present invention is to provide an image quality improvement device that removes flare components in the horizontal and vertical directions of the screen and at the same time performs correction for emphasizing the outline of the screen, all by digital means and on a small scale. It lies in realizing it in form.

[Means for solving problems]

The image quality improvement device of the present invention is provided for each series of three primary color video signals in a projection display type television receiver, inputs each video signal, performs A/D conversion,
After contour/flare correction, it is D/A converted and output.

The contour/flare correction section includes a compensation delay circuit, a contour/flare correction signal generation circuit having an inverse gamma correction circuit in the preceding stage and a gamma correction circuit in the subsequent stage, which are provided in parallel with respect to the digital video signal input. , and a synthesis circuit for synthesizing the outputs of the compensation delay circuit and the gamma correction circuit.

The contour/flare correction signal generation circuit performs contour correction and flare correction of an image in parallel, and (a) contour correction is performed in parallel in the vertical and horizontal directions of the image, with one delay in the vertical direction. A high-pass FIR filter that uses line memory.

In the horizontal direction, one delay is performed using a high-pass FIR filter using an A/D conversion clock register. (b) Flare correction is performed in parallel in the vertical and horizontal directions of the image, and in the vertical direction, one delay is applied. It has two stages of high-pass IIR filters using line memory and inverters that invert one field's worth of information alternately in series.
In the horizontal direction, it is made up of a circuit having two stages each of a high-pass IIR filter using an A/D conversion clock register as one delay and an inverter for inverting one line of information, alternately arranged in series.

Here, the coefficient circuits in the filters, gamma correction circuit, and inverse gamma correction circuit use RAM and write data during the video blanking period, and during the video period, the input signal of the coefficient circuit is the address signal of the RAM. The data is read out and becomes an output signal.

[Effect]

In the present invention, correction is provided separately for each series of three primary color video signals, so that appropriate correction can be obtained for each signal. Since the correction is all digital processing, it is input to the contour/flare correction section after A/D conversion. Since the input video signal has been gamma-processed and has become non-linear, it is linearized through an inverse gamma correction circuit and then corrected.

In the correction signal generation circuit, a contour correction signal generation circuit and a flare correction signal generation circuit are arranged in parallel, and correction of contour and flare is performed in parallel. The contour correction and flare correction are performed in parallel in the vertical and horizontal directions. As will be explained in detail in the example, the contour correction filter is F.
An IrR filter is used as an IR filter, and an IrR filter is used as a flare correction filter, giving it the characteristics of a high-pass filter.

The output of the contour/flare correction signal generation circuit is given gamma characteristics again, and then combined with the output that has passed through the compensation delay circuit in a synthesis circuit. Next, by D/A converting the output of this synthesis circuit, it is possible to obtain a three-primary color video signal with improved image quality.

Note that coefficient circuits are required for filters, gamma correction circuits, and inverse gamma correction circuits, but by using RAM,
Data can be written to M to change the coefficient value.

〔Example〕 An embodiment of the present invention will be described with reference to the drawings.

The basic configuration of the embodiment is shown in FIG. The video signals of the three primary colors are corrected by the same and independent circuits. In terms of the R signal, it is converted into a digital video signal by the A/D converter 11a, an inverse gamma correction circuit 16a, and a correction signal generation circuit 13a.

The correction signal generated by the gamma correction circuit 17a is combined with the signal obtained by delaying the digital video signal by the compensation delay circuit 12a, by the combination circuit 14a. The compensation delay is combined with the delay caused by the correction signal generation circuit 132 and the like. The digital video signal corrected in this way is output as an analog signal by the D/A converter 15a. In addition, in the following explanation,
In particular, since the description will be made without distinguishing between R, G, and B signals, the suffixes of the symbols will be omitted.

Reverse gamma correction circuit 16. The gamma correction circuit 17 is installed before and after the correction signal creation circuit 130 to create a correction signal for the linearized signal, and the reason for this will be explained below. Due to the characteristics of the cathode ray tube, the input signal to the projection tube is a nonlinear signal obtained by raising the input to the gamma power. When filtering such input signals to create a correction signal and adding it, the linearity of the correction signal itself is lost, and the sensitivity of the correction filter in dark areas of the screen where the signal level is low decreases, making it difficult to improve the image quality in dark areas. effectiveness decreases. Therefore, the signal is first converted into a linear signal by an inverse gamma correction circuit and then corrected.

Next, the correction signal generation circuit 13 will be explained. Figure 2 is
It is a circuit block diagram in which contour correction and flare correction are performed in parallel and independently. Since they can be executed independently of each other, by parallelizing them, the signal delay caused by correction is reduced. Further, for each correction, vertical correction and horizontal correction are performed in parallel.

Before explaining the overall configuration of FIG. 2, each filter will be explained. 21 and 22 are contour correction FIR filters for vertical and horizontal correction, respectively. Since the number of lines or dots involved in contour correction is small, it can be made small-scale even if it is configured with an FIR filter (transversal filter) that can be converted into a linear phase as a digital filter.

For example, as shown in FIG. 3, a delay element 200. Coefficient circuit 201
It is composed of a to 201d and an adder circuit 202. The adder circuit 202 matches the addition phases of the coefficient circuits 201a to 201d to obtain linear phase characteristics. The delay element 200 is a line memory in the case of vertical correction,
In the case of horizontal correction, it is an A/D conversion clock register.

Next, 23 and 24 are special flare correction filters for vertical and horizontal correction, respectively. Since flare correction involves a large number of lines and dots, an IIR filter (recursive filter) is used to reduce the scale. However, measuring the linear phase with an IIR filter requires special means.

In the present invention, a linear phase is obtained isometrically using a two-stage IfR filter in which the IIR filter output is inverted, the inverted output is further input to an IIR filter with the same characteristics, and the output is inverted. Hereinafter, it will be abbreviated as a composite IIR filter.

FIG. 4 is a block diagram of the composite IIR filter 23 for vertical flare correction. The IIR filter 230a includes a delay element 231 and a coefficient circuit 2 connected to each tap and input terminal.
This is a well-known type in which the signals 32a to 232d are combined by an adder circuit 233. Here, the delay element 231 is a line memory. The output of the IIR filter 230a is inverted on a field-by-field basis by a field inverter 234a, and further input to an IIR filter 230b having the same configuration, and the output thereof is inverted by a field inverter 234b. IIR filter 23
Since the phase delay of 0a is inverted and passed through the IIR filter 230b, the phase advances, so phase compensation is achieved.

FIG. 5 is a block diagram of the composite IIR filter 24 for horizontal flare correction. The circuit configuration is the same as that of the composite IIR filter 23 for vertical flare correction.

However, the difference is that the delay element 241 is a register for the A/D conversion clock, and is used as line inverters 2443 to 244b.

The configuration of the filter has been described above, and the contour correction and flare correction emphasize the high-pass characteristic and reduce the low-pass characteristic as frequency characteristics, and the filter is a high-pass type filter.

Since the filter has been explained above, the correction signal generation circuit 13 shown in FIG. 2 will be explained in general below.

The digital signal input is first input to the compensation delay device 25,
Signals given a predetermined amount of delay are sent from the taps to signal lines 1, 1z, m, , m, respectively. Signal line 2
,,22. Each input from vertical contour correction FIR
Filter 21. The horizontal contour correction FIR filter 22 performs contour correction, and the resulting signals are synthesized by a synthesis circuit 28a. In addition, the human power from ml, m, and H is applied to the vertical flare correction composite IIR filter 23. The horizontal flare correction composite IIR filter 24 performs flare correction, and the combined signal is synthesized by a synthesis circuit 28b. The coring circuits 27a and 27b will be explained later, but the outputs of the combining circuits 28a and 28b are further combined by a combining circuit 26 and output as a correction signal.

The signal line β1°7! output from the compensation delay device 25! z,
m1. mz gives different amounts of delay to the digital signal. Determining the amount of delay is quite complicated because it is determined so that the phases of the input signals to be combined are all matched in all of the combining circuits 28a, 28b, and 26. In this circuit, contour and flare corrections are performed in parallel in the vertical and horizontal directions. Another method is to perform the vertical and horizontal directions in series, which simplifies the compensating delay device. However, when high-pass filters are used in series for vertical correction and horizontal correction, in the case of a four-close window pattern on the screen, vertical and horizontal corrections are related, and the polarity and opposite polarity to be improved are The correction signal appears on the diagonal outer side of the window, which is diagonal to the inner corner of the window. In the present invention, since correction is performed in parallel in the vertical direction and in the horizontal direction, the corrections are not related to each other, and good correction can be obtained even at the four corners of the window pattern.

The above correction outputs can be immediately synthesized in the synthesis circuit 26 to obtain a correction signal output, but in the circuit shown in FIG. 2, the signals are synthesized after passing through the coring circuits 27a and 27b. The correction signal emphasizes the high-frequency components of the signal, and this is particularly noticeable in contour correction. At this time, noise in the same high-frequency region is also emphasized, and the S/N tends to deteriorate in small areas of the screen. Therefore, the coring circuits 27a and 27 are designed to reduce the correction signal to zero in areas where noise is a problem and where the signal level is low to prevent the noise from being emphasized.
It is b. In other words, a dead zone is provided near zero in the correction signal, but this is not necessarily necessary when the screen to be projected is small.

The circuit configuration of the present invention has been described above, and the present invention includes various filters and gamma correction circuits.

A large number of coefficient circuits are required for the inverse gamma correction circuit or coring circuit. The coefficient values of each coefficient circuit vary, and often require adjustment and setting for each receiver. Therefore, it is necessary to be able to make adjustments at the final stage of manufacturing the receiver, and even when the receiver is in use, changes in the installation environment will have a subtle effect on image quality. It is preferable that the user etc. can freely make adjustments in such cases as well.

In the present invention, a coefficient circuit that meets the above-mentioned requirements is created by using a randomly writable RAM.

FIG. 6(a) schematically shows a coefficient circuit, and FIG. 6(b) shows a circuit using a RAM. In this circuit,
Data is written from a separately provided CPU during the video blanking period. In the figure, the mode of the selector 31 is set to the CPU address side, and the CPU is sent to a predetermined address via the buffer 33.
Write data from U to RAM32. During the video period, the mode of the selector 31 is set to the coefficient circuit input side, and the buffer 3
4, the data multiplied by the coefficient is read out and sent out as the coefficient circuit output. Note that writing to the RAM may be performed in DMA mode. By setting data to be arbitrarily written from the CPU to the RAM 32, the coefficients of the coefficient circuit can be made variable.

〔Effect of the invention〕

As detailed above, the image quality of a large-screen projection television receiver can be significantly improved by performing contour and flare correction in parallel. The effects of the present invention include the following.

(1) Since each of the three primary color video signals is corrected, any image can be completely corrected. When a correction signal is extracted only from the G signal as in the conventional example, the correction effect is small for an image with a small G signal component, but the quality is high.

(2) FI for the former as a contour/flare correction filter
R filter, and a composite IIR filter on the latter.

By using this, it is possible to have a small-scale circuit configuration with a linear phase and a small number of elements. This is also the reason why the three primary colors can be corrected separately as shown in (1).

(3) Although the filter characteristic is a high-pass type, since vertical correction and horizontal correction are performed in parallel, there is no correlation between them, and good correction can be obtained even at the four corners of a quadrilateral window pattern. Furthermore, since all the filters are arranged in parallel, there is little delay in the correction signal generation circuit.

(4) Since an inverse gamma correction circuit is provided and the signal is linearized and then corrected, the correction effect for dark areas of the screen where the signal level is low does not deteriorate.

(5) Coefficients can be arbitrarily set by using RAM as coefficient circuits used in filters, inverse gamma correction circuits, gamma correction circuits, and the like. Adjustments and
Not only is it easy to set, but it can also be made variable even while the receiver is in operation, allowing the image quality to be kept at its optimum in any environment.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a basic configuration block diagram, FIG. 2 is a configuration block diagram of a correction signal generation circuit,
FIG. 3 is a block diagram of an FIR filter used for contour correction, FIGS. 4 and 5 are block diagrams of a composite IIR filter used for flare correction, and FIG. 6 is a diagram showing an example of a coefficient circuit. 11a to 11c A/D converter, 12a to 12
c.-compensation delay circuit, 13a-13c.-correction signal generation circuit, 142-14c
m・Synthesizing circuit, 15 a to 15 c-・-D/A converter, 16 a
~16 C- Reverse gamma correction circuit, 17a ~ 17 c-
Gamma correction circuit 21-22- Contour correction FIR filter, 23-24
・-Flare correction composite IIR filter, 25-Compensation delay device, 26.28a, 28b-Synthesizing circuit, 27 a to 27 b・-Coring circuit, 200-・
Delay elements, 201a to 201d - coefficient circuits, 202 - adder circuits, 230 a to 230 b - (high-pass type) IIR filters, 231.241 - delay elements, 234a to 234 b - field inverters, 240 a
~240b- (high-pass type) IIR filter, 244a ~244b-line inverter, 30-coefficient circuit, 31--selector, 32-RAM, 3
3.34-Buffer.

Claims (1)

[Scope of Claims] In a projection display type television receiver, each of the three primary color video signal series is provided, each video signal is input and A/D converted, and after contour/flare correction, the D/A
The image quality improvement device converts and outputs the image, and the contour/flare correction section includes a compensation delay circuit and an inverse gamma correction circuit in a preceding stage and a gamma correction circuit in a subsequent stage, which are provided in parallel with the digital video signal input. The contour/flare correction signal generation circuit includes a contour/flare correction signal generation circuit with an attached circuit, and a synthesis circuit that synthesizes the outputs of the compensation delay circuit and the gamma correction circuit, and the contour/flare correction signal generation circuit is configured to perform image contour correction and flare correction. (a) Contour correction is performed in parallel in the vertical and horizontal directions of the image, and 1 in the vertical direction.
High-pass FIR using line memory as delay
The filter is a high-pass FIR filter that uses an A/D conversion clock register with a delay of 1 in the horizontal direction, and (b) Flare correction is performed in parallel in the vertical and horizontal directions of the image, with a delay of 1 in the vertical direction. It has two stages of high-pass IIR filters that use line memory as a delay and an inverter that inverts one field's worth of information alternately in series, and a register for the A/D conversion clock as one delay in the horizontal direction. The coefficient circuit in the filters, gamma correction circuit, and inverse gamma correction circuit is made up of a circuit having two stages each of a high-pass IIR filter using . A television image quality improving device, which utilizes a RAM, and wherein during a video period, the input signal of the coefficient circuit is an address signal of the RAM, and the data is read out and becomes an output signal.