JPS61295791A - Improving device for television picture quality - Google Patents

Abstract

PURPOSE:To improve the picture quality of a large picture projection type television receiver by applying an A/D conversion to each of three color primary video signals, separating them to a luminance signal and two chrominance components at a reverse matrix circuit, and restoring them to the three color primary video signals at a matrix circuit with a delayed chrominance components after the outline/flare correction of the luminance signal. CONSTITUTION:At a correction signal generating circuit 13 of a luminance signal correcting part 10, generating circuits for an outline correction signal and for a flare correction signal are provided at parallel and furthermore, a vertical and a horizontal directions are set in series. Setting a filter as a low-pass type of filter using an FIR filter for an outline correction and an IIR filter for a flare correction, the characteristic of a high-press type of filter is given by subtracting the output of the filter from an input luminance signal. It is assumed that a correction signal is a corrected luminance signal with synthesizing the luminance signal delayed at a compensating delay circuits 12. At the next, by combining the phases of the corrected luminance signal and the two chrominance components, R, G and B signals are restored at a matrix circuit 19 and with applying a D/A conversion on each signal of them, color primary video signal color, the picture quality of which is improved, can be obtained.

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, "Improvement of Image Quality of Projection Displays for High-Definition Televisions - Removal of Flare Interference by 5AW Filter", Television Society of Japan 1982 National Annual Conference 5PI-14, There is a method using an analog filter in which a video signal from a safe or the like is once AM-modulated, passed through a SAW filter, and then 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, and even if the flare component in the horizontal direction of the screen can be removed, when applied to the vertical component, a very accurate one-line delay line is required. This is difficult to implement as a large number of them are required.

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 used in a projection display type television receiver, after A/D converting each of three primary color video signals, converting the signals into a luminance signal and two color signals using an inverse matrix circuit, and converting the luminance signal into a luminance signal and two color signals. After contour/flare correction is performed in the luminance signal correction section, the signal is input to the matrix circuit along with two color signals delayed by the compensation delay circuit,
The video signal is restored to three primary color video signals, each of which is D/A converted and output.

The luminance signal correction section includes a contour/flare correction signal generation circuit which is provided in parallel with the luminance signal input and has a compensation delay circuit and a subsequent gain adjustment circuit that changes the gain depending on the input level of the luminance signal. , and a combining circuit that combines the outputs of the compensation delay circuit and the gain adjustment circuit.

The contour/flare correction signal generation circuit performs contour correction and flare correction of the image in parallel; Low-pass FI using line memory
This is done by subtracting the signal output through the R filter and the low-pass FIR filter using the A/D conversion clock register with one delay in the horizontal direction from the signal that delayed the input of the correction signal creation circuit. (b) Flare correction is performed by alternating between a low-pass IIR filter using a line memory and an inverter that inverts one field of information in series in the vertical and horizontal directions of the image, with one delay in the vertical direction. In the horizontal direction, a low-pass IIR filter using an A/D conversion clock register and an inverter that inverts one line of information are alternately connected in series. This is done by subtracting the signal outputted through the circuit having stages from the signal input to the correction signal generation circuit with a delay.

Here, the coefficient circuits in the filters and gain adjustment circuits have coefficients that can be variably adjusted and set.

[Effect]

The present invention utilizes the fact that the luminance signal includes three primary color signals to correct the luminance signal obtained from the digital three primary color video signal. After that, the luminance signal is input to the luminance signal correction section and corrected.

The correction signal generation circuit of the brightness signal correction section has a contour correction signal generation circuit and a flare correction signal generation circuit arranged in parallel, and correction of contour and flare is performed in parallel. The contour correction and flare correction are further performed in series in the vertical and horizontal directions.

As will be explained in detail in the example, the contour correction filter is FI
The R filter is used as the flare correction filter, the IIR filter is used as the flare correction filter, and the above filter is a low-pass filter, and the filter output is subtracted from the input luminance signal to give it the characteristics of a high-pass filter. The amplitude of the correction signal is adjusted by a gain adjustment circuit in accordance with the level of the luminance signal, and the correction signal is output. The above correction signal is combined with a luminance signal delayed by a compensation delay circuit to obtain a corrected luminance signal.

Next, after matching the phases of the corrected luminance signal and the two color signals, the matrix circuit restores the RGB signals, and each signal is D/A converted to obtain a primary color video signal with improved image quality. can.

Note that coefficient circuits are required for filters and gain adjustment circuits, but variably adjustable circuits are used to optimally adjust and set them.

(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 converted into digital video signals by A/D converters 11a to 11c, and are input to the inverse matrix rgJ path 18 to generate a luminance signal Y and two color signals C+ and Cz. The color signal may be either a color difference signal or an E+ or Eo times signal. The Y signal is input to the luminance signal correction section 10 and input to the matrix circuit 19 as a corrected Y signal. Luminance signal correction section 1
0 outputs a corrected Y signal by combining the correction signal created by the correction signal creation circuit 13 with the Y signal whose phase has been matched by the compensation delay circuit 12a in the synthesis circuit 14 via the gain adjustment circuit 17. do.

The corrected Y signal and the corrected Y signal are matched in phase by compensation delay circuits 12b and 12c, respectively.
1 signal + CZ times signal is input to matrix circuit 19 and 3
Restore the primary color signals RGB.

The RGB signals are output as analog signals by D/A converters 15a to 15c.

Incidentally, 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 signal 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. To improve this point,
The gain adjustment circuit 17 is connected in series to the correction signal generation circuit 13.

The Y signal is input to the gain adjustment circuit 17 via the delay device 16 as a control signal that compensates for the signal delay of the correction signal generation circuit 13. When the signal level is low, the gain of the gain adjustment circuit 17 is increased to compensate for the decrease in sensitivity of the correction filter in the dark areas. Conversely, the gain is lowered where the signal level is high. This improves the image quality even in dark areas of the screen.

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 running them in parallel, the signal delay due to correction is reduced. Each correction is a vertical correction and a horizontal correction performed in series.

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
, 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, and is an A/Di conversion clock star in the case of horizontal correction.

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, special means are required to obtain a linear phase with an IIR filter. In the present invention, the IIR filter output is inverted,
The linear phase is obtained isometrically using a two-stage IIR filter in which the inverted output is further input to an IIR filter with the same characteristics and the output is inverted. In the following, the composite IIR
Abbreviated as 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 FIR 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 a line inverter 244a to 244b.

The configuration of the filter has been described above, but the frequency characteristics of contour correction and flare correction are to emphasize high-frequency components and attenuate low-frequency components, respectively, and both filters are high-pass filters. . However, if 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, the vertical and horizontal corrections are related, and the polarity is opposite to the one to be improved. A polarity correction signal appears on the diagonal outer side diagonally to the inner corner of the window. In the present invention, strictly considering this point, all filters are low-pass type, and the filter output is subtracted from the input signal to effectively make it high-pass type.
Continuity of correction at the four corners is obtained.

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

The Y signal is first input to the compensation delay device 25. The compensation delay device 25 delays the contour correction filter system β and the flare correction filter system m by matching the signal phases with a signal line n for transmitting a reference signal, which will be described later, and subtraction circuits 26a and 26b, respectively. It has three taps with different amounts. However, the signal line n may take out a signal delayed by an appropriate number of lines from the tap 21-1 of the line memory column included in the vertical contour correction FIR filter 21. Signal line! The input from vertical contour correction FIR filter 21. After passing through the horizontal contour correction FIR filter 22,
The signal is input to the subtraction circuit 26a and subtracted from the reference signal. This makes it possible to obtain effective high-frequency characteristics for contour correction, and at the same time, the correction at the four corners of the window pattern becomes continuous. Similarly, the input from the signal line m passes through vertical and horizontal flare correction composite IIR filters 23 and 24, and is subtracted from the reference signal by a subtraction circuit 26b, thereby effectively obtaining a correction signal with high frequency characteristics.

The outputs of the subtraction circuits 26a and 26b are immediately transferred to the synthesis circuit 2.
In the circuit shown in FIG. 2, the signals are combined after passing through 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 27b are circuits that set the correction signal to zero to prevent the noise from being emphasized in areas where the signal level is low and where noise is a problem. 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, but the present invention requires a large number of coefficient circuits for various filters, gain adjustment circuits, coring circuits, etc. 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 adjust the final stage of receiver manufacture.

In the present invention, an element as shown in FIG. 6 is used as an element whose coefficients can be variably adjusted and set.

FIG. 6 (al is a diagrammatic representation of the coefficient circuit; FIG. 6('b) is the ROM 31; FIG. 6(C) is the multiplication circuit 32.
In the same figure (di is the shifter circuit 33. In the same figure (R of bl
In the case of the OM31, the input is an address signal, and the data stored at that address is output, but the data may be the input multiplied by a coefficient. ROM during adjustment
It may be written in, or it may be made variable by storing various coefficient values in advance, providing enough address lines, and selecting the address lines during adjustment. In the case of the multiplication circuit 32 shown in FIG. 3C, the coefficient can be adjusted by setting the multiplication data (coefficient value). The same figure (d
l is a shifter circuit 33, for example shifters 331, 332
If they are connected in parallel, the shifter 331 shifts 2 bits.

If the shifter 332 performs a 3-bit shift, the input data will be 3/8 and output if it is a shift to the lower order. The coefficient can be variably adjusted and set by controlling the number of shifts or by preparing a sufficient number of shifters in advance and selecting them at the time of adjustment.

〔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) Create a luminance signal from the three primary color video signals using an inverse matrix circuit, and after correcting this luminance signal,
A matrix circuit restores the three primary color signals from the two color signals and the corrected luminance signal.

There is no need to provide complex correction signal generation circuits for the three primary colors, and only one is required, which greatly reduces device costs.Moreover, since the luminance signal includes the three primary colors, compared to when the correction signal is extracted only from the G signal. It has a correction effect on signals of arbitrary hue.

(2) FI for the former as a contour/flare correction filter
By using an R filter and a composite IIR filter for the latter, it is possible to have a small-scale circuit configuration with a linear phase and a small number of elements.

(3) The filter characteristic itself is a low-pass type, and by taking the difference from the reference signal, it is effectively made into a high-pass type, making it possible to obtain good correction even at the four corners of the quadrilateral window pattern. .

(4) By providing a gain adjustment circuit and adjusting its gain according to the signal level and increasing the gain when the signal level is low, the sensitivity of the correction filter in dark areas of the screen due to the gamma characteristics of the video signal can be reduced. Compensated.

(5) As coefficient circuits used in filters, gain adjustment circuits, etc., those whose coefficients can be variably adjusted and set are used, and adjustment is made easy, which is advantageous when mass producing devices.

[Brief explanation of the drawing]

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. 10... Luminance signal correction section, 11 a to 11 c-A/D converter, 12 a to 12
cm・-compensation delay circuit, 13-111 correction signal creation circuit, 14-combining circuit, 15 a to 15 c-D
/ A converter, 16- delay device, 17- gain adjustment circuit, 18-- inverse matrix circuit, 19-- matrix circuit, 21-22- contour correction FIR filter, 23-24-.
Flare correction composite IIR filter, 25--compensation delay device, 263-26b--subtraction circuit, 27a-27b--coring circuit, 28--combining circuit, 200-delay element,'l Q
l a ~ 201 d --- one coefficient circuit, 202 -- adder circuit, 230 a ~ 230 b -- (low pass type) IIR filter, 231.241 -- delay element, 234 a ~ 234 b -- field inverter , 240
a ~ 240 b - (low-pass type) IIR filter, 244 a ~ 244 b - line inverter, 30 - coefficient circuit, 31 - ROM, 32 - multiplier circuit, 33 -
shifter circuit.

Claims (1)

[Claims] In a projection display type television receiver, each of the three primary color video signals is A/D converted, and then converted into a luminance signal and two color signals by an inverse matrix circuit, and the luminance signal is converted into a luminance signal. After contour/flare correction in the signal correction section, the signal is input to the matrix circuit together with the two color signals delayed by the compensation delay circuit, and restored to three primary color video signals.
The image quality improvement device performs D/A conversion and outputs the respective signals, and the brightness signal correction section includes a compensation delay circuit provided in parallel with the brightness signal input and a gain adjustment circuit that adjusts the gain based on the input level of the brightness signal in a subsequent stage. It consists of a contour/flare correction signal generation circuit equipped with a variable gain adjustment circuit, and a synthesis circuit that synthesizes the outputs of the compensation delay circuit and the gain adjustment circuit, and the contour/flare correction signal generation circuit It performs contour correction and flare correction in parallel. (a) Contour correction is performed in series in the vertical and horizontal directions of the image, and in the vertical direction
Low-pass FIR using line memory as delay
This is done by subtracting the signal output through a low-pass FIR filter using an A/D conversion clock register with one delay in the horizontal direction from the signal that delayed the input of the correction signal creation circuit. (b) Flare correction is a low-pass type I that uses line memory in series in the vertical and horizontal directions of the image and with one delay in the vertical direction.
It has two stages of IR filters and inverters that invert one field's worth of information alternately in series, and a low-pass IIR filter that uses an A/D conversion clock register as one delay in the horizontal direction. This is done by subtracting the signal outputted through a circuit having two stages of inverters that invert information for each line alternately in series from the signal delayed from the input of the correction signal generation circuit, and the filters and 1. A television image quality improvement device, wherein the coefficient circuit in the gain adjustment circuit is capable of variably adjusting and setting the coefficients.