JPS61296880A - Device for improving picture quality of television - Google Patents

Abstract

PURPOSE:To make a scale small by disposing a vertical direction and a horizon tal direction in series in parallel to the correction of a contour and a flare, using an FIR filter for correcting the contour and an IIR filter for correcting the flare, using a RAM for coefficient circuit such as filters and correcting by a digital means. CONSTITUTION:A digital luminance signal is inputted to a compensating delay device 25, passes through a vertical contour correction filter 21, a horizontal contour correction FIR filter 22 from a signal line (l) to input to a subtraction circuit 26a, is subtracted from a reference signal from a signal line (n) and similarly, passes through vertical and horizontal flare correction composite IIR filters 23, 24 from a signal line (m), is subtracted from the reference signal in a subtraction circuit 26b to obtain correcting signals of high frequency characteristic, respectively. A selector 31 is disposed at a CPU address side and the data from the CPU is written in a prescribed address in a RAM 32 during an image blanking period through a buffer 33. During the image period, the selector 31 is disposed to an input side and the data multiplied by a coefficient through a buffer 34 is read and fed as an output of a factor circuit.

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. Conventionally, as a flare correction means proposed for high-definition televisions, there is an article published 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 by ±IMIIz 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 loOMHz or higher, and even if the horizontal flare component 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 in most cases only the horizontal direction of the screen is emphasized, 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 address the above problems and has a lot of flexibility 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 inputs a luminance signal and two color signals in a projection display type television receiver, performs A/D conversion on each, and then generates a contour/flare correction signal using the digital luminance signal. At the same time, the contour/flare correction signal is synthesized with the three primary color video signals which are restored from the digital luminance signal and color signal by the matrix circuit and delayed through the compensation delay circuit, and then the D/A It is converted and output.

The contour/flare correction signal generation section includes a contour/flare correction signal generation circuit that inputs a digital luminance signal, and a gain adjustment circuit that is connected in series to the correction signal generation circuit and changes its gain depending on the input level of the digital luminance signal. has been done.

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 a low-pass FIR filter using an A/D converter cloff 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.

The coefficient circuits in the filters and gain adjustment circuits use RAM, data is written during the video blanking period, and the input signals of the coefficient circuits are stored in the RAM during the video period.
This is an address signal from which the data is read out and becomes an output signal. [Function] The present invention provides a luminance signal (Y signal) and two color signals, namely a wideband color signal C,4, and a narrowband color signal CM(
The following are C1 signals.

It is possible to obtain a high-quality three-primary-color video signal by inputting a C2 signal (handled as a C2 signal) and correcting contours and flare.

The correction signal is created using one contour/flare correction signal generation unit (hereinafter referred to as the correction signal generation unit) that inputs the luminance signal.
Let's do it.

The correction signal generation section includes a correction signal generation circuit and a gain adjustment circuit, and the correction signal generation circuit includes a contour correction signal generation circuit and a flare correction signal generation circuit in parallel, and corrects contour and flare. done 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 filter is a low-pass filter, and the filter output is subtracted from the input Y signal to provide high-pass filter characteristics. The amplitude of the correction signal is adjusted by a gain adjustment circuit in accordance with the level of the Y signal, and then output.

The above-mentioned correction signal output is restored by a matrix circuit, and combined with each of the three primary color (RGB) video signals that have passed through a compensation delay circuit in a synthesis circuit, and then D/A converted, resulting in a three primary color video signal with improved image quality. can be obtained.

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 input signals Y signal and C3 signal + C2 signal are each input to the A/D converter 112~
The signal is converted into a digital video signal by the llc, inputted to the matrix circuit 18, and restored to an RGB signal. The RGB signals are each delayed by compensation delay circuits 12a to 12c, and the outputs of the correction signal generator 10 are synthesized by synthesis circuits 142 to 14C, respectively.

The compensation delay is combined with the delay occurring in the correction signal generating section 10. The digital video signal corrected in this way is converted to D
/A converters 15a to 15c output it as an analog signal.

The correction signal generator 10 generates a digital Y signal, that is, A/
A correction signal generation circuit 13 receives the output of the D converter 11a and generates a correction signal commonly used for each RGB signal.

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 correction signal generation section 10 has the configuration shown in FIG. 1, and a gain adjustment circuit 17 is connected in series to the correction signal generation circuit 13.

The digital video 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.

Note that the gain of the gain adjustment circuit 17 can be changed for each of the three primary colors to change the amplitude of the correction signal.

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. 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
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, and is a register for the A/D conversion clock 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 FIR filter output is inverted,
An equivalent linear phase is obtained 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 ITR 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 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 digital signal input is first input to the compensation delay device 25. The compensation delay device 25 is a filter system for contour correction! and a flare correction filter system m are connected to a signal line n that sends out a reference signal, which will be described later, and subtraction circuits 26a and 26, respectively.
b is used to match the phase of the signal, and has three taps with different amounts of delay. 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. The input from the signal line l is sent to the vertical contour correction FIR filter 21. The signal is inputted to the subtraction circuit 26a through the horizontal contour correction FIR filter 22, 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 is the vertical and horizontal flare correction composite I
By passing through the TR filters 23 and 24 and subtracting it from the reference signal in the subtracting circuit 26b, a correction signal with high frequency characteristics is effectively obtained.

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 that the receiver be adjustable at the final stage of manufacture;
Furthermore, even when the receiver is in practical use, changes in the installation environment 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 (al is a diagrammatic representation of a coefficient circuit, and Fig. 6 (b) shows a circuit using 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) A correction signal is created using a luminance signal as an input signal, and the signal is added to the three primary color video signals restored by a matrix circuit to correct the three primary color video signals. Therefore, the correction signal generation section including a complicated correction signal generation circuit, etc.
Only one piece is required, which has the advantage of significantly lowering the equipment cost. In addition, the luminance signal includes three primary color video signals,
Since the correction value is added for each of the three primary color video signals, the amount of correction can be adjusted appropriately.

(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, so good correction can be obtained even at the four corners of a 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) By using RAM as a coefficient circuit used in filters, gain adjustment circuits, etc., coefficients can be set arbitrarily. Not only is it easy to adjust and set during the manufacturing stage, 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. 10--Correction signal generation unit, 11a-11c--A/D converter, 12a-
12c--compensation delay circuit, 13--correction signal creation circuit, 14a-14C--combining circuit, 15 a-15c-D/A converter, 16--delay device, 17--gain adjustment circuit , 18-
・・Matrix circuit, 21-22・-Contour correction FIR filter, 23-24-
Flare correction composite IIR filter, 25 - compensation delay device, 26 a - 26 b - subtraction circuit, 27 a - 27 b - coring circuit, 28 - synthesis circuit, 200 - delay element, 201
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-selector, 32--RAM,
33.34 --- Buffer.

Claims (1)

[Claims] In a projection display type television receiver, a luminance signal and two color signals are input, and each is A/D.
After the conversion, a contour/flare correction signal is generated using the digital luminance signal, and a three primary color video signal is restored from the digital luminance signal and color signal by a matrix circuit and delayed through a compensation delay circuit. An image quality improvement device that synthesizes each of the contour and flare correction signals, performs D/A conversion, and outputs the resulting image, wherein the contour and flare correction signal generation section includes a contour and flare correction signal generation circuit that inputs a digital luminance signal. and a gain adjustment circuit that is cascaded to the correction signal generation circuit and changes the gain depending on the input level of the digital luminance signal, and the contour/flare correction signal generation circuit performs image 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 The coefficient circuit in the gain adjustment circuit uses RAM and writes data during the video blanking period, and the input signal of the coefficient circuit is transferred to the RAM during the video period.
1. A television image quality improvement device, characterized in that the address signal is an address signal, and the data is read out to become an output signal.