JPS61295790A - Improving device for television picture quality - Google Patents

Abstract

PURPOSE:To improve the picture quality of a large picture projection type television receiver by generating an outline/flare correction signal using a green digital video signal after an A/D conversion is applied to each of three color primary video signals, and synthesizing them to each of delayed three color primary digital video signals respectively. CONSTITUTION:Utilizing that a G signal is the largest signal among three color primary (R, G and B) video signals, a correction signal is generated at an outline/flare correction generating part that is one of parts where the G signal is inputted. A tap from each delay element at a delay element row 201 is put out to an FIR filter. A large number of lines (in a vertical correction) and dots (in a horizontal correction) are related for the flare correction and therefore, when an addition is executed at an adder 203 using all of taps, a straight line phase is obtained by fitting a phase. Next, so that a small number of lines and dots are related for the outline correction, a coefficient circuit group 205 is generated, and an outline correction signal 207 is obtained by adding each output of coefficient circuits at an adder 206. A flare correction signal 204 and the outline correction signal 207 are synthesized at a synthesizing circuit 208 and outputted.

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 the projection-type large-screen receiver is 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, [Improving Tut of projection displays for high-definition televisions - Removal of flare interference by 3AW filter-'' Television Society of Japan 1982 Annual Conference 5PI-14, Rational et al. 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 uses a modulated signal wave with ±], MHz near the modulating carrier frequency.
By applying attenuation with , low frequency components are attenuated for flare correction. However, this method requires the use of a high frequency modulation carrier frequency of 100 MHz or higher, and even if it is possible to remove the flare component in the horizontal direction of the screen, it is very difficult to apply it to the vertical component.
This requires a large number of line delay lines and 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 means 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 open 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 generates a contour/flare correction signal using a green digital video signal after A/D converting each of the three primary color video signals in a projection display type television receiver, and performs the correction. By combining the signals with the delayed three primary color digital video signals through a compensation delay circuit, the corrected signals are D/A converted and output.

The contour/flare correction signal generation section includes a contour/flare correction signal generation circuit that inputs a green digital video signal, and a gain adjustment that is connected in series to the correction signal generation circuit and changes the gain depending on the input level of the green digital video signal. It consists of a circuit.

The contour/flare correction signal generation circuit is a low-pass type Fi
A circuit that serially performs correction in the vertical and horizontal directions using a group of R filters and then subtracts from the delayed green digital video signal, wherein (a) the vertical FIR filter has a line memory with one delay; common columns,
A flare correction signal is obtained using all the taps, and a contour correction signal is obtained using a necessary number of taps in the center, and the two correction signals are synthesized, (b) the horizontal FIR filter is configured to have an A/ The D-conversion clock register has a common column with 1 delay, and all the taps are used to obtain the flare correction signal, and the required number of taps in the center are used to obtain the contour correction signal, respectively, and both correction signals are synthesized. be.

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

[Effect]

The present invention takes advantage of the fact that the G signal is the largest among the three primary color (RGB) video signals, and uses one contour/flare correction signal generation unit that inputs the G signal to generate the correction signal. (referred to as the department).

The correction signal generation section consists of a correction signal creation circuit and a gain adjustment circuit. A correction signal with band-pass characteristics is obtained. The low-pass FIR filter is configured to perform flare correction and contour correction in parallel, using a common delay column, using all taps for flare correction, and using the required number of taps in the center for contour correction.

The amplitude of the correction signal is adjusted by a gain adjustment circuit in accordance with the level of the G signal, and then output.

The correction signal output from the correction signal generation section is combined with each of the three primary color video signals that have passed through the compensation delay circuit in a synthesis circuit, and the D/A
By converting, three primary color video signals 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 video signals of the three primary colors are individually corrected. If you explain it with R signal,
A/D converter 11a converts the signal into a digital video signal;
A synthesis circuit 14a is applied to the signal delayed by the compensation delay circuit 12a.
The outputs of the correction signal generator 10 are synthesized. 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 sent to the D/A converter 1.
5a outputs it as an analog signal.

The correction signal generation section 10 inputs the green digital video signal, that is, the output of the A/D converter 11b, and generates a correction signal commonly used for each video signal in the correction signal generation circuit 13.

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 green 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 vertical correction and horizontal correction are performed in series. The vertical correction FIR filter 21 is a low-pass type filter that shares the line memory column 21a, and multiplies the signals from its taps by a coefficient and adds them to the product-sum calculator 21b2 for contour correction. 21c and
It is composed of a combining circuit 21d that combines the outputs of both product-sum calculators 21b and 21C. Horizontal correction FIR filter 23
is a low-pass filter with the same configuration, but 23a
The difference is that is a register string for the A/D conversion clock.

In this filter system, contour correction and flare correction are performed in parallel, and each correction is performed in series in the vertical and horizontal directions.

Details of the circuit of the FIR filters 21, 23 are shown in FIG. Note that the reference numerals in FIG. 3 are different from those in FIG. 2 in order to explain the configuration common to both vertical and horizontal directions.

A tap comes out from each delay element of the delay element array 201,
Flare correction uses all the taps to create a coefficient circuit group 202, and adds the outputs of each coefficient circuit in an adder circuit 203 to obtain a flare correction signal 204. For flare correction,
Since the number of lines (in the case of vertical correction) and the number of dots (in the case of horizontal correction) involved are large, all taps are used to configure the FIR filter. However, the FIR filter
When adding in the adding circuit 203, a linear phase can be easily obtained by matching the addition phases. Next, for contour correction, an FIR filter can be constructed using the central tap m of the delay element array 201 and several taps in its vicinity. Number of lines involved in contour correction.

Since there are fewer dots, fewer taps are required.

In the figure, three taps are used to create a coefficient circuit group 205, and an adder circuit 206 adds the outputs of each coefficient circuit to obtain a contour correction signal 207. Flare correction signal 2042
The contour correction signal 207 is synthesized by a synthesis circuit 208 and output.

Hereinafter, the explanation will be returned to FIG. 2 and the overall configuration will be explained. A signal 22 vertically corrected from the green digital video signal input by the vertical correction FIR filter 21 is sent to the horizontal correction F.
The signal is further horizontally corrected by an IR filter 23 and inputted to a subtraction circuit 26 as a correction signal 24 with low frequency characteristics.

One edge of the digital video signal is inputted to the subtraction circuit 26 by a compensating delay device 25, which provides a signal with a delay amount sufficient to match the phase delay caused by the filter group of the correction signal 24. As a result, the output 26a of the subtraction circuit 26 becomes a correction signal with high frequency characteristics.

The reason why the filter is configured as a low-pass filter and its output is subtracted from the digital video signal to create a high-pass filter will be explained below.

Contour correction and flare correction have frequency characteristics that emphasize high-frequency components and attenuate low-frequency components, respectively, and both 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. The polarity correction signal appears on the diagonal outer side diagonally to the inner inner corner. In the present invention, strictly considering this point, all filters are of low-pass type, and the filter output is subtracted from the input signal to effectively make it a high-pass type, so that correction at the four corners can be performed. Continuity is achieved.

Now, the output 26a of the subtraction circuit 26 may be directly output from the correction signal generation circuit 13, but in the circuit shown in FIG. 2, it is outputted via the coring circuit 27.

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 at narrow areas of the screen. Therefore, the coring circuit 27 is a circuit that sets 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. 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. 4 is used as an element whose coefficients can be variably adjusted and set.

FIG. 4(a) is a diagrammatic representation of the coefficient circuit, and FIG. 4(a) is a ROM 31. FIG. )'s RO
In the case of M31, 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. It may be possible to write into the ROM during adjustment, or it may be possible to store various coefficient values in advance, provide a sufficient number of address lines, and make the coefficients variable by 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 (dl
In the shifter circuit 33, for example, if shifters 331 and 332 are connected in parallel, 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) Since the correction signal is created using only the green signal, which has the largest signal component among the three primary color video signals, only one correction signal generation unit including a complicated correction signal creation circuit is required, which reduces the equipment cost. has the advantage of being significantly lower. Although the quality is slightly inferior to the case where a correction signal is created for each of the three primary color video signals, it is possible to obtain high enough quality for general use.

(2) As contour/flare correction filters, both F
It has linear phase characteristics as an IR filter. In the filter configuration, horizontal correction is performed in series after vertical correction, but the filters are connected in parallel so that flare correction and contour correction are performed in parallel in each direction. in this case,
By using a common delay element array for flare correction and contour correction, it is possible to reduce the size of the FIR filter.

(3) The filter characteristic itself is a low-pass type, and by taking the difference from the input signal, it is effectively made into a high-pass type.
Good correction can be obtained even at the four corners of a rectangular 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, which facilitates adjustment, which is advantageous when mass producing devices.

[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 fixer commonly used for contour correction and flare correction, and FIG. 4 is a diagram showing an example of a coefficient circuit. 10.-Correction signal generation unit, 11a to 11c-A/D converter, 12a to
12C--compensation delay circuit, 13--correction signal creation circuit, 143-14 C--combining circuit, 15 a--15 c--D/A converter, 16--
・Delay device, l'l-Gain adjustment circuit, 21--Vertical correction FIR filter, 23-Horizontal correction FIR filter, 25-Compensation delay device, 26-Subtraction circuit, 27--Coring circuit, 201 - Delay element array, 202, 205
-Coefficient circuit group (for flare correction 1 contour correction), 203.206-.-addition circuit, (for flare correction 9 contour correction), 208-composition circuit, 30-coefficient circuit, 31-ROM. 32-.- Multiplier circuit, 33-. Shifter circuit.

Claims (1)

[Claims] In a projection display type television receiver, after each of the three primary color video signals is A/D converted, a green digital video signal is used to generate a contour/flare correction signal, and the correction signal is An image quality improvement device that D/A converts and outputs a corrected signal by synthesizing it with three primary color digital video signals delayed through a compensation delay circuit, the contour/flare correction signal generating section comprising: , a contour/flare correction signal creation circuit that inputs a green digital video signal, and a gain adjustment circuit that is cascaded to the correction signal creation circuit and changes its gain depending on the input level of the green digital video signal; The correction signal creation circuit is a low-pass type FI
A circuit that serially performs correction in the vertical and horizontal directions using a group of R filters and then subtracts from the delayed green digital video signal, (a) The vertical FIR filter has a line memory with one delay. A configuration in which the columns are shared, a flare correction signal is obtained using all the taps, and a contour correction signal is obtained using the required number of taps in the center, and both correction signals are synthesized, (b) the horizontal direction FIR; The filter uses a common row of A/D conversion clock registers with one delay, uses all the taps to obtain the flare correction signal, and uses the required number of taps in the center to obtain the contour correction signal, respectively, and outputs both correction signals. What is claimed is: 1. A television image quality improvement device, characterized in that the filters and coefficient circuits in the gain adjustment circuit are configured to synthesize the coefficients of the filters and the gain adjustment circuit, and the coefficients thereof can be variably adjusted and set.