JPH0327149B2 - - Google Patents

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]

Due to manufacturing considerations, CRTs with large image surfaces are currently limited to about 40 inches. Beyond that, a method using a projection tube is currently practical. In the case of a large, high-quality screen, high quality cannot be obtained simply by increasing the size of the screen, so as the number of scans increases, the requirements for image quality become stricter. In particular, with the projection type, the current density of the projection tube beam is about 5 to 10 times that of the direct view type, so the beam becomes thicker.
In addition, a decrease in resolution due to the influence of the lens and flare caused by the high-brightness projection tube, lens, etc. were causes of deterioration in image quality.

Perhaps because the projection-type large screen image receiver is still in the development stage, the means for the flare correction and contour correction described above have not yet been fully established as fully established technologies. Conventionally,
As a flare correction method proposed for high-definition televisions, "Improvement of Image Quality of Projection Displays for High-Definition Televisions - Removal of Flare Interference by SAW Filters -" Television Society 1982 National Conference SP1
−14, Kanazawa et al.'s video signal is once AM modulated,
There is a method using an analog filter that passes through a SAW filter and demodulates again. This method uses a modulated signal wave with ±
By applying attenuation at 1MHz, 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 more, and even if the horizontal flare component of the screen can be removed, if you try to apply it to the vertical component, you will have to use a very accurate one-line delay line. 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;
In the latter case, a screen with a lot of flare has a shape in which the MTF (resolution characteristics) is lifted in the low range, so it gives an attenuation characteristic 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 if digital and analog methods are mixed, or if one method is unified. Therefore, there is no example in which both types of correction processing were performed.

[Problem that the invention seeks to solve]

As mentioned above, large-screen projection receivers have not yet fully adopted the necessary flare correction and contour correction means to obtain high-quality images. Here, "completely" means that contour/flare correction can be performed for both vertical and horizontal components. In the analog system, there are problems such as uniformity of filter characteristics and fluctuations due to temperature in the delay line, 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 corrections that emphasize 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 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 a matrix circuit together with two color signals delayed by a compensation delay circuit, restored to three primary color video signals, and each is D/A converted and output. be.

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 image contour correction and flare correction in parallel. A high-pass FIR filter using a line memory and a high-pass FIR filter using an A/D conversion clock register as one delay in the horizontal direction are used. (b) Flare correction is performed in the vertical and horizontal directions of the image. It has two stages of high-pass IIR filters using line memory as one delay in the vertical direction and an inverter that inverts one field's worth of information alternately in series, and one delay in the vertical direction. This is implemented by a circuit having two stages of high-pass IIR filters using A/D conversion clock registers as one delay and two stages of inverters that invert one line of information alternately in series.

Here, the coefficients of the filters and the coefficient circuits in the gain adjustment circuit 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 luminance signal correction section includes a contour correction signal generation circuit and a flare correction signal generation circuit 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 examples, the contour correction filter is an FIR filter, and the flare correction filter is
An IIR filter is used 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 then 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 signal, 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 example 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 circuit 18, where they are converted into a luminance signal Y and two color signals C ₁ and C ₂ . The color signal may be either a color difference signal or an E ₁ or _EQ signal. The Y signal is a luminance signal correction section 10
The signal is input to the matrix circuit 19 as a corrected Y signal. The brightness signal correction unit 10 is configured to perform correction by combining the correction signal created by the correction signal creation circuit 13 with the Y signal whose phase is matched by the compensation delay circuit 12a in the synthesis circuit 14 via the gain adjustment circuit 17. Outputs Y signal.

The corrected Y signal and C ₁ and C ₂ signals whose phases are matched to the corrected Y signal by compensation delay circuits 12b and 12c, respectively, are input to the matrix circuit 19 to restore the three 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 and add correction signals, the linearity of the correction signal itself is lost, and the sensitivity of the correction filter decreases in dark areas of the screen where the signal level is low, making it difficult to improve image quality in dark areas. effectiveness decreases. In order 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. FIG. 2 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 by using an FIR filter (transversal filter) that can be converted into a linear phase as a digital filter. For example, as shown in FIG.
01a to 201d, and an adder circuit 202. The adder circuit 202 allows the coefficient circuits 201a to 201a to
Linear phase characteristics are obtained by matching the addition phases of 201d. The delay element 200 is a line memory in the case of vertical correction, and is a line memory in the case of horizontal correction.
This is a register for the D conversion clock.

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, an equivalent linear phase is obtained using a two-stage IIR 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. In the following, the composite
It is abbreviated as IIR filter.

FIG. 4 is a block diagram of the composite IIR filter 23 for vertical flare correction. IIR filter 230a
is a delay element 231, coefficient circuits 232a to 232d connected to each tap and input terminal, and an adder circuit 2.
It is of a well-known format synthesized in 33 steps. Here, the delay element 231 is a line memory. The output of the IIR filter 230a is inverted field by field by a field inverter 234a, and further
The signal is input to an IIR filter 230b, and its output is inverted by a field inverter 234b. The phase delay of the IIR filter 230a is reversed and the phase delay of the IIR filter 230a is reversed.
30b, the phase advances, so phase compensation is performed.

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 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. .

Since the filter has been explained above, the general correction signal generation circuit 13 shown in FIG. 2 will be explained below.
The digital signal input is first input to the compensation delay device 25. The compensation delay device 25 receives the signals of the contour correction filter system l and the flare correction filter system m,
Each tap is used to match the phase of the signal in the combining circuit 26, and has two taps with different amounts of delay. The input from the signal line 1 is subjected to contour correction through a vertical contour correction FIR filter 21 and a horizontal contour correction FIR filter 22. On the other hand, the input from signal line m is vertical and horizontal flare correction composite IIR filter 2.
3 and 24, flare correction is performed.

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 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. Figure 6a is a diagrammatic representation of the coefficient circuit, Figure 6b is the ROM 31, Figure 6c is the multiplication circuit 3.
2. d in the figure is a shifter circuit 33. Figure b
In the case of the ROM 31, 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 to the ROM during adjustment, or it may be possible to store various coefficient values in advance, provide enough address lines, and make the values variable by selecting the address lines during adjustment.
In the case of the multiplication circuit 32 shown in FIG. 3C, the coefficients can be adjusted by setting multiplication data (coefficient values). d in the figure shows a shifter circuit 33, for example, a shifter 33.
If 1,332 are connected in parallel, the shifter 331 will shift 2 bits, and if the shifter 332 will shift 3 bits, the input data will be 3/8 when shifting to the lower order.
Output as follows. By controlling the number of shifts or preparing a sufficient number of shifters in advance and selecting them during adjustment, the coefficients can be variably adjusted and set.

〔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, correct this luminance signal, and then restore the three primary color signals from the two color signals and the corrected luminance signal using a matrix circuit. ing. There is no need to provide complex correction signal generation circuits for the three primary colors, and the cost of the device is significantly lowered because only one circuit is required.Furthermore, since the luminance signal includes the three primary colors, it is better than when extracting correction signals only from the G signal. It has a correction effect on signals of arbitrary hue.

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

(3) By providing a gain adjustment circuit and adjusting its gain according to the signal level, increasing the gain when the signal level is low, it is possible to prevent the sensitivity of the correction filter from decreasing in dark areas of the screen due to the gamma characteristics of the video signal. Compensated.

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

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and 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 configuration diagram of an FIR filter used for contour correction, and FIG. 4 - Fig. 5 is a block diagram 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, 11a to 11c...
A/D converter, 12a-12c... Compensation delay circuit, 13... Correction signal creation circuit, 14... Synthesis circuit, 15a-15c... D/A converter, 16...
Delay device, 17...Gain adjustment circuit, 18...Inverse matrix circuit, 19...Matrix circuit, 21-2
2... Contour correction FIR filter, 23-24... Flare correction composite IIR filter, 25... Compensation delay device, 26... Synthesis circuit, 27a-27b... Coring circuit, 200... Delay element, 201a- 2
01d... Coefficient circuit, 202... Addition circuit, 23
0a-230b...(high-pass type) IIR filter, 231, 241...Delay element, 234a-2
34b...field inverter, 240a to 240
b...(high-pass type) IIR filter, 244a~
244b...Line inverter, 30...Coefficient circuit,
31...ROM, 32...Multiplication circuit, 33...Shifter circuit.

Claims (1)

[Claims] 1. 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 and two color signals. After contour/flare correction is performed in the brightness signal correction section, the image quality improvement device inputs the two color signals delayed by the compensation delay circuit to the matrix circuit, restores them to three primary color video signals, and outputs them after D/A conversion. The brightness signal correction section includes a contour/flare correction circuit that is provided in parallel with the brightness signal input, and includes a compensation delay circuit and a subsequent gain adjustment circuit that changes the gain depending on the input level of the brightness signal. It consists of a signal generation 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 performs image contour correction and flare correction in parallel. (a) Contour correction is performed using a wide-pass FIR filter that uses a line memory in series in the vertical and horizontal directions of the image, with a 1-day delay in the vertical direction, and an A/D conversion clock as a 1-delay in the horizontal direction. (b) Flare correction is performed by a high-pass IIR filter using a line memory in series in the vertical and horizontal directions of the image, and a high-pass IIR filter using line memory as one delay in the vertical direction. It has two stages of inverters that invert the field's worth of information alternately in series, and in the horizontal direction it has a high-pass IIR filter that uses an A/D conversion clock register as one delay and one line's worth of information. and an inverter that inverts the gain, the coefficient circuit in the filters and the gain adjustment circuit is characterized in that the coefficients thereof can be variably adjusted and set. Television picture quality improvement device.