JPH0584996B2 - - 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 reached the stage of fully adopting 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 temperature-related fluctuations 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 materialize 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 provided for each series of three primary color video signals in a projection display type television receiver, inputs each video signal, performs A/D conversion, performs contour/flare correction, and performs D/D conversion. /
It is converted into A and output.

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

The contour/flare correction signal generation circuit performs contour correction and flare correction of the image 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 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 in the horizontal 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 coefficient circuits in the filters, gamma correction circuit, and inverse gamma correction circuit can have their coefficients variably adjusted and set.

[Effect]

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

The correction signal generation circuit includes a contour correction signal generation circuit and a flare correction signal generation circuit in parallel.
Contour and flare corrections are performed in parallel. The contour correction and flare correction are performed in parallel in the vertical and horizontal directions. As will be explained in detail in the embodiment, an FIR filter is used as the contour correction filter, and an IIR filter is used as the flare correction filter, giving them the characteristics of a high-pass filter.

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

Incidentally, coefficient circuits are required for the filter, gamma correction circuit, and inverse gamma correction circuit, but they are adjusted and set optimally using variably adjustable circuits.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings.
The basic configuration of the embodiment is shown in FIG. The video signals of the three primary colors are corrected by the same and independent circuits. In terms of the R signal, it is converted into a digital video signal by the A/D converter 11a, an inverse gamma correction circuit 16a, a correction signal generation circuit 13a,
The correction signal generated by the gamma correction circuit 17a is combined with the signal obtained by delaying the digital video signal by the compensation delay circuit 12a in the combination circuit 14. The compensation delay is combined with the delay caused by the correction signal generation circuit 13a and the like. The digital video signal corrected in this way is output as an analog signal by the D/A converter 15a. In addition, in the following explanation, especially R,
Since the explanation will be made without distinguishing between the G and B signals, the suffixes in the symbols will be omitted.

The inverse gamma correction circuit 16 and the gamma correction circuit 17 are provided before and after the correction signal creation circuit 13 to create a correction signal for the linearized signal, and the reason for this will be explained below. Due to the characteristics of the cathode ray tube, the input signal to the projection tube is a nonlinear signal obtained by raising the input to the gamma power. When filtering such input signals to create 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. Therefore, the signal is first converted into a linear signal by an inverse gamma correction circuit and then corrected.

Next, the correction signal generation circuit 13 will be explained. 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. Further, for each correction, vertical correction and horizontal correction are performed in parallel.

Before explaining the overall configuration of FIG. 2, each filter will be explained. 21 and 22 are contour correction FIR filters for vertical and horizontal correction, respectively. Since the number of lines or dots involved in contour correction is small, it can be made small-scale 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 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, 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 23
0a is of a well-known type in which a delay element 231 and coefficient circuits 232a to 232d connected to each tap and input terminal are synthesized by an adder circuit 233. Here, the delay element 231 is a line memory. IIR
The output of the filter 230a is inverted in field units by a field inverter 234a, and further input to an IIR filter 230b having the same configuration, and the output is inverted by a field inverter 234b. Since the phase delay of the IIR filter 230a is inverted and passed through the IIR filter 230b, the phase advances, so that phase compensation is achieved.

Figure 5 shows composite IIR filter 2 for horizontal flare correction.
4 is a block diagram of FIG. 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, and the contour correction and flare correction involve emphasizing the high-pass characteristic and lowering the low-pass characteristic as frequency characteristics, and the filter is a high-pass type filter.

Since the filter has been explained above, the correction signal generation circuit 13 shown in FIG. 2 will be explained in general below.
The digital signal input is first input to the compensation delay device 25, and signals given a predetermined amount of delay are sent from the taps to signal lines l ₁ , l ₂ , m ₁ , and m _{2 ,} respectively. Signal line
The inputs from l ₁ and l ₂ are subjected to contour correction by a vertical contour correction FIR filter 21 and a horizontal contour correction FIR filter 22, respectively, and then synthesized by a synthesis circuit 28a. Inputs from m ₁ and m ₂ are subjected to flare correction by a vertical flare correction compound IIR filter 23 and a horizontal flare correction compound IIR filter 24, respectively, and then synthesized by a synthesis circuit 28b. Coring circuit 2
7a and 27b will be described later, but the outputs of the combining circuits 28a and 28b are further combined by a combining circuit 26 and output as a correction signal.

Signal lines l ₁ , l ₂ , output from the compensation delay device 25
m ₁ and m ₂ provide different amounts of delay to the digital signal. Determination of this amount of delay is quite complicated because it is determined so that the phases of the input signals to be combined are all matched in all of the combining circuits 28a, 28b, and 26. In this circuit, contour and flare corrections are performed in parallel in the vertical and horizontal directions. Another method is to perform the vertical and horizontal directions in series,
Compensation delay device becomes simple. However, if high-pass filters are used in series for vertical and horizontal correction, in the case of a quadrilateral window pattern on the screen,
In connection with the vertical and horizontal corrections, a correction signal of polarity opposite to that to be improved appears on the diagonal outer side diagonally to the inner corner of the window. In the present invention, since the vertical and horizontal directions are performed in parallel, the corrections are not related to each other, and good correction can be obtained even at the four corners of the window pattern.

The above correction outputs can be immediately synthesized in the synthesis circuit 26 to obtain a correction signal output, but in the circuit shown in FIG. 2, the signals are synthesized after passing through the coring circuits 27a and 27b. The correction signal emphasizes the high-frequency components of the signal, and this is particularly noticeable in contour correction. At this time, noise in the same high-frequency region is also emphasized, and the S/N tends to deteriorate in small areas of the screen. Therefore, the coring circuits 27a and 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, gamma correction circuits, inverse gamma correction 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 have some degree of adjustability in the final stages 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 32,
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 coefficient can be adjusted by setting the multiplication data (coefficient value). 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 output as 3/8 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 correction is performed for each of the three primary color video signals, the correction is complete for any image. When a correction signal is extracted only from the G signal as in the conventional example, the correction effect is small for an image with a small G signal component, but the quality is high.

(2) The former is used as a contour/flare correction filter.
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. This is also why it is possible to correct the three primary colors separately as shown in (1).

(3) Although the filter characteristics are high-pass type, vertical correction and horizontal correction are performed in parallel, so good correction can be obtained even at the four corners of a quadrilateral wind pattern without mutual correlation. Furthermore, since all the filters are connected in parallel, there is little delay in the correction signal generation circuit.

(4) Since a reverse gamma correction circuit is provided and correction is performed after linearizing the signal, the correction effect for dark areas of the image where the signal level is low does not deteriorate.

(5) As coefficient circuits used in filters, inverse gamma correction circuits, gamma correction circuits, etc., use ones that can variably adjust and set the coefficients.
Since adjustment is easy, it is advantageous when mass producing devices.

[Brief explanation of the drawing]

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. 11a-11c...A/D converter, 12a-1
2c... compensation delay circuit, 13a-13c... correction signal creation circuit, 14a-14c... synthesis circuit,
15a-15c...DA/converter, 16a-16
c... Inverse gamma correction circuit, 17a-17c... Gamma correction circuit, 21-22... Contour correction FIR filter, 23-24... Flare correction composite IIR filter, 25... Compensation delay device, 26, 28a, 28
b...Synthesis circuit, 27a-27b...Coring circuit, 200...Delay element, 201a-201d
... Coefficient circuit, 202 ... Addition circuit, 230a ~
230b...(high-pass type) IIR filter, 23
1,241...delay element, 234a-234b...
...Field inverter, 240a-240b...
(High-pass type) IIR filter, 244a to 244
b... Line inverter, 30... Coefficient circuit, 31...
...ROM, 32...multiplication circuit, 33...shifter circuit, 331, 332...shifter.

Claims (1)

[Scope of Claims] 1. In a projection display type television receiver, each of the three primary color video signal series is provided, each video signal is input and A/D converted, and after contour/flare correction, D/A The image quality improvement device converts and outputs the image, and the contour/flare correction section includes a compensation delay circuit and an inverse gamma correction circuit in a preceding stage and a gamma correction circuit in a subsequent stage, which are provided in parallel to the digital video signal input. The contour/flare correction signal generation circuit includes a contour/flare correction signal generation circuit with an attached circuit, and a synthesis circuit that synthesizes the outputs of the compensation delay circuit and the gamma correction circuit, and the contour/flare correction signal generation circuit is configured to perform image contour correction and flare correction. (a) Contour correction is performed in parallel in the vertical and horizontal directions of the image, with a high-pass FIR filter using a line memory as 1 delay in the vertical direction and 1 delay in the horizontal direction. (b) Flare correction is performed using a high-pass FIR filter that uses the register of the A/D conversion clock as a delay. (b) Flare correction is performed in parallel in the vertical and horizontal directions of the image, and line memory is used as a 1-delay in the vertical direction. It has two stages of high-pass IIR filters and inverters that invert one field's worth of information alternately in series, and a high-pass filter that uses the register of the A/D conversion clock as one delay in the horizontal direction. It is made up of a circuit having two stages each of type IIR filters and inverters that invert one line's worth of information alternately in series. It can be adjusted and set. A television picture quality improvement device characterized by: