JPH0327145B2 - - 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 screens are currently limited to around 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, 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 and contour correction methods described above have not yet been 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 described 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 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 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, /
It converts the data into A and outputs it.

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 compensation signal generation circuit performs contour correction and flare correction of an image in parallel. The signal outputted through a low-pass FIR filter using a line memory and a low-pass FIR filter using an A/D conversion clock register as one delay in the horizontal direction is input to the correction signal generation circuit. (b) Flare correction is performed by subtracting 1 field from a low-pass IIR filter using line memory in series in the vertical and horizontal directions of the image, and in the vertical direction as 1 delay. It has two stages in series alternately with inverters that invert the information of This is done by subtracting a signal outputted through a circuit having two stages of inverters alternately arranged in series from a signal obtained by delaying the input of the correction signal generating circuit.

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 contour correction signal generation circuit and the flare correction signal generation circuit are connected in parallel, and correction of contour and flare is performed in parallel. The contour correction and flare correction are further performed in series in the vertical and horizontal directions. As will be explained in detail in the example, an FIR filter is used as the contour correction filter, and an IIR filter is used as the flare correction filter, which has the characteristics of a low-pass filter, and after correction, is subtracted from the input video signal to reduce the high-pass. A correction signal is created by giving it type filter characteristics.

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, by the combination circuit 14a. 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. Note that in the following explanation, the explanation will be made without particularly distinguishing between R, G, and B signals, so 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 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 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. 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, and the contour correction and flare correction emphasize the high-pass characteristic and reduce the low-pass characteristic as frequency characteristics, and the filter is a high-pass type filter. However, when high-pass filters are used in series for vertical and horizontal corrections, in the case of a quadrilateral window pattern on the screen, vertical and horizontal corrections are related, and the polarity to be improved is determined. A correction signal of opposite polarity appears on the diagonal outer side diagonally to the inner corner of the window. In the present invention, strictly considering this point,
All the filters are low-pass type, and by subtracting the filter output 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 used to match the signal phases of the contour correction filter system l and the flare correction filter system m with a signal line n serving as a reference, which will be described later, and subtraction circuits 26a and 26b. It has three different taps. However, the reference signal line n may be configured to take out a signal delayed by an appropriate number of lines from the tap 21-1 of the line memory column of the vertical contour correction FIR filter 21. signal line l
The input from the vertical contour correction FIR filter 21,
After passing through the horizontal contour correction FIR filter 22, the signal is input to the subtraction circuit 26a and subtracted from the reference signal. This makes it possible to obtain effective high-frequency characteristics for contour correction, and at the same time, the correction at the four corners of the window pattern becomes continuous.
Similarly, the input from the signal line m passes through vertical and horizontal flare correction composite IIR filters 23 and 24, and is subtracted from the reference signal by a subtraction circuit 26b, thereby effectively obtaining a correction signal with high frequency characteristics.

Although the outputs of the subtracting circuits 26a and 26b can be immediately combined in a combining circuit 28 to obtain a correction signal output, in the circuit shown in FIG. 2, the outputs 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.
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 be able to make some adjustments even in the final stage of manufacturing the receiver.

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, b is the ROM 31, and c 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 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 the shifter 332 will shift 3 bits, so if it is a shift to the lower order, the input data will be 3/8.
Output as follows. 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) 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 the quadrilateral window pattern. .

(4) Since a reverse gamma correction circuit is provided and the signal is linearized and then corrected, the correction effect for dark areas of the screen where the signal level is low does not deteriorate.

(5) As coefficient circuits used in filters, inverse gamma correction circuits, gamma correction circuits, etc., coefficients can be variably adjusted and set, making adjustment easy, which is advantageous when mass producing devices. It is.

[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 is a configuration diagram. - 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...D/A converter, 16a-16
c... Reverse gamma correction circuit, 17a-17c... Gamma correction circuit, 21-22... Contour correction FIR filter, 23-24... Flare correction complex IIR filter, 25... Compensation delay device, 26a-26b... …
Subtraction circuit, 27a-27b... coring circuit,
28...Synthesizing circuit, 200...Delay element, 201
a to 201d...coefficient circuit, 202...addition circuit, 230a to 230b...(low-pass type) IIR
Filter, 231, 241...Delay element, 234
a~234b...Field inverter, 240a~
240b...(Low pass type) IIR filter, 24
4a-244b... Line inverter, 30... Coefficient circuit, 31... ROM, 32... Multiplication circuit, 33
...Shifter circuit.

Claims (1)

[Scope of Claims] 1. In a projection display type television receiver, provided for each series of three primary color video signals,
An image quality improvement device that inputs each video signal, performs A/D conversion, performs contour/flare correction, performs D/A conversion, and outputs the image, wherein the contour/flare correction section inputs a digital video signal. A compensating delay circuit, a contour/flare correction signal generating circuit provided in parallel with an inverse gamma correction circuit in the preceding stage and a gamma correcting circuit in the succeeding stage, and synthesizing the outputs of the compensating delay circuit and the gamma correcting circuit. 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; The signal is output through a low-pass FIR filter using a line memory as one delay in the direction, and a low-pass FIR filter using an A/D conversion clock register as one delay in the horizontal direction. This is done by subtracting the input of the correction signal creation circuit from the delayed signal. (b) Flare correction is a low-pass type that uses line memory in series in the vertical and horizontal directions of the image, and as a 1-delay in the vertical direction. It has two stages of IIR filters and inverters that invert one field's worth of information alternately in series, and in the horizontal direction, a low-pass IIR filter that uses an A/D conversion clock register as one delay, and one This is done by subtracting the signal outputted through a circuit having two stages of inverters that invert the information for each line alternately in series from the signal delayed from the input of the correction signal generation circuit, and the filters , the gamma correction circuit, and the inverse gamma correction circuit, the coefficients of which can be variably adjusted and set. A television picture quality improvement device characterized by: