JPH0327152B2 - - 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.

[Problems to be Solved by the Invention] As stated above, it is necessary to fully adopt the necessary flare correction and contour correction means for large-screen projection receivers to obtain high-quality images. It hasn't improved to that point. 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 inputs a luminance signal and two color signals in a projection display type television receiver, performs A/D conversion on each, and then uses the digital luminance signal to generate a contour/flare correction 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 generating section is composed of a cascade connection of an inverse gamma correction circuit to which a digital luminance signal is input, a contour/flare correction signal generation circuit, and a gamma correction circuit.

The contour/flare correction signal generation circuit performs image contour correction and flare correction in parallel. The signal output through the low-pass FIR filter using line memory and the low-pass FIR filter using the 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 from the delayed signal, and (b) Flare correction is performed by using a low-pass IIR filter using a line memory and 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 one delay. It has two stages of inverters that invert the information alternately in series, and in the horizontal direction, it has one delay as a low-pass IIR filter using the A/D conversion clock register and inverts the information for one line. This is done by subtracting the signal output through a circuit having two stages of inverters alternately in series from the signal delayed from 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]

The present invention provides a luminance signal (Y signal) obtained by appropriately extracting each primary color signal of R, G, and B through an inverse matrix circuit, and two color signals, that is, a wideband color signal C _W ,
Narrow gamut color signal C _N (Hereinafter, C ₁ signal and C ₂ signal, respectively)
It is possible to obtain a high-quality three-primary color video signal by inputting a signal (handled as a signal) and correcting contours and flare. The correction signal is created by one contour/flare correction signal generation section (hereinafter referred to as a correction signal generation section) which inputs the luminance signal.

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. What is this contour correction and flare correction?
Furthermore, the vertical direction and the horizontal direction are arranged in series.
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.
A filter is used, and the filter is a low-pass filter, and by subtracting the filter output from the input Y signal, it has 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 the correction signal is 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, C ₁ signal, and C ₂ signal are converted into digital video signals by the A/D converters 11a to 11c, respectively, and input to the matrix circuit 18, where they are restored to RGB signals. Each RGB signal has a compensation delay circuit 1
2a to 12c, and the outputs of the correction signal generating section 10 are synthesized by synthesis circuits 14a to 14c, respectively.
The compensation delay is combined with the delay occurring in the correction signal generating section 10. The digital video signals corrected in this manner are outputted as analog signals by the D/A converters 15a to 15c.

The correction signal generator 10 inputs the digital Y signal, that is, the output of the A/D converter 11a, and generates each
A correction signal commonly used for RGB signals is generated by a correction signal generation circuit 13, and an inverse gamma correction circuit 16 is provided before and a gamma correction circuit 17 is provided after the correction signal generation circuit 13.

The above reason 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 inverse gamma correction circuit converts the signal into a linear signal and then performs correction. Note that the correction signal generating section 10 can change the gain 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. 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 reacted. 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 is described below, 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, 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 filters are low-pass type, and the filter output is subtracted from the input signal to effectively make it high-pass type, thereby ensuring continuity of correction at the four corners. I am getting .

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 for transmitting a reference signal, which will be described later, and subtraction circuits 26a and 26b. It has three taps with different amounts. However, the signal line n is connected to the tap 21- of the line memory column of the vertical contour correction FIR filter 21.
A signal delayed by an appropriate number of lines from 1 may be extracted. Input from signal line l is vertical contour correction FIR filter 21, horizontal contour correction FIR
After passing through the filter 22, it is input to the subtraction circuit 26a,
Subtract from reference signal. By this,
Effective high-frequency characteristics for contour correction can be obtained, and the correction at the four corners of the window pattern is 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 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 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 3/8 when shifting to the lower order.
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) 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 the matrix circuit to correct the three primary color video signals. Therefore, only one correction signal generation section including a complicated correction signal generation circuit is required.
This has the advantage of significantly lowering equipment costs. Further, since the luminance signal includes the three primary color video signals and the correction value is added for each of the three primary color video signals, the amount of correction can be adjusted appropriately.

(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.

(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 does not deteriorate in dark areas of the screen where the signal level is low.

(5) As coefficient circuits used in filters, gamma correction circuits, inverse 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 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... Correction signal generation section, 11a to 11c...
A/D converter, 12a-12c...compensation delay circuit, 13...correction signal creation circuit, 14a-14c
...Composition circuit, 15a-15c...D/A converter, 16...Inverse gamma correction circuit, 17...Gamma correction circuit, 18...Matrix circuit, 21-22
... Contour correction FIR filter, 23-24 ... Flare correction composite IIR filter, 25 ... Compensation delay device, 26a-26b ... Subtraction circuit, 27a-27
b...Coring circuit, 28...Synthesizing circuit, 20
0...Delay element, 201a-201d...Coefficient circuit, 202...Addition circuit, 230a-230b...
...(Low pass type) IIR filter, 231, 241
...Delay element, 234a-234b...Field inverter, 240a-240b...(low-pass type) IIR filter, 244a-244b...Line inverter, 30...Coefficient circuit, 31...ROM,
32... Multiplier circuit, 33... Shifter circuit.

Claims (1)

[Claims] 1. In a projection display type television receiver, a brightness signal and two color signals are input, each is A/D converted, and then a contour/flare correction signal is generated using the digital brightness signal. The contour/flare correction signal is synthesized with the three primary color video signals which are generated, restored by the matrix circuit from the digital luminance signal and color signal, and delayed through the compensation delay circuit, and then combined with the D/Flare correction signal.
The image quality improvement device performs A conversion and outputs the image quality, and the contour/flare correction signal generating section is a cascade of an inverse gamma correction circuit inputting a digital luminance signal, a contour/flare correction signal generation circuit, and a gamma correction 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; A correction signal is created from the signal outputted through a low-pass FIR filter using a line memory as a 1-delay, and a low-pass FIR filter using an A/D conversion clock register as a 1-delay in the horizontal direction. (b) Flare correction is performed by subtracting the input of the circuit from the delayed signal. (b) Flare correction is performed using a low-pass IIR filter 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 inverters that invert one field's worth of information alternately in series, and in the horizontal direction a low-pass IIR filter using an A/D conversion clock register as one delay, and one line's worth of inverters. This is done by subtracting the signal output through a circuit having two stages of inverters that invert information alternately in series from the signal delayed from the input of the correction signal generation circuit, and the filters and gamma correction circuit A television image quality improvement device, characterized in that the coefficient circuit in the inverse gamma correction circuit is capable of variably adjusting and setting the coefficients.