JPH0628390B2 - TV image quality improvement device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color television receiver, in particular a so-called projection receiver that obtains an image by projecting image light of three primary colors from a projection tube onto a large-screen screen. Regarding

[Conventional technology]

A CRT having a large image plane is currently limited to about 40 inches in manufacturing. Above that, the projection tube method is currently practical. In the case of high quality large screen, high quality cannot be obtained simply by enlarging the screen,
As the number of scans is increased, the demand for image quality becomes stricter. In particular, in the projection type, since the current density of the beam of the projection tube is made about 5 to 10 times that of the direct-view type, the beam becomes thick and the resolution is lowered due to the influence of the lens.
The flare caused by the high-brightness projection tube, lens, etc. caused the deterioration of image quality.

Is the projection type large screen receiver in the development stage?
The above-mentioned flare correction / contour correction means have not been established as a completely established technology. Conventionally, as a flare correction means proposed for high-definition television, "Improvement of image quality of projection display for high-definition television-removal of flare interference by SAW filter-", TV Conference 1982 National Convention SP1-14, Kanazawa et al. There is a method using an analog filter in which the video signal is once AM-modulated, passed through a SAW filter, and demodulated again. This method attenuates the low frequency component for flare correction by attenuating the modulated signal wave at ± 1 MHz near the modulation carrier frequency. However, this method requires the use of a high frequency with a modulation carrier frequency of 100 MHz or more, and even if the flare component in the horizontal direction of the screen can be removed, a very accurate 1-line delay line is obtained when it is applied to the vertical direction component. It is difficult to realize because a large number are required.

For contour correction, the method of extracting the contour component of the image and adding it to the original signal is generally used, but most of the methods are to enhance only the horizontal direction of the screen. There are few examples because I have to create

By the way, in order to prevent a reduction in resolution, the contour correction for emphasizing the contour and the flare correction for suppressing the flare are enhancement of high-frequency components including differentiation, and in the latter, a screen with many flares has a low MTF (resolution characteristic). Since it is lifted up in the frequency range, it gives attenuation characteristics to low frequency components. Therefore, the contour correction and the flare correction have a property that they can be performed in parallel in terms of frequency, but it is difficult to realize if a digital method and an analog method are mixed or if they are unified into one method. There is no example of performing both correction processes.

[Problems to be Solved by the Invention] As described above, regarding the large-screen projection receiver,
The necessary flare correction / contour correction means are fully adopted, and it has not reached the stage of obtaining a high quality image. Here, totally means that both the vertical and horizontal components can be corrected for contour / flare correction. For the analog method,
In particular, there are problems such as uniformity of filter characteristics and fluctuation of delay line due to temperature, and it is difficult to adjust the timing of all devices in a large-scale system. In principle, the digital method can sufficiently deal with the above-mentioned problems and is highly flexible in design. However, there is a difficulty in increasing the scale. The problem is 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 improving apparatus that removes flare components in the horizontal and vertical directions of the screen and simultaneously performs correction for emphasizing the contour of the screen in parallel by digital means, and in a small scale. It is to realize in the form.

[Means for solving problems]

An image quality improving apparatus of the present invention is provided for each series of three primary color video signals in a projection display type television receiver, and inputs each video signal for A / D conversion,
After the contour / flare correction, it is D / A converted and output.

The contour / flare correction section is provided in parallel with a digital video signal input, and has a delay circuit for compensation and a contour / flare correction signal generation circuit provided with an inverse gamma correction circuit in the preceding stage and a gamma correction circuit in the succeeding stage. , A compensating circuit that composes 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 an image in parallel. (A) The contour correction is performed in parallel in the vertical direction / horizontal direction of the image with one delay in the vertical direction. As a high-pass type FIR filter using a line memory and a high-pass type FIR filter using an A / D conversion clock register as one delay in the horizontal direction, (b) flare correction is performed in the vertical direction of the image. A high-pass type IIR filter using a line memory as one delay in parallel in the horizontal direction and an inverter that inverts information for one field are alternately arranged in two stages in series in the vertical direction.
In the horizontal direction, a circuit having two stages of a high-pass IIR filter using an A / D conversion clock register as one delay and an inverter that inverts information for one line is alternately arranged in series in the horizontal direction.

A RAM is used as the filter, the gamma correction circuit, and the coefficient circuit in the inverse gamma correction circuit, and data is written during the video blanking period, and the input signal of the coefficient circuit is the address signal of the RAM during the video period. The data is read out and becomes an output signal.

[Action]

According to the present invention, the correction is separately provided for each series of the three primary color image signals so that an appropriate correction can be obtained for each signal. Since all corrections are digital processing, they are input to the contour / flare correction unit after A / D conversion. Since the input video signal is gamma-processed to be non-linear, it is linearized through an inverse gamma correction circuit and then corrected.

In the correction signal generation circuit, the contour correction signal generation circuit and the flare correction signal generation circuit are arranged in parallel, and the contour and flare are corrected in parallel. The contour correction and the flare correction are arranged in parallel in the vertical direction and the horizontal direction. As will be described in detail in the embodiments, an FIR filter is used as a contour correction filter and an IIR filter is used as a flare correction filter, which has characteristics of a high-pass filter.

The output of the contour / flare correction signal generating circuit is given a gamma characteristic again, and then combined with the output of the compensating delay circuit in the combining circuit. Next, the output of this synthesizing circuit is subjected to D / A conversion, whereby a three-primary-color video signal with improved image quality can be obtained.

Although a filter, a gamma correction circuit, and an inverse gamma correction circuit require a coefficient circuit, RAM is used to
It is possible to write data in M and change the coefficient value.

〔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 independent constituent circuits. Describing the R signal, the A / D converter 11a forms a digital video signal, and the correction signal generated by the inverse gamma correction circuit 16a, the correction signal generation circuit 13a, and the gamma correction circuit 17a is delayed for compensating the digital video signal. The signal delayed by the circuit 12a is combined with the combining circuit 14a. The compensation delay is combined with the delay generated in the correction signal generation circuit 13a or the like. The digital video signal corrected in this way is used for D / A
The converter 15a outputs the analog signal. It should be noted that in the following description, the suffixes of the reference numerals will be omitted because the description will be made without distinction from the R, G, and B signals.

The inverse gamma correction circuit 16 and the gamma correction circuit 17 are provided before and after the correction signal generation circuit 13 to generate a correction signal for a linearized signal. The reason for this will be described below. Due to the characteristics of the cathode ray tube, the input signal of the projection tube is a non-linear signal that is gamma-powered with respect to the input. When such an input signal is filtered and a correction signal is created and added, the linearity of the correction signal itself is lost, the sensitivity of the correction filter is reduced in the dark area of the screen where the signal level is low, and the image quality of the dark area is reduced. The improvement effect decreases. Therefore, the signal is once corrected into a linear signal by the inverse gamma correction circuit and corrected.

Next, the correction signal generation circuit 13 will be described. Figure 2
It is a circuit block diagram in which contour correction and flare correction are independently performed in parallel. Since they can be executed independently of each other, parallelization reduces the signal delay caused by the correction. Further, for each correction, vertical correction and horizontal correction are performed in parallel.

Before describing the overall configuration of FIG. 2, each filter will be described. Reference numerals 21 and 22 are contour correction FIR filters for vertical and horizontal corrections, respectively. Since the number of lines or the number of dots involved in the correction is small, the contour correction can be performed on a small scale even if the digital filter is constituted by an FIR filter (transversal filter) capable of linear phase. For example, as shown in FIG. 3, it comprises a delay element 200, coefficient circuits 201a to 201d, and an adder circuit 202.
A linear phase characteristic is obtained by adjusting the addition phases of the coefficient circuits 201a to 201d by the addition circuit 202.
The delay element 200 is a line memory in the case of vertical correction. In the case of horizontal correction, it is a register of A / D conversion clock.

Next, 23 and 24 are special flare correction filters for vertical and horizontal corrections, respectively. Since the number of lines and dots involved in flare correction increases, an IIR filter (recursive filter) is used to reduce the scale. However, obtaining a linear phase with an IIR filter requires special means. In the present invention, the IIR filter output is inverted,
A linear phase is equivalently obtained by using a two-stage IIR filter in which the inverted output is further input to an IIR filter having the same characteristics and then the output is inverted. Below is the composite IIR
It is abbreviated as a filter.

FIG. 4 is a block diagram of the composite IIR filter 23 for vertical flare correction. The IIR filter 230a includes a delay element 231 and a coefficient circuit 2 connected to each tap and an input terminal.
This is a well-known type in which 32a to 232d are combined by the adder circuit 233. Here, the delay element 231 is a line memory. The output of the IIR filter 230a is inverted on a field-by-field basis by the field inverter 234a, input to the IIR filter 230b having the same configuration, and its output is inverted by the field inverter 234b. IIR filter 2
The phase delay of 30a is inverted and the IIR filter 230b is inverted.
Since the phase advances by passing through, the phase is compensated.

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. Just delay element 241
Is an A / D conversion clock register, and is different from the line inverters 244a and 244b.

The configuration of the filter has been described above. The contour correction and the flare correction are emphasis on high-pass characteristics and deterioration of low-pass characteristics as frequency characteristics, and a high-pass filter is used as the filter.

Since the filter has been described above, the general description of the correction signal generating circuit 13 in FIG. 2 will be given below. The digital signal input is first input to the compensating delay device 25, and the signals given a predetermined delay amount from the taps are input to the signal lines l ₁ , l ₂ ,
Send to m ₁ and m ₂ . Inputs from the signal lines l ₁ and l ₂ are contour-corrected by the vertical contour correction FIR filter 21 and the horizontal contour correction FIR filter 22, respectively, and are synthesized by the synthesis circuit 28a. The inputs from m ₁ and m ₂ are flare corrected by the vertical flare correction composite IIR filter 23 and the horizontal flare correction composite IIR filter 24, respectively, and are combined by the combining circuit 28b. Coring circuit 27
a. Although the description of 27b will be given later, the synthesis circuit 28a,
The output of 28b is further combined by the combining circuit 26 and output as a correction signal.

The signal lines l ₁ , l ₂ , output from the compensating delay device 25,
m ₁ and m ₂ give different delay amounts to the digital signal. This delay amount is determined by combining circuit 28a,
In all of 28b and 26, it is considerably complicated because the phases of the respective input signals to be combined are determined so as to match each other. In this circuit, both the contour and flare corrections are performed in parallel in the vertical and horizontal directions. As another method, it is possible to perform the vertical direction and the horizontal direction in series, which simplifies the compensating delay device. 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, the corrections in the vertical and horizontal directions are related, and the polarity to be improved and The polarity correction signal appears on the outside of the lick, which is diagonal to the inside angle of the window. In the present invention, since the vertical direction and the horizontal direction are performed in parallel, mutual corrections are not related to each other, and good correction can be obtained even at the four corners of the window pattern.

The correction output can be immediately obtained by synthesizing the correction output in the synthesizing circuit 26, but in the circuit of FIG. 2, the correction output is performed after passing through the coring circuits 27a and 27b. The correction signal emphasizes the high frequency component of the signal, and is particularly remarkable in contour correction. At this time, noise in the same high frequency region is also emphasized, and the S / N is
Tend to deteriorate. So noise becomes a problem,
In a place where the signal level is low, a circuit in which the correction signal is set to zero to prevent noise from being emphasized is the coring circuit 27a, 2a.
7b. That is, a dead zone is provided near zero of the correction signal, but it is not always necessary when the projected screen is small.

Although the circuit configuration of the present invention has been described above, the present invention requires a large number of coefficient circuits for various filters, a gamma correction circuit, an inverse gamma correction circuit, a coring circuit, and the like. Each coefficient value of the coefficient circuit becomes various, and it is often necessary to adjust and set for each receiver. Therefore, it is necessary to be adjustable in the final stage of manufacturing the image receiver, and even when the image receiver is put to practical use, the image quality is subtly affected when the installation environment changes. Even in such a case, it is preferable that the user can freely adjust.

In the present invention, a freely writable RAM is used to provide a coefficient circuit that meets the above demand. FIG. 6 (a) is a schematic representation of the coefficient circuit, and FIG. 6 (b) shows a circuit using a RAM. In this circuit, data is written from the separately provided CPU during the video blanking period. In the figure, the mode of the selector 31 is set to the CPU address side, and the data from the CPU is RAM-stored at a predetermined address via the buffer 33.
Write to 32. During the video period, the mode of the selector 31 is set to the input side of the coefficient circuit, and the data multiplied by the coefficient is read out via the buffer 34 and sent as the output of the coefficient circuit. Writing to the RAM may be in the DMA mode. The coefficient of the coefficient circuit can be made variable by arbitrarily setting the data to be written in the RAM 32 from the CPU.

〔The invention's effect〕

As described in detail above, the image quality of a large-screen projection television receiver can be made extremely high by performing contour / flare correction in parallel. The effects of the present invention are as follows.

(1) Since correction is performed for each of the three primary color video signals, the correction is perfect for any image. When the correction signal is extracted from only 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) FI is applied to the former as a contour / flare correction filter.
By using an R filter and a composite IIR filter for the latter, a small-scale circuit configuration with a linear phase and a small number of elements can be obtained. This is the reason why the three primary colors can be corrected separately as in (1).

(3) Filter characteristics are high-pass type, but vertical correction
Since the horizontal correction is performed in parallel, good correction can be obtained even at the four corners of the quadrilateral window pattern without mutual relation. Further, since all the filters are arranged in parallel, the delay of the correction signal generating circuit is small.

(4) Since the inverse gamma correction circuit is provided and the signal is linearized before the correction, the correction effect in the dark area of the screen where the signal level is low does not deteriorate.

(5) The coefficient can be arbitrarily set by using the RAM as a coefficient circuit used for filters, an inverse gamma correction circuit, a gamma correction circuit, and the like. Not only is it easy to adjust and set at the manufacturing stage, but it can be made variable even when the receiver is in operation, and the image quality can be kept in an optimum state in any environment.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1 is a basic block diagram of the configuration, FIG. 2 is a block diagram of a correction signal generating circuit,
FIG. 3 is a block diagram of an FIR filter used for contour correction, FIGS. 4 and 5 are block diagrams of a composite IIR filter used for flare correction, and FIG. 6 is a diagram showing an example of a coefficient circuit. 11a to 11c ... A / D converter, 12a to 12c ... Compensation delay circuit, 13a to 13c ... Correction signal creating circuit, 14a to 14c ... Combining circuit, 15a to 15c ... D / A converter, 16a to 16c ... Inverse gamma correction circuit, 17a to 17c ... Gamma correction circuit, 21 to 22 ... Contour correction FIR filter, 23 to 24 ... Flare correction composite IIR filter, 25 ... Compensation delay device, 26, 28a, 28b ... Combining circuit, 27a-27b ... Coring circuit, 200 ... Delay element, 201a-201d ... Coefficient circuit, 202 ... Addition circuit, 230a-230b ... (High-pass type) IIR filter , 231 and 241 ... delay element, 234a to 234b ... field inverter, 240a to 240b ... (high-pass type) IIR filter, 244 a to 244b ... Line inverter, 30 ... Coefficient circuit, 31 ... Selector, 32 ... RAM, 33, 34 ... Buffer.

Claims (1)

[Claims] 1. A projection display type television receiver is provided for each of the three primary color video signal series, inputs each video signal and A / D converts it, and after contour / flare correction, D / A conversion. The contour / flare correction unit includes a compensation delay circuit, an inverse gamma correction circuit in the preceding stage, and a gamma correction circuit in the succeeding stage, which are provided in parallel with the digital image signal input. The contour / flare correction signal generating circuit, and a synthesis circuit for synthesizing the outputs of the compensation delay circuit and the gamma correction circuit, the contour / flare correction signal generating circuit performs contour correction and flare correction of an image. (B) Contour correction is performed in parallel in the vertical and horizontal directions of the image, and a high-pass FIR filter using a line memory as one delay in the vertical direction, horizontal A high-pass FIR filter using A / D conversion clock registers is used as one delay in the direction, and (b) flare correction is performed in parallel in the vertical and horizontal directions of the image, and one line in the vertical direction as one delay. A high-pass IIR filter using a memory and an inverter that inverts information for one field are alternately arranged in two stages each in series, and an A / D conversion clock register is used as one delay in the horizontal direction. A high pass IIR filter and an inverter that inverts information for one line are alternately arranged in two stages in series, and the filters, the gamma correction circuit, and the coefficient circuit in the inverse gamma correction circuit are RAMs. During the video period, the input signal of the coefficient circuit is the address signal of the RAM, and the multiplication result for obtaining the desired characteristic is written in advance according to the input address signal. Crowded in Yes, the television picture quality improvement device, wherein the data corresponding to the input address signal is made the output signal is read.