JPH0330355B2 - - 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 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, and performs D/D conversion. /
It is converted into A and output.

The contour/flare correction section is configured to generate a contour/flare correction signal, which is provided in parallel with the digital video signal input, and includes a compensation delay circuit and a subsequent gain adjustment circuit that changes the gain depending on the input level of the digital video signal. It consists of a creation circuit and a synthesis circuit that synthesizes the outputs of the compensation delay circuit and the gain adjustment circuit.

The contour/flare correction signal creation circuit is a circuit that serially performs correction in the vertical and horizontal directions using a group of low-pass FIR filters, and then subtracts the signal from the delayed digital video signal, and (a) The vertical FIR filter uses a line memory with one delay in common, uses all taps to obtain a flare correction signal, uses the required number of taps in the center to obtain a contour correction signal, and synthesizes both correction signals. (b) The horizontal FIR filter has a common row of A/D conversion clock registers with one delay, and uses all the taps to generate the flare correction signal, and uses the required number of taps in the center to generate the flare correction signal. The contour correction signal is
The configuration is such that both correction signals are obtained respectively and combined.

Here, the filters and the coefficient circuit in the gain adjustment circuit use RAM and write data during the video blanking period, and during the video period, the input signal of the coefficient circuit is the address signal of the RAM, and the data is read. The signal is output as an output signal.

[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.

After the correction signal generation circuit performs vertical and horizontal correction using a low-pass FIR filter,
By subtracting it from the digital video signal input, a correction signal with high-pass characteristics is obtained. The low-pass FIR filter is configured to perform flare correction and contour correction in parallel, using a common delay column and using all taps for flare correction and the required number of taps in the center for contour correction.

A synthesis circuit combines the above correction signal with the output that has passed through the compensation delay 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.

Although a coefficient circuit is required for the filter and gain adjustment circuit, it is possible to change the coefficient value by writing data to the RAM using RAM.

〔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, a digital video signal is generated by the A/D converter 11a, a correction signal generated by the correction signal generation circuit 13a and the gain adjustment circuit 17a, and a signal obtained by delaying the digital video signal by the compensation delay circuit 12a. and is synthesized by the synthesis circuit 14a. The compensation delay is performed by the correction signal generation circuit 13a.
This should be taken into account the delays caused by such factors. The digital video signal corrected in this way is sent to the D/A converter 15.
A is output as an analog signal. Note that in the following explanation, the explanation will be made without distinguishing between R, G, and B signals, so the suffixes of the symbols will be omitted.

Incidentally, due to the characteristics of the cathode ray tube, the input signal to the projection tube is a nonlinear signal obtained by raising the input signal to the gamma power. When filtering such input signals to create and add correction signals, the linearity of the correction signal itself is lost, and the sensitivity of the correction filter decreases in dark areas of the screen where the signal level is low, making it difficult to improve image quality in dark areas. effectiveness decreases. In order to improve this point, in the configuration shown in FIG. 1, the gain adjustment circuit 17 is connected in series to the correction signal generation circuit 13. The digital video signal is input to the gain adjustment circuit 17 via the delay device 16 as a control signal that compensates for the signal delay of the correction signal generation circuit 13. When the signal level is low, the gain of the gain adjustment circuit 17 is increased to compensate for the decrease in sensitivity of the correction filter in the dark areas. Conversely, the gain is lowered where the signal level is high. This improves the image quality even in dark areas of the screen.

Next, the correction signal generation circuit 13 will be explained. FIG. 2 is a circuit block diagram in which vertical correction and horizontal correction are performed in series. The vertical correction FIR filter 21 is a low-pass type filter, which uses a common line memory column 21a, and has a product-sum calculator 21b for flare correction that multiplies the signal from the tap by a coefficient and adds it, and a product-sum calculator 21b for contour correction. It is composed of an arithmetic unit 21c and a synthesis circuit 21d that combines the outputs of both product-sum arithmetic units 21b and 21c. The horizontal correction FIR filter 23 is also a low-pass filter having the same configuration, except that 23a is a register string for the A/D conversion clock. In this filter system, contour correction and flare correction are performed in parallel, and each correction is performed in series in the vertical and horizontal directions.

The details of the circuit of the FIR filters 21 and 23 are shown in FIG. Note that in FIG. 3, the reference numerals are different from those in FIG. 2 in order to explain the common vertical and horizontal configurations.
Taps come out from each delay element in the delay element array 201, and for flare correction, all the taps are used to create a coefficient circuit group 202, and the outputs of each coefficient circuit are added in an adder circuit 203 to create a flare correction signal. 204
get. Flare correction involves a large number of lines (in the case of vertical correction) and many dots (in the case of horizontal correction), so all taps are used to configure the FIR filter. However, in the FIR filter, when adding in the adding circuit 203, a linear phase can be easily obtained by matching the addition phases. Next, for contour correction, an FIR filter can be constructed using the central tap m of the delay element array 201 and several taps in its vicinity. Since the number of lines and dots involved in contour correction is small, the number of taps can also be small. In the figure, the coefficient circuit group 205 is
A contour correction signal 207 is obtained by adding the outputs of each coefficient circuit in an adding circuit 206. The flare correction signal 204 and the contour correction signal 207 are combined by a combining circuit 208 and output.

Hereinafter, the explanation will be returned to FIG. 2 and the overall configuration will be explained. Vertical correction from digital video signal input
Signal 2 vertically corrected by FIR filter 21
2 is further horizontally corrected by a horizontal correction FIR filter 23 and inputted to a subtraction circuit 26 as a correction signal 24 with low frequency characteristics.

On the other hand, the delay device 2 for compensating the digital video signal input
5, a signal given a delay amount sufficient to match the phase delay of the correction signal 24 due to the filter group is input to the subtraction circuit 26. As a result, the output 26a of the subtraction circuit 26 becomes a correction signal with high frequency characteristics.

The reason why the filter is configured as a low-pass filter and its output is subtracted from the digital video signal to become a high-pass filter will be explained below.

Contour correction and flare correction mean emphasizing high-pass characteristics and lowering low-pass characteristics as frequency characteristics, and the filter is a high-pass type filter. However, vertical correction and
When used in series for horizontal correction, in the case of a quadrilateral window pattern on the screen, the vertical and horizontal corrections are related, and the correction signals of the polarity to be improved and the opposite polarity are distributed diagonally to the inner corner of the window. Naru diagonal appears on the outside. In the present invention, strictly considering this point, all filters are of low-pass type.
By subtracting the filter output from the input signal to effectively make it a high-pass type, continuity of correction at the four corners is obtained.

Now, the output 26a of the subtraction circuit 26 may be directly output from the correction signal generation circuit 13, but in the circuit shown in FIG. 2, it is outputted via the coring circuit 27.

The correction signal emphasizes the high frequency components of the signal.
This is especially 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 circuit 27 is a circuit that sets the correction signal to zero in areas where noise is a problem and where the signal level is low to prevent the noise from being emphasized. In other words, a dead zone is provided near zero in the correction signal, but this is not necessarily necessary when the screen to be projected is small.

The circuit configuration of the present invention has been described above, but the present invention requires a large number of coefficient circuits for various filters, gain adjustment circuits, coring circuits, etc. The coefficient values of each coefficient circuit vary, and often require adjustment and setting for each receiver. Therefore, it is necessary to be able to make adjustments at the final stage of manufacturing the receiver, and furthermore, even when the receiver is in practical use, changes in the installation environment will slightly affect the image quality. It is preferable that the user etc. can freely make adjustments in such cases as well.

In the present invention, a coefficient circuit that meets the above-mentioned demand is created by using an arbitrarily writable RAM.
FIG. 4a schematically shows a coefficient circuit, and FIG. 4b shows a circuit using RAM. In this circuit, data is written from a separate CPU during the video blanking period. In the figure, the mode of the selector 31 is set to the CPU address side, and data is transferred from the CPU to the RAM 32 via the buffer 33 to a predetermined address.
Write in. During the video period, the mode of the selector 31 is set to the coefficient circuit input side, and data multiplied by the coefficient is read out via the buffer 34 and sent out as the coefficient circuit output. Note that writing to RAM may be done in DMA mode. By setting data to be arbitrarily written from the CPU to the RAM 32, the coefficients of the coefficient circuit can be made variable.

〔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) As contour/flare correction filters, both have linear phase characteristics as FIR filters. The filter configuration performs horizontal correction on the vertical correction straight line, and the filters are connected in parallel so that flare correction and contour correction are performed in parallel in each direction. In this case, by using a common delay element array for flare correction and contour correction, it is possible to reduce the size of the FIR filter.

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

(5) Coefficients can be set arbitrarily by using RAM as coefficient circuits used in filters, gain adjustment circuits, etc. Not only is it easy to adjust and set during the manufacturing stage, but it can also be made variable even while the receiver is in operation, making it possible to maintain optimal image quality in any environment.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a basic configuration block diagram, Fig. 2 is a configuration block diagram of a correction signal generation circuit, and Fig. 3 is a configuration of an FIR filter commonly used for contour correction and flare correction. FIG. 4 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... Delay device, 17a-17c... Gain adjustment circuit, 21... Vertical correction FIR filter, 23... Horizontal correction FIR filter, 25... Compensation delay device, 2
6... Synthesis circuit, 27... Coring circuit, 20
1... Delay element row, 202-205... Coefficient circuit group (for flare correction, contour correction), 203, 20
6... Addition circuit, (for flare correction, contour correction),
208...Synthesis circuit, 30...Coefficient circuit, 31...
...Selector, 32...RAM, 33, 34...Batsufua.

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 changes the gain depending on the input level of the digital video signal in a compensation delay circuit and a subsequent stage provided in parallel with the digital video signal input. a contour/flare correction signal generation circuit equipped with a gain adjustment circuit, and a synthesis circuit that synthesizes the outputs of the compensation delay circuit and the gain adjustment circuit, and the contour/flare correction signal generation circuit is of a low-pass type. A circuit that serially performs correction in the vertical and horizontal directions using a group of FIR filters, and then subtracts from the delayed digital video signal, wherein (a) the vertical FIR filter is a column of line memories with one delay; (b) The horizontal direction FIR filter The A/D conversion clock register has a common column with one delay, and all the taps are used to generate the flare correction signal, and the required number of taps in the center are used to generate the contour correction signal.
The filters and the coefficient circuit in the gain adjustment circuit use RAM, data is written during the video blanking period, and the input signal of the coefficient circuit is not input during the video period. A television image quality improvement device characterized in that the address signal of the RAM is an output signal from which the data is read.