JPH0327154B2 - - 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-intensity injection 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. Since it has to be created, there are few examples.

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 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 three primary color video signals restored from the digital luminance signal and color signal by a matrix circuit and delayed through a compensation delay circuit, and the contour/flare correction signal are synthesized, respectively, and then D/A conversion is performed. and output it.

The contour/flare correction signal generation section includes a contour/flare correction signal generation circuit that inputs a digital luminance signal, and a gain adjustment circuit that is connected in series to the correction signal generation circuit and changes its gain depending on the input level of the digital luminance signal. The contour/flare correction signal generation 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 input of the correction signal generation circuit from the delayed signal. (a) The vertical FIR filter uses a line memory with one delay in common, and uses all the taps to obtain a flare correction signal, and uses the required number of taps in the center to obtain a contour correction signal. (b) The horizontal FIR filter has a common row of A/D conversion lock registers with one delay, and uses all the taps to combine the flare correction signal into the center. The configuration is such that contour correction signals are obtained using the required number of taps, respectively, and both correction signals are combined.

Here, the coefficients of the filters and the coefficient circuits in the gain adjustment circuit can be 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 ,
Narrowband color signal C _N (Hereinafter, C ₁ signal,
It is possible to obtain a high-quality three-primary color video signal by inputting C (treated as a _2- 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 consists of a correction signal generation circuit and a gain adjustment circuit.
After vertical and horizontal correction is performed using an FIR filter, a correction signal with high-pass characteristics is obtained by subtracting it from the input Y signal input. The reduction FIR filter is configured to perform flare correction and contour correction in parallel, using a common delay column, using a complete tap for flare correction, and using the required number of taps in the center for contour correction.

The amplitude of the correction signal is adjusted by a gain adjustment circuit in accordance with the level of the Y signal, and then output.

By combining the correction signal output from the correction signal generation section with each of the three primary color video signals that have passed through the compensation delay circuit in a synthesis circuit and performing D/A conversion, it is possible to obtain three original video signals with improved image quality. can.

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 X signal, _C1 signal, and _C2 signal are converted into digital Y signals by 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 generating circuit 13 generates a correction signal commonly used for RGB signals.

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, the correction signal generation section 10 has the configuration shown in FIG. 1, and the gain adjustment circuit 17 is connected in series to the correction signal generation circuit 13.
The digital Y 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 dark portion of the correction filter. Conversely, the gain is lowered where the signal level is high. This improves the image quality even in dark areas of the screen.
Note that the gain of the gain adjustment circuit 17 can be changed 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 vertical correction and horizontal correction are performed in series. The vertical correction FIR filter 21 is a low-pass type filter that shares a line memory column 21a, and a flare correction product-sum calculator 2 that multiplies the signal from the tap by a coefficient and adds the result.
1b, a synthesis circuit 2 that combines the outputs of the contour correction product-sum calculator 21c and both product-sum calculators 21b and 21c;
1d. Horizontal correction FIR filter 2
3 is also a reduced passage type filter with the same configuration, but
The difference is 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.

Details of the circuit of the FIR filters 21 and 23 are shown in FIG. Note that the reference numerals in FIG. 3 are different from those in FIG. 2 in order to explain the configuration common to both vertical and horizontal directions.
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, three taps are used to create a coefficient circuit group 205, and an adder circuit 206 adds the outputs of each coefficient circuit to obtain a contour correction signal 207. The flare correction signal 204 and the contour correction signal 207 are sent to the synthesis circuit 2.
08 to synthesize and output.

Hereinafter, the explanation will be returned to FIG. 2 and the overall configuration will be explained. A signal 22 that has been vertically corrected from the digital Y signal by a vertical correction FIR filter 21 is further horizontally corrected by a horizontal correction FIR filter 23, and is input to a subtraction circuit 26 as a correction signal 24 with low frequency characteristics.

On the other hand, the digital Y signal is given a delay amount corresponding to the phase delay caused by the filter group of the compensation signal 24 by the compensation delay device 25, and is input as a reference signal to the subtraction circuit 26. By subtracting the correction signal 24 from the reference signal, 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 input signal to become a high-pass filter will be explained below.

Contour correction and flare correction have frequency characteristics that 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 both sides, the 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 .

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 adjust the final stage of receiver manufacture.

In the present invention, an element as shown in FIG. 4 is used as an element whose coefficients can be variably adjusted and set. Figure 4a is a diagrammatic representation of the coefficient circuit, Figure 4b is the ROM 31, Figure 4c 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) As a contour/flare correction filter, it can be used for both.
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) 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) As coefficient circuits used in filters, gain adjustment circuits, etc., coefficients can be variably adjusted and set, making adjustment easy, which is advantageous when mass producing devices.

[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. 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...Delay device, 17...Gain adjustment circuit, 1
8... Matrix circuit, 21... Vertical correction FIR filter, 23... Horizontal correction FIR filter, 25...
... Compensation delay device, 26 ... Subtraction circuit, 27 ... Coring circuit, 201 ... Delay element array, 202,
205... Coefficient circuit group (for flare correction, contour correction), 203, 206... Addition circuit, (for flare correction, contour correction), 208... Synthesis circuit, 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, and the contour/flare correction signal generating section is connected in series to a contour/flare correction signal generation circuit that inputs a digital luminance signal and to the correction signal generation circuit, and outputs the digital luminance signal. It consists of a gain adjustment circuit that changes the gain depending on the input level, and the contour/flare correction signal generation circuit performs correction in the vertical and horizontal directions in series using a group of low-pass FIR filters, and then outputs the correction signal generation circuit. (b) The vertical FIR filter has a line memory with one delay in common, and uses all the taps to subtract the flare correction signal from the required number of taps in the center. The horizontal direction FIR filter has a configuration in which a contour correction signal is obtained using the respective taps and both correction signals are combined, and (b) the horizontal direction FIR filter has a common column in which the register of the A/D conversion clock has a one-delay. , the flare correction signal is generated using all the taps, the contour correction signal is generated using the required number of taps in the center,
What is claimed is: 1. A television picture quality improvement device, which is configured to synthesize both correction signals obtained from each other, and wherein coefficient circuits in the filters and the gain adjustment circuit can variably adjust and set the coefficients.