JPH07212716A - Interlaced scanning signal generating method - Google Patents

Abstract

PURPOSE:To eliminate loopback distortion with simple circuit configuration by eliminating a high frequency signal having a timewise frequency and a vertical frequency and interleaving a sequential scanning signal at an interval of every scanning line so as to convert the signal into a signal for interlaced scanning. CONSTITUTION:Cut-off frequencies of low pass filters VLPF1, F2 are respectively about 340/2cph and 240/2cph to limit a band in the vertical direction. A cyclic filter TLPF 4 receives a value subtracting an output of the VLPF 1 from an input to the VLPF 2 at a subtractor 3, a value obtained by multiplying the value with (1-k) by a (1-k) multiplier 41 and a signal resulting from multiplying an output of a 1-field delay circuit 44 with (k) at a k-multiple multiplier 43 are added by an adder 42. Thus, a high frequency component in the vertical direction and in a timewise direction is eliminated from a 2-dimension spectrum to eliminate loopback distortion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interlace scanning signal generating method, and more particularly to an interlacing scanning signal generating method capable of removing aliasing distortion with a simple circuit structure.

[0002]

2. Description of the Related Art As one method for improving the vertical resolution of a television image, a transmitting side performs sequential scanning at a horizontal scanning speed twice as high as that of a current television signal, and information obtained by the sequential scanning is obtained. There is a method of thinning out each scanning line and converting it into an interlaced scanning signal. This is described in detail in the background section of the invention of, for example, Japanese Patent Application Laid-Open No. 61-141286, "Television Signal Scan Converter". Then, as also described here, when the scanning lines obtained by the sequential scanning are simply thinned out and converted into the signals of the interlaced scanning, so-called folding noise occurs in the vertical high frequency part of the moving image, There is a problem of degrading image quality. In order to solve this problem, the technique disclosed in the above publication performs sequential scanning at a horizontal scanning speed twice as high as that of the current television signal on the transmitting side, and scans information obtained by the sequential scanning. When thinning out each line and converting it into an interlaced scanning signal, the signal is band-limited at least at one of the time frequency and the vertical frequency, and scanning lines are thinned from the band-limited scanning signal line to perform scan conversion. , In that case, the folding component is detected, and depending on the presence or absence of this detection output,
The above-mentioned band limitation is controlled. Figure 4
FIG. 5 shows an example of the two-dimensional spectrum of the progressive scanning signal in the vertical-time domain, and FIG. 5 shows an example of the two-dimensional spectrum of the interlaced scanning signal in the vertical-time domain. The hatched area in FIG. 5 will be described later.

[0003]

The above-mentioned prior art is capable of removing folding noise in a moving image in principle, but when applying this to an actual device,
It is necessary to detect motion, which complicates the device configuration and raises the cost of the device. The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems in the conventional technique and to perform interlaced scanning capable of removing aliasing distortion with a simple circuit configuration. It is to provide a signal generating method.

[0004]

SUMMARY OF THE INVENTION The above object of the present invention is to provide an interlaced scanning signal generating method in which a signal obtained by progressive scanning is thinned out for each scanning line and converted into an interlaced scanning signal. An interlaced scanning signal generating method comprising: a step of removing a high frequency signal of a frequency; and a step of thinning out a sequential scanning signal after the high frequency signal is removed for each scanning line to convert into an interlaced scanning signal. To be achieved.

[0005]

In the interlaced scanning signal generating method according to the present invention, the time frequency and vertical frequency of the progressive scanning signal to be processed are preceded by thinning out the progressive scanning signal for each scanning line and converting it into the interlaced scanning signal. Since the high frequency signal of is removed, it becomes possible to convert from the progressive scanning signal to the interlaced scanning signal in the state where there is no high frequency signal of the time frequency and the vertical frequency that causes the aliasing distortion, It is possible to achieve the intended purpose. The shaded area in FIG. 5 shows the principle of the present invention, and shows the area deleted by the interlaced scanning signal generating method according to the present invention.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a progressive scanning signal-> interlacing scanning signal converting device according to an embodiment of the present invention. In the figure, 1 is a first low-pass filter (hereinafter, referred to as "VLPF1") for limiting the band in the vertical direction.
2 indicates a second low-pass filter (hereinafter, referred to as “VLPF2”) having the same function. Here, the limited band of the VLPF 1 is, for example, 340.
It is set to about / 2 (cph), but is not limited to this, and may be changed according to the preference of the coordinator. In addition, VLPF
The limit band of 2 has a cutoff frequency of, for example, 240
It is set to about / 2 (cph), but this is not limited to this value either.

Reference numeral 3 is a subtractor, 4 is a low-pass filter in the time direction (hereinafter referred to as "TLPF"), 5 is an adder, 6 is a known sequential scanning signal → interlaced scanning signal conversion circuit (hereinafter, "sequential →
(Abbreviated as "jump conversion circuit"). The above-mentioned TLPF 4 has a (1-k) times multiplier 41, an adder 42, and a k.
This is a recursive filter composed of the elements of the double multiplier 43 and the 1-field delay circuit 44. Hereinafter, the operation of the progressive scanning signal-> interlacing scanning signal converting apparatus according to this embodiment configured as described above will be described. The input progressive scan signal is
First, the vertical low pass filter (VLPF1) is band-limited in the vertical direction.

The purpose of the band limitation here is to prevent line flicker in the interlaced scanning monitor. Therefore, the limit band of the VLPF 1 has the cutoff frequency set to, for example, about 340/2 (cph) as described above. As a result, the vertical high frequency component (area in Fig. 2)
Are removed. Next, the output of VLPF1 is further band-limited in the vertical direction in the second vertical low-pass filter (VLPF2). The cutoff frequency here is
As described above, for example, it is set to about 240/2 (cph). The output of VLPF2 is input to the subtractor 3, where the output of VLPF2 is subtracted from the input of VLPF2. The output of the subtractor 3 corresponds to the high frequency component in the vertical direction (area in FIG. 2). That is, it can be said that it is a substantially effective high frequency component.

The output of the subtractor 3 is then input to a low-pass filter (TLPF) 4 in the time direction. As described above, the TLPF 4 is a recursive filter, and the TLPF 4 shown in FIG.
Among the signal components in the region of, only the low frequency component is output in the time direction. By adding the output of the TLPF 4 to the output of the VLPF 2 in the adder 5, it is possible to extract the component of the shaded portion in FIG. By converting the output of the adder 5 from a sequential-> interlacing conversion circuit 6 to a sequential scanning signal-> interlacing scanning signal, it is possible to obtain a desired interlacing scanning signal, that is, an interlacing scanning signal that does not include aliasing distortion. it can.

The details of the operation of the above-mentioned recursive filter TLPF4 are as follows. In the TLPF 4, the subtractor 3
Of the VLPF2, that is, the output obtained by subtracting the output of the VLPF2 from the input of the VLPF2, and the signal obtained by multiplying the output of the VLPF2 by the (1-k) -times multiplier 41 and the 1-field delay circuit 4
A signal obtained by multiplying the output of 4 by k times by the k-times multiplier 43 is added by the adder 42. As a result, since the output of the 1-field delay circuit 44 is 0 at the beginning, the output of the TLPF 4 is the output of the subtractor 3. The output becomes (1-k) times, and in the next cycle,
The output is changed to (1-k) times the output of the subtractor 3 + (1-k) · k times the output of the subtractor 3 in the previous cycle.

A schematic representation of this is shown in FIG.
Here, when the value of k is increased, the attenuation is small and the shape becomes blunt, and when the value of k is decreased, the attenuation is large and the slope is steep. This value can be appropriately determined in design. According to the above embodiment, the low-pass filters VLPF1 and VLPF for limiting the vertical band are provided.
F2, an interlaced scanning signal capable of removing aliasing distortion by removing high-frequency components in the vertical direction and high-frequency components in the time direction from the two-dimensional spectrum shown in FIG. 4 by the low-pass filter TLPF in the time direction. The effect that the generation method can be realized with a simple circuit configuration,
The effect of achieving high image quality and low folding distortion can be obtained.

This can be realized by simple hardware without a time delay by using a recursive filter as the time direction filter. Moreover, since motion detection is not used, there is no malfunction and a high quality image is obtained. It is possible to obtain. It is needless to say that the above embodiment shows one example of the present invention, and the present invention should not be limited to this. For example,
Low-pass filter VL for limiting the band in the vertical direction
The cutoff frequencies of PF1 and VLPF2, the value of k in the low-pass filter TLPF in the time direction, and the like can be selected from a wide range in design.

[0013]

As described above in detail, according to the present invention, it is possible to realize the interlaced scanning signal generating method capable of removing the aliasing distortion with a simple circuit structure. Is.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a progressive scanning signal → interlaced scanning signal conversion circuit according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the embodiment.

FIG. 3 is a diagram showing a relationship between an input and an output in a low-pass filter TLPF in the time direction.

FIG. 4 is a diagram showing a general example of a two-dimensional spectrum in a vertical-time domain of a progressive scanning signal.

FIG. 5 is a diagram showing a general example of a two-dimensional spectrum in a vertical-time domain of an interlaced scanning signal.

[Explanation of symbols]

 1 VLPF1 2 VLPF2 3 Subtractor 4 TLPF 41 (1-k) times multiplier 42 adder 43 k times multiplier 44 1 field delay circuit 5 adder 6 sequential → jump conversion circuit

Claims (2)

[Claims] 1. A method for generating an interlaced scanning signal in which a signal obtained by sequential scanning is thinned out for each scanning line and converted into an interlaced scanning signal, and a step of removing high frequency signals of a time frequency and a vertical frequency, An interlaced scanning signal generating method comprising a step of thinning out a sequential scanning signal after removal of a high frequency signal for each scanning line and converting it into an interlaced scanning signal. 2. The interlaced scanning signal generating method according to claim 1, wherein the step of removing the high frequency signal of the time frequency is performed by using a recursive filter.