JPH05911B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to a method for converting an interlace scan image signal to a progressive scan image signal, or for interpolating an image signal whose signal structure has been converted, such as separating a luminance signal and a chromaticity signal. It relates to an adaptive control circuit that adaptively controls the passage characteristics of a spatiotemporal interpolation filter consisting of a filter and a vertical spatial filter to the amount of movement of an image represented by an input image signal, and in particular, an adaptive control circuit that controls the passage characteristics of a spatiotemporal interpolation filter consisting of a filter and a vertical spatial filter. This makes it possible to effectively remove noise components inside.

Prior Art The above-mentioned type of adaptive spatio-temporal interpolation filter whose pass characteristic is controlled by a conventional adaptive control circuit of this type is disclosed in Japanese Patent Application No. 57-88018 filed by the applicant.
and Japanese Patent Application No. 57-155788. This conventional adaptive spatio-temporal interpolation filter is configured as shown in FIG. are supplied to an adder 3 and a subtracter 4 to form an interframe sum signal and an interframe difference signal, respectively. One of these days,
The inter-frame sum signal from the adder 3 is supplied to the vertical high-pass filter 7 and the extracted high-frequency vertical spatial frequency component and the 1-field delayed signal from the intermediate connection point of the field memories 1 and 2 are sent to the vertical low-pass filter 8. The low vertical spatial frequency component extracted by supplying the
After controlling according to the amount of movement of the image as described later, the adder 9 performs addition and synthesis, and the combined output signal is supplied to the adder 12, where it is added and combined with the above-mentioned 1-field delay signal, and the converted output is sequentially performed. The scanning screen signal is being extracted.

The amount of motion of the image that controls the passing characteristics of the high-pass and reduction vertical spatial filters 7 and 8 described above is determined by converting the inter-frame difference signal from the subtracter 4 into a pure absolute value by an absolute value circuit 6, and The difference signal processing circuit 10 converts the inter-frame difference signal into an absolute value.
Coring is performed using the interframe sum signal formed by the adder 5 in the same manner as in the adder 3, and the core tongue signal component of the detected interframe difference signal absolute value is guided to the coefficient generation circuit 11. A coefficient having a value appropriate to the size is generated and applied to each vertical spatial filter 7, 8. Therefore, the noise component contained in the input image signal remains in the inter-frame difference signal, causing malfunction of the adaptive control.

Therefore, the inter-frame difference signal formed by sampling and quantizing the input image signal at the sampling period T is, for example, as shown in Figure 2a, whereas it is as shown in Figure 2b. Nozzle components of similar size are similarly sampled and quantized, and while the inter-frame difference signal exhibits a changing spectral distribution as shown in c of the same figure, the noise component exhibits a uniform spectral distribution as shown in Figure d. In other words, for an input image signal that is band-limited in the time axis direction, such as an imaging output signal from a television camera, the high frequency components in its spectral distribution are small, as shown in Figure 2(c), while the transmission line noise is small. The spectral distribution of the noise contained in the image signal is widely uniform from the low frequency range to the high frequency range, as shown in d of the same figure. Therefore, assuming that the inter-frame difference signal and the noise have the same energy, the high peak value in the distribution region of the noise spectrum is mostly the high-frequency noise component, and the difference signal processing circuit 10
It is difficult to remove by

In order to remove noise components, especially high-frequency noise components, from the inter-frame difference signals having the spectral distributions shown in FIG. 2c and d, a low-pass filter 13 is inserted as shown in FIG. 3a. It can be seen that it is effective to provide a passband characteristic as shown in FIG. b. However, signal processing only by inserting such a low-pass filter has the following drawbacks.

Generally, complex signal processing is performed by digital signal processing in view of the stability of the signal processing system. In such digital signal processing, it is necessary to consider the problem of reduced resolution due to the limited number of quantization bits. On the other hand, when a digital inter-frame difference signal is added to the digital reduction filter inserted as shown in FIG. 3a, noise is reduced, but at the same time, the peak value of the inter-frame difference signal is also reduced. As a result, as shown in Figure 4,
When the peak level of the digital inter-frame difference signal drops below the unit quantization level, there may be cases where no significant inter-frame difference signal is obtained as the filter output. In such a case, even if the level of coring signal component detection in coring is lowered, the noise output will only increase, and on the contrary, the noise reduction effect by inserting the reduction filter will not be obtained. Furthermore, the insertion of the reduction filter causes the inter-frame difference signal and noise to spread spatiotemporally as shown in FIG. 4, and both increase the probability of occurrence of malfunction in adaptive control. Such malfunction not only causes image quality deterioration in the inter-frame difference signal itself due to processing a still image area as a moving image area, but also reduces noise components and spreads them in space and time, resulting in so-called side-scanning noise. This causes the image to become visually noticeable, further increasing the deterioration of image quality. That is, the spread T ₁ of the interframe difference signal shown in FIG. 2a is
By inserting a low-pass filter, as shown in Figure 5, when the noise component doubles and spreads to T ₂ , the spread of the noise component also doubles, and a horizontally elongated noise appears by T ₂ - _{T 1} . It was hot.

SUMMARY OF THE INVENTION The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art;
Mixed into the image signal when controlling the passband characteristics of the spatiotemporal interpolation filter that performs interpolation on the converted image signal by adapting the amount of motion to the image, such as when converting an interlace scan image signal to a sequential scan image signal. An object of the present invention is to provide an adaptive control circuit that can effectively remove noise components from an adaptive control signal.

That is, the adaptive control circuit of the present invention includes at least a coefficient multiplier that increases the inter-frame difference signal of the input image signal by multiplying it by a required coefficient, and a multiplier that passes the low-frequency component of the inter-frame difference signal increased by the coefficient multiplier. an absolute value circuit that detects the absolute value of the low-frequency component of the inter-frame difference signal that has passed through the low-pass filter; and a low-level signal at the absolute value of the low-frequency component detected by the absolute value circuit. a coring circuit that detects a coring signal component consisting of a significant signal component excluding a noise component and a coring signal component, and forms a control signal for controlling a filter passage characteristic using the coring signal component;
a gate circuit that allows a detection output of another absolute value circuit that detects the absolute value of the inter-frame difference signal to pass as the control signal in accordance with the magnitude of the coring signal component detected by the coring circuit; The present invention is characterized in that the coefficients of the filters are changed by the control signal to respectively control the pass characteristics.

EXAMPLES The present invention will be explained in detail below using examples with reference to the drawings.

First, an example of the basic configuration of the adaptive control circuit of the present invention is shown in FIG. The adaptive control circuit of the present invention replaces the absolute value circuit 6 in the configuration of the adaptive spatio-temporal interpolation filter shown in FIG. In the illustrated configuration example, the inter-frame difference signal from the subtracter 4 in the first illustrated configuration is guided to the coefficient unit 14 and multiplied by a coefficient of k≧1 to increase the signal amplitude by k times. The inter-frame difference signal whose amplitude has been increased by the coefficient multiplier 14 is supplied to the low-pass filter 15. If the impulse response length of this low-pass filter is n, the amplitude value of the wave output is approximately 1/n
Therefore, the coefficient in the coefficient multiplier 14 described above, that is, the signal amplitude increase rate k, is set to k=n, and the wave output frame difference signal of the low-pass filter 15 is processed by the low-pass filter intervention described above with respect to the prior art. The low frequency range of the signal amplitude due to the interpolation is compensated by the coefficient multiplier 14, thereby preventing relatively small inter-frame difference signals from disappearing when the signal amplitude is below the unit quantization level.

Note that in order to prevent the inter-frame difference signal from disappearing due to a reduction in signal amplitude due to the insertion of such a low-pass filter, it is possible to prevent the inter-frame difference signal from disappearing due to a reduction in signal amplitude. Although it is possible to make the length longer, another drawback arises in that the number of quantization bits increases, so it is not suitable for achieving the purpose of the present invention.

The wave output signal whose noise component has been reduced by the low-pass filter 15 after compensating for the reduction in the signal amplitude of the inter-frame difference signal as described above is guided to the absolute value circuit 16 and converted into an absolute value, and then The signal is supplied to a coring circuit 17, and coring is performed to remove low-level noise by detecting the coring signal component. As described above, the signal amplitude value of the inter-frame difference signal is multiplied by k by the coefficient multiplier 14, but the coring signal detection level in the coring circuit 17 is the same as the coring level for the original inter-frame difference signal amplitude. shall be. However,
The inter-frame difference signal and noise component obtained at the output side of the coring circuit 17 are passed through a low-pass filter 15.
Since the time width has doubled as described above with the lowering of the frequency range, the coring output signal is not used as an adaptive control signal as it is, but is supplied to the gate circuit 19 and used as its gate control signal. That is, the output signal of the coring circuit 17 is in the form of a binary signal set to "1" or "0" depending on the presence or absence of a significant inter-frame difference signal, and is used to pass or block the gated signal in the gate circuit 19. control each. As the gated signal, the input frame difference signal is directly sent to the absolute value circuit 1.
8 is the absolute value of the input inter-frame difference signal obtained by supplying the input frame difference signal. Therefore, on the gate output side of the gate circuit 19, noise components are reduced and a significant inter-frame difference signal without spread is obtained as an effective and appropriate adaptive control signal. In other words, even if a false inter-frame difference signal is generated due to the mixing of noise, the low-pass filter 15 lowers the frequency and widens the time width, so that the noise component that has become visually noticeable becomes part of the adaptive control signal. The conventional drawbacks of remaining in the interior are largely eliminated.

Next, other configurations that are modified from the basic configuration shown in FIG. 6 will be described.

First, it is assumed that the transmission characteristic of the low-pass filter 15 in the basic configuration shown in FIG. 6 has a rectangular waveform impulse response as shown in FIG. 7a and an amplitude frequency characteristic as shown in FIG. 7b.
In other words, the pulse height value _{k 1} in the impulse response shown in FIG.
is only this k ₁ . Therefore, there is an advantage that the circuit device shown in FIG. 6 can be easily configured.

In addition, the absolute value circuit 18 and the gate circuit 19 in the basic configuration shown in FIG. 6 are omitted to simplify the structure as shown in FIG. If the coring output is used as an adaptive control signal, it is possible to prevent the significant inter-frame difference signal from disappearing due to a decrease in the level. The signal time width remains increased due to the lowering of the frequency by the low-pass filter, and the effect is far inferior to that of the configuration shown in FIG.

Effects As is clear from the above description, according to the present invention, an adaptive filter that adapts and controls the passage characteristics of a spatio-temporal interpolation filter that performs interpolation of an image signal whose signal structure has been converted is adapted to the amount of image motion. It is possible to effectively reduce noise components in the control circuit without causing the disappearance of significant inter-frame difference signals, and therefore, according to the output adaptive control signal subjected to adaptive processing, image quality deterioration due to malfunction due to noise can be reduced. This has the advantage that a good converted output image signal can be obtained without any noticeable difference.

Furthermore, the configuration of the circuit device can be simplified by making the impulse response of the low-pass filter, which lowers the frequency of noise and reduces its interference, into a square waveform.

Furthermore, the configuration of the circuit device can be further simplified by omitting the gate circuit and the absolute value circuit for compensating for the spread of signal and noise time widths due to the low-pass filter.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the conventional configuration of an adaptive spatio-temporal interpolation filter. 3A and 3B are diagrams showing the amplitude-frequency characteristics, respectively, and FIGS.
The figure is a signal wave diagram showing an example of how the amplitude of the inter-frame difference signal changes due to the insertion of the low-pass filter, and Figure 5 shows the change in the time width of the inter-frame difference signal due to the insertion of the low-pass filter. FIG. 6 is a block diagram showing the basic configuration of the adaptive control circuit of the present invention, and FIGS. 7a and b show the impulse response and frequency of the low-pass filter in the same basic configuration. FIG. 8 is a block diagram showing another example of the configuration of the adaptive control circuit. 1, 2...Field memory, 3, 5, 9, 1
2... Adder, 4... Subtractor, 6, 16, 18...
...Absolute value circuit, 7...Vertical high-pass filter, 8...
Vertical low-pass filter, 10...Difference signal processing circuit, 1
1... Coefficient generation circuit, 13, 15... Low-pass filter, 14... Coefficient unit, 17, 20... Coring circuit, 19... Gate circuit.

Claims (1)

[Claims] 1. At least a coefficient multiplier that multiplies an inter-frame difference signal of an input image signal by a required coefficient to increase it, and a low frequency component that passes the low-frequency component of the inter-frame difference signal increased by the coefficient multiplier. a low-level signal component in the absolute value of the low-frequency component detected by the absolute value circuit; a coring circuit that detects a coring signal component consisting of significant signal components other than the nozzle component and forms a control signal for filter passage characteristic control from the coring signal component; and the coring detected by the coring circuit. and a gate circuit that allows the detection output of another absolute value circuit that detects the absolute value of the inter-frame difference signal to pass through as the control signal according to the magnitude of the signal component, and the coefficient of the filter is changed by the control signal. An adaptive control circuit characterized in that the transmission characteristic is controlled by each of the following. 2. The adaptive control circuit according to claim 1, wherein the impulse response of the low-pass filter is a square waveform.