JPH0316413A - Adaptive filter device - Google Patents

Abstract

PURPOSE:To improve the visual picture of an object picture by providing at least one filter, a selector and a frequency analyzer, analyzing a frequency component of an input signal and eliminating the frequency component not almost included in the input signal. CONSTITUTION:An input signal 1 is converted into a filter output 3 subject to frequency conversion and inputted also to a frequency analyzer 4. The frequency analyzer 4 measures the local frequency distribution of the input signal 1 and outputs a control signal 5 commanding a selector 6 to select the filter output 3 when a frequency having a large distribution passes and a frequency with a small distribution is blocked. Means when the band of the local frequency of the input signal 1 is sufficiently large, the selector 6 is switched to output the input signal 1 as it is. The frequency having a small frequency distribution is almost quantized distortion and coded distortion and the deterioration in the picture quality by the adaptive filter is not almost caused.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an adaptive filter device used for converting an image whose image quality has been degraded due to band compression, signal processing, etc. to an image quality that is less visually unnatural. It is.

BACKGROUND OF THE INVENTION Conventional adaptive filter devices switch filters based on additional information.

FIG. 5 shows a block diagram of this conventional adaptive filter device, where 1 is an input signal, 2 is a filter that changes the frequency characteristics of this input signal 1, and 3 is a filter output frequency-converted by this filter 2. , 6 is a selector for switching between the input signal 1 and the filter output 3, and 7 is an output signal selected by the selector 6. Reference numeral 14 denotes an input signal indicating whether or not to use filter 2, which is encoded by an encoder (not shown). 15 is the input signal 1
4, and 18 is a control signal for switching the selector 6.

In the conventional adaptive filter device configured as described above, either the input signal 1 or the filter output 3 becomes the output signal 7 by switching the selector 6. The control signal 16 for switching the selector 6, that is, the human signal 14 for generating the control signal 16, must be generated in advance by an encoder and transmitted over the transmission path as additional information.

Problems to be Solved by the Invention However, the above configuration has the problem that additional information needs to be transmitted in order to generate the input signal used for switching the selector, and the amount of transmitted information increases. was.

In view of the above, an object of the present invention is to provide an adaptive filter device that can select an output with a simple device without additional information and improves the visual quality of a target image.

Means for Solving the Problems The present invention provides at least one filter that changes the frequency characteristics of an input signal, a selector that switches and outputs the input signal and the output of the filter, and measures the frequency characteristics of the input signal. The present invention is characterized by comprising a frequency analyzer that outputs a signal for switching the selector.

Note that, in place of the frequency analyzer, a subtracter that outputs a difference signal between the input signal and the filter output, and an absolute value converter that calculates the absolute value of the output of the subtracter, and this absolute value A comparator that compares the output of the quantizer with a threshold value, a quantization step of the inverse quantizer, or a predicted value of compound distortion of the compounder and outputs a signal for switching the selector depending on the magnitude relationship between the two. It is possible to have a different configuration.

Function: With the above-described configuration, the present invention can analyze the frequency components of an input signal and select a filter that deletes frequency components that are hardly included in the input signal without using additional information as in the conventional example. Quantization distortion without increasing transmission amount●
Distortion with little frequency dependence, such as encoding distortion, can be removed, and the visual quality of the target image can be improved.

Embodiment FIG. 1 shows a block diagram of an adaptive filter device according to a first embodiment of the present invention. In the same figure, l
is an input signal, 2 is a filter that changes the frequency characteristics of this input signal 1, 3 is a filter output frequency-converted by this filter 2, and 6 is a selector that switches and outputs the input signal 1 and the filter output 3. , 7 is an output signal selected by the selector 6, and 4 is a frequency analyzer that outputs a control signal 5 for switching the selector 6 based on the frequency characteristics of the input signal 1.

The operation of the adaptive filter device of this embodiment configured as described above will be described below. The input signal 1 is converted into a frequency-converted filter output 3 by a filter 2, and the input signal 1 is also input to a frequency analyzer 4. The frequency analyzer 4 measures the local frequency distribution of the input signal 1, and instructs the selector 6 to select the filter output 3 when the input signal 1 passes frequencies with a large frequency distribution and blocks frequencies with a small frequency distribution. A commanding control signal 5 is output. Furthermore, if the local frequency band of the input signal 1 is sufficiently wide, the selector 6 is switched so that the input signal 1 is output as is instead of the filter output 3. Frequencies with a small frequency distribution are mostly caused by quantization distortion and coding distortion, and almost no image quality deterioration occurs due to the adaptive filter described above.

As described above, according to this embodiment, image quality can be improved without increasing the amount of transmitted information due to transmitting additional information.

FIG. 2 is a block diagram of an adaptive filter in a second embodiment of the present invention. In the figure, 1 is the input signal, 2
is a filter that changes the frequency characteristics of this input signal 1,
3 is the filter output frequency-converted by this filter 2,
6 is a selector for switching between the input signal 1 and the filter output 3; 7 is an output signal selected by this selector 6;
8 is a subtracter that subtracts the input signal 1 and the filter output 3, 9 is the difference signal of this subtracter 8, 10 is an absolute value converter that converts this difference signal 9 into an absolute value, and 11 is this absolute value converter. A corner absolute value output 12 is a comparator that compares this absolute value output t1 with a threshold value and outputs a control signal i3 for switching the selector 6.

The operation of the adaptive filter device of this embodiment configured as described above will be described below. The input signal 1 is converted into a frequency-converted filter output 3 by the filter 2, and is also input to the subtracter 8 in the same way as the input signal 1. The subtracter 8 calculates the difference between the input signal l and the filter output 3 and outputs a difference signal 9.

If the important information of the input signal 1 is lost due to the band limit of the filter 2, the absolute value of the difference signal 9 will increase, and conversely, if the absolute value of the difference is small, the image quality will deteriorate due to the use of the filter 2. It represents little. Therefore, the difference signal 9 is converted into an absolute value by an absolute value converter 10, and a comparator 12
If the magnitude relationship is compared with the threshold value, the selector 6 may be switched to select the filter output 3 when the absolute value 11 is smaller than the threshold value.

As described above, according to this embodiment, by comparing the absolute value of the difference between the input signal 1 and the filter output 3 with a threshold value, an appropriate output can be selected with a simple configuration.

FIG. 3 is a block diagram of an adaptive filter device in a third embodiment of the present invention. In the figure, 17 is an inverse quantizer input signal, 18 is an inverse quantizer that inversely quantizes this inverse quantizer input signal 17, 19 is a quantization step of this inverse quantizer 18, and 20 is a comparator. Since the rest is the same as the second embodiment, the same reference numerals are given and the explanation thereof will be omitted.

The operation of the adaptive filter device of this embodiment configured as described above will be explained below. The basic configuration is the same as the second embodiment, and the differences from the second embodiment will be explained. The quantization step 19 is a parameter that directly affects the quality of the reproduced image, and the value of the input signal 1 changes in units of quantization steps. Therefore, the fact that the absolute value output 11 of the absolute value converter 10 in the comparator 20 is larger than the quantization step 19 indicates that the distortion caused by passing through the filter 2 is considerably large. Therefore, quantization step 19
By comparing the absolute value 11 with the comparator 20, the input signal 1 and the filter output 3 can be appropriately switched. Here, the comparator 20 may be switched not only based on the magnitude relationship between the quantization step l9 and the absolute value 11, but also based on the magnitude of the difference.

As described above, according to this embodiment, by using the difference between the absolute value 11 and the quantization step 19, an appropriate output can be selected with a simple configuration.

FIG. 4 is a block diagram of an adaptive filter device according to a fourth embodiment of the present invention. In the figure, 2l is a decoder input signal, 22 is a decoder that decodes this decoder input signal 21, 23 is a predictive coding distortion of this decoder 22, and the others are those of the third embodiment. is the same as

The operation of the adaptive filter device of this embodiment configured as described above will be explained below. The basic configuration is the same as the third embodiment, and the differences from the third embodiment will be explained. Although coding distortion is a parameter that directly affects the quality of reproduced images, it is impossible to accurately calculate coding distortion on the decoder side. However, it is possible to predict coding distortion from the encoder and coding parameters. Therefore, by comparing the predicted coding distortion 23 output from the decoder 22 with the absolute value 11 output from the absolute value converter 10 in the comparator 20, the input signal 1 and the filter output 3 can be appropriately switched. be able to. here,
The comparator 20 may be switched not only based on the magnitude relationship between the predictive coding distortion 23 and the absolute value 11, but also based on the magnitude of the difference.

As described above, according to this embodiment, by using the difference between the absolute value 11 and the predictive coding distortion 22, an appropriate output can be selected with a simple configuration.

Note that in the first and second embodiments, there is one filter 2, but a plurality of filters may be prepared and switched by the selector 6. Furthermore, in the third and fourth embodiments,
A signal processing circuit such as an orthogonal transformer may be provided between the inverse quantizer 18 or decoder 22 and the filter 2.

Effects of the Invention As explained above, according to the present invention, an input image can be converted to a visually preferable image quality without increasing the amount of transmission due to additional information or complicating the device, and without losing much of the information of the original signal. can be improved, and its practical effects are significant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an adaptive filter device according to a first embodiment of the present invention, FIG. 2 is a block diagram of an adaptive filter device according to a second embodiment of the present invention, and FIG. 3 is a block diagram of an adaptive filter device according to a second embodiment of the present invention. is a block diagram of an adaptive filter device according to a third embodiment of the present invention, FIG. 4 is a block diagram of an adaptive filter device according to a fourth embodiment of the present invention, and FIG. 5 is a block diagram of a conventional adaptive filter device. be. 2...Filter, 4...Frequency analyzer, 6...Selector, 8...Subtractor, 1
0... Absolute value generator, 12, 20... Comparator, 18... Inverse quantizer, 22...
Composite device.

Claims (4)

[Claims] (1) At least one that changes the frequency characteristics of the input signal
The present invention is characterized by comprising: a filter, a selector that switches and outputs the input signal and the output of the filter, and a frequency analyzer that measures the frequency characteristics of the input signal and outputs a signal that switches the selector. adaptive filter device. (2) at least one that changes the frequency characteristics of the input signal;
a selector that switches and outputs the input signal and the output of the filter; a subtracter that outputs a difference signal between the input signal and the filter output; and an absolute value that calculates the absolute value of the output of the subtracter. An adaptive filter device comprising: a value converter; and a comparator that compares the output of the absolute value converter with a threshold value and outputs a signal for switching the selector depending on the magnitude relationship between the two. (3) At least one that changes the frequency characteristics of the input signal
a selector that switches and outputs the input signal and the output of the filter; a subtracter that outputs a difference signal between the input signal and the filter output; and an absolute value that calculates the absolute value of the output of the subtracter. An adaptive filter comprising: a value generator; and a comparator that compares the output of the absolute value generator with a quantization step of an inverse quantizer and outputs a signal for switching the selector depending on the magnitude relationship between the two. Device. (4) At least one that changes the frequency characteristics of the input signal
a selector that switches and outputs the input signal and the output of the filter; a subtracter that outputs a difference signal between the input signal and the filter output; and an absolute value that calculates the absolute value of the output of the subtracter. The present invention is characterized by comprising a value converter and a comparator that compares the output of the absolute value converter with a predicted value of decoding distortion of a decoder and outputs a signal for switching the selector depending on the magnitude relationship between the two. Adaptive filter device.