JP2985752B2 - Video decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture decoding apparatus for decoding a highly efficient coded image signal, and more particularly to a control method of a post filter for removing noise generated when the image signal is decoded. The present invention relates to a moving picture decoding apparatus having the same.

[0002]

2. Description of the Related Art In an image transmission apparatus for transmitting a moving image signal using a low bit rate line, highly efficient encoding is performed in order to increase the transmission efficiency of the moving image signal. As a standard high-efficiency encoding method, ITU-T Recommendation H. 261. H. The H.261 high-efficiency coding method uses motion compensation inter-frame coding, DCT (Discr
et Cosine Transform), quantization, and variable-length coding to perform temporal and temporal
This excludes spatial redundancy.

[0003] A moving picture decoding apparatus which receives a highly efficient coded picture signal and generates a reproduced picture is provided with a variable length decoding,
An original video signal is obtained by performing inverse quantization, DCT inverse transform, and motion compensation. At this time, the reproduced image includes noise due to quantization, such as block distortion and mosquito noise, resulting in an unnatural image. Therefore,
A technique for removing these noises from the reproduced image is required.

Heretofore, as a technique for removing noise from a reproduced image, a method has been adopted in which a two-dimensional spatial filter is applied to the reproduced image to remove high-frequency noise that is visually uncomfortable.
In addition, in view of the fact that applying the two-dimensional spatial filter processing to the reproduced image causes deterioration of the image, and considering that the above-mentioned noise often occurs in a moving image, the two-dimensional spatial filtering processing is performed only on the moving part. May be applied. That is, the image signal is divided into small blocks of, for example, about 16 × 16 pixels, and the presence / absence of the movement of the small block image is determined based on the motion vector obtained for each obtained small block image. Then, the ON / OFF of the two-dimensional spatial filter is controlled for the small block,
The filter is turned on for a small block image having motion, and turned off for no motion. As a result, noise is removed by performing a two-dimensional spatial filter process on a moving part of the image, and deterioration of the resolution is prevented without performing a two-dimensional spatial filter process on a stationary portion of the image. As this kind of conventional technique, there is a technique described in Japanese Patent Application Laid-Open No. 4-35596.

[0005]

However, with only the filter control according to the above-described conventional technique, a two-dimensional image is obtained regardless of whether the image of the small block includes the outline of the entire image or the image of the small block has motion. There is a drawback that the spatial filter processing is applied, and the outline of the image in the small block is not preserved and is blurred.

Further, when decoding an image signal that does not include motion vector information, it is not possible to control ON / OFF of a two-dimensional spatial filter for each small block, resulting in image degradation.

The present invention solves the above-mentioned drawbacks of the prior art, and obtains an outline of a moving area of an image from a difference between frames of a reproduced image, and performs operation control in which the outline portion is not subjected to two-dimensional spatial filtering. By doing so, an object of the present invention is to provide an image decoding device capable of preventing the outline of an image from being blurred and preventing unnecessary image deterioration.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a decoder for inputting a highly efficient coded video signal and decoding it into an original video signal; A spatial filter that applies a two-dimensional spatial filter process to the image signal based on the control signal and outputs the signal, a delay signal generating unit that receives the decoded moving image signal and generates a delayed signal delayed by one frame A difference means for calculating a difference between the decoded moving image signal and the delayed signal delayed by one frame, and a result of the difference by the difference means being binarized and compared with a predetermined threshold value, If the result of the difference is larger than a threshold value, a first binarized signal indicating that the image based on the moving image signal is a moving image is output. The second that there is A judging means for outputting a binary signal, based on a determination result of said determining means, said first or second
Inspection of an area having a size of several pixels including pixels corresponding to the binarized signal of (a), and when all the binarized signals corresponding to the area are the first binarized signal, the spatial filter Outputs the control signal for performing a two-dimensional spatial filtering process on the spatial filter when at least one of the binary signals corresponding to the region includes the second binary signal. Outputting the control signal for not performing the two-dimensional spatial filtering on the moving image, based on the decoded moving image signal, excluding an outline portion in the moving image.
Spatial filter control means for controlling the spatial filter so as to perform two-dimensional spatial filter processing only on the portion .

In another aspect, the spatial filter system
Controlling means for generating a moving image signal corresponding to the area of several pixels.
Combined to obtain the judgment result by the judgment means
Any number of 1-line delay elements and any number of 1 lines
Moving image corresponding to the elementary delay element and the obtained arbitrary area
An AND circuit for calculating the logical product of the image signal determination results.
It is set to obtain configuration.

[0010]

[0011]

[0012]

[0013]

[0014]

According to the present invention, the spatial filter control means comprises:
By determining the difference between the moving image signal and a delayed signal obtained by delaying the moving image signal by one frame, it is determined whether the image based on the moving image signal is a moving image or a still image. In addition, the determination result of a predetermined region in the image based on the moving image signal is examined, and if at least one of the moving image signals corresponding to the region includes a moving image signal indicating a still image, 2
The spatial filter is controlled so as not to perform the dimensional spatial filtering. Thereby, of the images based on the moving image signal,
Applying two-dimensional spatial filter processing only to the moving part,
The still part and the contour part of the moving image can be subjected to the two-dimensional spatial filter processing.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of moving picture decoding according to one embodiment of the present invention.

As shown in the figure, a moving picture decoding apparatus according to the present embodiment receives a moving picture signal 20 which has been encoded with high efficiency and decodes it into an original moving picture signal 21; A spatial filter 16 for applying a two-dimensional spatial filtering process to the output 21, a frame memory 12 for receiving the moving image signal 21 and delaying it by one frame and outputting the same, a moving image delayed by one frame from the moving image signal 21 A subtracter 13 that receives the signal 22 to obtain a difference, a binarization circuit 14 that binarizes the difference signal 23 output from the subtractor 13, and a spatial filter based on an output signal of the binarization circuit 14. And a spatial filter control circuit 15 for controlling the control circuit 16.

The decoder 11 receives the highly efficient video signal 20, decodes the original video signal 21, and outputs it.
As a function of the decoder 11, for example, the ITU-T Recommendation H. 2
Variable length decoding, inverse quantization, DC defined in 61
Performs T inverse conversion and motion compensation processing. The video signal 21 output from the decoder 11 is delivered to the frame memory 12, the subtractor 13, and the spatial filter 16.

The frame memory 12 receives the input moving image signal 21, delays it by one frame, and outputs it. The moving image signal 22 output from the frame memory 12 and delayed by one frame is sent to the subtractor 13.

The subtractor 13 receives a moving picture signal 21 output from the decoder 11 and a moving picture signal 22 output from the frame memory 12, and calculates a difference between the two signals. The moving image signal 21 and the moving image signal 22 are the same moving image signal, but the moving image signal 22 is delayed by one frame from the moving image signal 21. Therefore, if the difference between the two signals is obtained, it is possible to determine whether or not the image generated by the moving image signals 21 and 22 is a moving image based on the result.

The binarization circuit 14 receives a difference signal 23 indicating the result of the difference by the subtractor 13 and inputs the difference signal 23.
Is binarized. That is, the binarization circuit 14 compares the predetermined threshold value Th with the difference signal 23,
If the difference signal 23 is larger than the threshold value Th, 1 is output, and if it is smaller, 0 is output.

The spatial filter control circuit 15 receives the binarized signal output from the binarizing circuit 14, and controls ON / OFF of the spatial filter 16 based on the binarized signal. That is, when at least one pixel is included in an appropriate area including a pixel corresponding to a predetermined binarized signal, 0 is set.
Is output, and when all the pixels are 1, 1 is output. The configuration of the spatial filter control circuit 15 will be described later.

The spatial filter 16 receives the video signal 21 output from the decoder 11 and performs a two-dimensional low-pass filtering process on the input video signal 21 under the control of the spatial filter control circuit 15. That is, if the output signal 25 of the spatial filter control circuit 15 is 1, the moving image signal 2
1 is subjected to low-pass filter processing and output. On the other hand, if the output signal 25 is 0, the low-pass filter processing is not performed, and the moving image signal 21 is output as it is.

FIG. 2 is a block diagram showing the configuration of the spatial filter control circuit 15.

As shown, the spatial filter control circuit 15
Comprises one-line delay elements 151 and 152 for delaying the input signal by one line and one-pixel delay elements 153 to 158 for delaying the input signal by one pixel. An input signal for a total of nine pixels, which is shifted one line pixel up and down, is obtained. Further, an AND circuit 159 for calculating the AND of these input signals is provided.

That is, the 2 input from the binarization circuit 14
The binarized signal 24 is sent as it is to the AND circuit 159 as a binarized signal 210 and the one-line delay element 15
One and one pixel delay elements 155 are distributed. The signal sent to the one-line delay element 151 is output after being delayed by one line and output as a binary signal 211.
9 and is distributed to a one-line delay element 152 and a one-pixel delay element 154. 1-line delay element 15
After being delayed by one line, the signal sent to 2 is output and sent to the AND circuit 159 as a binary signal 212, and is also distributed to the one-pixel delay element 153. The signals sent to the one-pixel delay elements 155, 154, and 153 are output after being delayed by one pixel, and output as the binary signal 21.
3, 214, and 215 are sent to the AND circuit 159, and are also distributed to the one-pixel delay elements 158, 157, and 156. The signals sent to the one-pixel delay elements 158, 157, and 156 are output after being delayed by one pixel and sent to the AND circuit 159 as binary signals 216, 217, and 218.

As described above, the binary signal 211 and the binary signal 210 from the binary signal 210 are delayed from the binary signal 210 by one line.
Binary signal 212 delayed by line, binary signal 21
Binary signals 213, 214, 215 delayed by one pixel and binary signals 216, 217, 218 delayed by two pixels are input from 0, 211, and 212, respectively.
Considering a two-dimensional display screen having scanning lines in a horizontal direction like a monitor screen in a normal display device, as shown in FIG. This corresponds to an image display area for a total of nine pixels for each pixel. Each of the binary signals 210 to 2
FIG. 4 shows the correspondence between 18 and the position of each pixel in FIG.

The AND circuit 159 obtains the logical product of the input binary signals 210 to 218 and calculates the logical product of the binary signals 210 to 218.
Is output. That is, 1 is output when all inputs are logic 1, and 0 is output when there is at least one logic 0. Referring to FIGS. 5 and 6,
An example of control on a display screen of 6 lines × 6 pixels will be described. In the figure, the hatched area indicates the binarized signal 21.
Assume that the image area corresponds to 0 to 218. In this example, in the case of FIG. 5, since the binarized signal at the position of P (-1, -1) is 0, the control signal 25 is 0. FIG.
In the case of (1), the binary signal corresponding to all the pixels is 1, so the control signal 25 is 1.

Here, when at least one binarized signal of logic 0 is included in an area of 3 lines × 3 pixels, the entire area is set to 0 because there is no motion as an image in the area. Since the region includes a portion (a portion where the difference and the result of the binarization are 0), the region is highly likely to be a contour portion of the image, and the region is not subjected to the two-dimensional spatial filter processing.
This is because it is preferable to maintain the sharpness of the image.

Next, the function of the spatial filter 16 will be described.

The spatial filter is realized by a low-pass filter of 3 lines × 3 pixels represented by the following equation (1). That is,
Assuming that the input of the spatial filter is X (i, j), X (0,
0) is a low-pass filtered output Y (0,0),
It is obtained by multiplying the coefficient C (i, j) corresponding to the X (i, j) pixel and accumulating the multiplication result.

[0032]

(Equation 1)

Further, by selecting the value 0 as the filter coefficient C (i, j), it is possible to prevent the input signal from being subjected to the two-dimensional spatial filter processing.
Therefore, based on the control signal 25 from the spatial filter control circuit 15, when the control signal 25 is 1, filter processing is performed, and when the control signal 25 is 0, the filter count C
(I, j) may be set to 0 so that the filtering process is not performed. As a result, two-dimensional spatial filter processing is performed only on the moving pixels excluding the outline of the moving image, and quantization noise such as mosquito noise included in the reproduced image is removed. Then, the outer part and the contour part of the motion of the image are not subjected to the two-dimensional spatial filter processing, thereby avoiding unnecessary deterioration of the image.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not necessarily limited to the above embodiments. For example, in the present embodiment, the outline portion of the image is determined by determining whether or not a non-moving portion is included in a region corresponding to a total of 9 pixels of 3 lines × 3 pixels. The area does not need to be three pixels, and can be set appropriately according to the type of image to be handled.

[0035]

As described above, according to the present invention,
In order to detect a contour portion of a moving image by judging whether or not a region having a certain extent includes a portion that does not move, a two-dimensional spatial filter process is not performed on the contour portion. In addition, it is possible to preserve the sharpness of the image of the outline portion and prevent the image from being blurred.

In addition, the difference between a predetermined moving image signal and a moving image signal delayed by one frame from the moving image signal is used to determine the presence or absence of movement of the image. No motion vector is required as in the spatial filter control technique in the device. Therefore, it is possible to appropriately remove quantization noise only from a portion having motion even for a moving image signal that does not include motion vector information.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a video decoding device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a spatial filter control circuit according to the present embodiment.

FIG. 3 is a diagram illustrating a determination area in the spatial filter control circuit of the present embodiment.

FIG. 4 is a diagram illustrating a relationship between a decision area and a binarized signal in the spatial filter control circuit of the present embodiment.

FIG. 5 is a diagram illustrating a control example of a spatial filter by the spatial filter control circuit of the present embodiment.

FIG. 6 is a diagram showing another control example of the spatial filter by the spatial filter control circuit of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Decoder 12 Frame memory 13 Subtractor 14 Binarization circuit 15 Spatial filter control circuit 16 Spatial filter 151, 152 One line delay element 153-158 One pixel delay element 159 Logical product circuit

Claims (2)

(57) [Claims] 1. A decoder for inputting a high-efficiency coded moving image signal and decoding the original moving image signal, and performing a two-dimensional spatial filtering process on the decoded moving image signal based on a control signal. A spatial filter for applying and outputting, a delay signal generating means for receiving the decoded video signal and generating a delay signal delayed by one frame, and delaying the decoded video signal by one frame. A difference means for obtaining a difference from the delayed signal, and a result obtained by binarizing the result of the difference by the difference means and comparing the result with a predetermined threshold value. A first binarized signal indicating that the image based on the signal is a moving image is output. If the image is smaller than the threshold value, a second binarized signal indicating a still image
Determining means for outputting a binary signal of the following; and, based on the determination result of the determining means, inspecting an area of several pixels wide including pixels corresponding to the first or second binary signal. Outputting, when all the binary signals corresponding to the region are the first binary signals, the control signal for performing the two-dimensional spatial filtering on the spatial filter, By outputting the control signal for not performing the two-dimensional spatial filtering on the spatial filter when at least one of the binary signals to be processed includes the second binary signal, A moving image decoding apparatus comprising: a spatial filter control unit that controls the spatial filter so as to perform a two-dimensional spatial filtering process only on an operation portion excluding a contour portion in a decoded moving image signal. 2. The method according to claim 1, wherein the spatial filter control means determines the moving image signal corresponding to the area of the several pixels.
Arbitrarily combined to obtain the result of the step
Number of one-line delay elements and arbitrary number of one-pixel delay elements
And determination of a moving image signal corresponding to the obtained arbitrary area.
And an AND circuit for calculating the AND of the result
2. The video decoding device according to claim 1, wherein: