JPH0984024A - Video signal encoder - Google Patents

Abstract

(57) Abstract: Provided is a moving picture signal coding device having high coding efficiency by effective noise reduction according to the characteristics of a moving picture signal and without quality deterioration of a reproduced image due to coding. To do. SOLUTION: A noise removal filter system is adaptively applied according to a feature of the moving image signal extracted from one or both of frame frame dropping information of the moving image signal and motion vector information in a moving image signal encoding device. Is selected, and effective noise reduction is performed on the moving image signal before encoding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture signal coding apparatus used in a videophone, a video conference, and the like.

[0002]

2. Description of the Related Art Generally, a moving picture signal coding apparatus first performs inter-frame prediction in order to remove temporal correlation, that is, performs motion compensation in pixel block (for example, 16 × 16 pixels) units of a previous frame. , The difference from the current frame is obtained in pixel block units. Next, in order to remove the spatial correlation, the difference value is subjected to orthogonal transformation, the orthogonal transformation coefficient is quantized, and the quantized output value and the motion vector used for motion compensation are coded to obtain a high efficiency code. The converted binary code string (bit stream) is output. The information amount of the quantized output value is much smaller than the information amount of the current frame. Next, the coded frame is stored in the transmission buffer, and the remaining amount of this buffer is used to control the input signal in the next frame and thereafter (frame dropping control), determine the quantization coefficient, and control the quantization output. Then, coding control is performed so that a desired coding rate is obtained.

On the other hand, a moving image signal captured by a video input device such as a camera contains noise components such as flicker, which impairs temporal correlation and spatial correlation, resulting in inter-frame prediction and orthogonality. Since the effect of information amount compression by conversion cannot be sufficiently obtained, the moving image signal input to the high-efficiency encoding circuit reduces the noise component through the noise removal filter, the encoding efficiency is high, and the noise is reduced. It is converted into a moving image signal and supplied to the high efficiency encoding circuit. Here, as the noise removal filter, a frame memory is used to delay one frame, a frame difference between the delayed signal and the current signal is obtained, and a calculation result by a limiter process or the like is added, and the input signal and the calculation process are performed again. Either a cyclic noise removal filter method for reducing the noise component is performed or an intra-area noise removal filter method for performing a filtering process such as a median filter on the current signal in units of 3 × 3 pixels without using a delayed signal is used. The method is adopted.

[0004]

However, although the above-mentioned cyclic noise elimination filter system can reduce the noise component which impairs the temporal correlation, it causes the afterimage noise of the moving body, so that the encoding control is performed. When the frame dropping is performed by the method, the images which are distant from each other in time are predicted, and the afterimage noise lowers the coding efficiency at the time of high efficiency coding, and further, the quality of the reproduced image quality is also impaired. There was a problem. Further, although the above-mentioned noise removal filter method in the area can reduce the noise component that spatially impairs the correlation, it reduces the resolution at the edge portion of the image and the still region of the image and reduces the noise component that impairs the temporal correlation. There is the problem that
It is impossible to perform filtering for noise removal with only a single filter method, and depending on the frame dropping, or the characteristics of moving image signals (ratio of moving images, still images, etc.), There is a problem that the filtering effect cannot be obtained sufficiently.

The present invention solves the above-mentioned problems of the prior art. When the frame is dropped, or when high-efficiency coding is performed without being affected by the characteristics of the moving image signal, the coding efficiency is improved. It is an object of the present invention to provide a moving picture signal coding device which realizes high efficiency coding by a moving picture signal in which a high noise component is reduced.

[0006]

In order to solve the above problems, the present invention detects a prediction error signal by performing motion detection and prediction in a pixel block unit from a previous frame for a moving image signal input in a frame unit. Orthogonal transform and quantize the orthogonal transform coefficient to code the quantized output with high efficiency.The coded frame and the coded frame are stored in the transmission buffer, and the residual amount of this buffer is used to control the input signal of the next and subsequent frames. , And a coding device having a coding control means for determining a quantized coefficient and controlling a quantized output, a noise removal filter having a plurality of filter systems for a moving image signal input in frame units, and A method for adaptively selecting the method of the noise removal filter based on either or both of the information of the motion detection result and the output information of the encoding control means. With.

[0007]

According to the above-described moving picture signal encoding apparatus of the present invention, a noise filter system is adaptively selected according to the characteristics of the moving picture signal extracted by the frame drop information and the motion vector information. Noise removal by
The encoding efficiency is high, and it is possible to realize a high quality image with a reduced rate of a reproduced image.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a moving picture signal encoding apparatus according to the present invention. In the figure, 1 is an input terminal to which a digitized moving picture signal is input, and 2 is the cyclic noise elimination filter system. A noise removal filter circuit having a built-in filter of two types of the area noise removal filter system, 3 is a first frame memory, 4 is a noise reduction (hereinafter referred to as NR) control circuit, 5 is an inter mode (interframe predictive coding) And an intra / intra determination circuit for determining the intra mode (intra-frame coding), 6 is a motion vector detection evaluation circuit, 7 is a switch (hereinafter referred to as SW),
8 is a motion compensation circuit, 9 is a discrete cosine transform (hereinafter DCT
Circuit, 10 is a quantization circuit, 11 is a second frame memory, 12 is an encoding control circuit, 13 is an inverse quantization circuit, 14 is an IDCT circuit for performing the inverse transformation of the DCT, 15 is an encoding circuit,
Reference numeral 16 is a buffer, which is arranged as shown in the drawing.

Next, the operation will be described. First, when the digitized moving image signal is input from the input terminal 1, the NR control circuit 4 adaptively determines the noise removal filter method from the frame drop control information from the encoding control circuit 12, and permits the input. The noise removal filter circuit 2 selects the noise removal filter type selection signal together with the signal or the input prohibition signal.
To send to. Now, when the former input permission signal is input, the noise removal filter circuit 2 captures the moving image signal, and based on the noise removal filter system selection signal that is also input, the noise removal filter system 2 selects the cyclic noise removal filter system. If one of the intra-area noise removal filter methods is selected and the cyclic noise removal filter method is selected, the first
Noise removal processing is performed using the moving image signal stored in the frame memory 3, and if the in-area noise removal filter method is selected, noise removal processing is performed without using the first frame memory 3. A moving image signal with a reduced noise component (hereinafter, the moving image signal output from the noise removal filter circuit 2 is referred to as an input moving image signal) is output, and this output signal is output to the motion vector detection evaluation circuit 6 and the inte.
It is input to the r / intra determination circuit 5 and the result is stored in the first frame memory 3. On the other hand, when the latter input prohibition signal is input, the noise removal filter circuit 2 captures the moving image signal and performs noise removal processing, but outputs nothing, so in this case, there is no input moving image signal. .

In the former case where the input moving image signal exists,
The following processing is performed for each pixel block (for example, 16 × 16 pixels). First, the motion vector detection / evaluation circuit 6 calculates a motion vector from the second frame memory 11 and the input moving image signal,
The result is output to the motion compensation circuit 8. This motion compensation circuit 8
Performs motion compensation using the calculated motion vector and the second frame memory 11. Here, the inter / intra determination circuit 5 determines the inter mode and the intra mode by using the input moving image signal and the second frame memory 11. As a result, the SW7 is turned on in the inter mode and turned off in the intra mode. Becomes In the inter / intra determination circuit 5, control is performed such that intraframe coding is selected for a portion where the correlation between frames is low such as a scene change.

Next, when SW7 is on, the subtracter S obtains the difference between the input moving image signal and this motion-compensated signal to obtain the prediction error signal. This prediction error signal is input to the DCT circuit 9, orthogonally transformed, and the orthogonal transformation coefficient is output to the quantization circuit 10. In the quantization circuit 10, quantization is performed using the quantization coefficient determined by the encoding control circuit 12. The quantized output value is input to the encoding circuit 15 and the inverse quantization circuit 13. The inverse quantization circuit 13 and the IDCT circuit 14 respectively perform inverse transformation to decode the prediction error signal, and the decoded prediction error signal and the motion-compensated signal are added by the adder A, and the second frame memory 11 Are stored in and are referenced again from the next frame. On the other hand, the encoding circuit 15 encodes the quantized output value and the motion vector, outputs a highly efficient encoded binary code sequence, and the encoded frame is stored in the buffer 16 and stored in the buffer 16. The coding control circuit 12 uses the residual amount to control the input signal from the next frame.
(Frame drop control information) is input to the NR control circuit 4.

The overall structure of the moving picture signal encoding apparatus of the present invention is as described above. Next, the three selection means by the NR control circuit 4 of the noise elimination filter system, which is the main point, will be described in more detail. explain.

The first means The NR control circuit 4 is provided with a counter for counting the number of continuously prohibited frames (the number of dropped frames), and the dropped frame control information of the encoding control circuit 12 is provided. When is allowed to input, if the value of this counter is less than a certain threshold value, the cyclic noise removal filter method is selected. In this case, the afterimage noise of the moving body has a small influence on the high-efficiency coding, and the inter mode that reduces the redundancy in the time direction is easily selected, and the cyclic noise removal filter method is considered to be more advantageous. is there. On the contrary, when the value of the counter exceeds a certain threshold, the in-area noise removal filter method is selected. In this case, the afterimage noise of the moving object may cause a reduction in encoding due to high-efficiency encoding, and the inter-frame correlation becomes low in the high-efficiency encoding circuit, resulting in an intra mode that reduces spatial redundancy. This is because the ratio is considered to increase, and the in-area noise removal filter method that removes noise that impairs spatial correlation is considered to be more advantageous.

Second Means In the NR control circuit 4, a feature of the moving picture signal is extracted from the motion vector in addition to a counter for counting the number of continuously prohibited frames (the number of frames dropped). This means is provided with, for example, an average of vector values of motion vectors, and when this average value exceeds a certain threshold value, this image has many moving regions and afterimage noise of the moving body is high. When it is determined that there is a risk of a reduction in the efficiency encoding, and the frame dropping control information of the encoding control circuit 12 is permitted to be input, the in-area noise removal filter method is selected. On the other hand, if the average value is less than or equal to a certain threshold value, it is determined that the image has many static areas, and it is considered that the afterimage noise of the moving body has a small influence on the high-efficiency encoding, and the cyclic noise removal filter method is selected.

Third means Using both a counter provided in the NR control circuit 4 for counting the number of frames (the number of frames dropped) and a means for extracting the feature of the image from the motion vector,
First, a means for extracting characteristics of a moving image signal is mainly used, and when the means determines that this image has many moving areas, afterimage noise of a moving object may cause a reduction in encoding in high efficiency encoding. If the value of the counter is less than a certain threshold value, the frame correlation is high, and it is considered that the afterimage noise of the moving body has a small influence on the high-efficiency coding, so that the frame dropping control information of the coding control circuit 12 is permitted to be input. When
Select the recursive denoising filter method. On the contrary, if the value of the counter is equal to or larger than a threshold value, the in-area noise removal filter method is selected.

Next, if the counter is mainly used and the value of the counter exceeds a certain threshold value, the afterimage noise of the moving object may cause the deterioration of the coding of the high efficiency coding, but If the average of the vector values of the motion vectors in the extracting means is below a certain threshold,
Since it is considered that the afterimage noise of the moving body has a small effect on the high-efficiency coding, if the cyclic noise reduction filter method is selected and conversely the average of the vector values of the motion vector is larger than a certain threshold, the noise in the area is Select the removal filter method.

The selection branches of the noise removal filter method corresponding to the characteristics of the image described above are organized into the following four types.

(1) In the case of an image having a low frame correlation and a large number of moving areas, the intra-area noise removal filter method is selected.

(2) In the case of an image having a low frame correlation and a large number of still regions, the cyclic noise removal filter method is selected.

(3) In the case of an image having a high frame correlation and a large number of moving regions, the cyclic noise removal filter method is selected.

(4) The intra-area noise removal filter method is selected for an image having a high frame correlation and a large number of still regions.

As is clear from the above description of the operation of the embodiment, noise is adaptively removed according to the characteristics of the moving image signal extracted from one or both of the frame drop information of the video signal and the motion vector information. Select the filter method,
By effectively reducing noise, it is possible to improve the coding efficiency of moving image signals.

[0023]

As described above, according to the present invention, noise is adaptively adjusted according to the characteristics of the moving image signal extracted from one or both of the frame drop information of the moving image signal and the motion vector information. To provide a moving picture signal coding apparatus having a high coding efficiency of a moving picture signal by selecting a removal filter method and effectively reducing noise, and having no deterioration in quality of a reproduced image due to the coding. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a moving image signal encoding apparatus of the present invention.

[Explanation of symbols]

1 ... Input terminal, 2 ... Noise removal filter circuit, 3 ...
First frame memory, 4 ... NR control circuit, 5 ... inter
/ Intra determination circuit, 6 ... Motion vector detection evaluation circuit,
7 ... SW, 8 ... Motion compensation circuit, 9 ... DCT circuit,
10 ... Quantization circuit, 11 ... Second frame memory, 12 ...
Encoding control circuit, 13 ... Inverse quantization circuit, 14 ... IDCT circuit, 15 ... Encoding circuit, 16 ... Buffer.

Claims (3)

[Claims] 1. A high-efficiency coding of a quantized output by performing prediction on a moving image signal input on a frame-by-frame basis in pixel block units from a previous frame, orthogonally transforming a prediction error signal and quantizing an orthogonal transform coefficient. The encoding circuit that stores the encoded frame in the transmission buffer, controls the input signal after the next frame by using the residual amount of this buffer, and determines the quantization coefficient to control the quantization output. In a coding device having a control means, a noise removal filter having a plurality of filter methods for moving image signals input in frame units, and a noise removal filter adaptively based on output information of the coding control means. An apparatus for encoding a moving image signal, characterized by comprising means for selecting a method. 2. A moving image signal input in a frame unit is subjected to motion detection and prediction in a pixel block unit from a previous frame to orthogonally transform a prediction error signal and quantize an orthogonal transform coefficient to enhance a quantized output. In an encoding device having a means for efficient encoding, a noise removal filter having a plurality of filter methods for moving image signals input in frame units, and a noise removal filter adaptively based on the information of the motion detection result. An apparatus for encoding a moving image signal, characterized by comprising means for selecting a method. 3. With respect to a moving image signal input in frame units, motion detection is performed in pixel block units from the previous frame, prediction is performed, the prediction error signal is orthogonally transformed, the orthogonal transformation coefficient is quantized, and the quantized output is enhanced. An encoding circuit for efficient encoding,
A code having a coded frame that stores a coded frame in a transmission buffer, controls an input signal of the next frame and subsequent frames by using the residual amount of the buffer, and determines a quantization coefficient to control a quantized output. In the encoding device, a noise removal filter having a plurality of filter methods for moving image signals input in frame units, and a noise removal filter adaptively based on the information of the motion detection result and the output information of the encoding control means. 2. An apparatus for encoding a moving picture signal, comprising: means for selecting the method of.