KR0169654B1 - Device for encoding moving picture signals - Google Patents

Abstract

In the video encoder according to the present invention, a motion vector of a motion compensation image of one frame before motion is compared with a motion vector of a motion compensation image of two frames before, and according to the comparison result, a motion compensation image of one frame before or two frames before By generating the difference image using the compensation image, there is an advantage of increasing the reconstruction quality.

Description

Video encoder

1 is a block diagram showing the configuration of a general video encoder.

2 is a block diagram showing the configuration of a video encoder according to the present invention.

* Explanation of symbols for main parts of the drawings

30: subtractor 32: discrete cosine conversion unit

34 quantizer 36 variable length encoder

38: inverse quantizer 40: inverse discrete cosine conversion unit

42: adder 44, 50: frame memory

46: motion estimation unit 48: motion compensation unit

52: comparator

The present invention relates to a video encoder, and in particular, comparing a motion vector of an image of a current frame and a motion vector of an image of a previous frame to transmit a motion compensation image of an image of a previous frame when the difference of the motion vector is large. A video encoder.

Information is one of the most important resources and is called the information society in modern times. As the amount of information to be accepted and processed is increasing day by day, data compression is indispensable to effectively use the existing transmission band.

In particular, since a digital video signal requires a lot of memory to express information, video information compression has an effect of more efficiently storing, retrieving, and transmitting information.

For this reason, many compression methods for image data have been developed, and these image data compression methods can be divided into lossless coding techniques of lossy coding according to whether information is lost, and spatial redundancy existing in still images is intraframe. It can be divided into interframe encoding using temporal redundancy present in encoding and video.

In addition, it is divided into the first generation coding method which has little information loss and the international standard is completed, and the second generation coding method which uses the characteristics of human visual structure and image. The first generation coding techniques include spatial coding such as Pulse Code Modulation (PCM), Differential PCM (Delta PCM), Delta Modulation (Delta Modulation), and conversion coding such as Karhunen-Loeve, Fourier, Cosine, Harr, Hadamard, and Sine, Hybrid coding combining the above two, and Motion Compensated Coding used for video. Second-generation coding techniques include pyramid coding, anisotropic nonnormal prediction coding, contour-texture-based techniques, and encoding techniques based on directional decomposition.

Since the transmission of video has more considerations than the still image and the compression effect is more prominent, the development of a technique to obtain a high compression ratio is of great interest. Motion compensation coding is used in the currently developed HDTV broadcasting system or MPEG. Motion compensation coding has a pixel cycling algorithm and a block matching algorithm. The block matching algorithm has a lower accuracy than the pixel cycling algorithm, but it is widely used in a video system because of its simple real-time processing and hardware implementation. Here, the block matching algorithm divides an image into blocks of a predetermined size, obtains a motion vector for each block, and performs a discrete cosine transform on the prediction error between the image obtained by the motion vector and the original image, and then the discrete cosine transform coefficient. It is a technique of transmitting together.

In general, video encoders which are widely used have the effect of data compression by removing temporal redundancy through motion processing and spatial redundancy through discrete cosine transform.

FIG. 1 is a block diagram showing the structure of a general video encoder, and is used in many standardized encoders such as H.261, MPEG-1, and MPEG-2.

Referring to FIG. 1, the subtractor 10 generates a difference image between frames by subtracting a motion compensation image of an original image of a current frame and a reconstructed image of a previous frame, which are input in units of frames.

The discrete cosine transforming unit (DCT) 12 outputs a discrete cosine transform coefficient by performing discrete cosine transforming of the inter-frame difference image into, for example, a block of 8x8 pixels in order to remove the correlation between pixels.

The quantizer Q 14 quantizes the discrete cosine transform coefficients of the interframe difference image output from the discrete cosine transforming unit 12 at a predetermined quantization interval and outputs the quantized interval.

The variable length encoder (VLC) 16 variably encodes the inter-frame difference image quantized by the quantizer 14 and transmits the variable length coder to a decoder (not shown) through a buffer (not shown).

That is, among the signals represented by 8 bits, for example, data with high frequency is represented by fewer bits, and data with less frequency is represented by many bits, thereby reducing the total number of bits representing the difference image.

An inverse quantizer (IQ) 18 is connected to the output terminal of the quantizer 14 and restores the quantized interframe difference image to a state before being input to the quantizer 14.

The inverse discrete cosine transform unit (IDCT) 20 is connected to the output terminal of the inverse quantizer 18 and before the inverse quantized inter-frame difference image is inputted to the discrete quantizer 18 by the inverse quantizer 18. Restore to state

The adder 22 adds the inter-frame difference image and the motion compensation image reconstructed by the inverse discrete cosine transform unit 20 and stores the reconstructed image of the previous frame in the frame memory 24.

The motion estimation unit (ME) 26 generally uses a block matching algorithm, estimates a similar portion between the input current image and the reconstructed image of the previous frame stored in the frame memory 24, and calculates the result of the position shift. Will output

The motion compensator (MC) 28 outputs the motion compensation image compensated by the motion vector to the subtractor 10 and the adder 22, respectively, by compensating the motion position of the reconstructed image of the previous frame stored in the frame memory 24, respectively. .

In summary, the above-described conventional video encoder generates a difference image by subtracting a motion compensated image that compensates for the movement of the previous frame from the image of the current frame by using a motion vector between the previous frame and the current frame, and encodes it. However, when a specific image data process, that is, a motion vector generation procedure is complicated, an error occurs in the generated motion vector, which sometimes degrades the quality of the reconstructed image.

Accordingly, the present invention compares the motion vector used in the motion compensation image of the current frame with the motion vector for the motion compensation image of the previous frame to solve the above-mentioned problems. It is an object of the present invention to provide a video encoder for transmitting a compensation image.

In order to achieve the above object, a video encoder according to the present invention includes: a subtractor for generating a difference image by subtracting a motion compensation image of an original image of a current frame and a reconstructed image of one frame before;

Discrete cosine transform unit for outputting a discrete cosine transform coefficient by the discrete cosine transform to convert the difference image output from the subtractor from the spatial domain to the frequency domain:

A quantization unit for quantizing and outputting the discrete cosine transform coefficients of the difference image output from the discrete cosine conversion unit at a predetermined quantization interval:

A variable length encoder for variable length encoding and outputting the quantized difference image by the quantizer;

An inverse quantizer for restoring a quantized difference image in the quantizer to a state before being input to the quantizer:

Inverse discrete cosine transform unit for restoring the inverse quantized difference image in the inverse quantizer to the state before inputting to the discrete cosine transform unit: motion compensation of one frame before and the difference image restored in the inverse discrete cosine transform unit An adder for adding an image and outputting the reconstructed image one frame before the frame; a first frame memory for storing the reconstructed image of the previous frame output from the adder in units of frames: the original image of the current frame and the first frame A motion estimator for estimating a similar part between reconstructed images before one frame stored in a memory and outputting a result of the position shift as a motion vector: a motion position of a reconstructed image before one frame stored in the first frame memory The motion compensation image compensated by the motion vector output from the motion estimation unit A motion compensation unit for outputting the motion compensation unit: a second frame memory for storing a motion compensation image before one frame output from the motion compensation unit: a motion vector of the motion compensation image before one frame output from the motion compensation unit and the A comparator for comparing the motion vectors in the motion compensation image of two frames previous from the second frame memory and outputting a control signal according to the comparison result: and outputted from the motion compensator according to the control signal output from the comparator And a switching unit for selectively outputting a motion compensation image before one frame or a motion compensation image before two frames output from the second frame memory to the subtractor.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

FIG. 2 is a block diagram showing a configuration of a video encoder according to the present invention, and a subtractor for generating a difference image by subtracting a motion compensation image of an original image of a current frame and a reconstructed image of one frame before inputted in a frame unit ( 30) and a discrete cosine transform unit 32 for outputting a discrete cosine transform coefficient by performing discrete cosine transform to convert the difference image output from the subtractor 30 from the spatial domain to the frequency domain. A quantizer 34 for quantizing and outputting the discrete cosine transform coefficients of the difference image outputted by 32) at a predetermined quantization interval: a variable field for variable length encoding and outputting the quantized difference image by the quantizer 34 Encoder 36: Inverse quantizer 38 for restoring a quantized difference image quantized by the quantizer 34 to a state before being input to the quantizer 38: The inverse quantizer 38 Inverse discrete cosine transform unit 40 for restoring the inverse quantized difference image to the state before being input to the discrete cosine transform unit: The difference image and the motion compensation image restored by the inverse discrete cosine transform unit 40 An adder 42 for adding and reconstructing a reconstructed image one frame before the frame; a first frame memory 44 for storing the reconstructed image one frame before the frame output by the adder 42 in units of frames; A motion estimation unit 46 for estimating a similar portion between the original image and the reconstructed image before one frame stored in the first frame memory 44 and outputting a result of the position movement as a motion vector: the first frame memory ( The adder 42 adds a motion compensated image one frame earlier than the frame compensated for by the motion vector output from the motion estimation unit 46 to the motion position of the reconstructed image one frame before. Motion compensator 48 for output: second frame memory 50 for storing the motion compensation image of one frame before the output from the motion compensator 48: 1 output from the motion compensator 48 A comparator 52 for comparing the motion vector in the motion compensation image before the frame with the motion vector in the motion compensation image before the two frames supplied from the second frame memory 50 and outputting a control signal according to the comparison result; According to the control signal output from the comparator 52, a motion compensation image of one frame before or outputted from the motion compensator 48 or a motion compensation image of two frames or more output from the second frame memory 50 is selectively selected. It consists of a switch unit 54 for outputting to the subtractor (30).

Here, the second frame memory 50 inputs a motion compensated image of one frame before that output from the motion compensator 48, and the motion compensated image of two frames before that output from the second frame memory 50 is a comparator. And a comparator 52 connected to the b input terminal of the switching unit 54 and the output compensator 1 before the frame output from the motion compensator 48 and the output 2 from the second frame memory 50. The motion compensation image before the frame is input, and the output of the comparator 52 is supplied to the control terminal of the switching unit 54, and 1 which is output from the motion compensation unit 48 to the a input terminal of the switching unit 54. The motion compensation image before the frame is applied, and the motion compensation image before the two frames output from the second frame memory 50 is applied to the b input terminal.

Looking at the operation of the present invention according to the configuration of Figure 2 as follows.

Here, the subtractor 30, the discrete cosine transformer 32, the quantizer 34, the variable length encoder 36, the inverse quantizer 38, the inverse discrete cosine transformer 40, the adder 42, the first frame Since the memory 44, the motion estimator 46, and the motion compensator 48 are the same as in FIG. 1, operation description is omitted, and the second frame memory 50, the comparator 52, and the switch 54 are provided. We will focus on the operation of).

The second frame memory 50 stores a motion compensation image of one frame before the frame output from the motion compensator 48, delays one frame, and then supplies a motion compensation image of two frames. Here, the motion compensation image before one frame includes a motion vector.

The comparator 52 compares the motion vector of the motion compensation image of one frame before and output from the motion compensator 48 with the motion vector of the motion compensation image of two frames from the second frame memory 50. According to the comparison result, the switching unit 54 is output as a control signal for switching. That is, when the coordinate difference between the motion vector in the motion compensation image before 1 frame and the motion vector in the motion compensation image before 2 frames is larger than a predetermined threshold value, a b switching signal is output, and the motion compensation image in the motion compensation image before 1 frame is output. If the difference between the motion vector and the motion vector in the motion compensation image two frames before is smaller than a predetermined threshold value, a switching signal is output. Here, since the motion difference between adjacent frames is small, the maximum difference that can occur with respect to the first motion vector between the previous frame and the current frame and the second motion vector between the current frame and the next frame is experimentally determined and set as the threshold. do. Accordingly, when the difference between the two motion vectors is larger than the threshold, it may be considered that an error occurs in the second motion vector.

The switching unit 54 selectively subtracts the motion compensated image one frame before the frame applied to the a input terminal or the motion compensated image two frames before the b input terminal according to the control signal output from the comparator 52 (30). )

That is, when the control signal output from the comparator 52 is a switching signal, the motion compensation image of the motion compensator 48 is changed by one frame before, and output to the subtractor 30. The motion compensation image of two frames of the two frame memory 50 is switched and output to the subtractor 30.

As described above, in the video encoder according to the present invention, when the difference between the first motion vector between the previous frame and the current frame and the second motion vector between the current frame and the next frame is larger than the threshold value, the maximum motion value is applied to the second motion vector. Since an error has occurred, in this case, the difference image is generated by using the motion compensation image of the first motion vector instead of the motion compensation image of the second motion vector, thereby improving the reconstruction quality.

Claims (2)

A subtractor 30 for generating a difference image by subtracting a motion compensation image of an original image of a current frame and a reconstructed image of one frame before, which is input in a frame unit: a difference image output from the subtractor 30 in a spatial domain Discrete cosine transform unit 32 for outputting discrete cosine transform coefficients by discrete cosine transform to transform into frequency domain: converting discrete cosine transform coefficients of difference image output from the discrete cosine transform unit 32 to a predetermined quantization interval Quantizer 34 for quantizing and outputting: Variable length coder 36 for variable-length encoding and outputting the quantized difference image in the quantizer 34: The quantized difference image in the quantizer 34 Inverse quantizer 38 for restoring to a state before input to a quantizer: a state before inputting a dequantized difference image by the inverse quantizer 38 to the discrete cosine transform unit Inverse discrete cosine transform unit 40 for reconstructing: An adder 42 for outputting a reconstructed image one frame before by adding the difference image reconstructed by the inverse discrete cosine transform unit 40 and a motion compensation image one frame before ): A first frame memory 44 for storing a reconstructed image of the previous frame output from the adder 42 in units of frames: an original image of the current frame and one frame stored in the first frame memory 44 Motion estimation unit 46 for estimating similar parts between the previous reconstructed images and outputting the result of the position movement as a motion vector: the motion position of the reconstructed image before one frame stored in the first frame memory 44. A motion compensator 48 for outputting a motion compensated image one frame before the frame compensated by the motion vector output from the motion estimator 46 to the adder: the motion compensator 48 A second frame memory 50 for storing a motion compensated image of one frame before the frame is output: comparing a motion vector of the motion compensated image of the frame before 1 frame with a motion vector of the motion compensated image of the frame 2 before A comparator 52 for outputting a control signal according to a result; and selectively subtracting the motion compensation image before the first frame or the motion compensation image before the two frames according to the control signal output from the comparator 52. 30) a switching unit (54) for outputting. According to claim 1, The switching unit 54 is output from the motion vector of the motion compensation image of the previous frame output from the motion compensation unit 48 from the comparator 52 and from the second frame memory 50 If it is determined that the difference of the motion vectors in the motion compensation image before 2 frames is greater than a predetermined threshold value, the motion compensation image before the 2 frames is selected, otherwise the motion compensation image for which the 1 frame delay is selected is selected. Video encoder, characterized in that.