KR20000073770A - Contour extraction method for video coding and decoding - Google Patents

Abstract

PURPOSE: A method of extracting a contour in moving image coding/decoding process is proposed to eliminate an area labeling operation requiring a long time, thereby increasing a processing efficiency. CONSTITUTION: The method of extracting a contour in moving image coding/decoding process comprises the steps: performing a rester scanning in a direction from a left upper side of a binary mask to a right lower side thereof until detecting a pixel satisfying a condition 1 or detecting the right lower side of the mask and selecting the pixel as a starting contour pixel when detecting the pixel satisfying the condition 1 and changing an existing object value into an object boundary value and ending the process when detecting the right lower side of the mask; in case the starting contour pixel is selected, rotating in a counter-clockwise until detecting a pixel having the object value and changing a background value of the pixel into a background boundary value and extracting the pixel having the object value as a next contour pixel and also changing the existing object value into an object boundary value. In the condition 1, a pixel value is the object value and also a left pixel value is the background value, the pixel value is the object boundary value and also the left pixel value is the background boundary value, or the pixel value is the object boundary value and also the left pixel value is the background value.

Description

Contour extraction method for video coding and decoding

The present invention relates to a contour extraction method in video encoding and decoding, which is applied to extract contours using a binary mask in a video encoding and decoding process.

First, a video encoding method of the background of the present invention will be outlined.

The video encoding method may be divided into a frame-based coding method for encoding a rectangular frame and an object-based coding method for encoding only an arbitrary shape region. The frame unit encoding method is a video encoding method for encoding and transmitting pixels of an entire frame, whereas the object unit encoding method is a video encoding method for encoding and transmitting only a target region to be encoded. In addition, the frame-based coding scheme is H.261, H.263 and ISO / IEC JTC1 /, which are standards established by the International Telecommunication Union-Telecommunicat-ion standardization sector (ITU-T). Adopted by MPEG-1 and MPEG-2, standards set by the Moving Picture Experts Group (MPEG) of SC29 / WG11 (International Standardization Organization / International Electrotechnical Commission Joint Technical Committee 1 / Sub-Committee 29 / Working Group 11) The object unit coding scheme is adopted to MPEG-4, which is a standard established by MPEG of ISO / IEC JTC1 / SC29 / WG11.

The object unit coding method can be used in various ways as compared with the frame unit coding method. That is, according to the frame-by-frame coding method, it is possible to decode only an object, replace the background with another image, synthesize both, or move or enlarge or reduce the object to an arbitrary area of the screen.

On the other hand, when the object unit coding scheme is adopted, shape information, which is information indicating which pixel belongs to the object and which pixel belongs to the background, is required among the pixels of the entire frame.

The compression encoding of the shape information may include a method of encoding a binary mask and a method of encoding a contour configuration. As shown in FIGS. 1A and 1B, the binary mask encoding method designates a background value for all pixels constituting the entire frame if the pixel belongs to the background and an object value for the pixel belonging to the object. By using the binary image (binary image) or binary mask (binary mask) to represent the shape information, on the other hand, the method of encoding the shape of the contour as shown in Figure 1a and 1c as shown in Figure 1a and 1c the shape information as a boundary between the object It is a way of indicating. In addition, the binary mask encoding method is a joint bi-level image coding experts group (JBIG) of ISO / IEC JTC1 / SC29 / WG11 or G3 and G4, which is a binary image coding operation performed before object unit coding is applied. It has been studied for standardization of T.4 and T.6 of ITU-T for facsimile, and recently has been adopted as Context-based Arithmetic Encoding (CAE) applied to MPEG-4. However, the method of encoding the shape of the contour has been studied in the fields of computer vision, pattern recognition, and computer graphics for a long time. Most of them have been used for feature extraction and shape information manipulation. As it is applied, it is applied in vertex-based coding.

Hereinafter, an example of a video encoder to which the video encoding method described above is applied will be described with reference to FIGS. 2A to 2C.

Referring to FIG. 2A, a configuration of an object unit encoder is performed. The object unit encoder separates an input video signal for each object (VOP, Vidio Object Plane) and obtains shape information and texture information for each object. A VOP forming unit 100, a plurality of VOP encoders 200 which receive a signal input from the VOP forming unit 100 and perform encoding for each VOP, and a bitstream input from the VOP encoder 200. It can be seen that it consists of a multiplexer 300 (MUX, multiplexer) for multiplexing.

Referring to FIG. 2B, a configuration of each VOP encoder 200 included in the object unit encoder is described. Each of the VOP encoders 200 encodes and reproduces shape information of an input binary mask. A motion information adder which finds movement information of the current VOP texture information by using the shape information encoder 210, the input texture information and the reproduced previous VOP texture information, and the reproduced shape information of the shape information encoder 210. A motion compensated prediction is performed using the moving part 220, the inputted motion information and the reproduced previous VOP texture information of the moving information estimating unit 220, and the reproduced shape information of the shape information encoder 210. A subtractor 240 for obtaining a prediction error, which is a difference between the texture information to be inputted and the texture information to be inputted and the texture information to be predicted by the mobile compensation unit 230. ctor), the texture information encoder 250 which encodes and reproduces a prediction error by using the predicted error of the subtractor 240 and the reproduced shape information of the shape information encoder 210. An adder 260 which adds the moving compensation prediction texture information of the compensator 230 and the reproduction prediction error of the texture information encoder 250 to form the reproduced previous VOP texture information, and the input of the adder 260. Reproduced previous VOP texture information which is stored and reproduced the previous VOP texture information which is reproduced in the movement information estimator 220 and the movement compensator 230 when the next VOP is encoded. A shape information bit string of the shape information encoder 210, a movement information bit string of the movement information estimator 220, and a texture information bit string of the texture information encoder 250. Multiplex VOP can be seen that consists of multiplexer 280.

Looking at the configuration of the vertex-based shape information encoder to which the present invention can be applied as an example of the shape information encoder 210 included in the VOP encoder 200 with reference to Figure 2c, the vertex-based shape information encoder, Contour extraction unit 211 for extracting the contour of the binary mask using the shape information of the binary mask type input, vertex selection unit 212 for finding a vertex in the contour from the input contour extraction unit 211 A vertex encoding unit 213 for encoding an extracted vertex from the vertex selecting unit 212 that is input, a contour reproducing unit 214 for making an approximate outline using the extracted vertex from the vertex selecting unit 212 that is input, And a contour filling unit 215 which reproduces a binary mask by using the reproduced contour from the contour reproducing unit 214 inputted.

On the other hand, the present invention is a video encoding that can be applied to extract the contour using a binary mask input from the contour extractor 211 of the vertex-based shape information encoder and the contour extractor of the vertex-based shape information decoder omitted description And a contour extraction method in decoding.

Hereinafter, a method of extracting contours in video encoding and decoding, which has been conventionally applied, will be described.

First, a first step of region labeling the input binary mask into respective regions is performed. At this time, the pixels belonging to the same area have the same value, while the pixels belonging to the other area have different values that can be distinguished from each other. As a specific method of realizing the region division, various methods are known. In addition, a result of performing region division by performing the first step using the binary mask illustrated in FIG. 3A is shown in FIG. 3B.

Next, in the direction from the upper left end of the divided binary mask to the lower right end of the binary mask until the pixel first having a value indicating that the area is different from the area to start scanning or the lower end of the binary mask is met. When performing a raster scan and first encountering a pixel having a value indicating that the area is different from the area where the scan starts, this pixel is the initial contour pixel which is the pixel which starts the contour of the area. On the other hand, in the case where it meets the lower right end of the binary mask, a second step of terminating the process is performed. As described above, a process of selecting a starting contour pixel by raster scanning is illustrated in FIG. 4.

Next, in the case where the starting contour pixel is selected as described above, among the eight pixels around the current contour pixel, the first contour pixel is extracted as the next contour pixel from the first pixel that meets the first pixel while rotating counterclockwise from the previous contour pixel. Step 3 (however, if the current contour pixel is the starting contour pixel, the left pixel of the starting contour pixel is regarded as the previous contour pixel). As described above, a process of extracting the next contour pixel is illustrated in FIG. 5.

Lastly, as described above, it is determined whether the extracted next contour pixel is a starting contour pixel. If the extracted next contour pixel is not a starting contour pixel, the next contour pixel is set as a current contour pixel, and then the third contour pixel is determined. If the extracted next contour pixel is the starting contour pixel while feeding back to the step, a fourth step of feeding back to the second step is performed.

However, according to the contour extraction method in the conventional video encoding and decoding, various problems occur.

First, there is a problem in that the area separation performed in the first step is very complicated and takes a long time, resulting in a decrease in overall processing efficiency.

Secondly, since the area is separated in the first step, the start contour pixel is selected based on the second and third steps, and the next contour pixel is tracked. Since the contour of the hole is extracted from the contour of the hole, the extraction of the contour is inaccurate. This problem is illustrated in FIG. 6, in which the result of extracting the contour by applying the prior art to FIG. 3A is shown.

Third, in the third step, an 8-connectivity relationship of selecting, as the next contour pixel, the pixel of the region that meets first while rotating counterclockwise from the previous contour pixel among the eight pixels around the current contour pixel. In the case of extracting the contour by using the contour pixels that are not extracted there is a problem that the extraction of the contour is inaccurate. This problem is illustrated in FIG. 7B, in which a result of extracting a contour by applying the prior art to the binary mask illustrated in FIG. 7A is shown. In FIG. 7B, the contour of the object existing in the hole is not extracted. Shows.

The object of the present invention is that the processing efficiency is increased by eliminating complex and time-consuming area division, and the contours surrounding the hole areas are extracted as the contours of the holes in the process of extracting the contours of the holes, so that the exact contours can be extracted. In order to provide a method of extracting contours in video encoding and decoding, in which a contour of an object existing in a hole is extracted even when a connection relationship is applied, the contour can be extracted accurately.

1A is a view showing an example of an experimental image,

FIG. 1B is a diagram illustrating shape information of the image of FIG. 1A represented by a binary mask; FIG.

FIG. 1C is a diagram illustrating shape information of an image of FIG. 1A as outlines; FIG.

2A is a block diagram illustrating a schematic configuration of an object unit encoder;

FIG. 2B is a block diagram showing the configuration of the VOP encoder shown in FIG. 2A;

FIG. 2C is a block diagram illustrating a configuration of a vertex-based shape information encoder as an example of the shape information encoder illustrated in FIG. 2B;

3A is a diagram illustrating shape information of an image as a binary mask;

FIG. 3B is a view showing the result of region division by applying the contour extraction method in the conventional video encoding and decoding to the binary mask shown in FIG. 3A; FIG.

4 is a diagram illustrating a starting contour pixel selection process according to the contour extraction method in conventional video encoding and decoding;

5 is a diagram illustrating a process of extracting the next contour pixel according to the contour extraction method in conventional video encoding and decoding;

FIG. 6 is a diagram illustrating a result of hole contour extraction according to the contour extraction method in the conventional video encoding and decoding for the binary mask shown in FIG. 3A; FIG.

FIG. 7A illustrates a binary mask in which a hole is present inside and an object is present inside the hole; FIG.

FIG. 7B is a view showing a contour extraction result of a hole according to the contour extraction method in the conventional video encoding and decoding for the binary mask shown in FIG. 7A;

8 is a diagram illustrating a starting contour pixel selection process according to the contour extraction method in video encoding and decoding according to the present invention;

FIG. 9 is a diagram showing a result of hole contour extraction by the contour extraction method in video encoding and decoding according to the present invention for the binary mask shown in FIG. 3A; FIG.

FIG. 10 is a view showing a contour extraction result of a hole by the contour extraction method in video encoding and decoding according to the present invention for the binary mask shown in FIG. 7A; FIG.

In order to achieve the object of the present invention described above, the present invention provides: Condition 1 (condition 1; the value of the pixel is the "object value" while the value of the left pixel is the "background value". A pixel that satisfies the "object value" and the value of the left pixel is "background boundary value", or the value of the pixel is "object boundary value" and the value of the left pixel is "background value", or When raster scan is performed from the upper left end of the binary mask to the lower right end of the binary mask until it meets the lower right end of the binary mask, the pixel is selected as the starting contour pixel when the pixel satisfying the condition 1 is met. And a first step of changing the " object value " already assigned to the pixel to " object boundary value " and ending the process when it meets the lower right end of the binary mask; In the case where the starting contour pixel is selected in the first step, the rotation process is performed while rotating counterclockwise until a pixel having an "object value" is encountered starting from the previous contour pixel among the pixels around the current contour pixel. While changing the "background value" of the pixel to "background boundary value" while extracting the pixel having the "object value" at the position where the rotation is terminated as the next contour pixel, " A second step of changing the object value "to an" object boundary value "(however, if the current contour pixel is the starting contour pixel, the left pixel of the starting contour pixel is regarded as the previous contour pixel); And determining whether the extracted next contour pixel is the starting contour pixel, and if the extracted next contour pixel is not the starting contour pixel, the next contour pixel is the current contour pixel, and then proceeds to the second step. On the other hand, when the extracted next contour pixel is a starting contour pixel, a third step of feeding back to the first step is provided, which provides an outline extraction method in video encoding and decoding.

Further, in order to achieve the above object of the present invention, the present invention provides a method for extracting the contour in the above-described video encoding and decoding, wherein, in the second step, the previous contour among the pixels around the current contour pixel. Starting from the pixel, it rotates counterclockwise until it encounters a pixel with "object value" or "object boundary value", changing the "background value" of the pixel that is encountered in the rotation process to "background boundary value", while rotating Provided is a method for extracting an outline in video encoding and decoding, wherein a pixel having the "object value" or "object boundary value" at the end position is extracted as the next contour pixel.

Hereinafter, a preferred embodiment of the contour extraction method in video encoding and decoding according to the present invention will be described with reference to FIGS. 8 to 10.

First, condition 1 (condition 1; the value of the pixel is "object value" and the value of the left pixel is "background value", the value of the pixel is "object value" and the value of the left pixel is "background"). Upper bound of the binary mask until a pixel meets the pixel satisfying the threshold value, or the pixel value is " object boundary value " while the value of the left pixel is " background value " If a pixel satisfying the condition 1 is encountered while performing a raster scan in the direction to the lower right end of the binary mask, the pixel is selected as the starting contour pixel and the "object value" already assigned to the pixel. Is changed to " object boundary value ", and the first step of terminating the process in the case of encountering the lower right end of the binary mask is performed. As described above, a process of selecting a starting contour pixel by raster scanning is illustrated in FIG. 8. In the first step, in order not to extract the contour of the region already extracted without assigning each region to each region by giving a separate value to each region, first, in the above condition 1 When the value of is "object boundary value" and the value of the left pixel is "background boundary value", the "object value" already assigned to the extracted starting contour pixel is replaced with "object boundary value". give.

Next, in the case where the start contour pixel is selected in the first step, half of the eight pixels around the current contour pixel starting from the previous contour pixel until a pixel having an "object value" or "object boundary value" is encountered. While rotating in the clockwise direction, the "background value" of the pixel meeting in the rotation process is changed to "background boundary value" while the pixel of the "object value" or "object boundary value" at the position where the rotation is finished is contoured next. The second step of extracting the pixel and converting the "object value" already assigned to the pixel to the "object boundary value" (but, if the current contour pixel is the starting contour pixel, transfer the left pixel of the starting contour pixel Is regarded as contour pixels). In the second step, in order not to extract the contour lines already extracted in the state where the region is not separated, the "background value" of the pixels encountered in the rotation process is changed to "background boundary value" while the extracted Changes the "object value" already assigned to the next contour pixel to "object boundary value"

Lastly, as described above, it is determined whether the extracted next contour pixel is the starting contour pixel. If the extracted next contour pixel is not the starting contour pixel, the next contour pixel is set as the current contour pixel, and then the second contour pixel is set as the current contour pixel. While feeding back to the step, if the extracted next contour pixel is the starting contour pixel, a third step of feeding back to the first step is performed.

Looking at the operation according to the embodiment is as follows.

According to the first step, the first object and the second step are already extracted as contour pixels by the condition 1, so that the "object boundary value" is assigned to the pixel and the "background boundary value" is assigned to the left pixel. The pixel is not selected as the starting contour pixel again, and in order to support this, the "object value" of the starting contour pixel extracted for the first time is changed to the "object boundary value", and when the raster scan meets the lower right end of the binary mask. In this case, since all contours have been extracted, the contour extraction process is terminated. In addition, when the starting contour pixel is selected as shown in FIG. 9 by applying the condition 1, an outline surrounding the hole region is extracted as the contour of the hole in the process of extracting the contour of the hole. This operation applies the present invention to FIG. 3A. 9 shows the result of extracting the contour.

According to the second step, the "background value" of the pixel existing on the left side of the pixel extracted to support the condition 1 is changed to the "background boundary value" while the first "object value" of the next contour pixel is extracted. It changes to "object boundary value". In addition, even when the contour is extracted using the 8-connectivity relationship, the contour of the object existing inside the hole region is extracted. This operation applies the present invention to the binary mask illustrated in FIG. 7A. The result of extraction is shown in FIG.

In addition, according to the third step, if the extracted next contour pixel is not the starting contour pixel, it means that the contour is not completely extracted, so that the next contour pixel is continuously extracted, while the extracted next contour pixel is In the case of the starting contour pixel, since the contour is completely extracted, the process of extracting another contour that is not extracted is performed.

According to the contour extraction method in video encoding and decoding according to the present invention, processing efficiency is increased by eliminating complicated and time-consuming area division, and the contour covering the hole area is extracted as the contour of the hole in the contour extraction process of the hole. Therefore, accurate contours can be extracted, and even when the 8-connectivity relationship is applied, the contours of the objects existing in the hole region are extracted, and the accurate contours can be extracted.

Claims (2)

Condition 1 (condition 1; the value of the pixel is "object value" and the value of the left pixel is "background value", the value of the pixel is "object value" and the value of the left pixel is "background boundary value"). At the upper left of the binary mask until it meets a pixel that satisfies " im, or the pixel value is " object boundary value " and the value of the left pixel is " background value " When performing a raster scan in the direction to the bottom right of the binary mask and encountering a pixel that satisfies the condition 1 above, the pixel is selected as the starting contour pixel and the " object value " A first step of changing the object boundary value "and terminating the process when it meets the lower right end of the binary mask; In the case where the starting contour pixel is selected in the first step, the rotation process is performed while rotating counterclockwise until a pixel having an "object value" is encountered starting from the previous contour pixel among the pixels around the current contour pixel. While changing the "background value" of the pixel to "background boundary value" while extracting the pixel having the "object value" at the position where the rotation is terminated as the next contour pixel, " A second step of changing the object value "to an" object boundary value "(however, if the current contour pixel is the starting contour pixel, the left pixel of the starting contour pixel is regarded as the previous contour pixel); And It is determined whether the extracted next contour pixel is the starting contour pixel as described above, and if the extracted next contour pixel is not the starting contour pixel, the next contour pixel is left as the current contour pixel and then fed back to the second step. On the other hand, if the extracted next contour pixel is a starting contour pixel, and comprises a third step of feeding back to the first step, the contour extraction method for video encoding and decoding. 2. The method of claim 1, wherein in the second step, among the pixels surrounding the current contour pixel, rotating in a counterclockwise direction until a pixel with an "object value" or "object boundary value" is encountered, starting from the previous contour pixel. While changing the "background value" of the pixels encountered in the rotation process to the "background boundary value" while extracting the pixel having the "object value" or "object boundary value" at the position where the rotation is completed as the next contour pixel. An outline extraction method in video encoding and decoding characterized by the above-mentioned.