KR100285594B1 - Contour coding method and apparatus - Google Patents

Abstract

The present invention relates to a technique of approximating and encoding a contour of an object represented by a digital video signal to a polygon. To this end, the present invention determines a pair of vertices on a contour, and generates a line segment connecting the pairs of vertices. Expand to create band segments. In addition, the contour segment corresponding to the line segment is detected to match the band segment with the contour segment. Extend the band segment until the contour segment is completely covered by the band segment to determine new vertices located between pairs of vertices on the contour. During the extension of the band segment, at least one contour pixel is detected on the contour segment, the detected contour pixel is finally covered by the extended band segment, and the center of the straight line connecting the pair of vertices between the detected contour pixels. The contour pixel near to is determined as the new vertex. The present invention performs a vertex detection process until all vertices on the contour are determined based on the vertices determined so that the contour can be approximated by the vertices.

Description

Contour coding method and apparatus

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for encoding an outline for use in an image signal encoder. More particularly, the present invention relates to a method and apparatus for encoding an outline of an object by polygonal approximation using a contour reproduction algorithm used in a decoder.

In digital television systems such as video telephony, teleconference, and high definition television systems, the video line signal of the video frame signal includes a sequence of digital data called pixel values, thereby defining each video frame signal. A great deal of digital data is needed. However, since the available frequency bandwidth of conventional transmission channels is limited, especially in low bit-rate video signal encoders such as video telephony and teleconferencing systems, a large amount of data can be obtained through various data compression techniques. Should be reduced.

One of coding methods for encoding video signals of a low transmission coding system is a so-called object oriented analysis synthesis coding technique.

According to the object-oriented analysis and synthesis encoding technique, the input image image is divided into objects, and factors defining motions, contours, and pixel data of each object are processed through different encoding channels.

In particular, in processing the contour image of an object, the contour information plays an important role in interpreting and synthesizing the shape of the object, and a conventional coding method used to represent the contour information is a chain coding method. Although there is no loss of contour information, a significant amount of bits are required to encode the contour.

Accordingly, in order to compensate for the shortcomings of the chain coding method, a contour coding method using a polygonal approximation method has been proposed. In the polygon approximation method, first, two start vertices are selected on an outline composed of a plurality of contour pixels. If the applied outline is an open curve, two end points are selected as starting vertices, and the outline is selected. For closed curves, select the two farthest points on the contour as the starting vertex. Draw a straight line segment between the two starting vertices, measure the vertical distance from each contour pixel on the contour segment corresponding to the line segment to the line segment, and locate the farthest distance and set the reference value Dmax The larger contour pixel is determined as the new vertex. When new vertices are determined, polygons are approximated by connecting each vertex, and the corresponding vertex determination process between the new line segment formed by the two adjacent vertices and the corresponding contour segment is applied repeatedly from the line segment. Polygonal approximation of the contour is performed by obtaining vertices until the maximum vertical distance to the contour segment is equal to or smaller than the reference value Dmax. That is, by performing the processing as shown in Figs. 6A to 6C, a plurality of vertices are detected on the outline, and vertex information indicating the positions of all the vertices on the outline is encoded and provided to a transmitter not shown.

The decoder reproduces (restores) the outline of an object using a polygonal approximation technique that matches the outline to a line, where each line uses two pixels based on the received vertex information to determine two adjacent vertices. Connect. For example, each line is determined using a well-known line generation algorithm, the Bresenham algorithm (see Steven Harrington, “Computer Graphics: A Programming Approach”, 2nd edition, pp. 17-20).

However, in the conventional method, since the straight line used in the process of detecting the vertex is different from the corresponding line segment reproduced by using the plurality of pixels in the decoder, it is unnecessary due to the difference between the straight line and the line segment corresponding to two adjacent vertices. The problem is that vertices can be detected, resulting in an increase in the amount of data to be transmitted through the transmitter.

Accordingly, an object of the present invention is to provide a method and apparatus for encoding an outline that can reduce the amount of transmission data by effectively approximating the outline of an object represented by an image signal using an improved vertex detection technique.

In accordance with an aspect of the present invention, there is provided a contour encoding method of encoding an outline of an object represented by a digital image signal by polygonal approximation, the method comprising: (a) starting a vertex at an outline including a plurality of contour pixels; Detecting; (b) selecting an adjacent pair of vertices between each detected vertex including the starting vertex; (c) generating a line segment connecting the pair of vertices by using a plurality of pixels; (d) generating a band segment by expanding each pixel on the line segment by a preset threshold; (e) detecting a contour segment corresponding to the line segment from the contour; (f) matching the contour segment to the band segment; (g) expanding the band segment to determine a new vertex located between the pair of vertices on the contour; And (h) repeating steps (b) to (g) until vertex information indicating positions of all vertices on the contour is provided by detecting all vertices on the contour. .

According to another aspect of the present invention, there is provided a contour encoding apparatus for polygonally approximating and encoding an outline of an object represented by a digital video signal, wherein the vertex information indicating a position of a detected vertex including a starting vertex is obtained. Means for storing; Means for selecting adjacent vertex pairs between detected vertices based on the vertex information; Means for generating a line segment connecting the adjacent pairs of vertices using a plurality of pixels; Means for generating a band segment by expanding each pixel on the line segment by a preset threshold; Means for detecting a contour segment corresponding to the line segment in the contour; Means for matching the contour segment to the band segment; And means for determining a new vertex located between the pair of vertices on the contour by extending the band segment based on the matching segment.

1 is a block diagram of a contour encoding apparatus according to a preferred embodiment of the present invention;

FIG. 2 is a detailed block diagram of the vertex determination block shown in FIG. 1;

3A and 3B illustrate an example of an expanded pixel when expanding a line segment according to the present invention;

4 is a diagram illustrating an example of patching contours and band segments for two adjacent vertices;

5 is a diagram illustrating an example of a slope region that determines an extension direction of a pixel;

6A to 6C are views illustrating a process of polygonal approximation of an outline of an object.

<Description of the code | symbol about the principal part of drawing>

100: start vertex selection block 200: vertex control block

300: line segment forming block 400: line segment expansion block

500: contour segment determination block 600: matching block

700 vertex determination block 710 matching determiner

720: vertex detector 800: vertex coding block

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

1 shows a contour encoding apparatus according to the present invention, and contour image data representing a contour composed of a plurality of contour pixels is applied to the start vertex detection block 100 and the contour segment determination block 500.

Referring to FIG. 1, the start vertex selection block 100 selects a start vertex of an outline in the same manner as in the related art by using the applied contour image data. When the outline is an open curve, it is shown in FIGS. 6A to 6C. As shown, the two end points A and B of the open curve are selected as starting vertices, and if the contour is a closed curve, the two furthest points on the contour are selected as starting vertices. The position information of the selected start vertex is provided to the next stage of the vertex control block 200.

In addition, the vertex control block 200 stores vertex information indicating the positions of the vertices detected on the contour and is adjacent to each other along the contour between the detection vertices including the two starting vertices based on the vertex information. The vertex pairs are selected, and the vertex information for the selected adjacent vertex pair is transmitted to the contour segment determination block 500, the line segment formation block 300, and the vertex determination block 700 through the line L20, respectively.

Next, the line segment formation block 300 selects the vertex control block 200 using a plurality of pixels according to a well-known line generation algorithm, that is, the Bresenham algorithm, based on the vertex information provided from the vertex control block 200. A line segment is generated that connects adjacent pairs of vertices, where the generated line segment is provided to the line segment extension block 400.

The line segment extension block 400 generates a band segment including a band segment formed between the line segments provided in the line segment formation block 300, that is, an extended pixel region surrounding each pixel on the line segment. The expansion pixel in is determined by performing an expansion process using the preset threshold TH1. The expansion process is completed along the line segment by forming, for each pixel on the line segment, an area containing neighboring pixels that satisfy the following equation (1).

Xn-xs | + | yn-ys | ≤ TH1

In Equation 1, xs and ys are x and y coordinate values of the target pixel on the line segment, xn and yn are x and y coordinate values of each pixel adjacent to the line segment, and TH1 is a preset threshold value.

3A and 3B show an enlarged pixel region surrounding the target pixel 20 according to a preferred embodiment of the present invention. When the preset threshold TH1 is 1, the expansion process for the target pixel 20 is completed as shown in FIG. 3A, whereas, when the preset threshold TH1 is 2, the expanded target pixel is As shown in Fig. 3B.

As a result, the band segment between the lie segments is formed by the neighboring pixels of the line segment satisfying equation (1) and the target pixel constituting the line segment. The band segment obtained in the line segment extension block 400 is provided to the next matching block 600.

On the other hand, the contour segment determination block 500 corresponds to the contour line corresponding to the line segment generated in the line segment formation block 300 based on the provided contour image data, that is, vertex information provided from the contour control block 200 through the line L20. The segment is detected and the detected contour segment is provided to the next matching block 600.

The matching block 600 matches the contour segment provided from the contour segment determination block 500 and the band segment provided from the line segment extension block 400 with each other. That is, as shown in FIG. 4 as an example, the band segment 50 corresponding to the line segment 30 is matched to the contour segment 40 on the basis of adjacent pairs of vertices, namely A and B. As shown in FIG. As a result, the matching block 600 provides matching information representing the matched segments 40 and 50 to the vertex determination block 700 via line L10.

Next, in the vertex determination block 700, adjacent vertices corresponding to the vertex information based on the vertex information provided from the vertex control block 200 through the line L20 and the matching information provided from the matching block 600 through the line L10. Detect new vertices located between pairs.

FIG. 2 is a detailed block diagram of the vertex decision block 700 illustrated in FIG. 1 and includes a matching determiner 710 and a vertex determiner 720.

Referring to FIG. 2, the matching determiner 710 checks whether the contour segment completely covers the corresponding band segment by using the matching information provided through the line L10, and as a result of the check, the contour segment identifies the band segment. When fully covered, the match determiner 710 generates a matching signal on the line L30 and provides it to the vertex control block 200. In addition, the matching determiner 710 directly provides the matching information to the vertex detector 720.

Accordingly, when the matching information is input, the vertex selector 720 calculates a slope of a straight line connecting adjacent pairs of vertices corresponding to the vertex information provided through the line L20.

Vertex selector 720 then detects a slope region between the vertical and horizontal slope regions in the calculated slope. As an example, as shown in FIG. 5, the vertical slope region V represents a slope comprising between π / 4 and 3π / 4 and between 5π / 4 and 7π / 4, and the horizontal slope region H is coplanar. The slope except for the slope included in the vertical slope region V in the above is shown.

In the above case, when the calculated slope includes the vertical slope area V, the vertex detector 720 horizontally moves the band segment by one pixel until the contour segment is completely covered by the extended band segment. Expand. In the opposite case, the vertex detector 720 extends the band segment in the vertical direction by one pixel until the contour segment is completely covered by the extended band segment.

The vertex detector 720 then detects at least one contour pixel on the contour segment (where the detected contour pixels are finally covered by the extended band segment) and adjacent pairs of vertices between the detected contour pixels. The contour pixel close to the center of the straight line connecting the is determined as a new vertex, and new vertex information indicating the position of the new vertex is provided to the vertex control block 200 through the line L30. For example, referring to FIG. 6C, point C is determined as a new vertex located between adjacent vertex pairs A and B, and the vertex information is provided to vertex control block 200.

In the situation as described above, when a matching signal or new vertex information is input, the vertex control block 200 stores the new vertex information, and then the new adjacent vertex is formed into the line segment forming block 300 and the contour segment determining block 500. And vertex determination block 700, respectively. As a second order, vertices A and C are selected as new adjacent vertex pairs, and these vertex information is provided to line segment forming block 300, contour segment determining block 500 and vertex determining block 700, respectively. That is, each of the blocks 300, 400, 500, 600, and 700 performs a process for vertex information provided from the vertex control block 200. If vertex D is determined as a new vertex between vertices A and C as a result of this process, the same process for both vertices A and D is repeated.

On the other hand, if the contour segment is completely covered by the corresponding extended band segment in the matching determiner 710 in the vertex determination block 700, for example, the two vertices A and D provided from the vertex control block 200 may be used. If the extended band segment for a fully covers the corresponding contour segment, the vertex determination block 700 no longer detects a new vertex as described above, where the matching signal is replaced by the vertex control block 200 instead of the new vertex information. Is provided. In this case, when a matching signal is input, the vertex control block 200 transfers the new adjacent vertex pairs D and C to the next processing block. This vertex detection process is repeated until all vertices, i.e. A to E, are detected as shown in Figs. 6A to 6C, for example.

The number of vertices varies according to the preset threshold TH1. Therefore, as can be seen from Figs. 6A to 6C, by making the predetermined threshold value TH1 smaller, the contour approximation by the line segment can be realized more precisely, in which case the coding efficiency is further improved.

Referring to FIG. 1, when all the vertices of the contour 10 are detected through the vertex detection process, vertex information indicating the positions of all the vertices detected on the contour 10, that is, the vertices A through E may be represented by a vertex control block ( Stored temporarily at 200) and then provided to the vertex coding block 800 via line L40.

Accordingly, the vertex coding block 800 encodes the vertex information provided from the vertex control block 200 using a typical syntax arithmetic code or binary arithmetic code, and the encoded vertex information is transmitted to a transmitter not shown.

As described above, the vertex detection process starts clockwise from the starting vertex A, but the final result is independent of the processing order as long as it covers all adjacent pairs of vertices.

Furthermore, in the above-described preferred embodiment, although the band segment is generated by extending the corresponding line segment according to Equation 1, a straight line connecting two adjacent vertices in the vertex detector 720 in the vertex determination block 700 is described. The band segment may be generated by extending the line segment by a predetermined threshold value TH1 through an extension method based on the slope of.

The vertex detection technique according to the present invention can be applied to a contour image encoding method based on vertices on an outline.

As described above, the present invention can reduce the amount of transmitted data by effectively approximating the outline of the object by the polygon approximation technique.

Although the present invention has been described with respect to specific embodiments, those skilled in the art can make various changes and modifications by the spirit as defined in the following claims.

Claims (8)

In the contour encoding method for encoding by approximating the contour of the object represented by the digital video signal by polygon, (a) detecting a starting vertex at an outline including a plurality of contour pixels; (b) selecting an adjacent pair of vertices between each detected vertex including the starting vertex; (c) generating a line segment connecting the pair of vertices by using a plurality of pixels; (d) generating a band segment by expanding each pixel on the line segment by a preset threshold; (e) detecting a contour segment corresponding to the line segment from the contour; (f) matching the contour segment to the band segment; (g) expanding the band segment to determine a new vertex located between the pair of vertices on the contour; And and (h) repeating steps (b) to (g) until all the vertices on the contour are detected so that vertex information indicating the positions of all the vertices on the contour is provided. The process of claim 1, wherein (g) comprises: (g1) checking whether the contour segment is completely covered by the band segment based on the matching segment generated in step (f); (g2) if the contour segment is not fully covered by the band segment, expanding the band segment until the contour segment is completely covered by an extended band segment; (g3) detecting at least one contour pixel on the contour segment, and the detected contour pixel is finally covered by the extended band segment; And (g4) determining the one of the detected contour pixels as a new vertex. In the contour encoding apparatus for polygonally approximating the contour of an object represented by a digital video signal, Means for storing vertex information indicative of the location of the detected vertex including the starting vertex; Means for selecting adjacent vertex pairs between detected vertices based on the vertex information; Means for generating a line segment connecting the adjacent pairs of vertices using a plurality of pixels; Means for generating a band segment by expanding each pixel on the line segment by a preset threshold; Means for detecting a contour segment corresponding to the line segment in the contour; Means for matching the contour segment to the band segment; And Means for determining a new vertex located between the pair of vertices on the contour by extending the band segment based on the matching segment. 4. The method of claim 3, wherein the new vertex determining means is: Means for expanding the band segment until the contour segment is completely covered by an extended band segment; Means for detecting at least one contour pixel on the contour segment, wherein the detected contour pixel is finally covered by the extended band segment; And Means for determining one of the detected contour pixels as a new vertex. 5. The contour encoding apparatus according to claim 4, wherein the new vertex determining means determines the contour pixel near the center of the straight line connecting the pair of vertices as the new vertex between the detected contour pixels. The method of claim 4 wherein the band segment expansion means comprises: Means for calculating a slope of a straight line connecting adjacent pairs of vertices; Means for detecting a slope region between the vertical and horizontal slope regions in the calculated slope; And In response to the detection result, means for extending the band segment in a vertical or horizontal direction until the contour segment is completely covered by the extended band segment. 7. The method of claim 6, wherein the band segment extends in the vertical direction if the calculated slope is in the vertical slope region, and the band segment extends in the horizontal direction if the calculated slope is in the horizontal slope region. The slope region indicates a slope included between π / 4 and 3π / 4 and between 5π / 4 and 7π / 4, and the horizontal slope indicates a slope other than the slope included in the vertical slope. . 4. The method of claim 3, wherein the band segment generating means comprises: Means for calculating a slope of a straight line connecting the adjacent pairs of vertices; And And means for generating the band segment by extending each pixel on the line segment in a vertical or horizontal direction according to the calculated slope.