GB2321359A - Polygonal approximation in video contour encoding system - Google Patents
Polygonal approximation in video contour encoding system Download PDFInfo
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- GB2321359A GB2321359A GB9705610A GB9705610A GB2321359A GB 2321359 A GB2321359 A GB 2321359A GB 9705610 A GB9705610 A GB 9705610A GB 9705610 A GB9705610 A GB 9705610A GB 2321359 A GB2321359 A GB 2321359A
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- contour
- segment
- vertices
- line segment
- pixel
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T9/00—Image coding
- G06T9/20—Contour coding, e.g. using detection of edges
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V10/00—Arrangements for image or video recognition or understanding
- G06V10/40—Extraction of image or video features
- G06V10/46—Descriptors for shape, contour or point-related descriptors, e.g. scale invariant feature transform [SIFT] or bags of words [BoW]; Salient regional features
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Multimedia (AREA)
- Theoretical Computer Science (AREA)
- Computer Vision & Pattern Recognition (AREA)
- Compression Of Band Width Or Redundancy In Fax (AREA)
- Compression Or Coding Systems Of Tv Signals (AREA)
- Image Processing (AREA)
- Compression, Expansion, Code Conversion, And Decoders (AREA)
Abstract
An apparatus determines a pair of vertices A,B on a contour. Then, a line segment 30 connecting the pair of vertices is generated and widened to thereby produce a band segment 50. A contour segment 40 corresponding to the line segment is selected and based on the pair of vertices, the band segment and the contour segment, a new vertex is determined. Based on the determined vertices, the apparatus recursively performs the above vertex detection process until all vertices on the contour are determined. Finally, vertex information representing the positions of all vertices on the contour is encoded for the transmission thereof.
Description
POLYGONAL APPROXIMATION METHOD AND APPARATUS FOR
USE IN A CONTOUR. ENCODING SYSTEM
The present invention relates to a method and apparatus for encoding a video signal; and, more particularly, to a method and apparatus capable of effectively polygonalapproximating a contour of an object contained in a video signal.
In digital television systems such as video-telephone, teleconference and high definition television systems, a large amount of digital data is needed to define each video frame signal since a video line signal in the video frame signal comprises a sequence of digital data referred to as pixel values. Since, however, the available frequency bandwidth of a conventional transmission channel is limited, in order to transmit the large amount of digital data therethrough, it is inevitable to compress or reduce the volume of data through the use of various data compression techniques, especially, in the case of such low bit-rate video signal encoders as.videotelephone and teleconference systems.
One of such techniques for encoding video signals for a low bit-rate encoding system is an object-oriented analysissynthesis coding technique, wherein an input video image is divided into objects and three sets of parameters for defining the motion, the contour and the pixel data of each object are processed through different encoding channels.
In processing the contour of an object, contour information is important for the analysis and synthesis of the object shape. A classical coding method for representing the contour information is a chain coding. method. The chain coding method, however, requires a substantial amount of bits for the representation thereof, although the method does not incur any loss in the contour information.
To overcome the drawback, there have been proposed several methods to encode the contour information. One of the methods is a contour encoding method employing a polygonal approximation. In the polygonal approximation, initial vertices of a contour are detected from a multiplicity of contour pixels constituting the contour. That is, if the contour is an open loop, the two ending points on the contour are determined as the initial vertices, and, if otherwise, the farthest two points on the contour become the initial vertices. After detecting two vertices on the contour, a straight line is drawn between the two vertices and then perpendicular distances from contour pixels on a contour segment connecting the two vertices to the straight line are determined. Among the contour pixels on the contour segment corresponding to the straight line, a contour pixel having a largest perpendicular distance is detected as a next vertex if the largest perpendicular distance is greater than a predetermined threshold value. By recursively performing the above process as shown in Figs. 2A to 2C, a number of vertices on the contour are detected, and vertex information representing the positions of all the vertices on the contour is coded and then provided to a transmitter(not shown) for the transmission thereof.
In a decoder, the contour of the object is reconstructed through the use of polygonal approximation for fitting the contour by lines each of which connects two adjacent vertices via a plurality of pixels based on the transmitted vertex information, wherein each of the line is determined by using a known line segment generation algorithm, e.g., a Bresenham's algorithm(see, Steven Harrington, "Computer Graphics: A
Programming Approach", 2nd edition, pp. 17-20).
Since, however, the straight line used in the process of detecting a vertex is different from a line segment connecting the two adjacent vertices by using a multiplicity of pixels, an unnecessary vertex can be detected by the difference between the straight line and the line segment corresponding to the two adjacent vertices; and, consequently, there may occur an increase in the amount of data to be transmitted through the transmitter.
It is, therefore, a primary object of the invention to provide an improved method and apparatus capable of effectively polygonal-approximating a contour of an object contained in a video signal by using a modified vertex detection technique to thereby reduce the amount of data to be transmitted.
In accordance with one aspect of the present invention, there is provided a polygonal approximation method for use in a contour encoder for encoding a contour of an object expressed in a digital video signal, comprising the steps of: (a) detecting initial vertices on the contour; (b) selecting a pair of vertices adjacent to each other among the detected vertices on the contour; (c) producing a line segment connecting the pair of vertices by using a multiplicity of pixels; (d) widening the line segment to thereby generate a band segment; (e) selecting a contour segment corresponding to the line segment from the contour; (f) detecting a new vertex based on the pair of vertices, the band segment and the contour segment; and (g) repeating the steps (b) to (f) until all vertices of the contour are detected, thereby providing vertex information representing the positions of all vertices of the contour.
In accordance with another aspect of the present invention, there is provided a polygonal approximation apparatus for use in a contour encoder for encoding a contour of an object expressed in a digital video signal, which comprises: a initial vertex detection block for detecting initial vertices on the contour; a storage block for storing vertex information representing the positions of the detected vertices; a selection block for choosing two adjacent vertices among the detected vertices based on the stored vertex information; a line segment formation block for producing a line segment connecting the two adjacent vertices by using a multiplicity of pixels; a widening block for widening the line segment to thereby generate a band segment; a contour segment determination block for selecting a contour segment corresponding to the line segment from the contour; and a new vertex determination block for detecting a new vertex based on the two adjacent vertices, the band segment and the contour segment and providing the new vertex to the storage block.
The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
Fig. 1 depicts a schematic block diagram of an apparatus for encoding contour image data in accordance with the present invention;
Figs. 2A to 2C illustrate an exemplary polygonal approximation process of the contour of an object;
Figs. 3A and 3B show widened pixels in accordance with the present invention; and
Fig. 4 represents a matching process of a contour and a band segments for two adjacent vertices.
Referring to Fig. 1, there is shown a schematic block diagram of an apparatus for encoding contour image dat:a inputted in accordance with the present invention, the contour image data representing positions of contour pixels constituting a contour of an object expressed in a video signal. The contour image data is provided to an initial vertex detection block 100 and a contour segment determination block 500.
The initial vertex detection block 100 finds two initial vertices of the contour based on the contour image data coupled thereto. If the contour image is of an open loop, two end points, e.g., A and B as shown in Fig. 2A, are selected as the two initial vertices. On the other hand, if the contour image is in the form of a closed loop, two farthest points on the contour are chosen as the two initial vertices. Once the two initial vertices are determined, initial vertex information representing the positions of the two initial vertices is fed to a vertex control block 200.
The vertex control block 200 stores vertex information coupled thereto, wherein the vertex information represents the positions of detected vertices on the contour; selects a pair of adjacent vertices disposed adjacent to each other along the contour among the detected vertices, e.g., the two initial vertices; and transfers their vertex information to the contour segment determination block 500, a line segment formation block 300, and a vertex determination block 700.
The line segment formation block 300 generates a line segment connecting the pair of adjacent vertices selected at the vertex control block 200 via a multiplicity of pixels by using a conventional line segment generation algorithm, e.g., a Bresenham's algorithm, based on the vertex information from the vertex control block 200. The line segment is fed to a line segment widening block 400.
The line segment widening block 400 produces a band segment formed along the line segment from the line segment formation block 300, wherein the band segment includes widened pixel area surrounding each pixel on the line segment, the widened pixel area being determined by employing a widening process using a predetermined threshold value TH1. The widening process along each line segment is accomplished by forming a region including neighboring pixels satisfying the following equation for each pixel on the line segment.
IXn - Xsl + IYn - Ys < TH1 EQ. 1 wherein x5 and y, are x and y coordinates of a target pixel on the line segment, respectively; xn and y, represent x and y coordinates of each pixel neighboring to the line segment, respectively; and TH1 is the predetermined threshold value
Referring to Figs. 3A and 3B, there are shown widened pixel area surrounding a target pixel 20 in accordance with an embodiment of the present invention. If the predetermined threshold value TH1 is 1, the widening process for the target pixel 20 is accomplished as shown in Fig. 3A. Fig 3B displays a widened target pixel when the predetermined threshold value TH1 is 2.
Conclusively, the band segment along the line segment is formed by neighboring pixels of the line segment satisfying
EQ. 1 and target pixels constituting the line segment. The band segment derived at the line segment widening block 400 is coupled to a matching block 600.
In the meantime, the contour segment determination block 500 selects a contour segment corresponding to the line segment produced at the line segment formation block 300 based on the contour image data fed thereto and the vertex information from the vertex control block 200, and delivers it to the matching block 600.
At the matching block 600, the contour segment from the contour segment determination block 500 and the band segment from the line segment widening block 400 are matched with each other. That is, as shown in Fig. 4, the band segment 50 along the line segment 30 is laid with the contour segment 40 on the same plane based on the pair of adjacent vertices, e.g., A and
B. Subsequently, the matching block 600 detects non-matched pixels, which are contour pixels on the contour segment, e.g., 40, located outside of the band segment, e.g., 50, and transfers matching information representing the positions of the non-matched pixels to the vertex determination block 70().
The vertex determination block 700 draws a straight line between the pair of adjacent vertices based on the vertex information from the vertex control block 200; calculates a perpendicular distance from each of the non-matched pixels to the straight line based on the matching information from the matching block 600; determines a non-matched pixel having a largest perpendicular distance which is greater than the predetermined threshold value TH1 as a new vertex; and delivers new vertex information representing a position of the new vertex to the vertex control block 200. Referring to Fig.
2A, the point C is determined as the new vertex positioned between the pair of adjacent vertices A and B and its vertex information is transferred to the vertex control block 200.
As stated above, the vertex control block 200 stores the new vertex information; and provides a new pair of adjacent vertices to next blocks 300, 500, and 700. In the second procedure, the vertices A and C are selected as the new pair of adjacent vertices and their vertex information is supplied to the above next blocks. The blocks 300, 400, 500, 600, and 700 respectively perform their functions as described in the above processes for the vertex information retrieved from the vertex control block 200. As a result of the above processes, if a vertex D is determined as a new vertex between vertices
A and C, the same processes are repeated for two vertices A and D. However, if there is not any non-matched pixel found in the matching process at the matching block 600, i.e., a band segment for two vertices, e.g., A and D, outputted from the vertex control block 200, covers completely a corresponding contour segment, the vertex determination block 700 could not detect any new vertex and there is no new vertex information transferred to the vertex control block 200. In that case, the vertex control block 200 supplies a new pair of adjacent vertices D and C to the next processing blocks. This vertex detection procedure is repeated until all vertices, e.g., A to E, for the contour 10 are determined as illustrated in Figs. 2A to 2C.
The number of vertices varies depending on the predetermined threshold value TH1. As can be seen from Figs.
2A to 2C, the approximation to the contour 10 by line segments becomes more accurate as the predetermined threshold value TH1 becomes smaller, at the expense of coding efficiency.
Referring back to Fig. 1, once all vertices are determined for the contour 10 through the use of the vertex detection procedure, vertex information representing the positions of all the detected vertices, e.g., A to E on the contour 10 is temporarily stored at the vertex control block 200, and then provided to the vertex coder 800.
The vertex coder 800 encodes the vertex information from the vertex control block 200 by using, e.g., a conventional syntax arithmetic code or the binary arithmetic code and provides the coded vertex information to a transmitter(not shown) for the transmission thereof.
In the above, the vertex detection procedure starts from the initial vertex A and proceeds in clockwise direction, but the final result does not depend on the proceeding sequence as long as all the pair of adjacent vertices are covered.
The above vertex detection technique in accordance with the present invention can be adopted to contour image encoding methods based on vertices on a contour.
While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
Claims (16)
1. A polygonal approximation method for use in a contour encoder for encoding a contour of an object expressed in a digital video signal, comprising the steps of:
(a) detecting initial vertices on the contour;
(b) selecting a pair of vertices adjacent to each other among the detected vertices on the contour;
(c) producing a line segment connecting the pair of vertices via a multiplicity of pixels;
(d) widening the line segment to thereby generate a band segment;
(e) selecting a contour segment corresponding to the line segment from the contour;
(f) detecting a new vertex based on the pair of vertices, the band segment and the contour segment; and
(g) repeating the steps (b) to (f) until all vertices of the contour are detected, thereby providing vertex information representing the positions of all vertices of the contour.
2. The method as recited in claim 1, wherein the line segment is produced by using a Bresenham's algorithm.
3. The method as recited in claim 1, wherein the band segment is obtained by widening pixel area surrounding each pixel on the line segment by using a predetermined threshold value.
4. The method as recited in claim 3, wherein the band segment includes neighboring pixels satisfying the following equation for each pixel on the line segment, lXn ~ Xs| + IYn - Ys | f TH1 wherein xs and ys are x and y coordinates of a target pixel on the line segment, respectively; xn and y, represent x and y coordinates of a pixel neighboring to the line segment, respectively; and TH1 is the predetermined threshold value.
5. The method as recited in claim 1, wherein the step (f) includes the steps of:
(fl) matching the band segment and the contour segment to thereby find non-matched pixels; and (f 2) determining the new vertex based on the non-matched pixels and the pair of vertices.
6. The method as recited in claim 5, wherein each of the nonmatched pixels is on the contour segment and also located outside of the band segment.
7. The method as recited in claim 6, wherein the step (f2) includes the steps of:
(f21) drawing a straight line connecting the pair of vertices;
(f22) calculating a perpendicular distance from each of the non-matched pixels to the straight line; and
(f23) determining a non-matched pixel having a largest perpendicular distance as the new vertex existing between the pair of vertices.
8. The method as recited in claim 7, wherein, in the step (f23), the non-matched pixel having the largest perpendicular distance is determined as the new vertex when the largest perpendicular distance is greater than the predetermined threshold value.
9. A polygonal approximation apparatus for use in a contour encoder for encoding a contour of an object expressed in a digital video signal, which comprises:
means for detecting initial vertices on the contour;
means for storing vertex information representing the positions of the detected vertices;
means for selecting two adjacent vertices among the detected vertices based on the stored vertex information;
means for producing a line segment connecting the two adjacent vertices by using a multiplicity of pixels;
means for widening the line segment to thereby generate a band segment;
means for selecting a contour segment corresponding to the line segment from the contour; and
means for detecting a new vertex based on the two adjacent vertices, the band segment and the contour segment and providing the new vertex to the storing means.
10. The apparatus according to claim 9, wherein the line segment is produced by using a Bresenham's algorithm.
11. The apparatus according to claim 9, wherein the band segment is obtained by widening pixel area surrounding each pixel constituting the line segment by using a predetermined threshold value.
12. The apparatus according to claim 11, wherein the band segment includes neighboring pixels satisfying the following equation for each pixel on the line segment, |Xn - Xs| +|yn - ys| # TH1 wherein x5 and y, are x and y coordinates of a target pixel on the line segment, respectively; xn and y, represent x and y coordinates of a pixel neighboring to the line segment, respectively; and TH1 is the predetermined threshold value.
13. The apparatus according to claim 11, wherein the new vertex detecting means includes:
a matching means for matching the band segment and the contour segment to thereby find non-matched pixels; and
a new vertex determination means for detecting the new vertex based on the non-matched pixels and the two adjacent vertices.
14. The apparatus according to claim 13, wherein each of the non-matched pixels is on the contour segment and also located outside of the band segment.
15. The apparatus according to claim 14, wherein the new vertex determination means includes:
means for producing a straight line connecting the two adjacent vertices;
means for calculating a perpendicular distance from each of the non-matched pixels to the straight line; and
means for determining a non-matched pixel having a largest perpendicular distance as the new vertex existing between the two adjacent vertices.
16. The apparatus according to claim 15, wherein the nonmatched pixel having the largest perpendicular distance is determined as the new vertex when the largest perpendicular distance is greater than the predetermined threshold value.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019970001561A KR100239592B1 (en) | 1997-01-21 | 1997-01-21 | Method and apparatus for coding contour image |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9705610D0 GB9705610D0 (en) | 1997-05-07 |
| GB2321359A true GB2321359A (en) | 1998-07-22 |
Family
ID=19495148
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9705610A Withdrawn GB2321359A (en) | 1997-01-21 | 1997-03-18 | Polygonal approximation in video contour encoding system |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH10222681A (en) |
| KR (1) | KR100239592B1 (en) |
| GB (1) | GB2321359A (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2114851A (en) * | 1982-02-04 | 1983-08-24 | Shaken Kk | A method for compressing character or pictorial image data |
| GB2203613A (en) * | 1987-04-06 | 1988-10-19 | Canon Kk | Image processing apparatus |
-
1997
- 1997-01-21 KR KR1019970001561A patent/KR100239592B1/en not_active IP Right Cessation
- 1997-03-18 GB GB9705610A patent/GB2321359A/en not_active Withdrawn
- 1997-03-24 JP JP9069758A patent/JPH10222681A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2114851A (en) * | 1982-02-04 | 1983-08-24 | Shaken Kk | A method for compressing character or pictorial image data |
| GB2203613A (en) * | 1987-04-06 | 1988-10-19 | Canon Kk | Image processing apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| KR19980066185A (en) | 1998-10-15 |
| JPH10222681A (en) | 1998-08-21 |
| KR100239592B1 (en) | 2000-01-15 |
| GB9705610D0 (en) | 1997-05-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |