Title of Invention	METHOD OF SELECTING A REFERENCE PICTURE
Abstract	The present invention relates to a method for coding a moving picture in a moving picture coding system using multiple reference picture. According to the method for coding an interlaced moving picture into a frame picture having frame/field macroblock, a reference picture index of the frame macroblock is determined at a macroblock level by determining the reference picture index of frame unit at a picture (or slice) level and respectively allocating a lower index and a higher index to a top reference field and a bottom reference field while sequentially visiting the reference frames according to an order of reference picture index of frame unit, the top and bottom field indexes being giving by an equation: top reference field index = 2 x picture index of reference frame; and bottom reference field index = 2 x picture index of reference frame + 1.

Title of Invention

METHOD OF SELECTING A REFERENCE PICTURE

Abstract

The present invention relates to a method for coding a moving picture in a moving picture coding system using multiple reference picture. According to the method for coding an interlaced moving picture into a frame picture having frame/field macroblock, a reference picture index of the frame macroblock is determined at a macroblock level by determining the reference picture index of frame unit at a picture (or slice) level and respectively allocating a lower index and a higher index to a top reference field and a bottom reference field while sequentially visiting the reference frames according to an order of reference picture index of frame unit, the top and bottom field indexes being giving by an equation: top reference field index = 2 x picture index of reference frame; and bottom reference field index = 2 x picture index of reference frame + 1.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13) 1. TITLE OF THE INVENTION : "METHOD OF SELECTING A REFERENCE PICTURE" 2. APPLICANT (S) (a) NAME LG ELECTRONICS, INC. (b) NATIONALITY Korean (c) ADDRESS 20, Yoido-dong, Youngdungpo-gu, Seoul 150-875, Korea 3. PREAMBLE TO THE DESCRIPTION PROVISIONAL The following specification describes the invention COMPLETE The following specification particularly describes the invention and the manner in which it is to be performed. i 4. DESCRIPTION (Description shall start from next page) 5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble - "l/we claim" on separate page) 6. DATE AND SIGNATURE (to be given at the end of last page of specification) 7. ABSTRACT OF THE INVENTION (to be given along with complete specification on separate page) METHOD OF SELECTING A REFERENCE PICTURE Technical Field The present invention relates to encoding and decoding a moving picture. Background Art Moving picture coding systems compensate for motion using motion vector information. In the case of moving picture coding system that uses multiple reference pictures, reference picture index information as well as motion vector information is required for motion compensation. The reference picture index is a value that is used to distinguish multiple reference pictures from each other. A coder transfers the reference picture index to a decoder. The decoder selects the reference picture as indicated by the reference picture index, and performs motion compensation using the selected reference picture. Generally, scanning methods for images are classified into either progressive scanning or interlaced scanning. In the case of the progressive scanning, an image of one frame consists of data that are sampled at the same time. In case of the interlaced scanning, an image of one frame consists of data that are sampled at different times, and the samples are alternated line by line. The interlaced image of a frame is usually divided into two fields called a top field and a bottom field. In the interlaced scanning, one frame is divided into two field images. In this specification, an image is treated based on a unit of a picture. A frame or a field may be referred to as a picture. Three coding methods for an interlaced moving picture are proposed. A first 'coding method is a field picture coding method which performs a coding process considering each field as an independent picture at a picture or slice level. A second coding method is the frame picture coding method which performs a coding process after combining two 2. PCT/KR 2004/0 00 44 1PEA/KR 27 042005. fields into one frame at a picture or slice level. A third coding method is a frame picture coding method with frame/field macroblock, which performs a coding process by combining two fields .into one frame and selecting a frame 5 mode- or a field mode at a macroblock level. . In' the third coding method, two vertically adjacent macroblocks are bound into a pair and the coding is performed in unit of a macrobiock pair. In FIG. 1, numbers assigned in the. macrobiock pairs indicate macrobiock addresses that are 10 used to distinguish, the macroblocks from each other. Here, a frame macrobiock- is a macrobiock which is coded at upper .and lower macroblocks of the macrobiock pair in- units of a frame.- In. other words, each macrobiock is coded in units of a frame- after two fields are combined into one 15 frame. Meanwhile, a field macrobiock is a macrobiock that is . coded at upper and lower, macroblocks of macrobiock pairs in units of a field. The macrobiock pair is divided into top and bottom field components . and each field is coded 20 independently. At this time, the macrobiock pairs are rearranged 'so**"that the' upper" and lower macroblocks may ' respectively contain only a top field component and only, a bottom. field component. The .upper macrobiock is called a top field macrobiock and the lower macrobiock is called a bottom 25 field macrobiock. A reference buffer for storing multiple reference pictures is configured in units of a frame. In the frame picture coding, all reference pictures are considered .as units of a frame in which two fields are combined into one 30 frame, and one picture among the reference frame ..pictures is used- for motion .compensation. Accordingly, values are allocated to the reference picture indexes .in units of a frame. .The reference picture ' index for a P frame is obtained 35 by sorting all -the reference frames -in an order reverse to a coding order and then sequentially allocating an index, which .. is increased by one, to -the- sorted reference 'frames. The 3 PCT/KR 2004/O 00445 1PEA/KR 2 7.012005. reference picture index for a. B frame 'is classified into a list 0 and a list 1, and is determined based on a display order of the reference frame. First, in case of the reference frame list 0, indexes 5 are allocated in a reverse order to the reference frame-s whose display order lags behind the B frame, and then, the remaining indexes are allocated in the display order to the reference frames whose display order leads the B frame. In case ' of the reference, frame, list 1, in contrast to the 10 reference frame list 0, indexes are allocated in the display order to the reference, frames whose display order leads the B- frame, and then, the remaining indexes are allocated in a reverse order to the reference frame whose display order lags behind the B frame. FIG. 2 shows a reference picture index 15 for a P frame when a size of the reference buffer is '5, and FIG. 3 shows the reference picture index lists 0 and 1 for a. B frame. . In the field picture coding, the fields of all reference pictures are considered as independent pictures and 20 one of ;. the reference, field- pictures is used for motion compensation. Accordingly, values are allocated to the -reference: picture indexes in units of a field. At. this time, ' life reference fields are combined in the unit of a frame, and then, the reference picture indexes in each field of the P 25 frame are sorted in an order reverse to a coding order of the frame. Then, index values that are increased by one are alternately allocated in an order- that starts from a reference field having parity equal to a current picture to a . reference field having parity different from the current 30 picture, while visiting the sorted reference frames in sequence . ' In addition, in the case of the reference picture index lists 0 and. 1 for each field of a B frame, all the reference fields are combined in units of a frame and then a reference 35 frame is sorted- in the same manner as the method of determining reference frame index of. a B frame. Thereafter, the indexes that; are increased- by one are ' alternately PCT/KR 2004/O 0 0 445 1PEA/KR 2 7.0 4 2005. allocated in an order that starts from a reference field having parity equal to a current picture to a reference field having parity different from the current picture, while visiting the sorted reference frames. in sequence. 5 FIG, 4- shows reference picture indexes of top and bottom .fields of a P frame when a size of a reference buffer is 5, and FIG. 5 shows reference picture index lists 0 and 1 of top and bottom fields of a B frame that can be used as a reference. 10 In order to improve coding efficiency, the moving picture coding system using multiple reference pictures provides a function of reordering the reference picture indexes before decoding a picture or a slice. The reference picture indexes are arbitrarily reordered so as to enhance 15 the coding efficiency after determining an initial reference picture index for the frame and field pictures. FIG. 6 shows a result of determining an initial reference picture index for a P frame and arbitrarily 'reordering" indexes according to the above-described method. 20 When . the moving picture coding system using the multiple reference pictures codes an' interlaced moving, picture into a frame; picture having frame/field macroblocks, all the reference pictures for the frame macroblock are considered as a frame unit and one of the reference frame 25 . pictures must be used for motion compensation. In addition, all the reference pictures for the field macroblock are considered as independent pictures, and one of the reference field pictures must be used for motion compensation. Accordingly, in. the frame picture coding that selects 30 the frame/field coding modes at the macroblock level, it is necessary to allocate values- to. the reference picture index in frame unit or field unit according to the coding mode of each macroblock. 35 Summary of the Invention An embodiment of the present invention provides reference picture information used for motion compensation by PCT/RE 2004/OO0445 1PEA/KR 2 7.04.2005, determining the reference picture index differently according a coding mode .of macroblock when interlaced moving picture is coded with a frame picture having frame/field macroblocks in a moving picture coding system using multiple 5 reference pictures. In one embodiment, the method of selecting a reference picture for processing a field macroblock includes selecting at least one reference picture for processing a field macroblock from at least one reference picture list using 10 . reference picture index information. Here, each selected at least one reference picture is a field. For example, the reference field may a top field or a bottom field. In another embodiment, the method may further include processing the field macroblock using the selected at least 15 one reference picture. In a further embodiment, the method may include forming the at least one reference picture list. For example, the forming .step may include initializing the at least one . reference picture list, and reordering the at least one 20 reference picture list;. In another embodiment, if the reference picture index information is an even index number, then the selected at' least one reference 'field has a same- field parity as the field macroblock. 25 In yet ' another embodiment, if the reference picture index information is an odd index number, then the selected at least one. reference field has a field parity different" from the field macroblock. In one embodiment, the method of selecting, a. reference 30 picture for processing a field macroblock includes selecting at" least one reference picture for processing a" field macroblock from at least one. reference picture list using reference picture index information. Here, each selected at least' one reference picture is a field, and a parity of the 35 selected at least one reference field may be based on the parity of the field macroblock and the reference picture index information. 6 PCT/RE 2004/O 0 0 445 1PEA/KR 2 H 4.2M5. Brief Description of the Drawings The accompanying drawings, which are included to provide a further understanding of the invention and are' incorporated 5 in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In .the drawings: FIG. 1 shows macroblock pair in frame picture having 10 general frame/field macroblock; FIG. 2 shows reference picture indexes of P frame coding in a moving picture coding system according to the related art; FIG. 3 shows the reference picture index lists 0 and. 15 of' B frame coding in a moving, picture coding system according to the related art; ' FIG. 4 shows reference picture indexes in a. coding of top and bottom .fields, of a P frame in a moving picture coding system according to the related art; 20 FIG. 5 shows reference picture index lists 0 and 1 in a coding of top- and bottom fields of a B frame in a moving picture coding system according to the related art; FIG. 6 shows, reference picture indexes reordered in a coding of a P frame in a moving picture coding system 25 according to the related art; . FIG. 7 shows reference picture indexes of a P frame and a B frame having frame macroblocks in a., moving picture coding system according to the .present invention; FIG. 8. shows reference-picture indexes of P frame and B 30 frame having . field macroblock in a moving picture ' coding system according to an embodiment of the present invention {case 1); FIG. 9, shows reference picture indexes of a P frame and a B frame having field macroblocks in a moving picture coding 35 system according to another embodiment of the present invention (case 2); -PCT/KR 2004/0 0 0 44 5. 1PEA/KR 2 7.0 4.2005. FIG. 10 shows reference picture indexes of a P frame having field macroblocks in a moving picture coding system according to another embodiment of the present invention (case 3}; 5 FIG. 11 shows reference picture indexes of a B frame having field macroblocks in a moving picture coding system according to a further embodiment of the present invention (case 3); and FIG. 12 shows reference picture indexes of a P frame 10 . and a B frame having field macroblocks in a moving picture coding system according to another embodiment of the present invention (case 4), Detail Description of Example Embodiments 15 Hereinafter, example embodiments of the present invention will be described"'. in detail with reference to. accompanying drawings. . As stated previously, moving picture .coding; systems, compensate for motion using motion vector information. In 20 the case of a moving picture coding system that; uses multiple reference pictures, reference picture index information as well as', motion vector information is used for motion compensation. ' The reference, picture index is a value that is used, to distinguish multiple reference pictures from . each 25 other. A coder' transfers the reference picture index to a decoder.. The decoder selects the reference picture as indicated by the reference picture-index, and performs motion compensation using the selected reference picture. When an interlaced moving picture is coded into a frame 30 . picture having frame/field macroblocks, a moving picture coding system using multiple reference pictures performs a motion compensation from. a reference frame in order for frame coding in the frame macroblock. In other words, the reference pictures may be considered as a frame unit. The 35 moving picture' coding system, however, performs a motion compensation from a reference .field in order for a field coding in the., field macroblocks. In other words, the 8 PCT/KR -2004/OO0 445 PEA/KR 2 7.0 4.2005. reference pictures .may be considered as a field unit. Accordingly, the frame pictures having frame/field macroblock use indexes having different structures at the macroblock level. For example,., the frame macroblock uses a reference picture index of a frame unit and the field macroblock uses a reference picture index of a field unit. It should be considered that the reference picture indexes may be reordered at a picture or slice level. Therefore, the frame picture having frame/field macroblocks should consider the reference picture in a frame unit at a picture or slice level and have the reordered reference picture indexes of a frame unit. The reference . picture index may be determined according to a coding mode of macroblock based on the reference picture indexes of the frame unit'at the macroblock level. The present invention provides an embodiment of a method for determining reference picture indexes in a. frame picture having frame/field macroblocks. The method includes .a process of: determining reference; picture indexes at a '.picture (or slice) level and a process of determining reference picture indexes at a macroblock level.. [1] Determination (or Initialization) of Reference Picture Indexes at a Picture (or Slice) Level The reference pictures may be. considered in a frame- . unit at a picture or slice level and reference picture indexes of frame unit are calculated. In the method of determining a' reference picture index for a P 'frame, reference frames are sorted in an order reverse to a coding order and indexes are allocated while 30- visiting the' sorted reference frames in sequence. Reference picture indexes .for a B frame are determined based on a display order of the reference frames. First, in case of a reference frame list 0, . indexes are allocated in a reverse order to reference frames whose display orders lag behind the B frame and the remaining indexes are allocated in. the display order to reference frames- whose display ordex lead the B frame. 9 PCT/KR 2004/O 00445 IPEA/KR 2 J.04.2095. In case of a reference frame list 1, in contrast to the reference frame list 0, indexes are- allocated in the display order to reference frames whose display orders are higher than the B frame and the remaining indexes are allocated in a reverse order to 'reference frames whose display orders are lower than the B frame. In this and the other embodiment described below, in order. to improve coding efficiency, the moving picture coding system using multiple reference pictures may provide' a function of reordering the reference picture indexes before decoding a picture or a slice The reference picture indexes are arbitrarily reordered so as to enhance the coding, efficiency after determining an initial reference picture index for the frame and field pictures^ When the reference picture indexes are reordered so as to enhance a coding efficiency, the reference picture "indexes of a frame unit may be reordered. [2]. Determination -(or reordering) of Reference Picture Index at Macroblock Level ] The reference picture index is modified according to the coding mode of the macroblock while performing a coding. in unit of a macroblock pair with respect to the reference picture indexes of a frame unit, which are obtained at the picture (or slice) level. This .process will be described below. . [2.1] Case of Frame Macroblock Since motion compensation may be performed to frame macroblocks from a reference frame, the reference picture index may be a frame unit. Accordingly, the reference 30' picture indexes of a frame unit, which are obtained at the picture (or slice) level, are used. A reference frame stored In a . reference buffer may be configured with a field pair having parities (e.g., top and bottom) opposite to each other.. . FIG. 7 shows reference 35 picture indexes for a frame macroblock in a P frame and a B frame when a size of the reference buffer is 5. [2.2] Case of Field Macroblock. PCT/KR 2004/0 0 0 44 IPEA/KR 2 7.04.2005. Since motion compensation- may be performed to field macroblocks from a reference field, the reference picture index may be a field unit. In this case, a field pair having parities opposite to each other is also present in the reference buffer. Accordingly, each 'reference frame is . divided into two. fields while sequentially visiting the reference frame according to the reference picture indexes of a frame unit, which are obtained at the picture (or slice) level. Then, the reference picture indexes are newly allocated to each field. The reference picture indexes for two fields of each reference frame are allocated in various methods (Cases 1 to 4). (Case 1] Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to the top reference field and a higher index is allocated to the bottom reference field when sequentially visiting the reference frames- in an order of. the reference picture indexes/ which are obtained at. the picture (or slice) level. In other words, the top and bottom reference field indexes may be given by. the equation below. Top .reference field index = 2 x picture index of reference frame Bottom reference field index = 2 x picture index of reference frame + 1 FIG. -8 shows reference picture, indexes for' field macroblocks of a P frame and a B frame. (Case 2) Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to the bottom reference field and a higher index is allocated to the top reference field while sequentially visiting the reference frames in an order of the reference picture indexes, which are obtained at the picture (or slice) level. In other words, the top and bottom reference field • indexes may be. given by an equation below. Top reference field index . - 2 x picture 'index of 11 AM EHDED. SHEET(ART. 34) reference frame + 1 Bottom reference field index = 2 x picture index of reference frame FIG. 9 shows reference picture indexes for field macroblocks of a P frame and a B frame. {Case 3J Indexes that are increased by one are alternately . allocated " to reference fields, starting from the reference field having a parity equal to the current field to the 10 reference field having a parity different from the current field, while sequentially visiting the reference frames according to a reference picture index order of the picture (or slice) level. FIGs. 10 and 11 show reference picture indexes for the. field macroblocks' of a P frame and a B frame. 15 (Case 4) Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to reference field close' to the current ' field in view of time and a higher index is allocated to reference field farther from the current field, in view- of time, while sequentially visiting the reference frames in an order of the reference picture indexes of the picture (or slice) level. . In other words, the . reference field indexes may be given by the equation below. Reference field index close to the current field = 2 x picture index of reference frame Reference field index far from the current field - 2 x picture index of reference frame + 1 In FIG. 12, there are shown reference picture indexes for a field macroblock of a P frame and a B' frame.. While the present invention has been described and illustrated herein with reference to the example embodiments thereof, it will be apparent to those skilled in the art that various modifications and- variations can be- made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations. 12 10 PCT/KR 2004/O 0 0 445 IPEA/KR 2 7.0 4 2005. According to- a coding a moving picture method of at least one embodiment of the. present invention, when a moving picture coding system using multiple reference pictures codes an. interlaced moving .picture into a frame picture having frame/field macroblocks, the' moving picture coding system' efficiently provides reference picture information used for motion compensation by differently determining reference picture indexes according to coding modes of macroblocks. We claim: 1. A method of selecting a reference picture for processing a field macroblock, comprising: selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference picture being a field. 2. The method of claim 1, further comprising: processing the field macroblock using the selected at least one reference picture. 3. The method of claim 1, wherein the reference field is one of a top field and a bottom field. 4. The method of claim 1, further comprising: forming the at least one reference picture list. 5. The method of claim 4, wherein the forming step comprises: initializing the at least one reference picture list; and reordering the at least one reference picture list. 6. The method of claim 1, wherein each selected at least one reference picture is a field of a reference frame. 7. The method of claim 1, wherein if the reference picture index information is an even index number, then the selected at least one reference field has a same field parity as the field macroblock. 8. The method of claim 7, wherein if the reference picture index information is an odd index number, then the 14 selected at least one reference field has a field parity different from the field macroblock. 9. The method of claim 1, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the field macroblock. 10. The method of claim 1, wherein if the reference picture index information is an even index number and the field macroblock is a top field macroblock, then the selected at one reference field is a top field. 11. The method of claim 1, wherein if the reference picture index information is an even index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a bottom field. 12. The method of claim 1, wherein if the reference picture index information is an odd index number and the field macroblock is a top field macroblock, then the selected at one reference field is a bottom field. 13. The method of claim 1, wherein if the reference picture index information is an odd index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a top field. 14. A method of selecting a reference picture for processing a field macroblock, comprising: selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference picture being a field, and a parity of the selected at least one reference filed being based on the parity of the field macroblock and the reference picture index information. 15. The method of claim 14, wherein if the reference picture index information is an even index number, then the selected' at least one reference field has a same field parity as the field macroblock. 16. The method of claim 15, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the filed macroblock. 17. The method of claim 14, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the field macroblock. 18. The method of claim 14, wherein if the reference picture index information is an even index number and the field macroblock is a top field macroblock, then the selected at one reference field is a top field. 19. The method of claim 14, wherein if the reference picture index information is an even index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a bottom field. 20. The method of claim 14, wherein if the reference picture index information is an odd index number and the field macroblock is a top field macroblock, then the selected at one reference field is a bottom field. 21. The method of claim 14, wherein if the reference picture index information is an odd index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a top field. 22. A system for selecting a reference picture for processing a field macroblock, comprising: 16 selecting means for selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference picture being a field. 23. The system as claimed in claim 22, further comprising: processing means for processing the field macroblock using the selected at least one reference picture. 24. The system as claimed in claim 22, wherein the reference field is one of a top field and a bottom field. 25. The system as claimed in claim 22, further comprising: forming means for forming the at least one reference picture list. 26. The system as claimed in claim 25, wherein the forming means comprises: initializing means for initializing the at least one reference picture list; and reordering means for reordering the at least one reference picture list. 27. The system as claimed in claim 22, wherein each selected at least one reference picture is a field of a reference frame. 28. A system for selecting a reference picture for processing a field macroblock, comprising: selecting means for selecting at least one reference picture for processing a field macroblock from at least 17 one reference picture list using reference picture index information, each selected at least one reference picture being a field, and a parity of the selected at least one reference filed being based on the parity of the field macroblock and the reference picture index information. 29. A method and system for selecting a reference picture for processing a field macroblock substantially as herein described with reference to the accompanying drawings. Dated this 30th day of September, 2005. 18 PCT/KR2004/000445 RO/KR oo.oo.2004 Abstract The present invention relates to a method for coding a moving picture in a moving picture coding system using multiple reference picture. According to the method for coding an interlaced moving picture into a frame picture having frame/field macroblock, a reference picture index of the frame macroblock is determined at a' macroblock level by determining the reference picture index of frame unit at a picture {or slice) level and respectively allocating a lower 10 index and a higher index to a top reference field and a bottom reference field while sequentially visiting the reference frames according to an order of reference picture index of frame unit, the top and bottom field indexes being giving by an equation: top reference field index = 2 x 15 picture index of reference frame; and bottom reference field index 2 x picture index of reference frame + 1. 19

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION :
"METHOD OF SELECTING A REFERENCE PICTURE"
2. APPLICANT (S)
(a) NAME LG ELECTRONICS, INC.
(b) NATIONALITY Korean
(c) ADDRESS 20, Yoido-dong, Youngdungpo-gu, Seoul 150-875,
Korea
3. PREAMBLE TO THE DESCRIPTION
PROVISIONAL
The following specification describes the invention COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.
i 4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble - "l/we claim" on separate page)
6. DATE AND SIGNATURE (to be given at the end of last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on separate page)

METHOD OF SELECTING A REFERENCE PICTURE Technical Field
The present invention relates to encoding and decoding a moving picture.
Background Art
Moving picture coding systems compensate for motion using motion vector information. In the case of moving picture coding system that uses multiple reference pictures, reference picture index information as well as motion vector information is required for motion compensation. The reference picture index is a value that is used to distinguish multiple reference pictures from each other. A coder transfers the reference picture index to a decoder. The decoder selects the reference picture as indicated by the reference picture index, and performs motion compensation using the selected reference picture.
Generally, scanning methods for images are classified into either progressive scanning or interlaced scanning. In the case of the progressive scanning, an image of one frame consists of data that are sampled at the same time. In case of the interlaced scanning, an image of one frame consists of data that are sampled at different times, and the samples are alternated line by line.
The interlaced image of a frame is usually divided into two fields called a top field and a bottom field. In the interlaced scanning, one frame is divided into two field images. In this specification, an image is treated based on a unit of a picture. A frame or a field may be referred to as a picture.
Three coding methods for an interlaced moving picture are proposed. A first 'coding method is a field picture coding method which performs a coding process considering each field as an independent picture at a picture or slice level. A second coding method is the frame picture coding method which performs a coding process after combining two
2.

PCT/KR 2004/0 00 44 1PEA/KR 27 042005.
fields into one frame at a picture or slice level. A third coding method is a frame picture coding method with frame/field macroblock, which performs a coding process by combining two fields .into one frame and selecting a frame
5 mode- or a field mode at a macroblock level. .
In' the third coding method, two vertically adjacent
macroblocks are bound into a pair and the coding is performed
in unit of a macrobiock pair. In FIG. 1, numbers assigned in
the. macrobiock pairs indicate macrobiock addresses that are
10 used to distinguish, the macroblocks from each other.
Here, a frame macrobiock- is a macrobiock which is coded
at upper .and lower macroblocks of the macrobiock pair in-
units of a frame.- In. other words, each macrobiock is coded
in units of a frame- after two fields are combined into one
15 frame.
Meanwhile, a field macrobiock is a macrobiock that is .
coded at upper and lower, macroblocks of macrobiock pairs in
units of a field. The macrobiock pair is divided into top
and bottom field components . and each field is coded
20 independently. At this time, the macrobiock pairs are
rearranged 'so**"that the' upper" and lower macroblocks may
' respectively contain only a top field component and only, a
bottom. field component. The .upper macrobiock is called a top
field macrobiock and the lower macrobiock is called a bottom
25 field macrobiock.
A reference buffer for storing multiple reference pictures is configured in units of a frame. In the frame picture coding, all reference pictures are considered .as units of a frame in which two fields are combined into one 30 frame, and one picture among the reference frame ..pictures is used- for motion .compensation. Accordingly, values are allocated to the reference picture indexes .in units of a frame.
.The reference picture ' index for a P frame is obtained
35 by sorting all -the reference frames -in an order reverse to a
coding order and then sequentially allocating an index, which
.. is increased by one, to -the- sorted reference 'frames. The
3

PCT/KR 2004/O 00445 1PEA/KR 2 7.012005.
reference picture index for a. B frame 'is classified into a list 0 and a list 1, and is determined based on a display order of the reference frame.
First, in case of the reference frame list 0, indexes
5 are allocated in a reverse order to the reference frame-s
whose display order lags behind the B frame, and then, the
remaining indexes are allocated in the display order to the
reference frames whose display order leads the B frame. In
case ' of the reference, frame, list 1, in contrast to the
10 reference frame list 0, indexes are allocated in the display
order to the reference, frames whose display order leads the B-
frame, and then, the remaining indexes are allocated in a
reverse order to the reference frame whose display order lags
behind the B frame. FIG. 2 shows a reference picture index
15 for a P frame when a size of the reference buffer is '5, and
FIG. 3 shows the reference picture index lists 0 and 1 for a.
B frame. .
In the field picture coding, the fields of all reference pictures are considered as independent pictures and
20 one of ;. the reference, field- pictures is used for motion compensation. Accordingly, values are allocated to the -reference: picture indexes in units of a field. At. this time, ' life reference fields are combined in the unit of a frame, and then, the reference picture indexes in each field of the P
25 frame are sorted in an order reverse to a coding order of the frame. Then, index values that are increased by one are alternately allocated in an order- that starts from a reference field having parity equal to a current picture to a . reference field having parity different from the current
30 picture, while visiting the sorted reference frames in sequence .
' In addition, in the case of the reference picture index lists 0 and. 1 for each field of a B frame, all the reference fields are combined in units of a frame and then a reference
35 frame is sorted- in the same manner as the method of determining reference frame index of. a B frame. Thereafter, the indexes that; are increased- by one are ' alternately

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allocated in an order that starts from a reference field having parity equal to a current picture to a reference field having parity different from the current picture, while visiting the sorted reference frames. in sequence.
5 FIG, 4- shows reference picture indexes of top and bottom .fields of a P frame when a size of a reference buffer is 5, and FIG. 5 shows reference picture index lists 0 and 1 of top and bottom fields of a B frame that can be used as a reference.
10 In order to improve coding efficiency, the moving picture coding system using multiple reference pictures provides a function of reordering the reference picture indexes before decoding a picture or a slice. The reference picture indexes are arbitrarily reordered so as to enhance
15 the coding efficiency after determining an initial reference picture index for the frame and field pictures. FIG. 6 shows a result of determining an initial reference picture index for a P frame and arbitrarily 'reordering" indexes according to the above-described method.
20 When . the moving picture coding system using the multiple reference pictures codes an' interlaced moving, picture into a frame; picture having frame/field macroblocks, all the reference pictures for the frame macroblock are considered as a frame unit and one of the reference frame
25 . pictures must be used for motion compensation. In addition, all the reference pictures for the field macroblock are considered as independent pictures, and one of the reference field pictures must be used for motion compensation.
Accordingly, in. the frame picture coding that selects
30 the frame/field coding modes at the macroblock level, it is
necessary to allocate values- to. the reference picture index
in frame unit or field unit according to the coding mode of
each macroblock.
35 Summary of the Invention
An embodiment of the present invention provides reference picture information used for motion compensation by

PCT/RE 2004/OO0445 1PEA/KR 2 7.04.2005,
determining the reference picture index differently according a coding mode .of macroblock when interlaced moving picture is coded with a frame picture having frame/field macroblocks in a moving picture coding system using multiple
5 reference pictures.
In one embodiment, the method of selecting a reference picture for processing a field macroblock includes selecting at least one reference picture for processing a field macroblock from at least one reference picture list using
10 . reference picture index information. Here, each selected at least one reference picture is a field. For example, the reference field may a top field or a bottom field.
In another embodiment, the method may further include processing the field macroblock using the selected at least
15 one reference picture.
In a further embodiment, the method may include forming
the at least one reference picture list. For example, the
forming .step may include initializing the at least one
. reference picture list, and reordering the at least one
20 reference picture list;.
In another embodiment, if the reference picture index information is an even index number, then the selected at' least one reference 'field has a same- field parity as the field macroblock.
25 In yet ' another embodiment, if the reference picture index information is an odd index number, then the selected at least one. reference field has a field parity different" from the field macroblock.
In one embodiment, the method of selecting, a. reference
30 picture for processing a field macroblock includes selecting at" least one reference picture for processing a" field macroblock from at least one. reference picture list using reference picture index information. Here, each selected at least' one reference picture is a field, and a parity of the
35 selected at least one reference field may be based on the parity of the field macroblock and the reference picture index information.
6

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1PEA/KR 2 H 4.2M5.
Brief Description of the Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are' incorporated
5 in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
In .the drawings:
FIG. 1 shows macroblock pair in frame picture having
10 general frame/field macroblock;
FIG. 2 shows reference picture indexes of P frame coding in a moving picture coding system according to the related art;
FIG. 3 shows the reference picture index lists 0 and.
15 of' B frame coding in a moving, picture coding system according to the related art;
' FIG. 4 shows reference picture indexes in a. coding of top and bottom .fields, of a P frame in a moving picture coding system according to the related art;
20 FIG. 5 shows reference picture index lists 0 and 1 in a coding of top- and bottom fields of a B frame in a moving picture coding system according to the related art;
FIG. 6 shows, reference picture indexes reordered in a coding of a P frame in a moving picture coding system
25 according to the related art; .
FIG. 7 shows reference picture indexes of a P frame and a B frame having frame macroblocks in a., moving picture coding system according to the .present invention;
FIG. 8. shows reference-picture indexes of P frame and B
30 frame having . field macroblock in a moving picture ' coding system according to an embodiment of the present invention {case 1);
FIG. 9, shows reference picture indexes of a P frame and a B frame having field macroblocks in a moving picture coding
35 system according to another embodiment of the present invention (case 2);

-PCT/KR 2004/0 0 0 44 5. 1PEA/KR 2 7.0 4.2005.
FIG. 10 shows reference picture indexes of a P frame having field macroblocks in a moving picture coding system according to another embodiment of the present invention (case 3};
5 FIG. 11 shows reference picture indexes of a B frame
having field macroblocks in a moving picture coding system according to a further embodiment of the present invention (case 3); and
FIG. 12 shows reference picture indexes of a P frame
10 . and a B frame having field macroblocks in a moving picture coding system according to another embodiment of the present invention (case 4),
Detail Description of Example Embodiments
15 Hereinafter, example embodiments of the present
invention will be described"'. in detail with reference to. accompanying drawings. .
As stated previously, moving picture .coding; systems,
compensate for motion using motion vector information. In
20 the case of a moving picture coding system that; uses multiple
reference pictures, reference picture index information as
well as', motion vector information is used for motion
compensation. ' The reference, picture index is a value that is
used, to distinguish multiple reference pictures from . each
25 other. A coder' transfers the reference picture index to a
decoder.. The decoder selects the reference picture as indicated by the reference picture-index, and performs motion compensation using the selected reference picture.
When an interlaced moving picture is coded into a frame
30 . picture having frame/field macroblocks, a moving picture coding system using multiple reference pictures performs a motion compensation from. a reference frame in order for frame coding in the frame macroblock. In other words, the reference pictures may be considered as a frame unit. The 35 moving picture' coding system, however, performs a motion compensation from a reference .field in order for a field coding in the., field macroblocks. In other words, the
8

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reference pictures .may be considered as a field unit.
Accordingly, the frame pictures having frame/field macroblock use indexes having different structures at the macroblock level. For example,., the frame macroblock uses a reference picture index of a frame unit and the field macroblock uses a reference picture index of a field unit. It should be considered that the reference picture indexes may be reordered at a picture or slice level.
Therefore, the frame picture having frame/field macroblocks should consider the reference picture in a frame unit at a picture or slice level and have the reordered reference picture indexes of a frame unit. The reference . picture index may be determined according to a coding mode of macroblock based on the reference picture indexes of the frame unit'at the macroblock level.
The present invention provides an embodiment of a method for determining reference picture indexes in a. frame picture having frame/field macroblocks. The method includes .a process of: determining reference; picture indexes at a '.picture (or slice) level and a process of determining reference picture indexes at a macroblock level..
[1] Determination (or Initialization) of Reference Picture Indexes at a Picture (or Slice) Level
The reference pictures may be. considered in a frame- . unit at a picture or slice level and reference picture indexes of frame unit are calculated.
In the method of determining a' reference picture index for a P 'frame, reference frames are sorted in an order reverse to a coding order and indexes are allocated while
30- visiting the' sorted reference frames in sequence.
Reference picture indexes .for a B frame are determined based on a display order of the reference frames. First, in case of a reference frame list 0, . indexes are allocated in a reverse order to reference frames whose display orders lag behind the B frame and the remaining indexes are allocated in. the display order to reference frames- whose display ordex lead the B frame.
9

PCT/KR 2004/O 00445 IPEA/KR 2 J.04.2095.
In case of a reference frame list 1, in contrast to the reference frame list 0, indexes are- allocated in the display order to reference frames whose display orders are higher than the B frame and the remaining indexes are allocated in a reverse order to 'reference frames whose display orders are lower than the B frame.
In this and the other embodiment described below, in order. to improve coding efficiency, the moving picture coding system using multiple reference pictures may provide' a function of reordering the reference picture indexes before decoding a picture or a slice The reference picture indexes are arbitrarily reordered so as to enhance the coding, efficiency after determining an initial reference picture index for the frame and field pictures^ When the reference picture indexes are reordered so as to enhance a coding
efficiency, the reference picture "indexes of a frame unit may be reordered.
[2]. Determination -(or reordering) of Reference Picture Index at Macroblock Level ]
The reference picture index is modified according to the coding mode of the macroblock while performing a coding. in unit of a macroblock pair with respect to the reference picture indexes of a frame unit, which are obtained at the picture (or slice) level. This .process will be described below. .
[2.1] Case of Frame Macroblock
Since motion compensation may be performed to frame
macroblocks from a reference frame, the reference picture
index may be a frame unit. Accordingly, the reference
30' picture indexes of a frame unit, which are obtained at the
picture (or slice) level, are used.
A reference frame stored In a . reference buffer may be
configured with a field pair having parities (e.g., top and
bottom) opposite to each other.. . FIG. 7 shows reference
35 picture indexes for a frame macroblock in a P frame and a B
frame when a size of the reference buffer is 5.
[2.2] Case of Field Macroblock.

PCT/KR 2004/0 0 0 44 IPEA/KR 2 7.04.2005.
Since motion compensation- may be performed
to field macroblocks from a reference field, the reference picture index may be a field unit. In this case, a field pair having parities opposite to each other is also present in the reference buffer. Accordingly, each 'reference frame is . divided into two. fields while sequentially visiting the reference frame according to the reference picture indexes of a frame unit, which are obtained at the picture (or slice) level. Then, the reference picture indexes are newly allocated to each field. The reference picture indexes for two fields of each reference frame are allocated in various methods (Cases 1 to 4). (Case 1]
Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to the top reference field and a higher index is allocated to the bottom reference field when sequentially visiting the reference frames- in an order of. the reference picture indexes/ which are obtained at. the picture (or slice) level. In other words, the top and bottom reference field indexes may be given by. the equation below.
Top .reference field index = 2 x picture index of reference frame
Bottom reference field index = 2 x picture index of reference frame + 1
FIG. -8 shows reference picture, indexes for' field macroblocks of a P frame and a B frame. (Case 2)
Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to the bottom reference field and a higher index is allocated to the top reference field while sequentially visiting the reference frames in an order of the reference picture indexes, which are obtained at the picture (or slice) level. In other words, the top and bottom reference field • indexes may be. given by an equation below.
Top reference field index . - 2 x picture 'index of
11
AM EHDED. SHEET(ART. 34)

reference frame + 1
Bottom reference field index = 2 x picture index of reference frame
FIG. 9 shows reference picture indexes for field macroblocks of a P frame and a B frame. {Case 3J
Indexes that are increased by one are alternately .
allocated " to reference fields, starting from the reference
field having a parity equal to the current field to the
10 reference field having a parity different from the current
field, while sequentially visiting the reference frames
according to a reference picture index order of the picture
(or slice) level. FIGs. 10 and 11 show reference picture
indexes for the. field macroblocks' of a P frame and a B frame.
15 (Case 4)
Regardless of the top and bottom field macroblocks of a current field macroblock, a lower index is allocated to reference field close' to the current ' field in view of time and a higher index is allocated to reference field farther from the current field, in view- of time, while sequentially visiting the reference frames in an order of the reference picture indexes of the picture (or slice) level. .
In other words, the . reference field indexes may be given by the equation below.
Reference field index close to the current field = 2 x picture index of reference frame
Reference field index far from the current field - 2 x picture index of reference frame + 1
In FIG. 12, there are shown reference picture indexes for a field macroblock of a P frame and a B' frame..
While the present invention has been described and illustrated herein with reference to the example embodiments thereof, it will be apparent to those skilled in the art that various modifications and- variations can be- made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations.
12

10

PCT/KR 2004/O 0 0 445
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According to- a coding a moving picture method of at least one embodiment of the. present invention, when a moving picture coding system using multiple reference pictures codes an. interlaced moving .picture into a frame picture having frame/field macroblocks, the' moving picture coding system' efficiently provides reference picture information used for motion compensation by differently determining reference picture indexes according to coding modes of macroblocks.
We claim:
1. A method of selecting a reference picture for
processing a field macroblock, comprising:
selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference picture being a field.
2. The method of claim 1, further comprising:
processing the field macroblock using the selected at least one reference picture.
3. The method of claim 1, wherein the reference field is one of a top field and a bottom field.
4. The method of claim 1, further comprising: forming the at least one reference picture list.
5. The method of claim 4, wherein the forming step comprises:
initializing the at least one reference picture list;
and
reordering the at least one reference picture list.
6. The method of claim 1, wherein each selected at least one reference picture is a field of a reference frame.
7. The method of claim 1, wherein if the reference picture index information is an even index number, then the selected at least one reference field has a same field parity as the field macroblock.
8. The method of claim 7, wherein if the reference picture index information is an odd index number, then the
14

selected at least one reference field has a field parity different from the field macroblock.
9. The method of claim 1, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the field macroblock.
10. The method of claim 1, wherein if the reference picture index information is an even index number and the field macroblock is a top field macroblock, then the selected at one reference field is a top field.
11. The method of claim 1, wherein if the reference picture index information is an even index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a bottom field.
12. The method of claim 1, wherein if the reference picture index information is an odd index number and the field macroblock is a top field macroblock, then the selected at one reference field is a bottom field.
13. The method of claim 1, wherein if the reference picture index information is an odd index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a top field.
14. A method of selecting a reference picture for processing a field macroblock, comprising:
selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference picture being a field, and a parity of the selected at least one reference filed being based on the parity of the field macroblock and the reference picture index information.

15. The method of claim 14, wherein if the reference picture index information is an even index number, then the selected' at least one reference field has a same field parity as the field macroblock.
16. The method of claim 15, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the filed macroblock.
17. The method of claim 14, wherein if the reference picture index information is an odd index number, then the selected at least one reference field has a field parity different from the field macroblock.
18. The method of claim 14, wherein if the reference picture index information is an even index number and the field macroblock is a top field macroblock, then the selected at one reference field is a top field.
19. The method of claim 14, wherein if the reference picture index information is an even index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a bottom field.
20. The method of claim 14, wherein if the reference picture index information is an odd index number and the field macroblock is a top field macroblock, then the selected at one reference field is a bottom field.
21. The method of claim 14, wherein if the reference picture index information is an odd index number and the field macroblock is a bottom field macroblock, then the selected at one reference field is a top field.
22. A system for selecting a reference picture for processing a field macroblock, comprising:
16

selecting means for selecting at least one reference picture for processing a field macroblock from at least one reference picture list using reference picture index information, each selected at least one reference
picture being a field.
23. The system as claimed in claim 22, further comprising:
processing means for processing the field macroblock using the selected at least one reference picture.
24. The system as claimed in claim 22, wherein the reference field is one of a top field and a bottom field.
25. The system as claimed in claim 22, further comprising:
forming means for forming the at least one reference picture list.
26. The system as claimed in claim 25, wherein the forming
means comprises:
initializing means for initializing the at least one
reference picture list;
and
reordering means for reordering the at least one
reference picture list.
27. The system as claimed in claim 22, wherein each selected at least one reference picture is a field of a reference frame.
28. A system for selecting a reference picture for processing a field macroblock, comprising:
selecting means for selecting at least one reference picture for processing a field macroblock from at least
17

one reference picture list using reference picture index information, each selected at least one reference picture being a field, and a parity of the selected at least one reference filed being based on the parity of the field macroblock and the reference picture index information.
29. A method and system for selecting a reference picture
for processing a field macroblock substantially as
herein described with reference to the accompanying
drawings.
Dated this 30th day of September, 2005.

18

PCT/KR2004/000445 RO/KR oo.oo.2004
Abstract
The present invention relates to a method for coding a moving picture in a moving picture coding system using multiple reference picture. According to the method for coding an interlaced moving picture into a frame picture having frame/field macroblock, a reference picture index of the frame macroblock is determined at a' macroblock level by determining the reference picture index of frame unit at a picture {or slice) level and respectively allocating a lower
10 index and a higher index to a top reference field and a bottom reference field while sequentially visiting the reference frames according to an order of reference picture index of frame unit, the top and bottom field indexes being giving by an equation: top reference field index = 2 x
15 picture index of reference frame; and bottom reference field index 2 x picture index of reference frame + 1.
19

METHOD OF SELECTING A REFERENCE PICTURE

Documents:

Inventors:

PCT Conventions: