Picture coding method and picture decoding method

1 . A picture coding method of coding a high-resolution input picture to be one of a high-resolution picture and a low-resolution picture, said method comprising:

deciding whether or not a to-be-coded picture is to be coded as a high-resolution picture or a low-resolution picture, depending on a picture type of the to-be-coded picture;

down-converting resolution of the to-be-coded picture, when the to-be-coded picture is decided to be coded as a low-resolution picture in said deciding;

down-converting resolution of a reference picture which has been coded as a high-resolution picture, when the reference picture is referred to by the to-be-coded picture decided to be coded as a low-resolution picture in said deciding; and

coding the to-be-coded picture whose resolution is down-converted in said down-converting of the resolution of the to-be-coded picture, referring to the reference picture whose resolution is down-converted in said down-converting of the resolution of the reference picture.

2 . The picture coding method according to claim 1 ,

wherein in said deciding, it is decided that an I-picture and a P-picture are coded as high-resolution pictures, and a B-picture is coded as a low-resolution picture, assuming that the B-picture is not referred to by any other pictures.

3 . The picture coding method according to claim 1 ,

wherein in said deciding, it is decided that only I-picture is coded as a high-resolution picture.

4 . The picture coding method according to claim 1 further comprising

up-converting resolution of a reference picture which has been coded as a low-resolution picture, when the reference picture is referred to by the to-be-coded picture decided to be coded as a high-resolution picture in said deciding,

wherein, in said coding, the to-be-coded picture refers to the reference picture whose resolution is up-converted in said up-converting.

5 . The picture coding method according to claim 4 ,

wherein said up-converting includes:

estimating a motion vector, per one or more pixels, for a first low-resolution picture from a second low-resolution picture, the first low-resolution picture being the reference picture of to-be-coded picture and coded as a low-resolution picture, and the second low-resolution picture being a reference picture of the first low-resolution picture in the coding of the first low-resolution picture;

obtaining, based on the estimated motion vector, a first pixel value of a pixel in a second high-resolution picture which corresponds to the pixel used in said estimating, the second high-resolution picture representing the same image as the second low-resolution picture but having different resolution; and

generating a first high-resolution picture, by using the obtained first pixel value, in order to be used as the actual reference picture of the to-be-coded picture, the first high-resolution picture representing the same image as the first low-resolution picture but having different resolution.

6 . The picture coding method according to claim 5 ,

wherein sad up-converting further includes:

estimating a motion vector for the first high-resolution picture from the second high-resolution picture, per one or more pixels each of which has been already generated in the first high-resolution picture;

obtaining, based on the estimated motion vector, a second pixel value of a pixel in the second high-resolution picture which is positioned at the same location as the pixel in the first high-resolution picture; and

generating the first high-resolution picture, by using the an average value of the obtained first and second pixel values in a corresponding pixel, in order to be used as the actual reference picture of the to-be-coded picture.

7 . The picture coding method according to claim 5 ,

wherein sad up-converting further includes:

estimating a plurality of motion vectors, regarding already-generated pixels, for the first low-resolution picture from a plurality of the second low-resolution pictures, and for the first high-resolution picture from a plurality of the second high-resolution pictures; and

generates a plurality of the first high-resolution pictures, using a plurality of the estimated motion vectors, and

said coding further includes

selecting one of the plurality of the high-resolution pictures generated in said up-converting, in order to be used as the actual reference picture of the to-be-coded picture.

8 . A picture decoding method of decoding a bitstream in which each moving picture is coded as a high-resolution picture or a low-resolution picture, said method comprising:

decoding a to-be-decoded picture coded in the bitstream;

up-converting resolution of a low-resolution decoded picture to generate a high-resolution picture, when the decoded picture has been coded as a low-resolution picture; and

outputting the high-resolution picture whose resolution is up-converted in said up-converting.

9 . The picture decoding method according to claim 8 ,

wherein said up-converting includes:

estimating a motion vector, per one or more pixels, for a first low-resolution picture from a second low-resolution picture, the first low-resolution picture being decoded in said decoding, and the second low-resolution being decoded in said decoding and having been used as a reference picture in coding of the first low-resolution picture;

obtaining, based on the estimated motion vector, a pixel value of a pixel in a second high-resolution picture which corresponds to the pixel used in said estimating, the second high-resolution picture representing the same image of the second low-resolution picture but having different resolution; and

generating a first high-resolution picture using the obtained pixel value, in order to be outputted as the high-resolution picture in said outputting, the first high-resolution picture representing the same image of the first low-resolution picture but having different resolution.

10 . A picture coding device which codes a high-resolution input picture to be one of a high-resolution picture and a low-resolution picture, said device comprising:

a coding control unit operable to decide whether or not a to-be-coded picture is to be coded as a high-resolution picture or a low-resolution picture, depending on a picture type of the to-be-coded picture;

a first down-conversion unit operable to down-convert resolution of the to-be-coded picture, when the to-be-coded picture is decided to be coded as a low-resolution picture in said coding control unit;

a second down-conversion unit operable to down-convert resolution of a reference picture which has been coded as a high-resolution picture, when the reference picture is referred to by the to-be-coded picture decided to be coded as a low-resolution picture in said coding control unit; and

a coding unit operable to code the to-be-coded picture whose resolution is down-converted in said first down-conversion unit, referring to the reference picture whose resolution is down-converted in said second down-conversion unit.

11 . A picture decoding device which decodes a bitstream in which each moving picture is coded as a high-resolution picture or a low-resolution picture, said device comprising:

a decoding unit operable to decode a to.-be-decoded picture coded in the bitstream;

a decoded-picture processing unit operable to up-convert resolution of a low-resolution decoded picture to generate a high-resolution picture, when the decoded picture has been coded as a low-resolution picture; and

an output unit operable to output the high-resolution picture whose resolution is up-converted in said decoded-picture processing unit.

12 . A program used in a picture coding device which codes a high-resolution input picture to be one of a high-resolution picture and a low-resolution picture, said program causing a computer to execute:

deciding whether or not a to-be-coded picture is to be coded as a high-resolution picture or a low-resolution picture, depending on a picture type of the to-be-coded picture;

down-converting resolution of the to-be-coded picture, when the to-be-coded picture is decided to be coded as a low-resolution picture in said deciding;

down-converting resolution of a reference picture which has been coded as a high-resolution picture, when the reference picture is referred to by the to-be-coded picture decided to be coded as a low-resolution picture in said deciding; and

coding the to-be-coded picture whose resolution is down-converted in said down-converting of the resolution of the to-be-coded picture, referring to the reference picture whose resolution is down-converted in said down-converting of the resolution of the reference picture.

13 . A program used in a picture decoding device which decodes a bitstream in which each moving picture is coded as a high-resolution picture or a low-resolution picture, said program causing a computer to execute:

decoding a to-be-decoded picture coded in the bitstream;

up-converting resolution of a low-resolution decoded picture to generate a high-resolution picture, when the decoded picture has been coded as a low-resolution picture; and

outputting the high-resolution picture whose resolution is up-converted in said up-converting.

14 . An integrated circuit having a picture coding device which codes a high-resolution input picture to be one of a high-resolution picture and a low-resolution picture, said integrated circuit comprising:

a coding control unit operable to decide whether or not a to-be-coded picture is to be coded as a high-resolution picture or a low-resolution picture, depending on a picture type of the to-be-coded picture;

a first down-conversion unit operable to down-convert resolution of the to-be-coded picture, when the to-be-coded picture is decided to be coded as a low-resolution picture in said coding control unit;

a second down-conversion unit operable to down-convert resolution of a reference picture which has been coded as a high-resolution picture, when the reference picture is referred to by the to-be-coded picture decided to be coded as a low-resolution picture in said coding control unit; and

a coding unit operable to code the to-be-coded picture whose resolution is down-converted in said first down-conversion unit, referring to the reference picture whose resolution is down-converted in said second down-conversion unit.

15 . An integrated circuit having a picture decoding device which decodes a bitstream in which each moving picture is coded as a high-resolution picture or a low-resolution picture, said integrated circuit comprising:

a decoding unit operable to decode a to-be-decoded picture coded in the bitstream;

a decoded-picture processing unit operable to up-convert resolution of a low-resolution decoded picture to generate a high-resolution picture, when the decoded picture has been coded as a low-resolution picture; and

an output unit operable to output the high-resolution picture whose resolution is up-converted in said decoded-picture processing unit.