Prediction mode selecting device in moving image coder

Claim 2

A moving image coder in which each of frames in a moving image sequence is divided into frame blocks and a data amount of the moving image is compressed by selecting one of a forward prediction mode, a backward prediction mode and a bidirectional prediction mode by using a motion vector for every frame block; the moving image coder comprising: a forward predicting motion vector/prediction error amount detecting section for detecting an optimum motion vector from a past frame, making a predicted image and calculating a first prediction error amount from a present frame; a backward prediction motion vector/prediction error amount detecting section for detecting an optimum motion vector from a future frame, making a predicted image arid calculating a second prediction error amount from the present frame; and a comparator/mode selecting section for receiving the first prediction error amount from said forward predicting motion vector/prediction error amount detecting section and the second prediction error amount from said backward predicting motion vector/prediction error amount detecting section, calculating a parameter as a function of difference between and/or ratio of the first and second prediction error amounts and selecting one of said forward prediction mode, said backward prediction mode and said bidirectional prediction mode, by comparing a value of said parameter with predetermined thresholds, so that the selecting operation is performed without calculating bidirectional prediction error amount based on the forward prediction motion vector and the backward prediction motion vector.

Claim 3

A moving image coder as claimed in claim 1, wherein the prediction error amounts from the forward predicting motion vector/prediction error amount detecting section and the backward predicting motion vector/prediction error amount detecting section are compared with each other in the comparator/mode selecting section by a differential value between these prediction error amounts.

Claim 4

A moving image coder as claimed in claim 1, wherein the prediction error amounts from the forward predicting motion vector/prediction error amount detecting section and the backward predicting motion vector/prediction error amount detecting section are compared with each other in the comparator/mode selecting section by a ratio of these prediction error amounts.

Claim 5

A moving image coder as claimed in claim 1, wherein the prediction error amounts from the forward predicting motion vector/prediction error amount detecting section and the backward predicting motion vector/prediction error amount detecting section are compared with each other in the comparator/mode selecting section by combining a differential value between these prediction error amounts with a ratio of these prediction error amounts.

Claim 6

A moving image coder as claimed in claim 1, wherein the moving image coder further comprises: an odd/even field separating section for separating odd and even fields from each other; a forward field predicting motion vector/prediction error amount detecting section for detecting a forward field predicting motion vector and a prediction error amount every each of the separated odd and even fields; a backward field predicting motion vector/prediction error amount detecting section for detecting a backward field predicting motion vector and a prediction error amount; and a comparator/mode selecting section.

Claim 7

A moving image coder as claimed in claim 1, wherein the moving image coder is arranged in a frame/field adaptive predicted moving image coder having six kinds of prediction modes obtained by combining three prediction modes composed of said forward prediction mode, said backward prediction mode and said bidirectional prediction mode with two prediction modes composed of a frame prediction mode and a field prediction mode; the frame/field adaptive predicted moving image coder comprises: said forward frame predicting motion vector/prediction error amount detecting section; said backward frame predicting motion vector/prediction error amount detecting section; said odd/even field separating section; said forward field predicting motion vector/prediction error amount detecting section; said backward field predicting motion vector/prediction error amount detecting section; and said comparator/mode selecting section, and this comparator/mode selecting section determines selection of any one of the forward prediction mode, the backward prediction mode and the bidirectional prediction mode after the frame prediction mode or the field prediction mode is determined in use.

Claim 8

A moving image coder as claimed in claim 6, wherein each of the frame prediction mode and the field prediction mode in the comparator/mode selecting section is selectively set to a frame/field mode in a prediction system for providing a minimum prediction error amount among a forward frame prediction error amount, a forward field prediction error amount, a backward frame prediction error amount and a backward field prediction error amount; the forward field prediction error amount is set to a sum of a forward directional odd field prediction error amount and a forward directional even field prediction error amount with respect to the same block as an object block of said forward frame prediction; and the backward field prediction error amount is set to a sum of a backward directional odd field prediction error amount and a backward directional even field prediction error amount with respect to the same block as an object block of said backward frame prediction.

Claim 9

A moving image coder as claimed in claim 6, wherein a sum of said forward frame prediction error amount and said backward frame prediction error amount is compared with a sum of said forward directional odd field prediction error amount, said forward directional even field prediction error amount, said backward directional odd field prediction error amount and said backward directional even field prediction error amount; and each of the frame prediction mode and the field prediction mode in the comparator/mode selecting section is selectively set to a frame/field mode in a prediction system for providing a smaller prediction error amount among said two sums.

Claim 10

A moving image coder as claimed in claim 1, wherein the moving image coder is arranged in a frame/field adaptive predicted moving image coder having six kinds of prediction modes obtained by combining three prediction modes composed of said forward prediction mode, said backward prediction mode and said bidirectional prediction mode with two prediction modes composed of a frame prediction mode and a field prediction mode; the frame/field adaptive predicted moving image coder comprises: said forward frame predicting motion vector/prediction error amount detecting section; said backward frame predicting motion vector/prediction error amount detecting section; said odd/even field separating section; said forward field predicting motion vector/prediction error amount detecting section; said backward field predicting motion vector/prediction error amount detecting section; and said comparator/mode selecting section, and a sum of said forward frame prediction error amount, said forward directional odd field prediction error amount and said forward directional even field prediction error amount, and a sum of said backward frame prediction error amount, said backward directional odd field prediction error amount and said backward directional even field prediction error amount are input to said comparator/mode selecting section; and selection of the frame prediction mode or the field prediction mode is determined by selecting a smaller one of said frame prediction error amount and the field prediction error amount as a sum of said odd field prediction error amount and said even field prediction error amount after one of the forward prediction mode, the backward prediction mode and the bidirectional prediction mode is determined in use.

Claim 13

A method as claimed in claim 10, wherein said step of calculating said parameter includes setting said parameter equal to a differential value between said first and said second prediction error amounts.

Claim 14

A method as claimed in claim 10, wherein said step of calculating said parameter includes setting said parameter equal to a ratio of said first and said second prediction error amounts.

Claim 15

A method as claimed in claim 10, wherein said step of calculating said parameter includes setting a first parameter equal to a difference between said first and said second prediction error amounts and setting a second parameter equal to a ratio of said first and said second prediction error amounts, and said selecting step is performed in accordance with a value of said first parameter and a value of said second parameter.

Claim 16

A method as claimed in claim 10 further comprising: separating odd and even fields from each other; detecting a forward field prediction motion vector and a prediction error amount every each of the separated odd and even fields; and a backward field prediction motion vector and a prediction error amount.

Claim 17

A method as claimed in claim 14, wherein modes to be selected include six kinds of prediction modes obtained by combining three prediction modes composed of said forward prediction mode, said backward prediction mode and said bidirectional prediction mode with two prediction modes composed of a frame prediction mode and a field prediction mode, wherein said selecting step includes selecting of any one of the forward prediction mode, the backward prediction mode and the bidirectional prediction mode after determining whether the frame prediction mode or the field prediction mode is used.

Claim 18

A method as claimed in claim 15 further comprising: setting said forward field prediction error amount equal to a sum of a forward directional odd field prediction error amount and a forward directional even field prediction error amount with respect to the same block as an object block of said step of detecting from said past frame; and setting said backward field prediction error amount equal to a sum of a backward directional odd field prediction error amount and a backward directional even field prediction error amount with respect to the same block as an object block of said step of detecting from said future frame.

Claim 19

A method as claimed in claim 15, further comprising: comparing a sum of said forward frame prediction error amount and said backward frame prediction error amount with a sum of said forward directional odd field prediction error amount, said forward directional even field prediction error amount, said backward directional odd field prediction error amount and said backward directional even field prediction error amount; and selectively setting each of the frame prediction mode and the field prediction mode to a frame/field mode in a prediction system for providing a smaller prediction error amount among said two sums.

Claim 20

A method as claimed in claim 15, wherein modes to be selected include six kinds of prediction modes obtained by combining three prediction modes composed of said forward prediction mode, said backward prediction mode and said bidirectional prediction mode with two prediction modes composed of a frame prediction mode and a field prediction mode, further comprising: computing a sum of said forward frame prediction error amount, said forward directional odd field prediction error amount and said forward directional even field prediction error amount, and a sum of said backward frame prediction error amount, said backward directional odd field prediction error amount and said backward directional even field prediction error amount; and selecting the frame prediction mode or the field prediction mode by selecting a smaller one of said frame prediction error amount and said field prediction error amount as a sum of said odd field prediction error amount as a sum of said odd field prediction error amount and said even field prediction error amount after determining which one of the forward prediction mode, the backward prediction mode and the bidirectional prediction mode is in use.