Picture coding apparatus, picture coding program, picture decoding apparatus, and picture decoding program

1. A picture coding apparatus comprising:

a temporary prediction mode determining unit configured to temporarily determine a prediction mode used to code a coding target pixel, based on a relation between a decoded value of a locally decoded pixel neighboring at least one line above the coding target pixel and decoded values of locally decoded pixels surrounding said neighboring pixel, and configured to set a value, indicating the temporarily determined prediction mode, to a temporary prediction mode index;

a temporary prediction mode index storage configured to store the temporary prediction mode index;

a final prediction mode determining unit configured to finally determine a prediction mode used to code the coding target pixel, based on the temporary prediction mode index of the coding target pixel read from the temporary prediction mode index storage and a relation between a decoded value of a locally decoded pixel located at least to the left of the coding target pixel and decoded values of locally decoded pixels surrounding said pixel located at least to the left thereof;

a prediction pixel selector configured to select a prediction pixel of the coding target pixel, based on the finally determined prediction mode;

a subtractor configured to subtract the value of the prediction pixel from the value of the coding target pixel; and

a prediction error coding unit configured to code a prediction error value derived by the subtractor,

wherein the temporary prediction mode determining unit temporarily determines the prediction mode used to code a coding target pixel P(0, 0),

based on a relation between each value of a first prediction point pixel P(0, 1), which is located immediately above the coding target pixel P(0, 0), a first reference pixel P(1, 2), which is an upper-left neighboring pixel of the first prediction point pixel P(0, 1), a second reference pixel P(0, 2), which is an immediately-above pixel of the first prediction point pixel P(0, 1), a third reference pixel P(−1, 2), which is an upper-right neighboring pixel of the first prediction point pixel P(0, 1), and a fourth reference pixel P(1, 1), which is a left neighboring pixel of the first prediction point pixel P(0, 1),

wherein, it is assumed that a pixel, whose difference value from the first prediction point pixel P(0, 1) is minimum, is the first reference pixel P(1, 2),

when a first difference value between the first prediction point pixel P(0, 1) and the first reference pixel P(1, 2) is greater than or equal to a second difference value between the second reference pixel P(0, 2) and the fourth reference pixel P(1, 1), the temporary prediction mode determining unit sets a value, indicating an upper-left prediction, to the temporary prediction mode index, and

when the first difference value is less than the second difference value, the temporary prediction mode determining unit sets a value, indicating possibility that the first prediction point pixel P(0, 1) is an upper-left vertex pixel of a block forming a checker pattern, to the temporary prediction mode index.

2. A picture coding apparatus according to claim 1 , wherein, when a value, which indicates the upper-left prediction, an upward prediction, an upper-right prediction or a left prediction, is set to the temporary prediction mode index, the final prediction mode determining unit finally determines the prediction direction to be the prediction mode used to code the coding target pixel P(0, 0), and

wherein, when the value, indicating possibility that the first prediction point pixel P(0, 1) is the upper-left vertex pixel, is set to the temporary prediction mode index, the final prediction mode determining unit finally determines the prediction mode, based on a relation between each value of a second prediction point pixel P(1, 0), which is a left neighboring pixel of the coding target pixel P(0, 0), the fourth reference pixel P(1, 1), which is an immediately-above pixel of the second prediction point pixel P(1, 0), and the first prediction point pixel P(0, 1), which is an upper-right neighboring pixel of the second prediction point pixel P(1, 0), and

wherein, when the value, indicating possibility that the first prediction point pixel P(0, 1) is the upper-left vertex pixel, is set to the temporary prediction mode index, and when a third difference value between the second prediction point pixel P(1, 0) and the fourth reference pixel P(1, 1) is greater than or equal to a fourth difference value between the second prediction point pixel P(1, 0) and the first prediction point pixel P(0, 1), the final prediction mode determining unit finally determines the upper-left direction to be the prediction mode, and

when the value, indicating possibility that it is the upper-left vertex pixel, is set to the temporary prediction mode index, and when the third difference value is less than the fourth difference value, the final prediction mode determining unit finally determines the upward direction to be the prediction mode.

3. A non-transitory computer-readable medium having embedded thereon a picture coding program,

the picture coding program comprising:

a temporary prediction mode determining module operative to temporarily determine a prediction mode used to code a coding target pixel, based on a relation between a decoded value of a locally decoded pixel neighboring at least one line above the coding target pixel and decoded values of locally decoded pixels surrounding said neighboring pixel, and setting a value, indicating the temporarily determined prediction mode, to a temporary prediction mode index;

a final prediction mode determining module operative to finally determine a prediction mode used to code the coding target pixel, based on the temporary prediction mode index of the coding target pixel and a relation between a decoded value of a locally decoded pixel located at least to the left of the coding target pixel and decoded values of locally decoded pixels surrounding said pixel located at least to the left thereof;

a prediction pixel selection module operative to select a prediction pixel of the coding target pixel, based on the finally determined prediction mode;

a subtraction module operative to subtract the value of the prediction pixel from the value of the coding target pixel; and

a prediction error coding module operative to code a prediction error value derived by the subtraction module,

wherein the temporary prediction mode determining module temporarily determines the prediction mode used to code a coding target pixel P(0, 0),

based on a relation between each value of a first prediction point pixel P(0, 1), which is located immediately above the coding target pixel P(0, 0), a first reference pixel P(1, 2), which is an upper-left neighboring pixel of the first prediction point pixel P(0, 1), a second reference pixel P(0, 2), which is an immediately-above pixel of the first prediction point pixel P(0, 1), a third reference pixel P(−1, 2), which is an upper-right neighboring pixel of the first prediction point pixel P(0, 1), and a fourth reference pixel P(1, 1), which is a left neighboring pixel of the first prediction point pixel P(0, 1),

wherein, it is assumed that a pixel, whose difference value from the first prediction point pixel P(0, 1) is minimum, is the first reference pixel P(1, 2),

when a first difference value between the first prediction point pixel P(0, 1) and the first reference pixel P(1, 2) is greater than or equal to a second difference value between the second reference pixel P(0, 2) and the fourth reference pixel P(1, 1), the temporary prediction mode determining module sets a value, indicating an upper-left prediction, to the temporary prediction mode index, and

when the first difference value is less than the second difference value, the temporary prediction mode determining module sets a value, indicating possibility that the first prediction point pixel P(0, 1) is an upper-left vertex pixel of a block forming a checker pattern, to the temporary prediction mode index.

4. A picture decoding apparatus comprising:

a temporary prediction mode determining unit configured to temporarily determine a prediction mode used to decode a decoding target pixel, based on a relation between a decoded value of an already-decoded pixel neighboring at least one line above the decoding target pixel and decoded values of already-decoded pixels surrounding said neighboring pixel, and configured to set a value, indicating the temporarily determined prediction mode, to a temporary prediction mode index;

a temporary prediction mode index storage configured to store the temporary prediction mode index;

a final prediction mode determining unit configured to finally determine a prediction mode used to decode the decoding target pixel, based on the temporary prediction mode index of the decoding target pixel read from the temporary prediction mode index storage and a relation between a decoded value of an already-decoded pixel located at least to the left of the decoding target pixel and decoded values of already-decoded pixels surrounding said pixel located at least to the left thereof;

a prediction pixel selector configured to select a prediction pixel of the decoding target pixel, based on the finally determined prediction mode;

a prediction error decoding unit configured to decode a prediction error value of the coded decoding-target pixel; and

an adder configured to restore the value of the decoding target pixel by adding up the selected prediction pixel and the decoded prediction error value,

wherein the temporary prediction mode determining unit temporarily determines the prediction mode used to decode a decoding target pixel P(0, 0),

based on a relation between each value of a first prediction point pixel P(0, 1), which is located immediately above the coding target pixel P(0, 0), a first reference pixel P(1, 2), which is an upper-left neighboring pixel of the first prediction point pixel P(0, 1), a second reference pixel P(0, 2), which is an immediately-above pixel of the first prediction point pixel P(0, 1), a third reference pixel P(−1, 2), which is an upper-right neighboring pixel of the first prediction point pixel P(0, 1), and a fourth reference pixel P(1, 1), which is a left neighboring pixel of the first prediction point pixel P(0, 1),

wherein, it is assumed that a pixel, whose difference value from the first prediction point pixel P(0, 1) is minimum, is the first reference pixel P(1, 2),

when a first difference value between the first prediction point pixel P(0, 1) and the first reference pixel P(1, 2) is greater than or equal to a second difference value between the second reference pixel P(0, 2) and the fourth reference pixel P(1, 1), the temporary prediction mode determining unit sets a value, indicating an upper-left prediction, to the temporary prediction mode index, and

when the first difference value is less than the second difference value, the temporary prediction mode determining unit sets a value, indicating possibility that the first prediction point pixel P(0, 1) is an upper-left vertex pixel of a block forming a checker pattern, to the temporary prediction mode index.

5. A picture decoding apparatus according to claim 4 , wherein, when a value, which indicates the upper-left prediction, an upward prediction, an upper-right prediction or a left prediction, is set to the temporary prediction mode index, the final prediction mode determining unit finally determines the prediction direction to be the prediction mode used to decode the decoding target pixel P(0, 0), and

wherein, when the value, indicating possibility that the first prediction point pixel P(0, 1) is the upper-left vertex pixel, is set to the temporary prediction mode index, the final prediction mode determining unit finally determines the prediction mode, based on a relation between each value of a second prediction point pixel P(1, 0), which is a left neighboring pixel of the coding target pixel P(0, 0), the fourth reference pixel P(1, 1), which is an immediately-above pixel of the second prediction point pixel P(1, 0), and the first prediction point pixel P(0, 1), which is an upper-right neighboring pixel of the second prediction point pixel P(1, 0), and

wherein, when the value, indicating possibility that the first prediction point pixel P(0, 1) is the upper-left vertex pixel, is set to the temporary prediction mode index, and when a third difference value between the second prediction point pixel P(1, 0) and the fourth reference pixel P(1, 1) is greater than or equal to a fourth difference value between the second prediction point pixel P(1, 0) and the first prediction point pixel P(0, 1), the final prediction mode determining unit finally determines the upper-left direction to be the prediction mode, and

when the value, indicating possibility that it is the upper-left vertex pixel, is set to the temporary prediction mode index, and when the third difference value is less than the fourth difference value, the final prediction mode determining unit finally determines the upward direction to be the prediction mode.

6. A non-transitory computer-readable medium having embedded thereon a picture decoding program,

the picture decoding program comprising:

a temporary prediction mode determining module operative to temporarily determine a prediction mode used to decode a decoding target pixel, based on a relation between a decoded value of an already-decoded pixel neighboring at least one line above the decoding target pixel and decoded values of already-decoded pixels surrounding said neighboring pixel, and setting a value, indicating the temporarily determined prediction mode, to a temporary prediction mode index;

a final prediction mode determining module operative to finally determine a prediction mode used to decode the decoding target pixel, based on the temporary prediction mode index of the decoding target pixel and a relation between a decoded value of an already-decoded pixel located at least to the left of the decoding target pixel and decoded values of already-decoded pixels surrounding said pixel located at least to the left thereof;

a prediction pixel selection module operative to select a prediction pixel of the decoding target pixel, based on the finally determined prediction mode;

a prediction error decoding module operative to decode a prediction error value of the coded decoding-target pixel; and

an adding module operative to restore the value of the decoding target pixel by adding up the selected prediction pixel and the decoded prediction error value,

wherein the temporary prediction mode determining module temporarily determines the prediction mode used to decode a decoding target pixel P(0, 0),

based on a relation between each value of a first prediction point pixel P(0, 1), which is located immediately above the coding target pixel P(0, 0), a first reference pixel P(1, 2), which is an upper-left neighboring pixel of the first prediction point pixel P(0, 1), a second reference pixel P(0, 2), which is an immediately-above pixel of the first prediction point pixel P(0, 1), a third reference pixel P(−1, 2), which is an upper-right neighboring pixel of the first prediction point pixel P(0, 1), and a fourth reference pixel P(1, 1), which is a left neighboring pixel of the first prediction point pixel P(0, 1),

wherein, it is assumed that a pixel, whose difference value from the first prediction point pixel P(0, 1) is minimum, is the first reference pixel P(1, 2),

when a first difference value between the first prediction point pixel P(0, 1) and the first reference pixel P(1, 2) is greater than or equal to a second difference value between the second reference pixel P(0, 2) and the fourth reference pixel P(1, 1), the temporary prediction mode determining module sets a value, indicating an upper-left prediction, to the temporary prediction mode index, and

when the first difference value is less than the second difference value, the temporary prediction mode determining module sets a value, indicating possibility that the first prediction point pixel P(0, 1) is an upper-left vertex pixel of a block forming a checker pattern, to the temporary prediction mode index.