Image coding method, image decoding method, image coding apparatus, and image decoding apparatus
According to an embodiment, an image coding method is for coding an image including a luminance component and color difference components. The method includes acquiring a reference image; and generating a predicted image by interpolating the luminance component and the color difference components in the reference image according to a motion vector. If a size of a block, which is designated as a unit of the interpolation, is equal to or smaller than a predetermined first threshold value, the generating includes inhibiting a bi-directional prediction, and performing only a uni-directional prediction to generate the predicted image according to the motion vector.
1. An image coding method of coding a target image including a luminance component and color difference components, the method comprising:
acquiring a reference image; and
generating a predicted image by interpolating the luminance component and the color difference components in the reference image according to a motion vector, wherein
if a size of a block, which is designated as a unit of the interpolation, is equal to or smaller than a predetermined first threshold value, the generating includes inhibiting a bi-directional prediction, and performing only a uni-directional prediction, to generate the predicted image according to the motion vector.
2. The image coding method according to claim 1 , wherein
in the generating, if the size of the block, which is designated as a unit of the interpolation, is equal to or smaller than a second threshold value that is different from the first threshold value, the uni-directional prediction is not performed.
3. The image coding method according to claim 1 , wherein
if the size of the block, which is designated as a unit of the interpolation, is equal to or smaller than the first threshold value, the generating includes changing the bi-directional prediction to the uni-directional prediction.
4. The image coding method according to claim 1 , wherein the predicted image is generated from two reference images if the bi-directional prediction is performed and generated from a single reference image if the uni-directional prediction is performed.
5. An image coding apparatus that codes a target image including a luminance component and color difference components, the apparatus comprising:
a generating unit configured to generate a predicted image by interpolating the luminance component and the color difference components in a reference image according to a motion vector; and
a coding unit configured to code coefficient information acquired from a prediction error indicating a difference between the predicted image and to the target image, wherein
if a size of a block, which is designated as a unit of the interpolation, is equal to or smaller than a predetermined first threshold value, the generating unit inhibits a bi-directional prediction, and performs only a uni-directional prediction to generate the predicted image according to the motion vector.
6. The image coding apparatus according to claim 5 , wherein
if the size of the block, which is designated as a unit of the interpolation, is equal to or smaller than a second threshold value that is different from the first threshold value, the generating unit does not perform the uni-directional prediction.
7. The image coding apparatus according to claim 5 , wherein
if the size of the block, which is designated as a unit of the interpolation, is equal to or smaller than the first threshold value, the generating unit changes the bi-directional prediction to the uni-directional prediction.
8. The image coding apparatus according to claim 5 , wherein
the predicted image is generated from two reference images if the bi-directional prediction is performed and generated from a single reference image if the uni-directional prediction is performed.
9. The image coding apparatus according to claim 5 , wherein
the generating unit and the coding unit are implemented as a processor.
10. The image coding apparatus according to claim 5 , wherein
the generating unit and the coding unit are implemented as a circuit.