Moving image coding device, moving image decoding device, and program

1. A moving image encoding device that performs encoding by converting and quantizing a prediction residual difference obtained by applying an interframe prediction or an intraframe prediction to each encoding tree block, which is a divided unit of a frame given by means of equirectangular projection, for each encoding block constituting the encoding tree block, the moving image encoding device comprising:

a calculation unit configured to calculate a quantization parameter (QP) to be applied to the encoding block on the basis of a pixel value of a pre-coding block and a position of the encoding block in the frame;

a prediction unit configured to obtain a prediction value (QP [prediction]) by predicting the quantization parameter (QP) to be applied on the basis of a quantization parameter calculated by the calculation unit with respect to a left neighboring block, an upper neighboring block, or an already encoded block of the encoding block;

a correction unit configured to correct the prediction value (QP [prediction]) and obtains a correction value (QP) [prediction] [correction]) when a condition is satisfied where the encoding block is positioned at a left end of the frame and the left neighboring block and the upper neighboring block belong to encoding tree blocks that are different from the encoding tree block to which the encoding block belongs, and that obtains the prediction value (QP [prediction]) as a correction value (QP [prediction] [correction]) when the condition is not satisfied; and

an encoding unit configured to encode a difference between the correction value (QP [correction] [prediction]) and the quantization parameter (QP) to be applied.

2. A moving image encoding device that performs encoding by converting and quantizing a prediction residual difference obtained by applying an interframe prediction or an intraframe prediction to each encoding tree block, which is a divided unit of a frame given by means of equirectangular projection, for each encoding block constituting the encoding tree block, the moving image encoding device comprising:

a prediction unit configured to obtain a prediction value (QP [prediction]) by predicting the quantization parameter (QP) to be applied to the encoding block on the basis of a quantization parameter calculated with respect to a left neighboring block, an upper neighboring block, or an already encoded block of the encoding block; and

an encoding unit configured to, when a condition is satisfied where the encoding block is positioned at a left end of the frame and the left neighboring block and the upper neighboring block belong to encoding tree blocks that are different from the encoding tree block to which the encoding block belongs, encodes a differential quantization parameter (ΔQP) using a predetermined function set on the basis of an area ratio at a time of projecting on a spherical surface from a rectangle in the frame by means of the equirectangular projection, and that encodes it as a quantization parameter at a vertical position in the frame of the quantization block by adding the differential quantization parameter (ΔQP) to a prediction value (QP [prediction]) obtained by the prediction unit.

3. A moving image decoding device that decodes an encoding stream obtained by converting and quantizing a prediction residual difference obtained by applying an interframe prediction or an intraframe prediction for each encoding tree block, which is a divided unit of a frame given by means of equirectangular projection, and by encoding a differential quantization parameter (ΔQP) between a quantization parameter (QP) to be applied and a prediction value (QP [prediction]) thereof, for each decoding block corresponding to the encoding block, the moving image decoding device comprising:

a prediction unit configured to predict a prediction value (QP [prediction]) of a quantization parameter (QP) to be applied to the decoding block, on the basis of the quantization parameter (QP) to be applied that has already been decoded with respect to a left neighboring block, an upper neighboring block, or an already decoded block of the decoding block;

a correction unit configured to correct the prediction value (QP [prediction]) and obtains a correction value (QP [prediction] [correction]) when a condition is satisfied where the decoding block is positioned at a left end of the frame, and the left neighboring block and the upper neighboring block belong to encoding tree blocks that are different from the encoding tree block to which the decoding block belongs, and that obtains the prediction value (QP [prediction]) as a correction value (QP [prediction] [correction]) when the condition is not satisfied; and

an addition unit configured to add a differential quantization parameter (ΔQP) of the decoding block obtained by decoding the encoding stream, to the correction value (QP [prediction] [correction]), to thereby obtain a quantization parameter (QP) to be applied to the decoding block.

4. The moving image decoding device according to claim 3 , wherein

when the decoding block satisfies the condition, the correction unit performs the correction by means of

an equation QP[prediction][correction]=QP[prediction]+COR( D [current])−COR( D [reference]) where:

the prediction value (QP [prediction]) is taken as a QP [prediction]; the correction value (QP [prediction] [correction]) is taken as a QP [prediction] [correction]; a function COR (D) is an increasing function of a distance D in a vertical direction from a center position in the vertical direction in the frame at a decoding block position; the decoding block position is taken as a distance D [current]; and the position of the already decoded block that has been referenced by the prediction unit to predict the prediction value (QP [prediction]) for the decoding block is taken as a distance D [reference].

5. The moving image decoding device according to claim 3 , wherein

when the condition is satisfied, the correction unit obtains a quantization parameter given to a slice to which the decoding block belongs, as the correction value (QP [prediction] [correction]).

6. The moving image decoding device according to claim 5 , wherein

a quantization parameter QP (D) given to the slice to which the decoding block belongs is given by means of

an equation QP( D )=QP(0)+COR( D ) where:

a function COR (D) is an increasing function of a distance D in a vertical direction from a center position in the vertical direction in the frame at a decoding block position; and a predetermined value of a quantization parameter to be applied to a center position in the vertical direction is QP (0).

7. The moving image decoding device according to claim 4 , wherein

the function COR (D) is a predetermined function that is set on the basis of an area ratio at a time of projecting on a spherical surface from a rectangle in the frame by means of the equirectangular projection, in a distance D at the position of the frame given by means of the equirectangular projection.

8. The moving image decoding device according to claim 6 , wherein

the function COR (D) is a predetermined function that is set on the basis of an area ratio at a time of projecting on a spherical surface from a rectangle in the frame by means of the equirectangular projection, in a distance D at the position of the frame given by means of the equirectangular projection.