Image decoding device, an image encoding device and a decoding method
Even in a case in which a color format is a format other than 4:2:0, an image coding device and an image decoding device capable of accurately locating a reference pixel position in inter-layer image prediction are realized. A hierarchical moving image decoding device ( 1 ) includes a parameter set decoding section ( 12 ) that decodes a scaled reference layer offset syntax that is coded in a chroma pixel unit and a predicted image generation section ( 1442 ) that derives a scale based on a scaled reference layer offset which is a product of the scaled reference layer offset syntax and a luminance chroma size ratio of a target layer picture and generates a predicted image.
1. An image decoding device for decoding coded data, the image decoding device comprising:
a parameter set decoding circuit derives a luma chroma width ratio and a luma chroma height ratio depending upon a chroma format, which is specified through a color format identifier; and
a predicted image generation circuit that generates an inter-layer predicted picture using a reference layer picture,
wherein:
the parameter set decoding circuit decodes a scaled reference layer left offset syntax element and a scaled reference layer top offset syntax element in a parameter set,
the predicted image generation circuit derives a reference position, which specifies a reference layer position in unit of 1/16-th sample, by using (i) a scaled reference layer left offset, (ii) a scaled reference layer top offset, (iii) a reference layer left offset, (iv) a reference layer top offset, (v) a horizontal scale and a vertical scale and (vi) a sample position of a current picture,
the scaled reference layer left offset is equal to a value of the scaled reference layer left offset syntax element multiplied by the luma chroma width ratio,
the scaled reference layer top offset is equal to a value of the scaled reference layer top offset syntax element multiplied by the luma chroma height ratio,
the reference layer left offset is derived by using the scaled reference layer left offset syntax element and the luma chroma width ratio,
the reference layer top offset is derived by using scaled reference layer top offset syntax element and the luma chroma height ratio,
the horizontal scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element, and
the vertical scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element.
2. An image encoding device for encoding data, the image encoding device comprising:
a parameter set encoding circuit derives a luma chroma width ratio and a luma chroma height ratio depending upon a chroma format, which is specified through a color format identifier; and
a predicted image generation circuit that generates an inter-layer predicted picture using a reference layer picture,
wherein:
the parameter set encoding circuit encodes a scaled reference layer left offset syntax element and a scaled reference layer top offset syntax element in a parameter set,
the predicted image generation circuit derives a reference position, which specifies a reference layer position in unit of 1/16-th sample, by using (i) a scaled reference layer left offset, (ii) a scaled reference layer top offset, (iii) a reference layer left offset, (iv) a reference layer top offset, (v) a horizontal scale and a vertical scale and (vi) a sample position of a current picture,
the scaled reference layer left offset is equal to a value of the scaled reference layer left offset syntax element multiplied by the luma chroma width ratio,
the scaled reference layer top offset is equal to a value of the scaled reference layer top offset syntax element multiplied by the luma chroma height ratio,
the reference layer left offset is derived by using the scaled reference layer left offset syntax element and the luma chroma width ratio,
the reference layer top offset is derived by using the scaled reference layer top offset syntax element and the luma chroma height ratio,
the horizontal scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element, and
the vertical scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element.
3. A decoding method for decoding coded data, the decoding method including:
deriving a luma chroma width ratio and a luma chroma height ratio depending upon a chroma format, which is specified through a color format identifier;
generating an inter-layer predicted picture using a reference layer picture;
decoding a scaled reference layer left offset syntax element and a scaled reference layer top offset syntax element in a parameter set; and
deriving a reference position, which specifies a reference layer position in unit of 1/16-th sample, by using (i) a scaled reference layer left offset, (ii) a scaled reference layer top offset, (iii) a reference layer left offset, (iv) a reference layer top offset, (v) a horizontal scale and a vertical scale and (vi) a sample position of a current picture, wherein
the scaled reference layer left offset is equal to a value the scaled reference layer left offset syntax element multiplied by the luma chroma width ratio,
the scaled reference layer top offset is equal to a value of the scaled reference layer top offset syntax element multiplied by the luma chroma height ratio,
the reference layer left offset is derived by using the scaled reference layer left offset syntax element and the luma chroma width ratio,
the reference layer top offset is derived by using the scaled reference layer top offset syntax element and the luma chroma height ratio,
the horizontal scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element, and
the vertical scale is derived by using the scaled reference layer left offset syntax element and the scaled reference layer top offset syntax element.