| CPC H04N 19/31 (2014.11) [H04N 19/46 (2014.11); H04N 19/587 (2014.11); H04N 19/70 (2014.11); H04N 21/845 (2013.01)] | 4 Claims |

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1. An image coding method of hierarchically coding a picture group to which a plurality of pictures belong to generate a bitstream, the plurality of pictures following a random-accessible I-picture and including at least one picture located differently in coding order and display order, the image coding method comprising:
coding each of the plurality of pictures, which belongs to any one of a plurality of hierarchical layers, with reference to a picture belonging to a hierarchical layer which is same as or lower than a hierarchical layer to which the picture belongs, and without reference to a picture belonging to a hierarchical layer which is higher than the hierarchical layer to which the picture belongs; and
generating the bitstream by coding the coded pictures and time information indicating decoding times of the coded pictures,
wherein, in the coding, all low-layer pictures which are the plurality of pictures belonging to low layers and are other than highest-layer pictures belonging to a highest layer among the plurality of hierarchical layers are coded at equal intervals, and the highest-layer pictures are coded alternately with the low-layer pictures, only each of the highest-layer pictures being coded without reference to a picture belonging to a second-highest layer and following the highest-layer picture in display order,
in the generating, the time information indicating that the decoding times are set at equal intervals for the low-layer pictures is coded,
the time information indicates that decoding times of all pictures belonging to the picture group precede decoding times of all pictures belonging to a subsequent picture group which follows a subsequent I-picture following the I-picture in display order,
each of the highest-layer pictures is coded without reference to a picture immediately following in display order and belonging to an immediately-lower hierarchical layer,
the highest-layer pictures include a plurality of B-pictures, and
a lead B-picture that is leading in display order among the plurality of B-pictures included in the highest-layer pictures is coded with reference to only a picture belonging to a lowest hierarchical layer and preceding the lead B picture in display order.
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