ture for which the corresponding primary coded picture precedes the target picture, in decoding order, and in which the values of frame_num, field_pic_flag (when present) and bottom_field_flag (when present) are equal to spareFrameNum[ 0], spare_field_flag and spare_bottom_field_flag[ respectively. The i-th spare picture is a decoded reference picture for which the corresponding primary coded picture precedes the - 1 )-th spare picture, in decoding order, and in which the values of frame_num, field_pic_flag (when present) and bottom_field_flag (when present) are equal to spareFrameNum[i], spare_field_flag and spare_bottom_field_flag[i], respectively. spare_area_idc| i indicates the method used to identify the spare slice group map units in the i-th spare picture. spare_area_idc[ shall be in the range of 0 to 2, inclusive. spare_area_idc| equal to 0 indicates that all slice group map units in the i-th spare picture are spare units. spare_area_idc[i] equal to 1 indicates that the value of the syntax element spare_unit_flag[ [[]] is used to identify the spare slice group map units. spare_area_idc[i equal to 2 indicates that the zero_run_length| i [[] syntax element is used to derive the values of spareUnitFlagInBoxOutOrder[i) as described below. spare_unit_flag[i][j equal to 0 indicates that the j-th slice group map unit in raster scan order in the i-th spare picture is a spare unit. spare_unit_flag[i][ equal to 1 indicates that the j-th slice group map unit in raster scan order in the i-th spare picture is not a spare unit. zero_run_length| ] is used to derive the values of spareUnitFlagInBoxOutOrder[i][j when spare_area_idc[i ] is equal to 2. In this case, the spare slice group map units identified in spareUnitFlagInBoxOutOrder[ i ][ j ] appear in counter-clockwise box-out order, as specified in clause 8.2.2.4, for each spare picture. spareUnitFlagInBoxOutOrder[ i I[ ] equal to 0 indicates that the j-th slice group map unit in counter-clockwise box-out order in the i-th spare picture is a spare unit. spareUnitFlag