nx_zigzag.nx

nx_zigzag.nx -- canonical 8x8 zigzag scan order (JPEG/MPEG/H.264). After a 2D DCT, energy concentrates in the low-frequency corner (top-left); high-frequency coefficients are mostly zero after quantisation. The zigzag scan re-orders the 64 coefficients so low-frequency entries come first and high-frequency entries last, turning sparse 8x8 blocks into 64-element vectors with long runs of zeros at the tail -- perfect for run-length encoding. Layout (row-major position -> position in zigzag stream): 0, 1, 5, 6, 14, 15, 27, 28, 2, 4, 7, 13, 16, 26, 29, 42, 3, 8, 12, 17, 25, 30, 41, 43, 9, 11, 18, 24, 31, 40, 44, 53, 10, 19, 23, 32, 39, 45, 52, 54, 20, 22, 33, 38, 46, 51, 55, 60, 21, 34, 37, 47, 50, 56, 59, 61, 35, 36, 48, 49, 57, 58, 62, 63 Equivalently, position-in-stream k -> (row, col) via the inverse table below. We expose both directions. genealogy_id: jpeg_iso_10918_1992 + h261_itu_1990 + h263_itu_1996 + nx_dct8_q10 lineage_id: nishi_zigzag_q10