nx_imgkp.nx

nx_imgkp.nx -- LOCAL FEATURES: FAST corners + BRIEF binary descriptors, integer, deterministic. The global descriptors (dHash, edge-orientation layout) hit a hard ceiling the ruler MEASURED: crop-30pct = 562, letterbox = 656 permille. That ceiling is structural -- a global fingerprint summarises the WHOLE frame, so removing a third of the pixels or padding a border changes it no matter how the summary is computed. TinEye clears exactly this by matching LOCAL regions and then checking they agree GEOMETRICALLY: even if half the picture is gone, the surviving corners still line up under one consistent shift. Every piece here is integer + zero-float + deterministic, which is the whole reason it belongs in the sovereign engine rather than an OpenCV shell-out: * FAST-9 corner test (Rosten & Drummond 2006) -- pure intensity comparisons on a Bresenham circle. * BRIEF-256 descriptor (Calonder 2010) -- 256 intensity-pair comparisons -> a 256-bit string whose distance is popcount Hamming, i.e. the nx_simhash kernel the engine already rides. * A FIXED sampling pattern regenerated from one seed every call, so index-time and query-time descriptors are bit-identical without any stored state. HONEST SCOPE, stated so it is not mistaken for more: plain BRIEF is NOT rotation-invariant. That is deliberate and correct here -- the orientation axis (mirror / quarter-turn) is already owned by the dihedral tier at the global level, and the two classes this rung targets (crop, letterbox) are pure translations. Oriented-BRIEF (ORB) to combine rotation WITH occlusion is a later refinement, filed. PACKED LAYOUT (one image's feature set as a flat i64 block, so it fits the tier vtable's fixed descriptor slot): out[0] = keypoint count; then KP_MAX records of 6 i64 each = [x, y, d0,d1,d2,d3]. genealogy_id: rosten_2006_fast + calonder_2010_brief. license_tier: ORIGINAL