Initial commit: scene-actor-extraction pipeline

Source (KPN++ pipeline nodes, ArcFace embedders, SCRFD/YuNet detectors,
gallery builder), build scripts, and eval artifacts.

- external/KPN as a git submodule (gitea.tourolle.paris/dtourolle/KPN)
- ONNX models tracked via Git LFS (models/*.onnx)
- generated outputs, TensorRT engines, reference repos, and media ignored

src/face_utils.hpp

@@ -0,0 +1,36 @@
+#pragma once
+#include "types.hpp"
+
+#include <opencv2/calib3d.hpp>
+#include <opencv2/imgproc.hpp>
+
+#include <cmath>
+
+// ── align_face ────────────────────────────────────────────────────────────────
+// Produces a 112×112 BGR crop using the ArcFace 5-point similarity transform.
+// Returns an empty Mat if the affine fit fails (degenerate detection).
+inline cv::Mat align_face(const cv::Mat& img,
+                           const std::array<cv::Point2f, 5>& landmarks) {
+    std::vector<cv::Point2f> src(landmarks.begin(), landmarks.end());
+    std::vector<cv::Point2f> dst(5);
+    for (int i = 0; i < 5; ++i) dst[i] = {kArcFaceRef[i][0], kArcFaceRef[i][1]};
+
+    cv::Mat M = cv::estimateAffinePartial2D(src, dst, cv::noArray(), cv::RANSAC, 3.0);
+    if (M.empty()) return {};
+
+    cv::Mat crop;
+    cv::warpAffine(img, crop, M, {112, 112},
+                   cv::INTER_LINEAR, cv::BORDER_CONSTANT, {0, 0, 0});
+    return crop;
+}
+
+// ── l2_normalise ──────────────────────────────────────────────────────────────
+inline Embedding l2_normalise(const float* row) {
+    float norm = 0.f;
+    for (int d = 0; d < 512; ++d) norm += row[d] * row[d];
+    norm = std::sqrt(norm);
+    if (norm < 1e-6f) norm = 1e-6f;
+    Embedding emb;
+    for (int d = 0; d < 512; ++d) emb[d] = row[d] / norm;
+    return emb;
+}