Function IOU

express/module/NMSModule.cpp:30–50

Return intersection-over-union overlap between boxes i and j

// Return intersection-over-union overlap between boxes i and j
static inline float IOU(const float* boxes, int i, int j) {
    const float yMinI = std::min<float>(boxes[i * 4 + 0], boxes[i * 4 + 2]);
    const float xMinI = std::min<float>(boxes[i * 4 + 1], boxes[i * 4 + 3]);
    const float yMaxI = std::max<float>(boxes[i * 4 + 0], boxes[i * 4 + 2]);
    const float xMaxI = std::max<float>(boxes[i * 4 + 1], boxes[i * 4 + 3]);
    const float yMinJ = std::min<float>(boxes[j * 4 + 0], boxes[j * 4 + 2]);
    const float xMinJ = std::min<float>(boxes[j * 4 + 1], boxes[j * 4 + 3]);
    const float yMaxJ = std::max<float>(boxes[j * 4 + 0], boxes[j * 4 + 2]);
    const float xMaxJ = std::max<float>(boxes[j * 4 + 1], boxes[j * 4 + 3]);
    const float areaI = (yMaxI - yMinI) * (xMaxI - xMinI);
    const float areaJ = (yMaxJ - yMinJ) * (xMaxJ - xMinJ);
    if (areaI <= 0 || areaJ <= 0)
        return 0.0;
    const float intersectionYMin = std::max<float>(yMinI, yMinJ);
    const float intersectionXMin = std::max<float>(xMinI, xMinJ);
    const float intersectionYMax = std::min<float>(yMaxI, yMaxJ);
    const float intersectionXMax = std::min<float>(xMaxI, xMaxJ);
    const float intersectionArea = std::max<float>(intersectionYMax - intersectionYMin, 0.0) *
                                   std::max<float>(intersectionXMax - intersectionXMin, 0.0);
    return intersectionArea / (areaI + areaJ - intersectionArea);
}

static void NonMaxSuppressionSingleClasssImpl(const float* boxesPtr, const float* scores, int numBoxes, int maxDetections,
                                              float iouThreshold, float scoreThreshold, std::vector<int32_t>* selected) {