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//
// Copyright © 2020 Arm Ltd and Contributors. All rights reserved.
// SPDX-License-Identifier: MIT
//
#include "NonMaxSuppression.hpp"
#include <algorithm>
namespace od
{
static std::vector<unsigned int> GenerateRangeK(unsigned int k)
{
std::vector<unsigned int> range(k);
std::iota(range.begin(), range.end(), 0);
return range;
}
/**
* @brief Returns the intersection over union for two bounding boxes
*
* @param[in] First detect containing bounding box.
* @param[in] Second detect containing bounding box.
* @return Calculated intersection over union.
*
*/
static double IntersectionOverUnion(DetectedObject& detect1, DetectedObject& detect2)
{
uint32_t area1 = (detect1.GetBoundingBox().GetHeight() * detect1.GetBoundingBox().GetWidth());
uint32_t area2 = (detect2.GetBoundingBox().GetHeight() * detect2.GetBoundingBox().GetWidth());
float yMinIntersection = std::max(detect1.GetBoundingBox().GetY(), detect2.GetBoundingBox().GetY());
float xMinIntersection = std::max(detect1.GetBoundingBox().GetX(), detect2.GetBoundingBox().GetX());
float yMaxIntersection = std::min(detect1.GetBoundingBox().GetY() + detect1.GetBoundingBox().GetHeight(),
detect2.GetBoundingBox().GetY() + detect2.GetBoundingBox().GetHeight());
float xMaxIntersection = std::min(detect1.GetBoundingBox().GetX() + detect1.GetBoundingBox().GetWidth(),
detect2.GetBoundingBox().GetX() + detect2.GetBoundingBox().GetWidth());
double areaIntersection = std::max(yMaxIntersection - yMinIntersection, 0.0f) *
std::max(xMaxIntersection - xMinIntersection, 0.0f);
double areaUnion = area1 + area2 - areaIntersection;
return areaIntersection / areaUnion;
}
std::vector<int> NonMaxSuppression(DetectedObjects& inputDetections, float iouThresh)
{
// Sort indicies of detections by highest score to lowest.
std::vector<unsigned int> sortedIndicies = GenerateRangeK(inputDetections.size());
std::sort(sortedIndicies.begin(), sortedIndicies.end(),
[&inputDetections](int idx1, int idx2)
{
return inputDetections[idx1].GetScore() > inputDetections[idx2].GetScore();
});
std::vector<bool> visited(inputDetections.size(), false);
std::vector<int> outputIndiciesAfterNMS;
for (int i=0; i < inputDetections.size(); ++i)
{
// Each new unvisited detect should be kept.
if (!visited[sortedIndicies[i]])
{
outputIndiciesAfterNMS.emplace_back(sortedIndicies[i]);
visited[sortedIndicies[i]] = true;
}
// Look for detections to suppress.
for (int j=i+1; j<inputDetections.size(); ++j)
{
// Skip if already kept or suppressed.
if (!visited[sortedIndicies[j]])
{
// Detects must have the same label to be suppressed.
if (inputDetections[sortedIndicies[j]].GetLabel() == inputDetections[sortedIndicies[i]].GetLabel())
{
auto iou = IntersectionOverUnion(inputDetections[sortedIndicies[i]],
inputDetections[sortedIndicies[j]]);
if (iou > iouThresh)
{
visited[sortedIndicies[j]] = true;
}
}
}
}
}
return outputIndiciesAfterNMS;
}
} // namespace od
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