From c5fb1155aec4eaf193fe94ebf169f7ee25bc7c33 Mon Sep 17 00:00:00 2001
From: Michael Kuc <michaelkuc6@gmail.com>
Date: Tue, 4 Sep 2018 21:05:31 +0100
Subject: [PATCH] Implemented histogram matching

---
 Build.sh   |   3 ++
 Solver.cpp | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 134 insertions(+)
 create mode 100755 Build.sh
 create mode 100644 Solver.cpp

diff --git a/Build.sh b/Build.sh
new file mode 100755
index 0000000..548ab61
--- /dev/null
+++ b/Build.sh
@@ -0,0 +1,3 @@
+#!/usr/bin/env sh
+
+g++ --std=c++17 -lopencv_core -lopencv_imgproc -lopencv_imgcodecs Solver.cpp -O3 -o Solver
diff --git a/Solver.cpp b/Solver.cpp
new file mode 100644
index 0000000..ab63c06
--- /dev/null
+++ b/Solver.cpp
@@ -0,0 +1,131 @@
+#include <opencv2/core.hpp>
+#include <opencv2/imgcodecs.hpp>
+#include <opencv2/imgproc/imgproc.hpp>
+#include <string>
+#include <iostream>
+#include <array>
+#include <fstream>
+
+using namespace cv;
+using namespace std;
+
+array<Mat, 3> getHistograms(const Mat &img);
+array<Mat, 3> getCumulativeHistograms(const Mat &img);
+array<array<uint16_t, 256>, 3> getLUT(const Mat &img, const array<Mat, 3> &refCumHist);
+Mat doLUT(const string &filename, const array<Mat, 3> &refCumHist);
+
+int main()
+{
+	const constexpr size_t digitCount = 5;
+	const constexpr size_t frameCount = 20505;
+	auto refHistos = getCumulativeHistograms(imread("Frame00001.png", IMREAD_COLOR));
+
+	for (size_t i = 2; i < frameCount; i++)
+	{
+		clog << "Processing frame: " << i << endl;
+		string filename{ "Frame" };
+		string numeric{ to_string(i) };
+
+		filename += string(digitCount - numeric.size(), '0') + numeric + ".png";
+
+		const auto lutted = doLUT(filename, refHistos);
+		imwrite("processed/" + filename, lutted);
+	}
+
+	return 0;
+}
+
+array<Mat, 3> getHistograms(const Mat &img)
+{
+	array<Mat, 3> compPlanes;
+	split(img, compPlanes);
+
+	const int histSize = 256;
+
+	const float range[]{ 0.f, 256.f };
+	const float* histRange{ range };
+	bool uniform = true, accumulate = false;
+
+	array<Mat, 3> histos;
+
+	for (size_t i = 0u; i < 3; i++)
+		calcHist(&compPlanes[i], 1, nullptr, Mat{}, histos[i], 1, &histSize, &histRange, uniform, accumulate);
+
+	for (size_t histI = 0u; histI < histos.size(); histI++)
+	{
+		double histTotal = 0.0;
+
+		for (size_t i = 0u; i < histos[histI].rows; i++)
+			histTotal += histos[histI].at<float>(i);
+
+		for (size_t i = 0u; i < histos[histI].rows; i++)
+			histos[histI].at<float>(i) /= histTotal;
+	}
+
+	return histos;
+}
+
+array<Mat, 3> getCumulativeHistograms(const Mat &img)
+{
+	auto histos = getHistograms(img);
+
+	for (size_t histI = 0; histI < histos.size(); histI++)
+	{
+		double cumulativeTotal = 0.0;
+
+		for (size_t i = 0; i < histos[histI].rows; i++)
+		{
+			cumulativeTotal += histos[histI].at<float>(i);
+			histos[histI].at<float>(i) = cumulativeTotal;
+		}
+	}
+
+	return histos;
+}
+
+array<array<uint16_t, 256>, 3> getLUT(const Mat &img, const array<Mat, 3> &refCumHist)
+{
+	const auto cumulativeHistos = getCumulativeHistograms(img);
+	array<array<uint16_t, 256>, 3> luts{};
+
+	auto comp = [](float a, float b){ return (b - a) > 1.0e-6f; };
+
+	for (size_t lut = 0; lut < luts.size(); lut++)
+	{
+		uint16_t targetBin = 1;
+
+		for (uint16_t bin = 0; bin < luts[lut].size(); bin++)
+		{
+			while (comp(refCumHist[lut].at<float>(targetBin), cumulativeHistos[lut].at<float>(bin)) && targetBin < luts[lut].size())
+				targetBin++;
+
+			luts[lut][bin] = targetBin - 1;
+		}
+	}
+
+	return luts;
+}
+
+Mat doLUT(const string &filename, const array<Mat, 3> &refCumHist)
+{
+	Mat img{ imread(filename, IMREAD_COLOR) };
+
+	if (!img.data)
+	{
+		cerr << "Failed to load image \'" << filename << "\'" << endl;
+		return {};
+	}
+
+	const auto luts = getLUT(img, refCumHist);
+
+	for (size_t x = 0; x < img.rows; x++)
+	{
+		for (size_t y = 0; y < img.cols; y++)
+		{
+			for (size_t c = 0; c < 3; c++)
+				img.at<Vec3b>(x, y)[c] = luts[c][img.at<Vec3b>(x, y)[c]];
+		}
+	}
+
+	return img;
+}