Implements #41 colour correction

Allows gamma and temperature to be specified for each net or snapshot source independently. Todo: allow vision nodes to apply correction on GPU (maybe), and automate the colour calibration by automatic discovery of correct gamma and temperature values.

components/rgbd-sources/src/colour.cpp

+#include "colour.hpp"
+
+#include <vector>
+#include <tuple>
+
+using std::vector;
+
+static void gammaCorrection(const cv::Mat &img, const double gamma_){
+	using namespace cv;
+
+    Mat lookUpTable(1, 256, CV_8U);
+    uchar* p = lookUpTable.ptr();
+    for( int i = 0; i < 256; ++i)
+        p[i] = saturate_cast<uchar>(pow(i / 255.0, gamma_) * 255.0);
+
+    Mat res = img.clone();
+    LUT(img, lookUpTable, img);
+}
+
+static const std::vector<std::tuple<uchar,uchar,uchar>> kelvin_table = {
+    {255,56,0},		// 1000
+    {255,109,0},		// 1500
+    {255,137,18},		// 2000
+    {255,161,72},		// 2500
+    {255,180,107},	// 3000
+    {255,196,137},	// 3500
+    {255,209,163},	// 4000
+    {255,219,186},	// 4500
+    {255,228,206},	// 5000
+    {255,236,224},	// 5500
+    {255,243,239},	// 6000
+    {255,249,253},	// 6500
+    {245,243,255},	// 7000
+    {235,238,255},	// 7500
+    {227,233,255},	// 8000
+    {220,229,255},	// 8500
+    {214,225,255},	// 9000
+    {208,222,255},	// 9500
+    {204,219,255}};	// 10000
+
+template <int C>
+inline float kelvinFactor(int temp) {
+	int index = (temp / 500) - 2;
+	if (index >= kelvin_table.size()) index = kelvin_table.size();
+	else if (index < 0) index = 0;
+	return (float)std::get<C>(kelvin_table[index]) / 255.0f;
+}
+
+void ftl::rgbd::colourCorrection(cv::Mat &img, float gamma, int temp) {
+	using namespace cv;
+
+	Mat lutRed(1, 256, CV_8U);
+	Mat lutGreen(1, 256, CV_8U);
+	Mat lutBlue(1, 256, CV_8U);
+
+	// TODO(Nick): Cache these lookup tables if used every frame...
+    uchar* pr = lutRed.ptr();
+	uchar* pg = lutGreen.ptr();
+	uchar* pb = lutBlue.ptr();
+    for( int i = 0; i < 256; ++i) {
+        float g = pow(i / 255.0f, gamma) * 255.0f;
+		pr[i] = saturate_cast<uchar>(g * kelvinFactor<2>(temp));
+		pg[i] = saturate_cast<uchar>(g * kelvinFactor<1>(temp));
+		pb[i] = saturate_cast<uchar>(g * kelvinFactor<0>(temp));
+	}
+
+	vector<Mat> channels(3);
+	split(img, channels);
+    LUT(channels[0], lutBlue, channels[0]);
+	LUT(channels[1], lutGreen, channels[1]);
+	LUT(channels[2], lutRed, channels[2]);
+	merge(channels, img);
+}