Add first proof of concept

CMakeLists.txt

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+cmake_minimum_required(VERSION 2.8.3)
+project(papillon)
+
+find_package(catkin REQUIRED COMPONENTS
+  roscpp
+  std_msgs
+  image_transport
+  cv_bridge
+)
+find_package(OpenCV)
+
+catkin_package(CATKIN_DEPENDS
+  roscpp
+  std_msgs
+  image_transport
+  cv_bridge
+)
+
+include_directories  (${catkin_INCLUDE_DIRS})
+
+add_executable       (papillon src/papillon.cpp)
+target_link_libraries(papillon ${catkin_LIBRARIES})
+set_property         (TARGET papillon APPEND PROPERTY INCLUDE_DIRECTORIES ${OpenCV_INCLUDE_DIRS})
+set_property         (TARGET papillon APPEND PROPERTY INCLUDE_DIRECTORIES ${catkin_INCLUDE_DIRS})
+set_property         (TARGET papillon APPEND PROPERTY LINK_LIBRARIES      ${OpenCV_LIBRARIES})
+
+
+install(TARGETS papillon DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION})
+
+add_definitions(-Wall -std=c++11)

package.xml

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+<?xml version="1.0"?>
+<package>
+  <name>papillon</name>
+  <version>0.0.0</version>
+  <description>Papillon : les drones font la chenille</description>
+
+  <!-- One maintainer tag required, multiple allowed, one person per tag -->
+  <!-- Example:  -->
+  <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> -->
+  <maintainer email="goulven.kermarec@metz.supelec.fr">Goulven</maintainer>
+  <maintainer email="jean-christophe.carli@metz.supelec.fr">JC</maintainer>
+
+
+  <!-- One license tag required, multiple allowed, one license per tag -->
+  <!-- Commonly used license strings: -->
+  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
+  <license>TODO</license>
+
+
+  <!-- Url tags are optional, but mutiple are allowed, one per tag -->
+  <!-- Optional attribute type can be: website, bugtracker, or repository -->
+  <!-- Example: -->
+  <!-- <url type="website">http://wiki.ros.org/test-opencv</url> -->
+
+
+  <!-- Author tags are optional, mutiple are allowed, one per tag -->
+  <!-- Authors do not have to be maintianers, but could be -->
+  <!-- Example: -->
+  <!-- <author email="jane.doe@example.com">Jane Doe</author> -->
+
+
+  <!-- The *_depend tags are used to specify dependencies -->
+  <!-- Dependencies can be catkin packages or system dependencies -->
+  <!-- Examples: -->
+  <!-- Use build_depend for packages you need at compile time: -->
+  <!--   <build_depend>message_generation</build_depend> -->
+  <!-- Use buildtool_depend for build tool packages: -->
+  <!--   <buildtool_depend>catkin</buildtool_depend> -->
+  <!-- Use run_depend for packages you need at runtime: -->
+  <!--   <run_depend>message_runtime</run_depend> -->
+  <!-- Use test_depend for packages you need only for testing: -->
+  <!--   <test_depend>gtest</test_depend> -->
+  <buildtool_depend>catkin</buildtool_depend>
+  <build_depend>roscpp</build_depend>
+  <build_depend>std_msgs</build_depend>
+  <build_depend>image_transport</build_depend>
+  <build_depend>cv_bridge</build_depend>
+  <run_depend>roscpp</run_depend>
+  <run_depend>std_msgs</run_depend>
+  <run_depend>image_transport</run_depend>
+  <run_depend>cv_bridge</run_depend>
+
+
+
+  <!-- The export tag contains other, unspecified, tags -->
+  <export>
+    <!-- Other tools can request additional information be placed here -->
+
+  </export>
+</package>

src/papillon.cpp

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+#include "ros/ros.h"
+#include <image_transport/image_transport.h>
+#include <cv_bridge/cv_bridge.h>
+#include <sensor_msgs/image_encodings.h>
+
+#include <opencv/cv.h>
+
+#include <sstream>
+
+using namespace cv;
+using namespace std;
+
+class Traite_image {
+	public:
+		Mat prev;
+		bool first = true;
+		int resize_f = 8;
+
+		ros::NodeHandle n;
+
+		image_transport::ImageTransport it;
+		image_transport::Publisher      pub;
+		image_transport::Subscriber     sub;
+
+
+		Traite_image() : n("~"),it(n) {
+			pub = it.advertise("/image_out", 1);
+			sub = it.subscribe("/usb_cam/image_raw", 1, [this](const sensor_msgs::ImageConstPtr& img) -> void { this->on_image(img);},ros::VoidPtr(),image_transport::TransportHints("compressed"));
+		}
+
+
+		// This processes an image and publishes the result.
+		void on_image(const sensor_msgs::ImageConstPtr& msg) {
+
+			cv_bridge::CvImageConstPtr bridge_input;
+			try {
+				bridge_input = cv_bridge::toCvShare(msg,sensor_msgs::image_encodings::RGB8);
+			}
+			catch (Exception& e) {
+				std::ostringstream errstr;
+				errstr << "cv_bridge exception caught: " << e.what();
+				return;
+			}
+
+			//Mat& input  = const_cast<Mat&>(bridge_input->image);
+			const Mat& input = bridge_input->image;
+			Mat next;
+			resize(input, next, Size(input.size().width/resize_f, input.size().height/resize_f));
+			cvtColor(next, next, CV_BGR2GRAY);
+			Mat output; //   (input.rows, input.cols, CV_32FC2);
+			ROS_INFO("got input");
+			if (first) {
+				prev = next.clone();
+				first = false;
+				ROS_INFO("first done");
+			}
+
+			//unsigned int size           = input.rows * input.cols * 3;
+			//unsigned char* begin_input  = (unsigned char*)(input.data);
+			//unsigned char* end_input    = (unsigned char*)(input.data) + size;
+			//unsigned char* out          = (unsigned char*)(output.data);
+			//unsigned char* in           = begin_input;
+
+			// This is an efficient way to process each channel in each pixel,
+			// with an iterator taste.
+			//while(in != end_input) {
+			//  *(out++) = *(ptr_prev) - *(in);
+			//  *(ptr_prev++) = *(in++);
+			//}
+
+			Mat_<Point2f> flow;
+			Ptr<DenseOpticalFlow> tvl1 = createOptFlow_DualTVL1();
+
+			tvl1->calc(prev, next, flow);
+
+			drawOpticalFlow(flow, output);
+
+			pub.publish(cv_bridge::CvImage(msg->header, "rgb8", output).toImageMsg());
+			// bridge_input is handled by a smart-pointer. No explicit delete needed.
+
+			ROS_INFO("pub");
+
+			prev = next.clone();
+		}
+
+		inline bool isFlowCorrect(Point2f u)
+		{
+			return !cvIsNaN(u.x) && !cvIsNaN(u.y) && fabs(u.x) < 1e9 && fabs(u.y) < 1e9;
+		}
+
+		Vec3b computeColor(float fx, float fy)
+		{
+			static bool first = true;
+
+			// relative lengths of color transitions:
+			// these are chosen based on perceptual similarity
+			// (e.g. one can distinguish more shades between red and yellow
+			//  than between yellow and green)
+			const int RY = 15;
+			const int YG = 6;
+			const int GC = 4;
+			const int CB = 11;
+			const int BM = 13;
+			const int MR = 6;
+			const int NCOLS = RY + YG + GC + CB + BM + MR;
+			static Vec3i colorWheel[NCOLS];
+
+			if (first)
+			{
+				int k = 0;
+
+				for (int i = 0; i < RY; ++i, ++k)
+					colorWheel[k] = Vec3i(255, 255 * i / RY, 0);
+
+				for (int i = 0; i < YG; ++i, ++k)
+					colorWheel[k] = Vec3i(255 - 255 * i / YG, 255, 0);
+
+				for (int i = 0; i < GC; ++i, ++k)
+					colorWheel[k] = Vec3i(0, 255, 255 * i / GC);
+
+				for (int i = 0; i < CB; ++i, ++k)
+					colorWheel[k] = Vec3i(0, 255 - 255 * i / CB, 255);
+
+				for (int i = 0; i < BM; ++i, ++k)
+					colorWheel[k] = Vec3i(255 * i / BM, 0, 255);
+
+				for (int i = 0; i < MR; ++i, ++k)
+					colorWheel[k] = Vec3i(255, 0, 255 - 255 * i / MR);
+
+				first = false;
+			}
+
+			const float rad = sqrt(fx * fx + fy * fy);
+			const float a = atan2(-fy, -fx) / (float)CV_PI;
+
+			const float fk = (a + 1.0f) / 2.0f * (NCOLS - 1);
+			const int k0 = static_cast<int>(fk);
+			const int k1 = (k0 + 1) % NCOLS;
+			const float f = fk - k0;
+
+			Vec3b pix;
+
+			for (int b = 0; b < 3; b++)
+			{
+				const float col0 = colorWheel[k0][b] / 255.f;
+				const float col1 = colorWheel[k1][b] / 255.f;
+
+				float col = (1 - f) * col0 + f * col1;
+
+				if (rad <= 1)
+					col = 1 - rad * (1 - col); // increase saturation with radius
+				else
+					col *= .75; // out of range
+
+				pix[2 - b] = static_cast<uchar>(255.f * col);
+			}
+
+			return pix;
+		}
+
+		void drawOpticalFlow(const Mat_<Point2f>& flow, Mat& dst, float maxmotion = -1)
+		{
+			dst.create(flow.size(), CV_8UC3);
+			dst.setTo(Scalar::all(0));
+
+			// determine motion range:
+			float maxrad = maxmotion;
+
+			if (maxmotion <= 0)
+			{
+				maxrad = 1;
+				for (int y = 0; y < flow.rows; ++y)
+				{
+					for (int x = 0; x < flow.cols; ++x)
+					{
+						Point2f u = flow(y, x);
+
+						if (!isFlowCorrect(u))
+							continue;
+
+						maxrad = max(maxrad, sqrt(u.x * u.x + u.y * u.y));
+					}
+				}
+			}
+
+			for (int y = 0; y < flow.rows; ++y)
+			{
+				for (int x = 0; x < flow.cols; ++x)
+				{
+					Point2f u = flow(y, x);
+
+					if (isFlowCorrect(u))
+						dst.at<Vec3b>(y, x) = computeColor(u.x / maxrad, u.y / maxrad);
+				}
+			}
+		}
+
+};
+
+
+int main(int argc, char **argv)
+{
+	ros::init(argc, argv, "test_opencv");
+	Traite_image dataset=Traite_image();
+	ros::spin();
+
+	return 0;
+}