"SimpleFlow" optical flow estimation algorithm (GSoC project) declaration in…

"SimpleFlow" optical flow estimation algorithm (GSoC project) declaration in includes, implementation, usage example, test

modules/video/doc/motion_analysis_and_object_tracking.rst

@@ -597,6 +597,48 @@ Returns background image
 See :ocv:func:`BackgroundSubtractor::getBackgroundImage`.
 
 
+calcOpticalFlowSF
+-----------
+Calculate an optical flow using "SimpleFlow" algorithm.
+
+.. ocv:function:: void calcOpticalFlowSF( Mat& prev, Mat& next, Mat& flowX, Mat& flowY, int layers, int averaging_block_size, int max_flow, double sigma_dist, double sigma_color, int postprocess_window, double sigma_dist_fix, double sigma_color_fix, double occ_thr, int upscale_averaging_radiud, double upscale_sigma_dist, double upscale_sigma_color, double speed_up_thr)
+
+    :param prev: First 8-bit 3-channel image.
+
+    :param next: Second 8-bit 3-channel image 
+
+    :param flowX: X-coordinate of estimated flow
+
+    :param flowY: Y-coordinate of estimated flow
+
+    :param layers: Number of layers
+
+    :param averaging_block_size: Size of block through which we sum up when calculate cost function for pixel
+
+    :param max_flow: maximal flow that we search at each level
+
+    :param sigma_dist: vector smooth spatial sigma parameter
+
+    :param sigma_color: vector smooth color sigma parameter
+
+    :param postprocess_window: window size for postprocess cross bilateral filter
+
+    :param sigma_dist_fix: spatial sigma for postprocess cross bilateralf filter
+
+    :param sigma_color_fix: color sigma for postprocess cross bilateral filter
+
+    :param occ_thr: threshold for detecting occlusions
+
+    :param upscale_averaging_radiud: window size for bilateral upscale operation
+
+    :param upscale_sigma_dist: spatial sigma for bilateral upscale operation
+
+    :param upscale_sigma_color: color sigma for bilateral upscale operation
+
+    :param speed_up_thr: threshold to detect point with irregular flow - where flow should be recalculated after upscale
+
+See [Tao2012]_. And site of project - http://graphics.berkeley.edu/papers/Tao-SAN-2012-05/. 
+
 .. [Bouguet00] Jean-Yves Bouguet. Pyramidal Implementation of the Lucas Kanade Feature Tracker.
 
 .. [Bradski98] Bradski, G.R. "Computer Vision Face Tracking for Use in a Perceptual User Interface", Intel, 1998
@@ -612,3 +654,5 @@ See :ocv:func:`BackgroundSubtractor::getBackgroundImage`.
 .. [Lucas81] Lucas, B., and Kanade, T. An Iterative Image Registration Technique with an Application to Stereo Vision, Proc. of 7th International Joint Conference on Artificial Intelligence (IJCAI), pp. 674-679.
 
 .. [Welch95] Greg Welch and Gary Bishop “An Introduction to the Kalman Filter”, 1995
+
+.. [Tao2012] Michael Tao, Jiamin Bai, Pushmeet Kohli and Sylvain Paris. SimpleFlow: A Non-iterative, Sublinear Optical Flow Algorithm. Computer Graphics Forum (Eurographics 2012)

modules/video/include/opencv2/video/tracking.hpp

@@ -326,7 +326,26 @@ CV_EXPORTS_W void calcOpticalFlowFarneback( InputArray prev, InputArray next,
 // that maps one 2D point set to another or one image to another.
 CV_EXPORTS_W Mat estimateRigidTransform( InputArray src, InputArray dst,
                                          bool fullAffine);
-    
+  
+//! computes dense optical flow using Simple Flow algorithm
+CV_EXPORTS_W void calcOpticalFlowSF(Mat& from, 
+                                    Mat& to, 
+                                    Mat& flowX,
+                                    Mat& flowY,
+                                    int layers,
+                                    int averaging_block_size, 
+                                    int max_flow,
+                                    double sigma_dist,
+                                    double sigma_color,
+                                    int postprocess_window, 
+                                    double sigma_dist_fix, 
+                                    double sigma_color_fix,
+                                    double occ_thr,
+                                    int upscale_averaging_radius,
+                                    double upscale_sigma_dist,
+                                    double upscale_sigma_color,
+                                    double speed_up_thr);
+
 }
 
 #endif

modules/video/src/simpleflow.cpp

+/*M///////////////////////////////////////////////////////////////////////////////////////
+//
+//  IMPORTANT: READ BEFORE DOWNLOADING, COPYING, INSTALLING OR USING.
+//
+//  By downloading, copying, installing or using the software you agree to this license.
+//  If you do not agree to this license, do not download, install,
+//  copy or use the software.
+//
+//
+//                           License Agreement
+//                For Open Source Computer Vision Library
+//
+// Copyright (C) 2000-2008, Intel Corporation, all rights reserved.
+// Copyright (C) 2009, Willow Garage Inc., all rights reserved.
+// Third party copyrights are property of their respective owners.
+//
+// Redistribution and use in source and binary forms, with or without modification,
+// are permitted provided that the following conditions are met:
+//
+//   * Redistribution's of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//
+//   * Redistribution's in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//
+//   * The name of the copyright holders may not be used to endorse or promote products
+//     derived from this software without specific prior written permission.
+//
+// This software is provided by the copyright holders and contributors "as is" and
+// any express or implied warranties, including, but not limited to, the implied
+// warranties of merchantability and fitness for a particular purpose are disclaimed.
+// In no event shall the Intel Corporation or contributors be liable for any direct,
+// indirect, incidental, special, exemplary, or consequential damages
+// (including, but not limited to, procurement of substitute goods or services;
+// loss of use, data, or profits; or business interruption) however caused
+// and on any theory of liability, whether in contract, strict liability,
+// or tort (including negligence or otherwise) arising in any way out of
+// the use of this software, even if advised of the possibility of such damage.
+//
+//M*/
+
+#include "precomp.hpp"
+#include "simpleflow.hpp"
+
+//
+// 2D dense optical flow algorithm from the following paper:
+// Michael Tao, Jiamin Bai, Pushmeet Kohli, and Sylvain Paris.
+// "SimpleFlow: A Non-iterative, Sublinear Optical Flow Algorithm"
+// Computer Graphics Forum (Eurographics 2012)
+// http://graphics.berkeley.edu/papers/Tao-SAN-2012-05/
+//
+
+namespace cv
+{
+
+WeightedCrossBilateralFilter::WeightedCrossBilateralFilter(
+  const Mat& _image,
+  int _windowSize,
+  double _sigmaDist,
+  double _sigmaColor)
+  : image(_image), 
+    windowSize(_windowSize), 
+    sigmaDist(_sigmaDist), 
+    sigmaColor(_sigmaColor) {
+    
+  expDist.resize(2*windowSize*windowSize+1);
+  const double sigmaDistSqr = 2 * sigmaDist * sigmaDist;
+  for (int i = 0; i <= 2*windowSize*windowSize; ++i) {
+    expDist[i] = exp(-i/sigmaDistSqr);
+  }
+
+  const double sigmaColorSqr = 2 * sigmaColor * sigmaColor;
+  wc.resize(image.rows);
+  for (int row = 0; row < image.rows; ++row) {
+    wc[row].resize(image.cols);
+    for (int col = 0; col < image.cols; ++col) {
+      int beginRow = max(0, row - windowSize);
+      int beginCol = max(0, col - windowSize);
+      int endRow = min(image.rows - 1, row + windowSize);
+      int endCol = min(image.cols - 1, col + windowSize);
+      wc[row][col] = build<double>(endRow - beginRow + 1, endCol - beginCol + 1);
+
+      for (int r = beginRow; r <= endRow; ++r) {
+        for (int c = beginCol; c <= endCol; ++c) {
+          wc[row][col][r - beginRow][c - beginCol] = 
+            exp(-dist(image.at<Vec3b>(row, col), 
+                      image.at<Vec3b>(r, c)) 
+                / sigmaColorSqr);
+        }
+      }
+    }
+  }
+}
+
+Mat WeightedCrossBilateralFilter::apply(Mat& matrix, Mat& weights) {
+  int rows = matrix.rows;
+  int cols = matrix.cols;
+
+  Mat result = Mat::zeros(rows, cols, CV_64F);
+  for (int row = 0; row < rows; ++row) {
+    for(int col = 0; col < cols; ++col) {
+      result.at<double>(row, col) = 
+        convolution(matrix, row, col, weights);
+    }
+  }
+  return result;
+}
+
+double WeightedCrossBilateralFilter::convolution(Mat& matrix, 
+                                                 int row, int col, 
+                                                 Mat& weights) {
+  double result = 0, weightsSum = 0;
+  int beginRow = max(0, row - windowSize);
+  int beginCol = max(0, col - windowSize);
+  int endRow = min(matrix.rows - 1, row + windowSize);
+  int endCol = min(matrix.cols - 1, col + windowSize);
+  for (int r = beginRow; r <= endRow; ++r) {
+    double* ptr = matrix.ptr<double>(r);
+    for (int c = beginCol; c <= endCol; ++c) {
+      const double w = expDist[dist(row, col, r, c)] *
+                       wc[row][col][r - beginRow][c - beginCol] *
+                       weights.at<double>(r, c);
+      result += ptr[c] * w;
+      weightsSum += w;
+    }
+  }
+  return result / weightsSum;
+}
+
+static void removeOcclusions(const Flow& flow, 
+                             const Flow& flow_inv,
+                             double occ_thr,
+                             Mat& confidence) {
+  const int rows = flow.u.rows;
+  const int cols = flow.v.cols;
+  int occlusions = 0;
+  for (int r = 0; r < rows; ++r) {
+    for (int c = 0; c < cols; ++c) {
+      if (dist(flow.u.at<double>(r, c), flow.v.at<double>(r, c),
+               -flow_inv.u.at<double>(r, c), -flow_inv.v.at<double>(r, c)) > occ_thr) {
+        confidence.at<double>(r, c) = 0;
+        occlusions++;
+      }
+    }
+  }
+}
+
+static Mat wd(int top_shift, int bottom_shift, int left_shift, int right_shift, double sigma) {
+  const double factor = 1.0 / (2.0 * sigma * sigma);
+  Mat d = Mat(top_shift + bottom_shift + 1, right_shift + left_shift + 1, CV_64F);
+  for (int dr = -top_shift, r = 0; dr <= bottom_shift; ++dr, ++r) {
+    for (int dc = -left_shift, c = 0; dc <= right_shift; ++dc, ++c) {
+      d.at<double>(r, c) = -(dr*dr + dc*dc) * factor;
+    }
+  }
+  Mat ed;
+  exp(d, ed);
+  return ed;
+}
+
+static Mat wc(const Mat& image, int r0, int c0, int top_shift, int bottom_shift, int left_shift, int right_shift, double sigma) {
+  const double factor = 1.0 / (2.0 * sigma * sigma);
+  Mat d = Mat(top_shift + bottom_shift + 1, right_shift + left_shift + 1, CV_64F);
+  for (int dr = r0-top_shift, r = 0; dr <= r0+bottom_shift; ++dr, ++r) {
+    for (int dc = c0-left_shift, c = 0; dc <= c0+right_shift; ++dc, ++c) {
+      d.at<double>(r, c) = -dist(image.at<Vec3b>(r0, c0), image.at<Vec3b>(dr, dc)) * factor;
+    }
+  }
+  Mat ed;
+  exp(d, ed);
+  return ed;
+}
+
+inline static void dist(const Mat& m1, const Mat& m2, Mat& result) {
+  const int rows = m1.rows;
+  const int cols = m1.cols;
+  for (int r = 0; r < rows; ++r) {
+    const Vec3b *m1_row = m1.ptr<Vec3b>(r);
+    const Vec3b *m2_row = m2.ptr<Vec3b>(r);
+    double* row = result.ptr<double>(r);
+    for (int c = 0; c < cols; ++c) {
+      row[c] = dist(m1_row[c], m2_row[c]);
+    }
+  }
+}
+
+static void calcOpticalFlowSingleScaleSF(const Mat& prev, 
+                                         const Mat& next,
+                                         const Mat& mask,
+                                         Flow& flow,
+                                         Mat& confidence,
+                                         int averaging_radius, 
+                                         int max_flow,
+                                         double sigma_dist,
+                                         double sigma_color) {
+  const int rows = prev.rows;
+  const int cols = prev.cols;
+  confidence = Mat::zeros(rows, cols, CV_64F);
+
+  for (int r0 = 0; r0 < rows; ++r0) {
+    for (int c0 = 0; c0 < cols; ++c0) {
+      int u0 = floor(flow.u.at<double>(r0, c0) + 0.5);
+      int v0 = floor(flow.v.at<double>(r0, c0) + 0.5);
+
+      const int min_row_shift = -min(r0 + u0, max_flow);
+      const int max_row_shift = min(rows - 1 - (r0 + u0), max_flow);
+      const int min_col_shift = -min(c0 + v0, max_flow);
+      const int max_col_shift = min(cols - 1 - (c0 + v0), max_flow);
+
+      double min_cost = DBL_MAX, best_u = u0, best_v = v0;
+
+      Mat w_full_window;
+      double w_full_window_sum;
+      Mat diff_storage;
+
+      if (r0 - averaging_radius >= 0 && 
+          r0 + averaging_radius < rows &&
+          c0 - averaging_radius >= 0 &&
+          c0 + averaging_radius < cols &&
+          mask.at<uchar>(r0, c0)) {
+          w_full_window = wd(averaging_radius, 
+                             averaging_radius, 
+                             averaging_radius, 
+                             averaging_radius, 
+                             sigma_dist).mul(
+                          wc(prev, r0, c0, 
+                             averaging_radius, 
+                             averaging_radius, 
+                             averaging_radius, 
+                             averaging_radius, 
+                             sigma_color));
+
+          w_full_window_sum = sum(w_full_window)[0];
+          diff_storage = Mat::zeros(averaging_radius*2 + 1, averaging_radius*2 + 1, CV_64F);
+      }
+
+      bool first_flow_iteration = true;
+      double sum_e, min_e;
+
+      for (int u = min_row_shift; u <= max_row_shift; ++u) {
+        for (int v = min_col_shift; v <= max_col_shift; ++v) {
+          double e = dist(prev.at<Vec3b>(r0, c0), next.at<Vec3b>(r0 + u0 + u, c0 + v0 + v));
+          if (first_flow_iteration) {
+            sum_e = e;
+            min_e = e;
+            first_flow_iteration = false;
+          } else {
+            sum_e += e;
+            min_e = std::min(min_e, e);
+          }
+          if (!mask.at<uchar>(r0, c0)) {
+            continue;
+          }
+
+          const int window_top_shift = min(r0, r0 + u + u0, averaging_radius);
+          const int window_bottom_shift = min(rows - 1 - r0, 
+                                              rows - 1 - (r0 + u + u0), 
+                                              averaging_radius);
+          const int window_left_shift = min(c0, c0 + v + v0, averaging_radius);
+          const int window_right_shift = min(cols - 1 - c0, 
+                                             cols - 1 - (c0 + v + v0), 
+                                             averaging_radius);
+
+          const Range prev_row_range(r0 - window_top_shift, r0 + window_bottom_shift + 1);
+          const Range prev_col_range(c0 - window_left_shift, c0 + window_right_shift + 1);
+
+          const Range next_row_range(r0 + u0 + u - window_top_shift, 
+                                     r0 + u0 + u + window_bottom_shift + 1);
+          const Range next_col_range(c0 + v0 + v - window_left_shift, 
+                                     c0 + v0 + v + window_right_shift + 1); 
+          
+          Mat diff2;
+          Mat w;
+          double w_sum;
+          if (window_top_shift == averaging_radius &&
+              window_bottom_shift == averaging_radius &&
+              window_left_shift == averaging_radius &&
+              window_right_shift == averaging_radius) {
+            w = w_full_window;
+            w_sum = w_full_window_sum;
+            diff2 = diff_storage;
+
+            dist(prev(prev_row_range, prev_col_range), next(next_row_range, next_col_range), diff2);
+          } else {
+            diff2 = Mat::zeros(window_bottom_shift + window_top_shift + 1,  
+                                   window_right_shift + window_left_shift + 1, CV_64F);
+            
+            dist(prev(prev_row_range, prev_col_range), next(next_row_range, next_col_range), diff2);
+
+            w = wd(window_top_shift, window_bottom_shift, window_left_shift, window_right_shift, sigma_dist).mul( 
+                wc(prev, r0, c0, window_top_shift, window_bottom_shift, window_left_shift, window_right_shift, sigma_color));
+            w_sum = sum(w)[0];
+          }
+          multiply(diff2, w, diff2);
+      
+          const double cost = sum(diff2)[0] / w_sum;
+          if (cost < min_cost) {
+            min_cost = cost;
+            best_u = u + u0;
+            best_v = v + v0;
+          }
+        }
+      }
+      int square = (max_row_shift - min_row_shift + 1) *
+                   (max_col_shift - min_col_shift + 1);
+      confidence.at<double>(r0, c0) = (square == 0) ? 0
+                                                   : sum_e / square - min_e;
+      if (mask.at<uchar>(r0, c0)) {
+        flow.u.at<double>(r0, c0) = best_u;
+        flow.v.at<double>(r0, c0) = best_v;
+      }
+    }
+  }
+}
+
+static Flow upscaleOpticalFlow(int new_rows, 
+                               int new_cols,
+                               const Mat& image,
+                               const Mat& confidence,
+                               const Flow& flow,
+                               int averaging_radius,
+                               double sigma_dist,
+                               double sigma_color) {
+  const int rows = image.rows;
+  const int cols = image.cols;
+  Flow new_flow(new_rows, new_cols);
+  for (int r = 0; r < rows; ++r) {
+    for (int c = 0; c < cols; ++c) {
+      const int window_top_shift = min(r, averaging_radius);
+      const int window_bottom_shift = min(rows - 1 - r, averaging_radius);
+      const int window_left_shift = min(c, averaging_radius);
+      const int window_right_shift = min(cols - 1 - c, averaging_radius);
+      
+      const Range row_range(r - window_top_shift, r + window_bottom_shift + 1);
+      const Range col_range(c - window_left_shift, c + window_right_shift + 1);
+      
+      const Mat w = confidence(row_range, col_range).mul(
+        wd(window_top_shift, window_bottom_shift, window_left_shift, window_right_shift, sigma_dist)).mul( 
+        wc(image, r, c, window_top_shift, window_bottom_shift, window_left_shift, window_right_shift, sigma_color));
+
+      const double w_sum = sum(w)[0];
+      double new_u, new_v;
+      if (fabs(w_sum) < 1e-9) {
+        new_u = flow.u.at<double>(r, c);
+        new_v = flow.v.at<double>(r, c);
+      } else {
+        new_u = sum(flow.u(row_range, col_range).mul(w))[0] / w_sum;
+        new_v = sum(flow.v(row_range, col_range).mul(w))[0] / w_sum;
+      }
+      
+      for (int dr = 0; dr <= 1; ++dr) {
+        int nr = 2*r + dr;
+        for (int dc = 0; dc <= 1; ++dc) {
+          int nc = 2*c + dc;
+          if (nr < new_rows && nc < new_cols) {
+            new_flow.u.at<double>(nr, nc) = 2 * new_u;
+            new_flow.v.at<double>(nr, nc) = 2 * new_v;
+          }
+        }
+      }
+    }
+  }
+  return new_flow;
+}
+
+static Mat calcIrregularityMat(const Flow& flow, int radius) {
+  const int rows = flow.u.rows;
+  const int cols = flow.v.cols;
+  Mat irregularity = Mat::zeros(rows, cols, CV_64F);
+  for (int r = 0; r < rows; ++r) {
+    const int start_row = max(0, r - radius);
+    const int end_row = min(rows - 1, r + radius);
+    for (int c = 0; c < cols; ++c) {
+      const int start_col = max(0, c - radius);
+      const int end_col = min(cols - 1, c + radius);
+      for (int dr = start_row; dr <= end_row; ++dr) {
+        for (int dc = start_col; dc <= end_col; ++dc) {
+          const double diff = dist(flow.u.at<double>(r, c), flow.v.at<double>(r, c), 
+                                   flow.u.at<double>(dr, dc), flow.v.at<double>(dr, dc));
+          if (diff > irregularity.at<double>(r, c)) {
+            irregularity.at<double>(r, c) = diff;
+          }
+        }
+      }
+    }
+  }
+  return irregularity;
+}
+
+static void selectPointsToRecalcFlow(const Flow& flow, 
+                                     int irregularity_metric_radius,
+                                     int speed_up_thr,
+                                     int curr_rows,
+                                     int curr_cols,
+                                     const Mat& prev_speed_up,
+                                     Mat& speed_up,
+                                     Mat& mask) {
+  const int prev_rows = flow.u.rows;
+  const int prev_cols = flow.v.cols;
+
+  Mat is_flow_regular = calcIrregularityMat(flow, 
+                                                irregularity_metric_radius)
+                              < speed_up_thr;
+  Mat done = Mat::zeros(prev_rows, prev_cols, CV_8U);
+  speed_up = Mat::zeros(curr_rows, curr_cols, CV_8U);
+  mask = Mat::zeros(curr_rows, curr_cols, CV_8U);
+
+  for (int r = 0; r < is_flow_regular.rows; ++r) {
+    for (int c = 0; c < is_flow_regular.cols; ++c) {
+      if (!done.at<uchar>(r, c)) {
+        if (is_flow_regular.at<uchar>(r, c) && 
+            2*r + 1 < curr_rows && 2*c + 1< curr_cols) {
+
+          bool all_flow_in_region_regular = true;
+          int speed_up_at_this_point = prev_speed_up.at<uchar>(r, c);
+          int step = (1 << speed_up_at_this_point) - 1;
+          int prev_top = r;
+          int prev_bottom = std::min(r + step, prev_rows - 1);
+          int prev_left = c;
+          int prev_right = std::min(c + step, prev_cols - 1);
+
+          for (int rr = prev_top; rr <= prev_bottom; ++rr) {
+            for (int cc = prev_left; cc <= prev_right; ++cc) {
+              done.at<uchar>(rr, cc) = 1;
+              if (!is_flow_regular.at<uchar>(rr, cc)) {
+                all_flow_in_region_regular = false;
+              }
+            }
+          }
+
+          int curr_top = std::min(2 * r, curr_rows - 1);
+          int curr_bottom = std::min(2*(r + step) + 1, curr_rows - 1);
+          int curr_left = std::min(2 * c, curr_cols - 1);
+          int curr_right = std::min(2*(c + step) + 1, curr_cols - 1);
+
+          if (all_flow_in_region_regular && 
+              curr_top != curr_bottom &&
+              curr_left != curr_right) {
+            mask.at<uchar>(curr_top, curr_left) = MASK_TRUE_VALUE;
+            mask.at<uchar>(curr_bottom, curr_left) = MASK_TRUE_VALUE;
+            mask.at<uchar>(curr_top, curr_right) = MASK_TRUE_VALUE;
+            mask.at<uchar>(curr_bottom, curr_right) = MASK_TRUE_VALUE;
+            for (int rr = curr_top; rr <= curr_bottom; ++rr) {
+              for (int cc = curr_left; cc <= curr_right; ++cc) {
+                speed_up.at<uchar>(rr, cc) = speed_up_at_this_point + 1; 
+              }
+            }
+          } else {
+            for (int rr = curr_top; rr <= curr_bottom; ++rr) {
+              for (int cc = curr_left; cc <= curr_right; ++cc) {
+                mask.at<uchar>(rr, cc) = MASK_TRUE_VALUE;
+              }
+            }
+          }
+        } else {
+          done.at<uchar>(r, c) = 1;
+          for (int dr = 0; dr <= 1; ++dr) {
+            int nr = 2*r + dr;
+            for (int dc = 0; dc <= 1; ++dc) {
+              int nc = 2*c + dc;
+              if (nr < curr_rows && nc < curr_cols) {
+                mask.at<uchar>(nr, nc) = MASK_TRUE_VALUE;
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
+static inline double extrapolateValueInRect(int height, int width,
+                                            double v11, double v12,
+                                            double v21, double v22,
+                                            int r, int c) {
+  if (r == 0 && c == 0) { return v11;}
+  if (r == 0 && c == width) { return v12;}
+  if (r == height && c == 0) { return v21;}
+  if (r == height && c == width) { return v22;}
+  
+  double qr = double(r) / height;
+  double pr = 1.0 - qr;
+  double qc = double(c) / width;
+  double pc = 1.0 - qc;
+
+  return v11*pr*pc + v12*pr*qc + v21*qr*pc + v22*qc*qr; 
+}
+                                              
+static void extrapolateFlow(Flow& flow,
+                            const Mat& speed_up) {
+  const int rows = flow.u.rows;
+  const int cols = flow.u.cols;
+  Mat done = Mat::zeros(rows, cols, CV_8U);
+  for (int r = 0; r < rows; ++r) {
+    for (int c = 0; c < cols; ++c) {
+      if (!done.at<uchar>(r, c) && speed_up.at<uchar>(r, c) > 1) {
+        int step = (1 << speed_up.at<uchar>(r, c)) - 1;
+        int top = r;
+        int bottom = std::min(r + step, rows - 1);
+        int left = c;
+        int right = std::min(c + step, cols - 1);
+
+        int height = bottom - top;
+        int width = right - left;
+        for (int rr = top; rr <= bottom; ++rr) {
+          for (int cc = left; cc <= right; ++cc) {
+            done.at<uchar>(rr, cc) = 1;
+            flow.u.at<double>(rr, cc) = extrapolateValueInRect(
+                                          height, width, 
+                                          flow.u.at<double>(top, left),
+                                          flow.u.at<double>(top, right),
+                                          flow.u.at<double>(bottom, left),
+                                          flow.u.at<double>(bottom, right),
+                                          rr-top, cc-left); 
+
+            flow.v.at<double>(rr, cc) = extrapolateValueInRect(
+                                          height, width, 
+                                          flow.v.at<double>(top, left),
+                                          flow.v.at<double>(top, right),
+                                          flow.v.at<double>(bottom, left),
+                                          flow.v.at<double>(bottom, right),
+                                          rr-top, cc-left); 
+          }
+        }
+      }
+    }
+  }
+}
+
+static void buildPyramidWithResizeMethod(Mat& src,
+                                  vector<Mat>& pyramid,
+                                  int layers,
+                                  int interpolation_type) {
+  pyramid.push_back(src);
+  for (int i = 1; i <= layers; ++i) {
+    Mat prev = pyramid[i - 1];
+    if (prev.rows <= 1 || prev.cols <= 1) {
+      break;
+    }
+
+    Mat next;
+    resize(prev, next, Size((prev.cols + 1) / 2, (prev.rows + 1) / 2), 0, 0, interpolation_type);
+    pyramid.push_back(next);
+  }
+}
+
+static Flow calcOpticalFlowSF(Mat& from, 
+                       Mat& to, 
+                       int layers,
+                       int averaging_block_size, 
+                       int max_flow,
+                       double sigma_dist,
+                       double sigma_color,
+                       int postprocess_window, 
+                       double sigma_dist_fix, 
+                       double sigma_color_fix,
+                       double occ_thr,
+                       int upscale_averaging_radius,
+                       double upscale_sigma_dist,
+                       double upscale_sigma_color,
+                       double speed_up_thr) {
+  vector<Mat> pyr_from_images;
+  vector<Mat> pyr_to_images;
+
+  buildPyramidWithResizeMethod(from, pyr_from_images, layers - 1, INTER_CUBIC);
+  buildPyramidWithResizeMethod(to, pyr_to_images, layers - 1, INTER_CUBIC);
+//  buildPyramid(from, pyr_from_images, layers - 1, BORDER_WRAP);
+//  buildPyramid(to, pyr_to_images, layers - 1, BORDER_WRAP);
+
+  if ((int)pyr_from_images.size() != layers) {
+      exit(1);
+  }
+
+  if ((int)pyr_to_images.size() != layers) {
+      exit(1);
+  }
+
+  Mat first_from_image = pyr_from_images[layers - 1];
+  Mat first_to_image = pyr_to_images[layers - 1];
+
+  Mat mask = Mat::ones(first_from_image.rows, first_from_image.cols, CV_8U);
+  Mat mask_inv = Mat::ones(first_from_image.rows, first_from_image.cols, CV_8U);
+
+  Flow flow(first_from_image.rows, first_from_image.cols);
+  Flow flow_inv(first_to_image.rows, first_to_image.cols);
+
+  Mat confidence;
+  Mat confidence_inv;
+
+  calcOpticalFlowSingleScaleSF(first_from_image, 
+                               first_to_image, 
+                               mask,
+                               flow,
+                               confidence,
+                               averaging_block_size, 
+                               max_flow, 
+                               sigma_dist, 
+                               sigma_color);
+
+  calcOpticalFlowSingleScaleSF(first_to_image, 
+                               first_from_image, 
+                               mask_inv,
+                               flow_inv,
+                               confidence_inv,
+                               averaging_block_size, 
+                               max_flow, 
+                               sigma_dist, 
+                               sigma_color);
+
+  removeOcclusions(flow, 
+                   flow_inv,
+                   occ_thr,
+                   confidence);
+
+  removeOcclusions(flow_inv, 
+                   flow,
+                   occ_thr,
+                   confidence_inv);
+
+  Mat speed_up = Mat::zeros(first_from_image.rows, first_from_image.cols, CV_8U);
+  Mat speed_up_inv = Mat::zeros(first_from_image.rows, first_from_image.cols, CV_8U);
+
+  for (int curr_layer = layers - 2; curr_layer >= 0; --curr_layer) {
+    const Mat curr_from = pyr_from_images[curr_layer];
+    const Mat curr_to = pyr_to_images[curr_layer];
+    const Mat prev_from = pyr_from_images[curr_layer + 1];
+    const Mat prev_to = pyr_to_images[curr_layer + 1];
+
+    const int curr_rows = curr_from.rows;
+    const int curr_cols = curr_from.cols;
+
+    Mat new_speed_up, new_speed_up_inv;
+
+    selectPointsToRecalcFlow(flow,
+                             averaging_block_size,
+                             speed_up_thr,
+                             curr_rows,
+                             curr_cols,
+                             speed_up,
+                             new_speed_up,
+                             mask);
+
+    int points_to_recalculate = sum(mask)[0] / MASK_TRUE_VALUE;
+
+    selectPointsToRecalcFlow(flow_inv,
+                             averaging_block_size,
+                             speed_up_thr,
+                             curr_rows,
+                             curr_cols,
+                             speed_up_inv,
+                             new_speed_up_inv,
+                             mask_inv);
+
+    points_to_recalculate = sum(mask_inv)[0] / MASK_TRUE_VALUE;
+
+    speed_up = new_speed_up;
+    speed_up_inv = new_speed_up_inv;
+
+    flow = upscaleOpticalFlow(curr_rows,
+                              curr_cols,
+                              prev_from,
+                              confidence,
+                              flow, 
+                              upscale_averaging_radius,
+                              upscale_sigma_dist,
+                              upscale_sigma_color);
+
+    flow_inv = upscaleOpticalFlow(curr_rows,
+                                  curr_cols,
+                                  prev_to,
+                                  confidence_inv,
+                                  flow_inv,
+                                  upscale_averaging_radius,
+                                  upscale_sigma_dist,
+                                  upscale_sigma_color);
+
+    calcOpticalFlowSingleScaleSF(curr_from, 
+                                 curr_to, 
+                                 mask,
+                                 flow,
+                                 confidence,
+                                 averaging_block_size, 
+                                 max_flow, 
+                                 sigma_dist, 
+                                 sigma_color);
+
+    calcOpticalFlowSingleScaleSF(curr_to,
+                                 curr_from, 
+                                 mask_inv,
+                                 flow_inv,
+                                 confidence_inv,
+                                 averaging_block_size, 
+                                 max_flow, 
+                                 sigma_dist, 
+                                 sigma_color);
+
+    extrapolateFlow(flow, speed_up);
+    extrapolateFlow(flow_inv, speed_up_inv);
+
+    removeOcclusions(flow, flow_inv, occ_thr, confidence);
+    removeOcclusions(flow_inv, flow, occ_thr, confidence_inv);
+  }
+
+  WeightedCrossBilateralFilter filter_postprocess(pyr_from_images[0], 
+                                                  postprocess_window,
+                                                  sigma_dist_fix,
+                                                  sigma_color_fix);
+
+  flow.u = filter_postprocess.apply(flow.u, confidence);
+  flow.v = filter_postprocess.apply(flow.v, confidence);
+
+  Mat blured_u, blured_v;
+  GaussianBlur(flow.u, blured_u, Size(3, 3), 5);
+  GaussianBlur(flow.v, blured_v, Size(3, 3), 5);
+
+  return Flow(blured_v, blured_u);
+}
+
+void calcOpticalFlowSF(Mat& from, 
+                       Mat& to, 
+                       Mat& flowX, 
+                       Mat& flowY,
+                       int layers,
+                       int averaging_block_size, 
+                       int max_flow,
+                       double sigma_dist,
+                       double sigma_color,
+                       int postprocess_window, 
+                       double sigma_dist_fix, 
+                       double sigma_color_fix,
+                       double occ_thr,
+                       int upscale_averaging_radius,
+                       double upscale_sigma_dist,
+                       double upscale_sigma_color,
+                       double speed_up_thr) {
+
+  Flow flow = calcOpticalFlowSF(from, to, 
+                                layers,
+                                averaging_block_size,
+                                max_flow,
+                                sigma_dist,
+                                sigma_color,
+                                postprocess_window,
+                                sigma_dist_fix,
+                                sigma_color_fix,
+                                occ_thr,
+                                upscale_averaging_radius,
+                                upscale_sigma_dist,
+                                upscale_sigma_color,
+                                speed_up_thr);
+  flowX = flow.u;
+  flowY = flow.v;
+}
+
+}
+

modules/video/src/simpleflow.hpp

+/*M///////////////////////////////////////////////////////////////////////////////////////
+//
+//  IMPORTANT: READ BEFORE DOWNLOADING, COPYING, INSTALLING OR USING.
+//
+//  By downloading, copying, installing or using the software you agree to this license.
+//  If you do not agree to this license, do not download, install,
+//  copy or use the software.
+//
+//
+//                          License Agreement
+//                For Open Source Computer Vision Library
+//
+// Copyright (C) 2000-2008, Intel Corporation, all rights reserved.
+// Copyright (C) 2009, Willow Garage Inc., all rights reserved.
+// Third party copyrights are property of their respective owners.
+//
+// Redistribution and use in source and binary forms, with or without modification,
+// are permitted provided that the following conditions are met:
+//
+//   * Redistribution's of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//
+//   * Redistribution's in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//
+//   * The name of the copyright holders may not be used to endorse or promote products
+//     derived from this software without specific prior written permission.
+//
+// This software is provided by the copyright holders and contributors "as is" and
+// any express or implied warranties, including, but not limited to, the implied
+// warranties of merchantability and fitness for a particular purpose are disclaimed.
+// In no event shall the Intel Corporation or contributors be liable for any direct,
+// indirect, incidental, special, exemplary, or consequential damages
+// (including, but not limited to, procurement of substitute goods or services;
+// loss of use, data, or profits; or business interruption) however caused
+// and on any theory of liability, whether in contract, strict liability,
+// or tort (including negligence or otherwise) arising in any way out of
+// the use of this software, even if advised of the possibility of such damage.
+//
+//M*/
+
+#ifndef __OPENCV_SIMPLEFLOW_H__
+#define __OPENCV_SIMPLEFLOW_H__
+
+#include <vector>
+
+using namespace std;
+
+#define MASK_TRUE_VALUE 255
+#define UNKNOWN_FLOW_THRESH 1e9
+
+namespace cv {
+
+struct Flow {
+  Mat u, v;
+
+  Flow() {;}
+
+  Flow(Mat& _u, Mat& _v)
+    : u(_u), v(_v) {;}
+  
+  Flow(int rows, int cols) {
+    u = Mat::zeros(rows, cols, CV_64F);
+    v = Mat::zeros(rows, cols, CV_64F);
+  }
+};
+
+inline static double dist(const Vec3b& p1, const Vec3b& p2) {
+  return (p1[0] - p2[0]) * (p1[0] - p2[0]) +
+         (p1[1] - p2[1]) * (p1[1] - p2[1]) +
+         (p1[2] - p2[2]) * (p1[2] - p2[2]);
+}
+
+inline static double dist(const Point2f& p1, const Point2f& p2) {
+  return (p1.x - p2.x) * (p1.x - p2.x) +
+         (p1.y - p2.y) * (p1.y - p2.y);
+}
+
+inline static double dist(double x1, double y1, double x2, double y2) {
+  return (x1 - x2) * (x1 - x2) +
+         (y1 - y2) * (y1 - y2);
+}
+
+inline static int dist(int x1, int y1, int x2, int y2) {
+  return (x1 - x2) * (x1 - x2) +
+         (y1 - y2) * (y1 - y2);
+}
+
+template<class T>
+inline static T min(T t1, T t2, T t3) {
+  return (t1 <= t2 && t1 <= t3) ? t1 : min(t2, t3);
+}
+
+template<class T>
+vector<vector<T> > build(int n, int m) {
+  vector<vector<T> > res(n);
+  for (int i = 0; i < n; ++i) {
+    res[i].resize(m, 0);
+  }
+  return res;
+}
+
+class WeightedCrossBilateralFilter {
+public:
+  WeightedCrossBilateralFilter(const Mat& _image,
+                       int _windowSize,
+                       double _sigmaDist,
+                       double _sigmaColor);
+
+  Mat apply(Mat& matrix, Mat& weights);
+
+private:
+  double convolution(Mat& matrix, int row, int col, Mat& weights);
+
+  Mat image;
+  int windowSize;
+  double sigmaDist, sigmaColor;
+
+  vector<double> expDist;
+  vector<vector<vector<vector<double> > > > wc;
+};
+}
+
+#endif

modules/video/test/test_simpleflow.cpp

+/*M///////////////////////////////////////////////////////////////////////////////////////
+//
+//  IMPORTANT: READ BEFORE DOWNLOADING, COPYING, INSTALLING OR USING.
+//
+//  By downloading, copying, installing or using the software you agree to this license.
+//  If you do not agree to this license, do not download, install,
+//  copy or use the software.
+//
+//
+//                        Intel License Agreement
+//                For Open Source Computer Vision Library
+//
+// Copyright (C) 2000, Intel Corporation, all rights reserved.
+// Third party copyrights are property of their respective owners.
+//
+// Redistribution and use in source and binary forms, with or without modification,
+// are permitted provided that the following conditions are met:
+//
+//   * Redistribution's of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//
+//   * Redistribution's in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//
+//   * The name of Intel Corporation may not be used to endorse or promote products
+//     derived from this software without specific prior written permission.
+//
+// This software is provided by the copyright holders and contributors "as is" and
+// any express or implied warranties, including, but not limited to, the implied
+// warranties of merchantability and fitness for a particular purpose are disclaimed.
+// In no event shall the Intel Corporation or contributors be liable for any direct,
+// indirect, incidental, special, exemplary, or consequential damages
+// (including, but not limited to, procurement of substitute goods or services;
+// loss of use, data, or profits; or business interruption) however caused
+// and on any theory of liability, whether in contract, strict liability,
+// or tort (including negligence or otherwise) arising in any way out of
+// the use of this software, even if advised of the possibility of such damage.
+//
+//M*/
+
+#include "test_precomp.hpp"
+
+#include <string>
+
+using namespace std;
+
+/* ///////////////////// simpleflow_test ///////////////////////// */
+
+class CV_SimpleFlowTest : public cvtest::BaseTest
+{
+public:
+    CV_SimpleFlowTest();
+protected:
+    void run(int);
+};
+
+
+CV_SimpleFlowTest::CV_SimpleFlowTest() {}
+
+static void readOpticalFlowFromFile(FILE* file, cv::Mat& flowX, cv::Mat& flowY) {
+  char header[5];
+  if (fread(header, 1, 4, file) < 4 && (string)header != "PIEH") {
+    return;
+  }
+
+  int cols, rows;
+  if (fread(&cols, sizeof(int), 1, file) != 1||
+      fread(&rows, sizeof(int), 1, file) != 1) {
+    return;
+  }
+
+  flowX = cv::Mat::zeros(rows, cols, CV_64F);
+  flowY = cv::Mat::zeros(rows, cols, CV_64F);
+
+  for (int i = 0; i < rows; ++i) {
+    for (int j = 0; j < cols; ++j) {
+      float uPoint, vPoint;
+      if (fread(&uPoint, sizeof(float), 1, file) != 1 ||
+          fread(&vPoint, sizeof(float), 1, file) != 1) {
+        flowX.release();
+        flowY.release();
+        return;
+      }
+  
+      flowX.at<double>(i, j) = uPoint;
+      flowY.at<double>(i, j) = vPoint;
+    }
+  }
+}
+
+static bool isFlowCorrect(double u) {
+  return !isnan(u) && (fabs(u) < 1e9);
+}
+
+static double calc_rmse(cv::Mat flow1X, cv::Mat flow1Y, cv::Mat flow2X, cv::Mat flow2Y) {
+  long double sum;
+  int counter = 0;
+  const int rows = flow1X.rows;
+  const int cols = flow1X.cols;
+
+  for (int y = 0; y < rows; ++y) {
+    for (int x = 0; x < cols; ++x) {
+      double u1 = flow1X.at<double>(y, x);
+      double v1 = flow1Y.at<double>(y, x);
+      double u2 = flow2X.at<double>(y, x);
+      double v2 = flow2Y.at<double>(y, x);
+      if (isFlowCorrect(u1) && isFlowCorrect(u2) && isFlowCorrect(v1) && isFlowCorrect(v2)) {
+        sum += (u1-u2)*(u1-u2) + (v1-v2)*(v1-v2);
+        counter++;
+      }
+    }
+  }
+  return sqrt((double)sum / (1e-9 + counter));
+}
+
+void CV_SimpleFlowTest::run(int) {
+    int code = cvtest::TS::OK;
+    
+    const double MAX_RMSE = 0.6;
+    const string frame1_path = ts->get_data_path() + "optflow/RubberWhale1.png";
+    const string frame2_path = ts->get_data_path() + "optflow/RubberWhale2.png";
+    const string gt_flow_path = ts->get_data_path() + "optflow/RubberWhale.flo";
+
+    cv::Mat frame1 = cv::imread(frame1_path);
+    cv::Mat frame2 = cv::imread(frame2_path);
+
+    if (frame1.empty()) {
+      ts->printf(cvtest::TS::LOG, "could not read image %s\n", frame2_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+    
+    if (frame2.empty()) {
+      ts->printf(cvtest::TS::LOG, "could not read image %s\n", frame2_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+
+    if (frame1.rows != frame2.rows && frame1.cols != frame2.cols) {
+      ts->printf(cvtest::TS::LOG, "images should be of equal sizes (%s and %s)",
+                 frame1_path.c_str(), frame2_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+
+    if (frame1.type() != 16 || frame2.type() != 16) {
+      ts->printf(cvtest::TS::LOG, "images should be of equal type CV_8UC3 (%s and %s)",
+                 frame1_path.c_str(), frame2_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+
+    cv::Mat flowX_gt, flowY_gt;
+
+    FILE* gt_flow_file = fopen(gt_flow_path.c_str(), "rb");
+    if (gt_flow_file == NULL) {
+      ts->printf(cvtest::TS::LOG, "could not read ground-thuth flow from file %s",
+                 gt_flow_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+    readOpticalFlowFromFile(gt_flow_file, flowX_gt, flowY_gt);
+    if (flowX_gt.empty() || flowY_gt.empty()) {
+      ts->printf(cvtest::TS::LOG, "error while reading flow data from file %s",
+                 gt_flow_path.c_str());
+      ts->set_failed_test_info(cvtest::TS::FAIL_MISSING_TEST_DATA);
+      return;
+    }
+    fclose(gt_flow_file);
+
+    cv::Mat flowX, flowY;
+    cv::calcOpticalFlowSF(frame1, frame2, 
+                          flowX, flowY,
+                          3, 4, 2, 4.1, 25.5, 18, 55.0, 25.5, 0.35, 18, 55.0, 25.5, 10);
+
+    double rmse = calc_rmse(flowX_gt, flowY_gt, flowX, flowY);
+    
+    ts->printf(cvtest::TS::LOG, "Optical flow estimation RMSE for SimpleFlow algorithm : %lf\n",
+               rmse);
+
+    if (rmse > MAX_RMSE) {
+      ts->printf( cvtest::TS::LOG,
+                 "Too big rmse error : %lf ( >= %lf )\n", rmse, MAX_RMSE);
+      ts->set_failed_test_info(cvtest::TS::FAIL_BAD_ACCURACY);
+      return;
+    }
+}
+
+
+TEST(Video_OpticalFlowSimpleFlow, accuracy) { CV_SimpleFlowTest test; test.safe_run(); }
+
+/* End of file. */

samples/cpp/simpleflow_demo.cpp

+#include "opencv2/video/tracking.hpp"
+#include "opencv2/imgproc/imgproc.hpp"
+#include "opencv2/highgui/highgui.hpp"
+
+#include <cstdio>
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+static void help()
+{
+    // print a welcome message, and the OpenCV version
+    printf("This is a demo of SimpleFlow optical flow algorithm,\n"
+           "Using OpenCV version %s\n\n", CV_VERSION);
+
+    printf("Usage: simpleflow_demo frame1 frame2 output_flow"
+           "\nApplication will write estimated flow "
+           "\nbetween 'frame1' and 'frame2' in binary format"
+           "\ninto file 'output_flow'"
+           "\nThen one can use code from http://vision.middlebury.edu/flow/data/"
+           "\nto convert flow in binary file to image\n");
+}
+
+// binary file format for flow data specified here:
+// http://vision.middlebury.edu/flow/data/
+static void writeOpticalFlowToFile(const Mat& u, const Mat& v, FILE* file) {
+  int cols = u.cols;
+  int rows = u.rows;
+  
+  fprintf(file, "PIEH");
+   
+  if (fwrite(&cols, sizeof(int), 1, file) != 1 ||
+      fwrite(&rows, sizeof(int), 1, file) != 1) {
+    fprintf(stderr, "writeOpticalFlowToFile : problem writing header\n");
+    exit(1);
+  }
+
+  for (int i= 0; i < u.rows; ++i) {
+    for (int j = 0; j < u.cols; ++j) {
+      float uPoint = u.at<double>(i, j);
+      float vPoint = v.at<double>(i, j);
+
+      if (fwrite(&uPoint, sizeof(float), 1, file) != 1 ||
+          fwrite(&vPoint, sizeof(float), 1, file) != 1) {
+        fprintf(stderr, "writeOpticalFlowToFile : problem writing data\n");
+        exit(1);
+      }
+    }
+  }
+}
+int main(int argc, char** argv) {
+    help();
+
+    if (argc < 4) {
+      fprintf(stderr, "Wrong number of command line arguments : %d (expected %d)\n", argc, 4);
+      exit(1);
+    }
+    
+    Mat frame1 = imread(argv[1]);
+    Mat frame2 = imread(argv[2]);
+
+    if (frame1.empty() || frame2.empty()) {
+      fprintf(stderr, "simpleflow_demo : Images cannot be read\n");
+      exit(1);
+    }
+
+    if (frame1.rows != frame2.rows && frame1.cols != frame2.cols) {
+      fprintf(stderr, "simpleflow_demo : Images should be of equal sizes\n");
+      exit(1);
+    }
+
+    if (frame1.type() != 16 || frame2.type() != 16) {
+      fprintf(stderr, "simpleflow_demo : Images should be of equal type CV_8UC3\n");
+      exit(1);
+    }
+
+    printf("simpleflow_demo : Read two images of size [rows = %d, cols = %d]\n", 
+           frame1.rows, frame1.cols);
+
+    Mat flowX, flowY;
+
+    calcOpticalFlowSF(frame1, frame2, 
+                      flowX, flowY,
+                      3, 2, 4, 4.1, 25.5, 18, 55.0, 25.5, 0.35, 18, 55.0, 25.5, 10);
+
+  FILE* file = fopen(argv[3], "wb");
+  if (file == NULL) {
+    fprintf(stderr, "simpleflow_demo : Unable to open file '%s' for writing\n", argv[3]); 
+    exit(1);
+  }
+  printf("simpleflow_demo : Writing to file\n");
+  writeOpticalFlowToFile(flowX, flowY, file);
+  fclose(file);
+  return 0;
+}