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samples/cpp/tutorial_code/Histograms_Matching/calcBackProject_Demo2.cpp

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+/**
+ * @file BackProject_Demo2.cpp
+ * @brief Sample code for backproject function usage ( a bit more elaborated )
+ * @author OpenCV team
+ */
+
+#include "opencv2/imgproc.hpp"
+#include "opencv2/imgcodecs.hpp"
+#include "opencv2/highgui.hpp"
+
+#include <iostream>
+
+using namespace cv;
+using namespace std;
+
+/// Global Variables
+Mat src, hsv, mask;
+
+int low = 20, up = 20;
+const char* window_image = "Source image";
+
+/// Function Headers
+void Hist_and_Backproj( );
+void pickPoint (int event, int x, int y, int, void* );
+
+/**
+ * @function main
+ */
+int main( int, char** argv )
+{
+    /// Read the image
+    src = imread( argv[1] );
+
+    /// Transform it to HSV
+    cvtColor( src, hsv, COLOR_BGR2HSV );
+
+    /// Show the image
+    namedWindow( window_image );
+    imshow( window_image, src );
+
+    /// Set Trackbars for floodfill thresholds
+    createTrackbar( "Low thresh", window_image, &low, 255, 0 );
+    createTrackbar( "High thresh", window_image, &up, 255, 0 );
+    /// Set a Mouse Callback
+    setMouseCallback( window_image, pickPoint, 0 );
+
+    waitKey();
+    return 0;
+}
+
+/**
+ * @function pickPoint
+ */
+void pickPoint (int event, int x, int y, int, void* )
+{
+    if( event != EVENT_LBUTTONDOWN )
+    {
+        return;
+    }
+
+    // Fill and get the mask
+    Point seed = Point( x, y );
+
+    int newMaskVal = 255;
+    Scalar newVal = Scalar( 120, 120, 120 );
+
+    int connectivity = 8;
+    int flags = connectivity + (newMaskVal << 8 ) + FLOODFILL_FIXED_RANGE + FLOODFILL_MASK_ONLY;
+
+    Mat mask2 = Mat::zeros( src.rows + 2, src.cols + 2, CV_8U );
+    floodFill( src, mask2, seed, newVal, 0, Scalar( low, low, low ), Scalar( up, up, up), flags );
+    mask = mask2( Range( 1, mask2.rows - 1 ), Range( 1, mask2.cols - 1 ) );
+
+    imshow( "Mask", mask );
+
+    Hist_and_Backproj( );
+}
+
+/**
+ * @function Hist_and_Backproj
+ */
+void Hist_and_Backproj( )
+{
+    Mat hist;
+    int h_bins = 30; int s_bins = 32;
+    int histSize[] = { h_bins, s_bins };
+
+    float h_range[] = { 0, 180 };
+    float s_range[] = { 0, 256 };
+    const float* ranges[] = { h_range, s_range };
+
+    int channels[] = { 0, 1 };
+
+    /// Get the Histogram and normalize it
+    calcHist( &hsv, 1, channels, mask, hist, 2, histSize, ranges, true, false );
+
+    normalize( hist, hist, 0, 255, NORM_MINMAX, -1, Mat() );
+
+    /// Get Backprojection
+    Mat backproj;
+    calcBackProject( &hsv, 1, channels, hist, backproj, ranges, 1, true );
+
+    /// Draw the backproj
+    imshow( "BackProj", backproj );
+}