added multiple thinning algorithms

added thinning sample
added thinning tests

modules/ximgproc/include/opencv2/ximgproc.hpp

@@ -71,6 +71,11 @@ namespace cv
 namespace ximgproc
 {
 
+enum ThinningTypes{
+    THINNING_ZHANGSUEN    = 0, // Thinning technique of Zhang-Suen
+    THINNING_GUOHALL      = 1  // Thinning technique of Guo-Hall
+};
+
 //! @addtogroup ximgproc
 //! @{
 
@@ -110,8 +115,9 @@ The function transforms a binary blob image into a skeletized form using the tec
 
 @param src Source 8-bit single-channel image, containing binary blobs, with blobs having 255 pixel values.
 @param dst Destination image of the same size and the same type as src. The function can work in-place.
+@param thinningType Value that defines which thinning algorithm should be used. See cv::ThinningTypes
  */
-CV_EXPORTS_W void thinning( InputArray src, OutputArray dst);
+CV_EXPORTS_W void thinning( InputArray src, OutputArray dst, int thinningType = THINNING_ZHANGSUEN);
 
 
 //! @}

modules/ximgproc/samples/thinning.cpp

+#include <iostream>
+
+#include "opencv2/imgproc.hpp"
+#include "opencv2/highgui.hpp"
+
+#include "opencv2/ximgproc.hpp"
+
+using namespace std;
+using namespace cv;
+
+int main()
+{
+    Mat img = imread("opencv-logo.png", IMREAD_COLOR);
+
+    /// Threshold the input image
+    Mat img_grayscale, img_binary;
+    cvtColor(img, img_grayscale,COLOR_BGR2GRAY);
+    threshold(img_grayscale, img_binary, 0, 255, THRESH_OTSU | THRESH_BINARY_INV);
+
+    /// Apply thinning to get a skeleton
+    Mat img_thinning_ZS, img_thinning_GH;
+    //ximgproc::thinning(img_binary, img_thinning_ZS, THINNING_ZHANGSUEN);
+    //ximgproc::thinning(img_binary, img_thinning_GH, THINNING_GUOHALL);
+
+    /// Make 3 channel images from thinning result
+    Mat result_ZS(img.rows, img.cols, CV_8UC3), result_GH(img.rows, img.cols, CV_8UC3);
+
+    Mat in[] = { img_thinning_ZS, img_thinning_ZS, img_thinning_ZS };
+    Mat in2[] = { img_thinning_GH, img_thinning_GH, img_thinning_GH };
+    int from_to[] = { 0,0, 1,1, 2,2 };
+    mixChannels( in, 3, &result_ZS, 1, from_to, 3 );
+    mixChannels( in2, 3, &result_GH, 1, from_to, 3 );
+
+    /// Combine everything into a canvas
+    Mat canvas(img.rows, img.cols * 3, CV_8UC3);
+    img.copyTo( canvas( Rect(0, 0, img.cols, img.rows) ) );
+    result_ZS.copyTo( canvas( Rect(img.cols, 0, img.cols, img.rows) ) );
+    result_GH.copyTo( canvas( Rect(img.cols*2, 0, img.cols, img.rows) ) );
+
+    /// Visualize result
+    imshow("Skeleton", canvas); waitKey(0);
+
+    return 0;
+}

modules/ximgproc/src/thinning.cpp

@@ -6,31 +6,60 @@ namespace cv {
 namespace ximgproc {
 
 // Applies a thinning iteration to a binary image
-static void thinningIteration(Mat img, int iter){
+static void thinningIteration(Mat img, int iter, int thinningType){
     Mat marker = Mat::zeros(img.size(), CV_8UC1);
-    for (int i = 1; i < img.rows-1; i++)
-    {
-        for (int j = 1; j < img.cols-1; j++)
+
+    if(thinningType == THINNING_ZHANGSUEN){
+        for (int i = 1; i < img.rows-1; i++)
+        {
+            for (int j = 1; j < img.cols-1; j++)
+            {
+                uchar p2 = img.at<uchar>(i-1, j);
+                uchar p3 = img.at<uchar>(i-1, j+1);
+                uchar p4 = img.at<uchar>(i, j+1);
+                uchar p5 = img.at<uchar>(i+1, j+1);
+                uchar p6 = img.at<uchar>(i+1, j);
+                uchar p7 = img.at<uchar>(i+1, j-1);
+                uchar p8 = img.at<uchar>(i, j-1);
+                uchar p9 = img.at<uchar>(i-1, j-1);
+
+                int A  = (p2 == 0 && p3 == 1) + (p3 == 0 && p4 == 1) +
+                         (p4 == 0 && p5 == 1) + (p5 == 0 && p6 == 1) +
+                         (p6 == 0 && p7 == 1) + (p7 == 0 && p8 == 1) +
+                         (p8 == 0 && p9 == 1) + (p9 == 0 && p2 == 1);
+                int B  = p2 + p3 + p4 + p5 + p6 + p7 + p8 + p9;
+                int m1 = iter == 0 ? (p2 * p4 * p6) : (p2 * p4 * p8);
+                int m2 = iter == 0 ? (p4 * p6 * p8) : (p2 * p6 * p8);
+
+                if (A == 1 && (B >= 2 && B <= 6) && m1 == 0 && m2 == 0)
+                    marker.at<uchar>(i,j) = 1;
+            }
+        }
+    }
+    if(thinningType == THINNING_GUOHALL){
+        for (int i = 1; i < img.rows-1; i++)
         {
-            uchar p2 = img.at<uchar>(i-1, j);
-            uchar p3 = img.at<uchar>(i-1, j+1);
-            uchar p4 = img.at<uchar>(i, j+1);
-            uchar p5 = img.at<uchar>(i+1, j+1);
-            uchar p6 = img.at<uchar>(i+1, j);
-            uchar p7 = img.at<uchar>(i+1, j-1);
-            uchar p8 = img.at<uchar>(i, j-1);
-            uchar p9 = img.at<uchar>(i-1, j-1);
-
-            int A  = (p2 == 0 && p3 == 1) + (p3 == 0 && p4 == 1) +
-                     (p4 == 0 && p5 == 1) + (p5 == 0 && p6 == 1) +
-                     (p6 == 0 && p7 == 1) + (p7 == 0 && p8 == 1) +
-                     (p8 == 0 && p9 == 1) + (p9 == 0 && p2 == 1);
-            int B  = p2 + p3 + p4 + p5 + p6 + p7 + p8 + p9;
-            int m1 = iter == 0 ? (p2 * p4 * p6) : (p2 * p4 * p8);
-            int m2 = iter == 0 ? (p4 * p6 * p8) : (p2 * p6 * p8);
-
-            if (A == 1 && (B >= 2 && B <= 6) && m1 == 0 && m2 == 0)
-                marker.at<uchar>(i,j) = 1;
+            for (int j = 1; j < img.cols-1; j++)
+            {
+                uchar p2 = img.at<uchar>(i-1, j);
+                uchar p3 = img.at<uchar>(i-1, j+1);
+                uchar p4 = img.at<uchar>(i, j+1);
+                uchar p5 = img.at<uchar>(i+1, j+1);
+                uchar p6 = img.at<uchar>(i+1, j);
+                uchar p7 = img.at<uchar>(i+1, j-1);
+                uchar p8 = img.at<uchar>(i, j-1);
+                uchar p9 = img.at<uchar>(i-1, j-1);
+
+                int C  = ((!p2) & (p3 | p4)) + ((!p4) & (p5 | p6)) +
+                         ((!p6) & (p7 | p8)) + ((!p8) & (p9 | p2));
+                int N1 = (p9 | p2) + (p3 | p4) + (p5 | p6) + (p7 | p8);
+                int N2 = (p2 | p3) + (p4 | p5) + (p6 | p7) + (p8 | p9);
+                int N  = N1 < N2 ? N1 : N2;
+                int m  = iter == 0 ? ((p6 | p7 | (!p9)) & p8) : ((p2 | p3 | (!p5)) & p4);
+
+                if ((C == 1) && ((N >= 2) && ((N <= 3)) & (m == 0)))
+                    marker.at<uchar>(i,j) = 1;
+            }
         }
     }
 
@@ -38,7 +67,7 @@ static void thinningIteration(Mat img, int iter){
 }
 
 // Apply the thinning procedure to a given image
-void thinning(InputArray input, OutputArray output){
+void thinning(InputArray input, OutputArray output, int thinningType){
     Mat processed = input.getMat().clone();
     // Enforce the range of the input image to be in between 0 - 255
     processed /= 255;
@@ -47,8 +76,8 @@ void thinning(InputArray input, OutputArray output){
     Mat diff;
 
     do {
-        thinningIteration(processed, 0);
-        thinningIteration(processed, 1);
+        thinningIteration(processed, 0, thinningType);
+        thinningIteration(processed, 1, thinningType);
         absdiff(processed, prev, diff);
         processed.copyTo(prev);
     }

modules/ximgproc/test/test_thinning.cpp

+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+#include "test_precomp.hpp"
+
+using namespace cv;
+using namespace cv::ximgproc;
+
+namespace {
+
+static int createTestImage(Mat& src)
+{
+    src = Mat::zeros(Size(256, 256), CV_8UC1);
+    for (int x = 50; x < src.cols - 50; x += 50)
+    {
+        cv::circle(src, Point(x, x/2), 30 + x/2, Scalar(255), 5);
+    }
+    int src_pixels = countNonZero(src);
+    EXPECT_GT(src_pixels, 0);
+    return src_pixels;
+}
+
+TEST(ximpgroc_Thinning, simple_ZHANGSUEN)
+{
+    Mat src;
+    int src_pixels = createTestImage(src);
+
+    Mat dst;
+    thinning(src, dst, THINNING_ZHANGSUEN);
+    int dst_pixels = countNonZero(dst);
+    EXPECT_LE(dst_pixels, src_pixels);
+
+#if 0
+    imshow("src", src); imshow("dst", dst); waitKey();
+#endif
+}
+
+TEST(ximpgroc_Thinning, simple_GUOHALL)
+{
+    Mat src;
+    int src_pixels = createTestImage(src);
+
+    Mat dst;
+    thinning(src, dst, THINNING_GUOHALL);
+    int dst_pixels = countNonZero(dst);
+    EXPECT_LE(dst_pixels, src_pixels);
+
+#if 0
+    imshow("src", src); imshow("dst", dst); waitKey();
+#endif
+}
+
+}