Distance Transform－天天向上

Distance Transform [2]經常應用在二值影像，其運算結果則為一灰階影像，

其強度並非表示亮度值，而是表示物件內部每一點與物件邊緣的距離。

如果以 1 表示物件像素，0 是背景像素，則 distance transform 定義為

對於每一個物件區域的像素，計算其與最近的背景像素的距離，並以此距離值取代原像素值。

debug環境設定檔案

http://www.mediafire.com/download/l2kf42zva55u23q/VS2010OpenCV249X86Debug.props

release環境設定檔案

http://www.mediafire.com/download/3y9uer5ni6e0a0t/VS2010OpenCV249X86Release.props

參數

1. 來源影像

2. 輸出影像

3. 距離種類

以下為常見的距離量測[2]

對應上述距離種類的參數設定

/* Distance types for Distance Transform and M-estimators */
enum
{
    CV_DIST_USER    =-1,  /* User defined distance */
    CV_DIST_L1      =1,   /* distance = |x1-x2| + |y1-y2| */
    CV_DIST_L2      =2,   /* the simple euclidean distance */
    CV_DIST_C       =3,   /* distance = max(|x1-x2|,|y1-y2|) */
    CV_DIST_L12     =4,   /* L1-L2 metric: distance = 2(sqrt(1+x*x/2) - 1)) */
    CV_DIST_FAIR    =5,   /* distance = c^2(|x|/c-log(1+|x|/c)), c = 1.3998 */
    CV_DIST_WELSCH  =6,   /* distance = c^2/2(1-exp(-(x/c)^2)), c = 2.9846 */
    CV_DIST_HUBER   =7    /* distance = |x|<c ? x^2/2 : c(|x|-c/2), c=1.345 */
};

4. 遮罩大小

//! computes the distance transform map
CV_EXPORTS_W void distanceTransform( InputArray src, OutputArray dst,
                                     int distanceType, int maskSize );

標頭檔

// DistanceTransformSample.cpp : 定義主控台應用程式的進入點。
//

#include "stdafx.h"

#include <opencv2\highgui\highgui.hpp>
#include <opencv2\opencv.hpp>

using namespace cv;
using namespace std;

主程式如下

// Load the image
    //char* file = "C:\\OpenCV\\images\\art5.png";
    //char* file = "C:\\OpenCV\\images\\art6.png";
    //char* file = "C:\\OpenCV\\images\\art7.png";
    //char* file = "C:\\OpenCV\\images\\art5cha2.png";
    //char* file = "C:\\OpenCV\\images\\art5noi1.png";
    char* file = "C:\\OpenCV\\images\\phn1.png";
    
    Mat src = imread(file);
    
    if(src.empty())
        return -1;

    int wid = src.size().width;
     // Show source image
    imshow("Source Image", src); moveWindow("Source Image", 0, 0);

    //-------------------------------------------
    // Create binary image from source image
    Mat bw;
    cvtColor(src, bw, CV_BGR2GRAY);
    threshold(bw, bw, 100, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);
    //threshold(bw, bw, 100, 255, CV_THRESH_BINARY_INV | CV_THRESH_OTSU);
    imshow("Binary Image", bw); moveWindow("Binary Image", wid, 0);

    //-------------------------------------------
    // Perform the distance transform algorithm
    Mat dist;
    distanceTransform(bw, dist, CV_DIST_L2, 3);
    // Normalize the distance image for range = {0.0, 1.0}
    // so we can visualize and threshold it
    normalize(dist, dist, 0, 1., NORM_MINMAX);
    imshow("Distance Transform Image", dist);  moveWindow("Distance Transform Image", 2*wid, 0);
    
    waitKey(0);
    return 0;