关于widthStep造成的问题

大家好，又见面了，我是你们的朋友全栈君。

最近遇到一个很奇怪的问题，一直没有解决，就是在A图像中设置一个ROI，将其clone给B，然后对B进行二值化，输入

为B,输出为C，这时二值化完后的图像C跟ROI区域的图像区域不同。通过查看发现罪魁祸首是widthStep变了。

无意中解决了这个问题，做法如下：

方法1：就是在A图像中设置一个ROI，将其clone给B，新建一个C，大小、位数和通道数同B，将B clone给C，然后对C进行

InToIn的二值化操作，这个问题就解决了。

方法2：只拿二值化的阈值，在otsu函数里面不进行二值化操作，然后调用cvThreshold函数进行二值化。

现象1：异常

源代码：

// Otsu.cpp : Defines the entry point for the console application. //

#include “stdafx.h” #include <iostream.h> #include <math.h> #include <cv.h> #include <highgui.h> #include <stdio.h> #include <windows.h>

int height;int width; int otsu(IplImage* A, IplImage* B) { long N = height * width; int h[256]; double p[256],u[256],w[256]; for(int i = 0; i < 256; i++) { h[i] = 0; p[i] = 0; u[i] = 0; w[i] = 0; }

for(i = 0; i < height; i++) for(int j = 0; j < width; j++) for(int k = 0; k < 256; k++) { if(((uchar*)(A->imageData + A->widthStep*i))[j] == k) h[k]++; }

for(i = 0; i < 256; i++) p[i] = h[i] / double(N);

int T = 0; double uT,thegma2fang; double thegma2fang_max = -10000;

for(int k = 0; k < 256; k++) { uT = 0; for(i = 0; i <= k; i++) { u[k] += i*p[i]; w[k] += p[i]; }

for(i = 0; i < 256; i++) uT += i*p[i]; thegma2fang = (uT*w[k] – u[k])*(uT*w[k] – u[k]) / (w[k]*(1-w[k])); if(thegma2fang > thegma2fang_max) { thegma2fang_max = thegma2fang; T = k; } } for(i = 0; i < height; i++) //根据最佳阈值，对原图像进行处理二值化处理 for(int j = 0; j < width; j++) if(((uchar*)(A->imageData + A->widthStep*i))[j] > T) ((uchar*)(B->imageData + B->widthStep*i))[j] = 255; else ((uchar*)(B->imageData + B->widthStep*i))[j] = 0;

return T; }

int main(int argc, char** argv) { const char* filename = argc >= 2 ?argv[1] : “lena.jpg”; IplImage* source = cvLoadImage( filename, 0 ); int Th;

height = source->height; width = source->width; CvRect rect; rect.x=50; rect.y=30; rect.width=height/2; rect.height=width/2; IplImage *roi = cvCreateImage(cvSize(rect.width,rect.height),IPL_DEPTH_8U,1); IplImage *bw = cvCreateImage(cvSize(rect.width,rect.height),IPL_DEPTH_8U,1);

cvSetImageROI(source,rect); roi=cvCloneImage(source); cvResetImageROI(source); Th = otsu(roi,bw);

printf(“Th=%d\n”,Th); cvNamedWindow( “Resource”, 1 ); cvShowImage( “Resource”, source ); cvNamedWindow( “Result”, 1 ); cvShowImage( “Result”, roi); cvNamedWindow( “BW”, 1 ); cvShowImage( “BW”, bw); cvWaitKey(0); return 0; }

现象2：正常

// Otsu.cpp : Defines the entry point for the console application. //

#include “stdafx.h” #include <iostream.h> #include <math.h> #include <cv.h> #include <highgui.h> #include <stdio.h> #include <windows.h>

int height;int width; int otsu(IplImage* A, IplImage* B) { long N = height * width; int h[256]; double p[256],u[256],w[256]; for(int i = 0; i < 256; i++) { h[i] = 0; p[i] = 0; u[i] = 0; w[i] = 0; }

for(i = 0; i < height; i++) for(int j = 0; j < width; j++) for(int k = 0; k < 256; k++) { if(((uchar*)(A->imageData + A->widthStep*i))[j] == k) h[k]++; }

for(i = 0; i < 256; i++) p[i] = h[i] / double(N);

int T = 0; double uT,thegma2fang; double thegma2fang_max = -10000;

for(int k = 0; k < 256; k++) { uT = 0; for(i = 0; i <= k; i++) { u[k] += i*p[i]; w[k] += p[i]; }

for(i = 0; i < 256; i++) uT += i*p[i]; thegma2fang = (uT*w[k] – u[k])*(uT*w[k] – u[k]) / (w[k]*(1-w[k])); if(thegma2fang > thegma2fang_max) { thegma2fang_max = thegma2fang; T = k; } } return T; }

int main(int argc, char** argv) { const char* filename = argc >= 2 ?argv[1] : “lena.jpg”; IplImage* source = cvLoadImage( filename, 0 ); int Th;

height = source->height; width = source->width; CvRect rect; rect.x=0; rect.y=0; rect.width=height/2; rect.height=width/2; IplImage *roi = cvCreateImage(cvSize(rect.width,rect.height),IPL_DEPTH_8U,1); IplImage *bw = cvCreateImage(cvSize(rect.width,rect.height),IPL_DEPTH_8U,1);

cvSetImageROI(source,rect); roi=cvCloneImage(source); cvResetImageROI(source);

bw = cvCloneImage(roi); Th = otsu(bw,bw); cvThreshold(roi,bw,Th,255,CV_THRESH_BINARY);

printf(“roi->widthStep=%d,bw->widthStep=%d\n”,roi->widthStep,bw->widthStep); printf(“Th=%d\n”,Th); cvNamedWindow( “Resource”, 1 ); cvShowImage( “Resource”, source ); cvNamedWindow( “Result”, 1 ); cvShowImage( “Result”, roi); cvNamedWindow( “BW”, 1 ); cvShowImage( “BW”, bw); cvWaitKey(0); return 0; }

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