OpenCV 和 ROS：cvMAT 中的空指针错误
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【中文标题】OpenCV 和 ROS：cvMAT 中的空指针错误【英文标题】：OpenCV and ROS: NULL Pointer error in cvMAT 【发布时间】：2012-08-17 09:17:41 【问题描述】：我正在使用以下方法来检测两个彩色对象的位置、方向。 除非相机无法对这两个物体（黄色和蓝色）中的任何一个进行精细处理，或者当我将手放在相机前时，否则一切正常。它抛出以下错误：
OpenCV 错误：cvGetMat 中的空指针（传递了空数组指针），文件 /tmp/buildd/libopencv-2.3.1+svn6514+branch23/modules/core/src/array.cpp，第 2382 行 在抛出 'cv::Exception' 的实例后调用终止 what(): /tmp/buildd/libopencv-2.3.1+svn6514+branch23/modules/core/src/array.cpp:2382: 错误: (-27) 函数 cvGetMat 传递了 NULL 数组指针
如果有人能帮我解决这个错误，我将不胜感激。
谢谢
#include <ros/ros.h>
#include <opencv/cv.h>
#include <opencv/highgui.h>
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <geometry_msgs/Twist.h>
#define MAX_CONTOUR_LEVELS 5 //This will be used when displaying contours
#define PI 3.14159265
using namespace cv;
using namespace std;
// Class Definition
class color_control
public:
void mainLoop1();
void mainLoop2();
double R_X, R_Y; /* red center of gravity x,y in the frame normalized from -1.0 to 1.0 */
int C_C;
double setSpeed( double, double );
void do_some_magic( IplImage* , int , int , int , int );
color_control()
// node creation in root-namespace
ros::NodeHandle m_nodeHandle("/");
m_commandPublisher = m_nodeHandle.advertise<geometry_msgs::Twist> ("cmd_vel", 20);
~color_control()
cvDestroyWindow("result");
protected:
ros::NodeHandle m_nodeHandle;
// Publisher und Membervariable für die Fahrbefehle
ros::Publisher m_commandPublisher;
geometry_msgs::Twist m_roombaCommand;
;
int abort_error_handler(int status, char const* func_name, char const* err_msg, char const* file_name, int line, void*)
cout << "ERROR: in " << func_name << "(" << file_name << ":" << line << ") Message: " << err_msg << endl;
abort();
IplImage* GetThresholdedImage1(IplImage* img)
IplImage* imgHSV = cvCreateImage(cvGetSize(img), 8, 3);
cvCvtColor(img, imgHSV, CV_BGR2HSV);
IplImage* imgThreshed1=cvCreateImage(cvGetSize(img),8,1);
//cvInRangeS(imgHSV, cvScalar(20, 100, 100), cvScalar(30, 255, 255), imgYellow);
cvInRangeS(imgHSV, cvScalar(22, 100, 100), cvScalar(32, 255, 255), imgThreshed1);
cvReleaseImage(&imgHSV);
//cvAdd(imgYellow,imgGreen,imgThreshed);
//if (imgThreshed1 != NULL)
return imgThreshed1;
//cvShowImage( "result", imgThreshed1 );
IplImage* GetThresholdedImage2(IplImage* img)
IplImage* imgHSV = cvCreateImage(cvGetSize(img), 8, 3);
cvCvtColor(img, imgHSV, CV_BGR2HSV);
IplImage* imgThreshed2=cvCreateImage(cvGetSize(img),8,1);
//cvInRangeS(imgHSV, cvScalar(20, 100, 100), cvScalar(30, 255, 255), imgYellow);
cvInRangeS(imgHSV, cvScalar(100,100,100^3),cvScalar(120,255,255^3), imgThreshed2);
cvReleaseImage(&imgHSV);
//cvAdd(imgYellow,imgGreen,imgThreshed);
//if (imgThreshed2 == NULL)
return imgThreshed2;
// find the largest contour (by area) from a sequence of contours and return a
// pointer to that item in the sequence
CvSeq* findLargestContour(CvSeq* contours)
CvSeq* current_contour = contours;
double largestArea = 0;
CvSeq* largest_contour = NULL;
// check we at least have some contours
if (contours == NULL)return NULL;
// for each contour compare it to current largest area on
// record and remember the contour with the largest area
// (note the use of fabs() for the cvContourArea() function)
while (current_contour != NULL)
double area = fabs(cvContourArea(current_contour));
if(area > largestArea)
largestArea = area;
largest_contour = current_contour;
current_contour = current_contour->h_next;
// return pointer to largest
return largest_contour;
// normalize center of color to propulsion command
double color_control::setSpeed( double center, double width )
double normedCenter = (12.0*center/width) - 6.0;
//ROS_INFO("normed center: %f", normedCenter);
double retval = 0.0;
if ( fabs( normedCenter ) > 1.0 )
retval = (trunc( normedCenter )/10.0 );
return retval;
//
// comments R 4 mollycoddles, guess what i'm doing!
//
// Please help me ! I need someone writing comments. Thanx
//
void color_control::do_some_magic( IplImage* img, int red, int green, int blue, int tolerance)
int radius = 20 ;
int width = img->width;
int height = img->height;
int channels = img->nChannels;
int step = img->widthStep;
unsigned char redP = 0, greenP = 0, blueP = 0;
double S_x = 0.0 ;
double S_y = 0.0 ;
int red_difference, green_difference, blue_difference = 255;
C_C = 0 ;
for(int y=0;y<height;y++)
for(int x=0;x<width;x++)
blueP = img->imageData[y*step+x*channels+0] ;
greenP = img->imageData[y*step+x*channels+1] ;
redP = img->imageData[y*step+x*channels+2] ;
red_difference = fabs(red - (int)redP);
green_difference = fabs(green - (int)greenP);
blue_difference = fabs(blue - (int)blueP);
if ( (red_difference + green_difference + blue_difference) < tolerance )
C_C++ ;
S_x += x;
S_y += y;
//ROS_INFO( "Difference to target color: %i", (red_difference + green_difference + blue_difference) );
S_x = S_x / (C_C) ;
S_y = S_y / (C_C) ;
R_X = setSpeed( S_x, img->width );
R_Y = setSpeed( S_y, img->height );
// for monitoring, draw a circle and display the respective picture
CvPoint center;
center.x = S_x;
center.y = S_y;
cvCircle( img, center, radius, CV_RGB( 255 - red, 255 - green, 255 - blue ) , 3, 8, 0 );
cvShowImage( "result", img );
// Main Loop
void color_control::mainLoop1()
// determines the number of frames per second
ros::Rate loop_rate(20);
int radius ;
CvCapture* capture = 0;
//IplImage *frame, *frame_copy = 0;
IplImage* imgScribble=NULL;
// open the camera
capture = cvCaptureFromCAM( 0 );
cvSetCaptureProperty(capture,CV_CAP_PROP_FRAME_HEIGHT, 640);
cvSetCaptureProperty(capture,CV_CAP_PROP_FRAME_WIDTH, 480);
//capture = cvCaptureFromCAM( 1 );
//cvRedirectError(abort_error_handler);
// loop stops, e.g. if the node recieves a kill signal
while (m_nodeHandle.ok())
IplImage* frame=0;
frame=cvQueryFrame(capture);
if(!frame)
break;
// if(imgScribble == NULL)
//
// imgScribble=cvCreateImage(cvGetSize(frame),8,1);
//
IplImage* imgYellowThresh = GetThresholdedImage1(frame);
IplImage* imgGreenThresh = GetThresholdedImage2(frame);
//CvMemStorage and CvSeq are structures used for dynamic data collection. CvMemStorage contains pointers to the actual
//allocated memory, but CvSeq is used to access this data. Here, it will hold the list of image contours.
CvMemStorage *storage = cvCreateMemStorage(0);
CvSeq *contours = 0;
//Once we have a binary image, we can look for contours in it. cvFindContours will scan through the image and store connected contours in "sorage".
//"contours" will point to the first contour detected. CV_RETR_TREE means that the function will create a contour hierarchy. Each contour will contain
//a pointer to contours that are contained inside it (holes). CV_CHAIN_APPROX_NONE means that all the contours points will be stored. Finally, an offset
//value can be specified, but we set it to (0,0).
cvFindContours(imgYellowThresh, storage, &contours, sizeof(CvContour), CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));
//This function will display contours on top of an image. We can specify different colours depending on whether the contour in a hole or not.
CvSeq* largest_contour = NULL;
largest_contour = findLargestContour(contours);
//cvDrawContours(imgYellowThresh, largest_contour, CV_RGB(255,255,255), CV_RGB(0,255,0), MAX_CONTOUR_LEVELS, 3, CV_AA, cvPoint(0,0));
if(largest_contour!=NULL)
cvDrawContours(imgYellowThresh, largest_contour, CV_RGB(255,255,255), CV_RGB(0,255,0), 0, 2, 8, cvPoint(0,0));
static int posX_Yellow=0;
static int posY_Yellow=0;
//int lastX=posX;
//int lastY=posY;
CvMoments moments1,cenmoments1;
double M00, M01, M10;
cvMoments(largest_contour,&moments1);
M00 = cvGetSpatialMoment(&moments1,0,0);
M10 = cvGetSpatialMoment(&moments1,1,0);
M01 = cvGetSpatialMoment(&moments1,0,1);
posX_Yellow = (int)(M10/M00);
posY_Yellow = (int)(M01/M00);
double theta = 0.5 * atan(
(2 * cvGetCentralMoment(&moments1, 1, 1)) /
(cvGetCentralMoment(&moments1, 2, 0) - cvGetCentralMoment(&moments1, 0, 2)));
theta = (theta / PI) * 180;
// fit an ellipse (and draw it)
if (largest_contour->total >= 6) // can only do an ellipse fit
// if we have > 6 points
CvBox2D box = cvFitEllipse2(largest_contour);
if ((box.size.width < imgYellowThresh->width) && (box.size.height < imgYellowThresh->height))
// get the angle of the ellipse correct (taking into account MS Windows
// seems to draw ellipses differently
box.angle = 270 - box.angle;
#ifndef WIN32
if( imgYellowThresh->origin )
box.angle = - box.angle;
#endif
cvEllipseBox(imgYellowThresh, box, CV_RGB(255, 255 ,255), 3, 8, 0 );
CvFont font;
cvInitFont(&font, CV_FONT_HERSHEY_PLAIN, 1, 1 , 0, 2, 8 );
#ifdef WIN32
int height_offset = 20;
#else
int height_offset = 5;
#endif
char outputString[255];
sprintf(outputString, "angle: %.10f", theta);
cvPutText(imgYellowThresh, outputString,
cvPoint(10,imgYellowThresh->height - height_offset), &font, CV_RGB(255, 255,255));
CvMemStorage *storageG = cvCreateMemStorage(0);
CvSeq *contoursG = 0;
//Once we have a binary image, we can look for contours in it. cvFindContours will scan through the image and store connected contours in "sorage".
//"contours" will point to the first contour detected. CV_RETR_TREE means that the function will create a contour hierarchy. Each contour will contain
//a pointer to contours that are contained inside it (holes). CV_CHAIN_APPROX_NONE means that all the contours points will be stored. Finally, an offset
//value can be specified, but we set it to (0,0).
cvFindContours(imgGreenThresh, storageG, &contoursG, sizeof(CvContour), CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));
//This function will display contours on top of an image. We can specify different colours depending on whether the contour in a hole or not.
CvSeq* largest_contourG = NULL;
largest_contourG = findLargestContour(contoursG);
if(largest_contourG!=NULL)
//cvDrawContours(imgYellowThresh, largest_contour, CV_RGB(255,255,255), CV_RGB(0,255,0), MAX_CONTOUR_LEVELS, 3, CV_AA, cvPoint(0,0));
cvDrawContours(imgGreenThresh, largest_contourG, CV_RGB(255,255,255), CV_RGB(0,255,0), 0, 2, 8, cvPoint(0,0));
//cvShowImage( "result2", imgGreenThresh );
CvMoments moments2;
double M00g, M01g, M10g;
cvMoments(largest_contourG,&moments2);
M00g = cvGetSpatialMoment(&moments2,0,0);
M10g = cvGetSpatialMoment(&moments2,1,0);
M01g = cvGetSpatialMoment(&moments2,0,1);
static int posX_Green=0;
static int posY_Green=0;
posX_Green = (int)(M10g/M00g);
posY_Green = (int)(M01g/M00g);
//printf("%d\n",M00g);
//ROS_INFO("position (%d,%d)\n",posX_Yellow,posY_Yellow);
//ROS_INFO("position (%d,%d)\n",posX_Green,posY_Green);
//do_some_magic( frame , 0, 0, 0, 100);
// if(lastX>0 && lastY>0 && posX>0 && posY>0)
//
// cvLine(imgScribble,cvPoint(posX,posY),cvPoint(lastX,lastY),cvScalar(0,255,255), 5);
//
// cvAdd(frame,imgScribble,frame);
cv::Point centerY(posX_Yellow,posY_Yellow);
//centerY.x = posX_Yellow;
//centerY.y = posY_Yellow;
//radius = sqrt(areaY/3.14);
cvCircle( frame, centerY, 10, CV_RGB( 255, 255, 255) , 3, 8, 0 );
cv::Point centerG(posX_Green,posY_Green);
//centerG.x = posX_Green;
//centerG.y = posY_Green;
cv::Point diff = centerY - centerG;
//radius = sqrt(areaG/3.14);
cvCircle( frame, centerG, 10, CV_RGB( 255, 255, 255) , 3, 8, 0 );
//float angle = atan2(centerY,centerX);
int slope = ((diff.y)/(diff.x));
int len = cv::sqrt(diff.x*diff.x + diff.y*diff.y);
double newdist = (len / 2000000);
cvLine(frame, centerY, centerG, CV_RGB( 255, 255, 255), 5,8,0);
//cvCircle( frame, diff, 10, CV_RGB( 255, 255, 255) , 3, 8, 0 );
//ROS_INFO("angle : %d\n",theta);
//ROS_INFO("len: %d slope: %d\n",len,slope);
//printf("len: %f\n", slope);
cvShowImage( "result", frame );
cvShowImage( "result1", imgYellowThresh );
cvShowImage( "result2", imgGreenThresh );
if( cvWaitKey( 10 ) >= 0 )
break;
//ROS_INFO( "C_C: %d", C_C );
// set driving direction and velocity
// if (len > 50 || slope > 0)
//
// m_roombaCommand.linear.x = 0.1;
// m_roombaCommand.angular.z = 0.0;
// else
// m_roombaCommand.linear.x = 0.0;
// m_roombaCommand.angular.z = 0.1;
//
//
// ROS_INFO("Forward: %f - Turning: %f", m_roombaCommand.linear.x, m_roombaCommand.angular.z);
//
// // send the driving command to the roomba
//m_commandPublisher.publish(m_roombaCommand);
// spinOnce is doing the loop exactly once
ros::spinOnce();
//cvReleaseCapture( &capture );
// sleep stops the process for approx ~50ms, to keep the timing for the looprate
loop_rate.sleep();
//cvReleaseImage( &frame_copy );
int main(int argc, char** argv)
//sleep(10);
// Initialize
ros::init(argc, argv, "color_control");
ros::NodeHandle n;
color_control f_g;
f_g.mainLoop1();
//color_control g_g;
//g_g.mainLoop2();
ros::spin();
//cvRedirectError(abort_error_handler);
return 0;
//cvNamedWindow("Video");
//cvNamedWindow("thresh");
【问题讨论】：
代码太多，无法阅读和理解。你能试着做一个有这个错误的更短的例子吗？另请阅读sscce.org 当周围没有彩色对象时，findlargestContour 函数返回空值。因此错误。我怎样才能避免这种情况，以便程序仍然运行而不会出现此错误？ 为了让 OP 明白：这个问题看起来不错，但这里发布的 looooong 代码反映了对社区的低评价。好问题很容易阅读。对于这个，必须有人阅读 10 分钟，这太多了 附注：您似乎从某个地方获取了此代码，并且没有足够的编程知识来使用它。我建议开始学习 C++，然后转向更复杂的东西，例如计算机视觉 【参考方案1】：当您调用findlargestContour 时，您会在调用cvDrawContours 时检查NULL 的返回值。但是，您也可以在此之后使用返回的值，而不检查 NULL。
简单的解决方案是在使用返回值之前为NULL 添加更多检查。
【讨论】：
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