Opencv 利用分割的图像掩膜来完善检测前景

 在目标检测中，经常会出现目标断开、不连续或空洞的情况，针对该钟情况，我们总是要想各种方法去填补空洞，使断开的部分连接起来。下面介绍一个函数来实现该功能：

void cvRefineForegroundMaskBySegm( CvSeq* segments, IplImage*  pFrImg )
{
   IplImage* tmp_image = cvCreateImage(cvSize(pFrImg->width,pFrImg->height),
                                            IPL_DEPTH_8U, 1);
  for( ; segments; segments = ((CvSeq*)segments)->h_next )
  {
      CvSeq seq = *segments;
      seq.v_next = seq.h_next = NULL;
     cvZero(tmp_image);
     cvDrawContours( tmp_image, &seq, CV_RGB(0, 0, 255), CV_RGB(0, 0, 255), 10, -1);
     int num1 = cvCountNonZero(tmp_image);
      cvAnd(tmp_image, pFrImg, tmp_image);
     int num2 = cvCountNonZero(tmp_image);
    if( num2 > num1*0.5 )
          cvDrawContours( pFrImg, &seq, CV_RGB(0, 0, 255), CV_RGB(0, 0, 255), 10, -1);
    else
        cvDrawContours( pFrImg, &seq, CV_RGB(0, 0, 0), CV_RGB(0, 0, 0), 10, -1);
  }
      cvReleaseImage(&tmp_image);  
 }

其中，segments是利用图像分割算法得到的轮廓序列，而pFrImg则是目标检测算法检测到的前景目标，这样就可以分割图像的结果来对目标检测的区域进行填充。另外，对于如何得到分割图像，也可以采用以下函数来实现：

CvSeq*cvSegmentFGMask( CvArr* _mask, int poly1Hull0, float perimScale,
                 CvMemStorage* storage, CvPoint offset )
{
    CvMat mstub, *mask = cvGetMat( _mask, &mstub );
    CvMemStorage* tempStorage = storage ? storage : cvCreateMemStorage();
    CvSeq *contours, *c;
    int nContours = 0;
    CvContourScanner scanner;
    
    // clean up raw mask
    cvMorphologyEx( mask, mask, 0, 0, CV_MOP_OPEN, 1 );
    cvMorphologyEx( mask, mask, 0, 0, CV_MOP_CLOSE, 1 );
    // find contours around only bigger regions
    scanner = cvStartFindContours( mask, tempStorage,
        sizeof(CvContour), CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, offset );
    
    while( (c = cvFindNextContour( scanner )) != 0 ) 
    {
        double len = cvContourPerimeter( c );
        double q = (mask->rows + mask->cols)/perimScale; // calculate perimeter len threshold
        if( len < q ) //Get rid of blob if it's perimeter is too small
            cvSubstituteContour( scanner, 0 );
        else //Smooth it's edges if it's large enough
        {
            CvSeq* newC;
            if( poly1Hull0 ) //Polygonal approximation of the segmentation 
                newC = cvApproxPoly( c, sizeof(CvContour), tempStorage, CV_POLY_APPROX_DP, 2, 0 ); 
            else //Convex Hull of the segmentation
                newC = cvConvexHull2( c, tempStorage, CV_CLOCKWISE, 1 );
            cvSubstituteContour( scanner, newC );
            nContours++;
        }
    }
    contours = cvEndFindContours( &scanner );
    // paint the found regions back into the image
    cvZero( mask );
    for( c=contours; c != 0; c = c->h_next ) 
        cvDrawContours( mask, c, cvScalarAll(255), cvScalarAll(0), -1, CV_FILLED, 8,
            cvPoint(-offset.x,-offset.y));
    if( tempStorage != storage )
    {
        cvReleaseMemStorage( &tempStorage );
        contours = 0;
    }
    return contours;
}

_mask是一个二值图像，可以是Canny边缘检测或cvThreshold等函数得到的二值图像。