OpenCV。匹配时绘制矩形

我使用 OpenCv 来查找与参考图像上的模板匹配的区域。当代码找到与模板匹配的区域时，在该区域周围绘制一个矩形，但我想要的是当代码找不到该区域时，代码不会绘制任何矩形

code:

IplImage    *res;
    CvPoint     minloc, maxloc;
    double      minval, maxval;
    int         img_width, img_height;
    int         tpl_width, tpl_height;
    int         res_width, res_height;

    NSString *path = [[NSBundle mainBundle] pathForResource:@"reference" ofType:@"jpg"];
    reference.image = [UIImage imageWithContentsOfFile:path];

    NSString *pathPatron = [[NSBundle mainBundle] pathForResource:@"template" ofType:@"jpg"];
    template.image = [UIImage imageWithContentsOfFile:pathPatron];

    IplImage *img = [self CreateIplImageFromUIImage:original.image];//
    IplImage *tpl = [self CreateIplImageFromUIImage:patron.image];

    img_width  = img->width;
    img_height = img->height;
    tpl_width  = tpl->width;
    tpl_height = tpl->height;
    res_width  = img_width - tpl_width + 1;
    res_height = img_height - tpl_height + 1;    
    res = cvCreateImage( cvSize( res_width, res_height ), IPL_DEPTH_32F, 1 );

    /* choose template matching method to be used */
    cvMatchTemplate( img, tpl, res, CV_TM_SQDIFF );

      cvMinMaxLoc( res, &minval, &maxval, &minloc, &maxloc, 0 );

        /* draw red rectangle */

    cvRectangle( img, 
                cvPoint( minloc.x, minloc.y ), 
                cvPoint( minloc.x + tpl_width, minloc.y + tpl_height ),
                cvScalar( 0, 0, 255, 0 ), 1, 0, 0 );    

    /* display images */
    reference.image = [self UIImageFromIplImage:img];

    cvReleaseImage(&img);
    cvReleaseImage(&tpl);
    cvReleaseImage(&res);

提前致谢

cvMatchTemplate并没有真正找到匹配 - 它只是计算图像和模板的相似度图。接下来，您需要确定是否存在真正的匹配或没有匹配。最简单的解决方案是与某个阈值进行比较：

if (minval < THRESHOLD)
{
    //draw rectangle
}

您需要进行一些实验才能找到该值的工作值THRESHOLD.