如何在 C++ OpenCV 中显示带有 putText 的计时器结果？

Posted 2023-02-22

【中文标题】如何在 C++ OpenCV 中显示带有 putText 的计时器结果？

【英文标题】：How can I display results of a timer with a putText in C++ OpenCV?

【发布时间】：2013-01-26 18:07:51

【问题描述】：

如何在我的 OpenCV android 应用程序中显示带有 putText 的计时器的结果？它是从相机检测视图上的特征，主要算法和计时器是用 C++ 编写的。我的 C++ JNI 文件的完整代码：

#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <vector>

using namespace std; 
using namespace cv;

extern "C" 
JNIEXPORT void JNICALL  
Java_org_opencv_samples_tutorial3_Sample3View_FindFeatures(JNIEnv* env, jobject, jint 
width, jint height, jbyteArray yuv, jintArray bgra)   

jbyte* _yuv  = env->GetByteArrayElements(yuv, 0);
jint*  _bgra = env->GetIntArrayElements(bgra, 0);

Mat myuv(height + height/2, width, CV_8UC1, (unsigned char *)_yuv);
Mat mbgra(height, width, CV_8UC4, (unsigned char *)_bgra);
Mat mgray(height, width, CV_8UC1, (unsigned char *)_yuv);

//Please make attention about BGRA byte order
//ARGB stored in java as int array becomes BGRA at native level
cvtColor(myuv, mbgra, CV_YUV420sp2BGR, 4);

vector<KeyPoint> v;

OrbFeatureDetector  detector(1);
double t = (double)getTickCount();
detector.detect(mgray, v);
t = ((double)getTickCount() - t)/getTickFrequency();
putText(mbgra, t+" detection time", Point2f(100,100), FONT_HERSHEY_PLAIN, 2, Scalar(0,0,255,255), 2);
for( size_t i = 0; i < v.size(); i++ )
    circle(mbgra, Point(v[i].pt.x, v[i].pt.y), 10, Scalar(0,0,255,255));
env->ReleaseIntArrayElements(bgra, _bgra, 0);
env->ReleaseByteArrayElements(yuv, _yuv, 0); 

问题与 putText 一致：我收到错误“'double' 和 'char const [15]' 类型的无效操作数到二进制 'operator+'”。我的计时器好吗？我还能如何显示它的结果？我会很感激你的帮助。

【参考方案1】：

't' 属于 double 类，常量“检测时间”被视为字符串。 String + double 是编译器不理解的东西，这就是它向你吐槽的原因。

请尝试以下方法：

std::stringstream s;
s << t;
s << " detection time";

putText(mbgra, s.str(), Point2f(100,100), FONT_HERSHEY_PLAIN, 2, Scalar(0,0,255,255), 2);

在上面的代码中，stringstream 类具有内置于“