[英]OpenCV histogram doesn't update, despite new video data
我正在尝试计算来自单通道黑白视频流的每一帧的直方图。 最终,我将这些直方图的投影反馈给OpenCV的camshift函数。
这是我的代码:
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/opencv.hpp"
#include "opencv2/core/core.hpp"
#include <iostream>
#include <vector>
using namespace std;
using namespace cv;
int main(int argc, char* argv[]) {
Mat frame, back, fore, hist, image, v_hist;
BackgroundSubtractorMOG2 bgs;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
int bins = 8;
int histSize[] = { bins };
float range[] = { 0, 255 }; //values will range from 0 to 256
const float* histRange = { range };
bool uniform = true, accumulate = true;
VideoCapture cap(0);
if (!cap.isOpened()) {
cout << "Cannot open the video cam" << endl;
return -1;
}
namedWindow("histogram",CV_WINDOW_AUTOSIZE);
namedWindow("Foreground",CV_WINDOW_AUTOSIZE);
for (;;) {
if (!cap.read(frame)){
cout << "No frame" << endl;
break;
}
frame.copyTo(image);
//***start mask computation***
bgs.operator()(image, fore);
bgs.getBackgroundImage(back);
findContours(fore, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);
int idx = 0;
for( ; idx >= 0; idx = hierarchy[idx][0] ){
Scalar color( 255, 255, 255 );
drawContours( fore, contours, idx, color, CV_FILLED, 8, hierarchy );
}
erode(fore, fore, Mat());
erode(fore, fore, Mat());
dilate(fore, fore, Mat());
dilate(fore, fore, Mat());
//****end mask computation****
calcHist( &fore, 1, 0, Mat(), v_hist, 1, histSize, &histRange, uniform, accumulate);
int hist_w = 512; int hist_h = 400;
int bin_w = cvRound( (double) hist_w/ (*histSize) );
Mat histImage( hist_h, hist_w, CV_8UC3, Scalar(0, 0, 0) );
normalize( v_hist, v_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
//draw histogram
for (int i = 1; i < *histSize; i++)
line ( histImage,
Point(bin_w*(i-1), hist_h - cvRound(v_hist.at<float>(i-1)) ),
Point( bin_w*(i), hist_h - cvRound(v_hist.at<float>(i)) ),
Scalar( 255, 255, 255), 2, 8, 0 );
if(!histImage.empty()) imshow("histogram", histImage);
if(!fore.empty()) imshow("Foreground", fore);
if (waitKey(30) >= 0) break;
}
return 0;
}
这是输出最初的样子(请记住,一开始,前景遮罩全是黑色的):
..但即使在前景提取之后,直方图仍保持不变:
该直方图似乎仅适用于第一个全黑图像,这就是为什么线从x =(x轴的长度)/ 8开始到y = 0的原因。 这是有道理的,因为直方图有8个bin,此原始图片中的所有值均为0。(FWIW:当只有2个bin时,线从x =(x轴的长度)开始到y = 0 / 2)。
我过去曾使用OpenCV绘制过线和矩形,并且与我在这里所做的没什么不同,因此我可以肯定地说,这与任何绘制功能都没有关系。 如果是这样,随着新视频数据的进入,直方图似乎没有更新。
有谁知道为什么会这样吗?
虽然我还没有找出绘制的直方图为什么不更新的确切原因,但我已经进行了一些测试,现在充满信心,直方图会在不同帧之间变化。
这是我添加到先前程序中的代码:
//new declarations
Mat last_hist;
bool first = true;
//code is the same, leading up to...
normalize( v_hist, v_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat() );
if (!first){
eq = std::equal( v_hist.begin<uchar>(), v_hist.end<uchar>(), last_hist.begin<uchar>() );
if (eq)
cout << "hists equal" << endl;
else
cout << "hists not equal" << endl;
}
else
first = false;
//draw histogram
for (int i = 1; i < *histSize; i++)
//...
if(!frame.empty())imshow("Frame", frame);
v_hist.copyTo(last_hist);
if (waitKey(30) >= 0) break;
//from here to end is the same
normalize()
之后在条件语句中使用STL equal()
来自如何检查OpenCV中两个矩阵是否相同 。
当我运行此代码时,在前景蒙版受到充分干扰后,我会看到“历史不相等”打印了几帧。
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