Ways to better thread the code to decrease computation time [closed] - c++

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I have written an opencv code that reads a video, looks for red pixels in each frame, and exports the frame as a png file if the number of red pixels exceeds a certain amount. The code works well, but I am looking for ways to further reduce computation time because the videos are 4-5 hrs long. I was reading posts on using parallel_pipeline and was wondering if using that would substantially speed up the process. Based on what I read, it seems that I will have to assign a thread for each major task (reading video frames, color detection/thresholding with inRange, and image saving). So my question is:
1) Would this speed up the process compared to the default multithreading that opencv does?
2) Given what the code needs to do, are there more appropriate ways for multithreading than parallel_pipeline?
I am fairly new to this topic, so any help is much appreciated!
/**
* #CheckMotionParallel
* #Motion detection using color detection and image thresholding
*/
//opencv
#include "opencv2/imgcodecs.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/videoio.hpp"
#include <opencv2/highgui.hpp>
#include <opencv2/video.hpp>
//C
#include <stdio.h>
//C++
#include <iostream>
#include <sstream>
#include "tbb/blocked_range.h"
#include "tbb/parallel_for.h"
#include "tbb/parallel_reduce.h"
#include "tbb/task_scheduler_init.h"
#include "tbb/mutex.h"
#include "tbb/tbb_thread.h"
#include "tbb/blocked_range2d.h"
using namespace cv;
using namespace std;
using namespace tbb;
void help();
void help()
{
cout
<< "--------------------------------------------------------------------------" << endl
<< "Note for program CheckMotion" << endl
<< "CheckMotion does the following" << endl
<< "1) It searches each frame in a video and looks for a specified range of colors in the frame" << endl
<< "2) Pixels falling within the range will be converted to white while everything else is turned to black" << endl
<< "3) For each frame, the program gives: frame number/time stamp, total pixel count, and white pixel count" << endl
<< "4) For frames whose white pixel count exceeds a threshold, it will export those frames as individial png files" << endl
<< "--------------------------------------------------------------------------" << endl
<< endl;
}
int64 startTime;
int NumThreads = task_scheduler_init::default_num_threads();
int main(int argc, char**)
{
//Print out program note
help();
///Part I: Read-in the video
VideoCapture cap("/Users/chi/Desktop/Video analyses/testvideo4.mp4");
//Error message if the video cannot be opened
//Create an object denoting the frames
//Create a window for showing the video as CheckMotion runs
//For loop looking through frames
if(cap.isOpened()) {
startTime = getTickCount();
Mat frame;
for(;;)
{
//Show each frame in the video window previously created
double tfreq = getTickFrequency();
double secs = ((double) getTickCount()-startTime)/tfreq;
cap >> frame;
// namedWindow("Frame");
// imshow("Frame",frame);
//
waitKey(10);
//Create a string for frame number that gets updated for each cycle of the loop
stringstream ss;
ss << cap.get(CAP_PROP_POS_FRAMES);
string FrameNumberString = ss.str();
stringstream maskedfilename;
stringstream rawfilename;
//Create filenames for later use in result output and image save using frame number as ref
maskedfilename << "/Users/chi/Desktop/test/masked" << FrameNumberString.c_str() << ".png";
rawfilename << "/Users/chi/Desktop/test/raw" << FrameNumberString.c_str() << ".png";
///Part II: Image thresholding and image saving
//Create an object representing new images after thresholding
Mat masked;
//inRange function that convert the pixels that fall within the specified range to white and everything else to black
//The Range is specified by a lower [Scalar(200,200,200)] and an upper [Scalar(255,255,255)] threshold
//A color is defined by its BGR score
//The thresholded images will then be represented by the object "masked"
inRange(frame, Scalar(10,0,90), Scalar(50,50,170), masked);
//Creating integer variables for total pixel count and white pixel count for each frame
int totalpixel;
int whitepixel;
//Total pixel count equals the number of rows and columns of the frame
totalpixel = masked.rows*masked.cols;
//Using countNonZero function to count the number of white pixels
whitepixel = countNonZero(masked);
//Output frame number, total pixel count and white pixel count for each frame
//Exit the loop when reaching the last frame (i.e. pixel count drops to 0)
if(totalpixel==0){
cout << "End of the video" << endl;
cout << "Number of threads: " << NumThreads << endl;
cap.release();
break;
}
else {
cout
<< "Frame:" << ss.str() << endl
<< "Number of total pixels:" << totalpixel << endl
<< "Pixels of target colors:" << whitepixel << endl
<< "Run time = " << fixed << secs << "seconds" << endl
<< endl;
//Save the frames with white pixel count larger than a user-determined value (100 in present case)
//Save both the orignal as well as the procesed images
if (whitepixel > 50){
imwrite(rawfilename.str(),frame);
imwrite(maskedfilename.str(),masked);
}
}
}
}
}

Answer 1

Just remove this line :)
waitKey(10);
Then replace endl with '\n'.