Slow FPS with OpenCV C++ RaspberryPi - c++

Question

I have written a simple C++ program using OpenCV to test fps on raspberry pi.
#include <iostream>
#include <chrono>
#include <thread>
#include <unistd.h>
#include <string>
#include <opencv2/opencv.hpp>
#include <opencv2/tracking.hpp>
#include <opencv2/core/ocl.hpp>
using namespace cv;
using namespace std;
using namespace std::chrono;
using namespace std::this_thread;
using namespace cv::ml;
int main(void)
{
VideoCapture camera(0);
camera.set(CAP_PROP_FRAME_WIDTH, 640);
camera.set(CAP_PROP_FRAME_HEIGHT, 480);
camera.set(CAP_PROP_FPS, 25);
Mat frame;
while (camera.read(frame)) {
for (size_t i = 0; i < frame.dataend - frame.datastart; i++)
std::cout << frame.data[i];
}
}
I then use the following scrips to test fps.
The first uses raspvid as the input, the second used my C++ program as input
The raspvid version gets to the 25fps.
My C++ program never goes over 10fps.
Any ide why this is?
raspivid -w 640 -h 480 -fps 25 -t 120000 -o -| ffmpeg -re -i pipe:0 -y -an -c:v copy -f null /dev/null
and
./PiImageAnalyzer.out | ffmpeg -re -f rawvideo -pixel_format bgr24 -video_size 640x480 -framerate 25 -i pipe:0 -y -an -c:v copy -f null /dev/null
Update
these scripts can also be used
raspivid -w 640 -h 480 -fps 25 -t 120000 -o -| ffplay -i -
and
./PiImageAnalyzer.out | ffplay -f rawvideo -pixel_format bgr24 -video_size 640x480 -framerate 25 -i -