how to Extract Video Frames and Save them as Images using c++ - c++

Question

I am now trying to save the frames of the video file into images on my pc. I am using Visual studio 2010 and opencv 2.3.1. In this code(shown bellow) it can save frames of image sequence but for video file I can not save the frames.
the problem specifically seems to be here:
in the function of vidoeprocessing()
string imageToSave =("output_MOG_" + frameNumberString + ".png");
bool saved = imwrite( imageToSave,fgMaskMOG);
if(!saved) {
cerr << "Unable to save " << imageToSave << endl;
}
any one can help to solve this?
Thanks in advance.
my code is this:
//opencv
#include < opencv2/opencv.hpp>
#include < opencv2/core/core.hpp>
#include < opencv2/highgui/highgui.hpp>
#include < opencv2/video/background_segm.hpp>
//#include <opencv2/imgcodecs.hpp>
#include <opencv2/imgproc/imgproc.hpp>
//#include "opencv2/videoio.hpp"
#include <opencv2/video/video.hpp>
//C
#include <stdio.h>
//C++
#include <iostream>
#include <sstream>
using namespace cv;
using namespace std;
// Global variables
Mat frame; //current frame
Mat fgMaskMOG; //fg mask fg mask generated by MOG method
Ptr<BackgroundSubtractor> pMOG; //MOG Background subtractor
int keyboard; //input from keyboard
/** Function Headers */
void help();
void processVideo(char* videoFilename);
void processImages(char* firstFrameFilename);
void help()
{
cout
<< "--------------------------------------------------------------------- -----" << endl
<< "This program shows how to use background subtraction methods provided by " << endl
<< " OpenCV. You can process both videos (-vid) and images (-img)." << endl
<< endl
<< "Usage:" << endl
<< "./bs {-vid <video filename>|-img <image filename>}" << endl
<< "for example: ./bs -vid video.avi" << endl
<< "or: ./bs -img /data/images/1.png" << endl
<< "--------------------------------------------------------------------------" << endl
<< endl;
}
/**
* #function main
*/
int main(int argc, char* argv[])
{
//print help information
help();
//check for the input parameter correctness
if(argc != 3) {
cerr <<"Incorret input list" << endl;
cerr <<"exiting..." << endl;
return EXIT_FAILURE;
}
//create GUI windows
namedWindow("Frame");
namedWindow("FG Mask MOG ");
//create Background Subtractor objects
pMOG = new BackgroundSubtractorMOG();
if(strcmp(argv[1], "-vid") == 0) {
//input data coming from a video
processVideo(argv[2]);
}
else if(strcmp(argv[1], "-img") == 0) {
//input data coming from a sequence of images
processImages(argv[2]);
}
else {
//error in reading input parameters
cerr <<"Please, check the input parameters." << endl;
cerr <<"Exiting..." << endl;
return EXIT_FAILURE;
}
//destroy GUI windows
destroyAllWindows();
return EXIT_SUCCESS;
}
//function processVideo
void processVideo(char* videoFilename) {
//create the capture object
VideoCapture capture(videoFilename);
if(!capture.isOpened()){
//error in opening the video input
cerr << "Unable to open video file: " << videoFilename << endl;
exit(EXIT_FAILURE);
}
//read input data. ESC or 'q' for quitting
while( (char)keyboard != 'q' && (char)keyboard != 27 ){
//read the current frame
if(!capture.read(frame)) {
cerr << "Unable to read next frame." << endl;
cerr << "Exiting..." << endl;
exit(EXIT_FAILURE);
}
//update the background model
pMOG->operator()(frame, fgMaskMOG,0.9);
//get the frame number and write it on the current frame
stringstream ss;
rectangle(frame, cv::Point(10, 2), cv::Point(100,20),
cv::Scalar(255,255,255), -1);
ss << capture.get(CV_CAP_PROP_POS_FRAMES);
string frameNumberString = ss.str();
putText(frame, frameNumberString.c_str(), cv::Point(15, 15),
FONT_HERSHEY_SIMPLEX, 0.5 , cv::Scalar(0,0,0));
//show the current frame and the fg masks
imshow("Frame", frame);
imshow("FG Mask MOG ", fgMaskMOG);
//get the input from the keyboard
keyboard = waitKey( 30 );
}
/*
string imageToSave =("output_MOG_" + frameNumberString + ".bmp");
bool saved = imwrite( imageToSave,fgMaskMOG);
if(!saved) {
cerr << "Unable to save " << imageToSave << endl;
}
*/
//delete capture object
capture.release();
}
/**
* #function processImages
*/
void processImages(char* fistFrameFilename) {
//read the first file of the sequence
frame = imread(fistFrameFilename);
if(frame.empty()){
//error in opening the first image
cerr << "Unable to open first image frame: " << fistFrameFilename << endl;
exit(EXIT_FAILURE);
}
//current image filename
string fn(fistFrameFilename);
//read input data. ESC or 'q' for quitting
while( (char)keyboard != 'q' && (char)keyboard != 27 ){
//update the background model
pMOG->operator()(frame, fgMaskMOG,0.9);
//get the frame number and write it on the current frame
size_t index = fn.find_last_of("/");
if(index == string::npos) {
index = fn.find_last_of("\\");
}
size_t index2 = fn.find_last_of(".");
string prefix = fn.substr(0,index+1);
string suffix = fn.substr(index2);
string frameNumberString = fn.substr(index+1, index2-index-1);
istringstream iss(frameNumberString);
int frameNumber = 0;
iss >> frameNumber;
rectangle(frame, cv::Point(10, 2), cv::Point(100,20),
cv::Scalar(255,255,255), -1);
putText(frame, frameNumberString.c_str(), cv::Point(15, 15),
FONT_HERSHEY_SIMPLEX, 0.5 , cv::Scalar(0,0,0));
//show the current frame and the fg masks
imshow("Frame", frame);
imshow("FG Mask MOG ", fgMaskMOG);
//get the input from the keyboard
keyboard = waitKey( 30 );
//search for the next image in the sequence
ostringstream oss;
oss << (frameNumber + 1);
string nextFrameNumberString = oss.str();
string nextFrameFilename = prefix + nextFrameNumberString + suffix;
//read the next frame
frame = imread(nextFrameFilename);
if(frame.empty()){
//error in opening the next image in the sequence
cerr << "Unable to open image frame: " << nextFrameFilename << endl;
exit(EXIT_FAILURE);
}
//update the path of the current frame
fn.assign(nextFrameFilename);
// save subtracted images
string imageToSave =("output_MOG_" + frameNumberString + ".png");
bool saved = imwrite( imageToSave,fgMaskMOG);
if(!saved) {
cerr << "Unable to save " << imageToSave << endl;
}
}
}

Answer 1

This is a small sample using your webcam. You can easily adapt it to use a video:
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
Ptr<BackgroundSubtractor> pMOG = new BackgroundSubtractorMOG2();
Mat fg_mask;
Mat frame;
int count = -1;
for (;;)
{
// Get frame
cap >> frame; // get a new frame from camera
// Update counter
++count;
// Background subtraction
pMOG->operator()(frame, fg_mask);
imshow("frame", frame);
imshow("fg_mask", fg_mask);
// Save foreground mask
string name = "mask_" + std::to_string(count) + ".png";
imwrite("D:\\SO\\temp\\" + name, fg_mask);
if (waitKey(1) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}