Read a sequence of frames using OpenCV/C++ - opencv

Question

I want to read a sequence of frames from any folder using openCV. All frames are in sequence i.e. (1).jpg,(2).jpg,....
I tried
VideoCapture cap;
cap.open("Directory/");
for(;;)
{
Mat frame;
cap >> frame;
}
but it doesn't work.
This question has been asked before but i don't know why this answer doesn't work for me.
OpenCV: Reading image series from a folder
do i need to rename the images?.

Answer 1

cap open should be cap.open("Directory/(%02d).jpg"); and you have to rename your images so that they look like (01).jpg,(02).jpg etc so that they have fixed length. if the images are like (001).jpg then you should use `cap.open("Directory/(%03d).jpg");
edit
#include "opencv2/opencv.hpp"
using namespace cv;
int main()
{
VideoCapture cap;
cap.open("imgs/(%02d).jpg");
int i=0;
for(;;)
{
if(i++%37==0)cap=VideoCapture("imgs/(%02d).jpg");//there are 37 frames in the dir
Mat frame;
cap >> frame;
imshow("frame",frame);
if(waitKey(1)==27)
exit(0);
}
return 0;
}

Answer 2

Try to prepare an xml/yaml file with list of names with path to the images, in the desired order. Then load the list as a vector or some resembling structure, and then open them one by one in a loop.

Answer 3

Here the full code to do read a sequence of frames with five zeros in name "frame00000.jpg, frame00001.jpg,.....,frame00010.jpg...) using string concatination idea just like matlab.
#include "stdafx.h"
#include <stdlib.h>
#include <math.h>
#include <opencv/cv.h> // include it to used Main OpenCV functions.
#include <opencv/highgui.h> //include it to use GUI functions.
using namespace std;
using namespace cv;
string intToStr(int i,string path){
string bla = "00000";
stringstream ss;
ss<<i;
string ret ="";
ss>>ret;
string name = bla.substr(0,bla.size()-ret.size());
name = path+name+ret+".jpg";
return name;
}
int main(int, char**)
{
string previous_window = "Previous frame";
string current_window = "Current frame ";
int i=0;
for(int i = 1 ; i< 10 ; i++)
{
Mat Current, Previous;
string Curr_name = intToStr(i,"D:/NU/Junior Scientist/Datasets/egtest04/frame");
string Prev_name = intToStr(i-1,"D:/NU/Junior Scientist/Datasets/egtest04/frame");
Current = imread(Curr_name,1);
Previous = imread(Prev_name,1);
namedWindow(current_window,WINDOW_AUTOSIZE);
namedWindow(current_window,WINDOW_AUTOSIZE);
imshow(current_window,Current);
imshow(previous_window,Previous);
waitKey(0);
}
}
Where "D:/NU/Junior Scientist/Datasets/egtest04/frame" is the path sting.