How to read multiple images from a folder in open cv (using C)

Question

I am new to open CV and C. How do i specify multiple images for the same kind of operation.

Answer 1

if your images are (sequentially) numbered, you could abuse a hidden feature with VideoCapture, just pass it a (format) string:

VideoCapture cap("/my/folder/p%05d.jpg"); // would work with: "/my/folder/p00013.jpg", etc
while( cap.isOpened() )
{
    Mat img;
    cap.read(img);
    // process(img);
}

Answer 2

OpenCV doesn't provide any functionality for this. you can use a third party lib for reading the files from the file system. in case your images are sequentially numbered you can use @berak technique but if your files are not sequential then use can use boost::filesystem (heavy and my favorite) for reading the file. or dirent.h (small, single header only) library.
Following code uses dirent.h for this job

#include <iostream>
#include <opencv2\opencv.hpp>
#include "dirent.h"
int main(int argc, char* argv[])
{

    std::string inputDirectory = "D:\\inputImages";
    std::string outputDirectory = "D:\\outputImages";
    DIR *directory = opendir (inputDirectory.c_str());
    struct dirent *_dirent = NULL;
    if(directory == NULL)
    {
        printf("Cannot open Input Folder\n");
        return 1;
    }
    while((_dirent = readdir(directory)) != NULL)
    {
        std::string fileName = inputDirectory + "\\" +std::string(_dirent->d_name);
        cv::Mat rawImage = cv::imread(fileName.c_str());
        if(rawImage.data == NULL)
        {
            printf("Cannot Open Image\n");
            continue;
        }
        // Add your any image filter here
        fileName = outputDirectory + "\\" + std::string(_dirent->d_name);
        cv::imwrite(fileName.c_str(), rawImage);
    }
    closedir(directory);
}