open image files with unicode names using imread

Question

I need reading image files with Unicode names however openCV function imread's argument for image names supports only strings. how can I save my Unicode path to string objects. Is there any solution for this?

Answer 1

You can:

1. open the file with ifstream,
2. read it all in a std::vector<uchar>,
3. decode it with cv::imdecode.

See the example below that loads into img2 an image with a Unicode filename using ifstream:

#include <opencv2\opencv.hpp>
#include <vector>
#include <fstream>

using namespace cv;
using namespace std;

int main()
{
    // This doesn't work with Unicode characters

    Mat img = imread("D:\\SO\\img\\æbärnɃ.jpg");
    if (img.empty()) {
        cout << "Doesn't work with Unicode filenames\n";
    }
    else {
        cout << "Work with Unicode filenames\n";
        imshow("Unicode with imread", img);
    }

    // This WORKS with Unicode characters

    // This is a wide string!!!
    wstring name = L"D:\\SO\\img\\æbärnɃ.jpg";

    // Open the file with Unicode name
    ifstream f(name, iostream::binary);

    // Get its size
    filebuf* pbuf = f.rdbuf();
    size_t size = pbuf->pubseekoff(0, f.end, f.in);
    pbuf->pubseekpos(0, f.in);

    // Put it in a vector
    vector<uchar> buffer(size);
    pbuf->sgetn((char*)buffer.data(), size);

    // Decode the vector
    Mat img2 = imdecode(buffer, IMREAD_COLOR);

    if (img2.empty()) {
        cout << "Doesn't work with Unicode filenames\n";
    }
    else {
        cout << "Work with Unicode filenames\n";
        imshow("Unicode with fstream", img2);
    }

    waitKey();
    return 0;
}

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If you're using Qt, you can do this a little more conveniently with QFile and QString, since QString natively handle Unicode characters, and QFile provides an easy way to the the file size:

QString name = "path/to/unicode_img";
QFile file(name);
file.open(QFile::ReadOnly);
qint64 sz = file.size();
std::vector<uchar> buf(sz);
file.read((char*)buf.data(), sz);
cv::Mat3b img = cv::imdecode(buf, cv::IMREAD_COLOR);

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For completeness, here you can see how to do this in Python