OpenCV MatchTemplate in C# is too slow compared to Python

Question

I've programmed a solution in Python which worked great, but required several libraries to install and a lot of burocratic setup to work. I've decided to build it with a GUI in C# on Visual Studio Community 2017 but in the first successful function the result was way slower than in Python. Which IMO it should actually be faster.

The code essentially is just doing a needle in a haystack image search, by getting all images from a folder and testing each needle (total 60 images) in a haystack, in python I return the string, but in C# I'm only printing.

My code in Python is the following:

def getImages(tela):
    retorno = []
    folder = 'Images'
    img_rgb = cv2.imread(tela)
    for filename in os.listdir(folder):
        template = cv2.imread(os.path.join(folder,filename))
        w, h = template.shape[:-1]
        res = cv2.matchTemplate(img_rgb, template, cv2.TM_CCOEFF_NORMED)
        threshold = .96
        loc = np.where(res >= threshold)
        if loc[0]>0:
            retorno.append(filename[0]+filename[1].lower())
            if len(retorno)> 1:
                return retorno

and in C#:

Debug.WriteLine(ofd.FileName);
Image<Bgr, byte> source = new Image<Bgr, byte>(ofd.FileName);
string filepath = Directory.GetCurrentDirectory().ToString()+"\\Images";
DirectoryInfo d = new DirectoryInfo(filepath);
var files = d.GetFiles();
foreach (var fname in files){
    Image<Bgr, byte> template = new Image<Bgr, byte>(fname.FullName);
    Image<Gray, float> result = source.MatchTemplate(template, Emgu.CV.CvEnum.TemplateMatchingType.CcoeffNormed);
    double[] minValues, maxValues;
    Point[] minLocations, maxLocations;
    result.MinMax(out minValues, out maxValues, out minLocations, out maxLocations);
    if (maxValues[0] > 0.96) {
        Debug.WriteLine(fname);
    }
}

I didn't measure the time elapsed between each one, but I can say the result in C# takes about 3 seconds and in Python about 100ms.

There is room for optimization, if anyone would like to suggest any improvements, they are welcome.

Answer 1

The issue is that in Python code you finish the iteration when at least one match is added to retorno:

if len(retorno)> 1:
  return retorno

In C# sample you continue iteration until all files are looped through.