Letterbox resize for Arapaho (https://github.com/prabindh/darknet/issues/72)

arapaho-resize-letterbox.cpp

// Call like below
// boxedMat will contain resized image
// boxedMat = __LetterBoxResize(floatMat, net->w, net->h);
//
// Taken mostly from https://jdhao.github.io/2017/11/06/resize-image-to-square-with-padding/

cv::Mat ArapahoV2::__LetterBoxResize(cv::Mat img, int w, int h)
{
    cv::Mat intermediateImg, outputImg;
    int delta_w, delta_h, top, left, bottom, right;
    int new_w = img.size().width;
    int new_h = img.size().height;

    if (((float)w / img.size().width) < ((float)h / img.size().height)) {
        new_w = w;
        new_h = (img.size().height * w) / img.size().width;
    }
    else {
        new_h = h;
        new_w = (img.size().width * h) / img.size().height;
    }
    cv::resize(img, intermediateImg, cv::Size(new_w, new_h));

    delta_w = w - new_w;
    delta_h = h - new_h;
    top = floor(delta_h / 2);
    bottom = delta_h - floor(delta_h/2);
    left = floor(delta_w / 2);
    right = delta_w - floor(delta_w/2);
    cv::copyMakeBorder(intermediateImg, outputImg, top, bottom, left, right, cv::BORDER_CONSTANT, (0,0,0));

    return outputImg;
}

Can you update the code since my last pull request on fixArapahoLibDarknetUsed, I will test it. Thanks