Resize an image to a square but keep aspect ratio c++ opencv

Question

Is there a way of resizing images of any shape or size to say [500x500] but have the image\'s aspect ratio be maintained, levaing the empty space be filled with whi

Answer 1

A general approach:

cv::Mat utilites::resizeKeepAspectRatio(const cv::Mat &input, const cv::Size &dstSize, const cv::Scalar &bgcolor)
{
    cv::Mat output;

    double h1 = dstSize.width * (input.rows/(double)input.cols);
    double w2 = dstSize.height * (input.cols/(double)input.rows);
    if( h1 <= dstSize.height) {
        cv::resize( input, output, cv::Size(dstSize.width, h1));
    } else {
        cv::resize( input, output, cv::Size(w2, dstSize.height));
    }

    int top = (dstSize.height-output.rows) / 2;
    int down = (dstSize.height-output.rows+1) / 2;
    int left = (dstSize.width - output.cols) / 2;
    int right = (dstSize.width - output.cols+1) / 2;

    cv::copyMakeBorder(output, output, top, down, left, right, cv::BORDER_CONSTANT, bgcolor );

    return output;
}