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

Alireza's answer is good, however I modified the code slightly so that I don't add the vertical borders when the image fits vertically and I don't add horizontal borders when the image fits horizontally (this is closer to the original request):

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

    // initially no borders
    int top = 0;
    int down = 0;
    int left = 0;
    int right = 0;
    if( h1 <= dstSize.height) 
    {
        // only vertical borders
        top = (dstSize.height - h1) / 2;
        down = top;
        cv::resize( input, output, cv::Size(dstSize.width, h1));
    } 
    else 
    {
        // only horizontal borders
        left = (dstSize.width - w2) / 2;
        right = left;
        cv::resize( input, output, cv::Size(w2, dstSize.height));
    }

    return output;
}