Convert one pixel from color space to another

Question

How can I convert just one pixel from from one color space to another? I figured out that cv::cvtColor does not accept cv::Scalar neither cv::Vec3f. Or in other words, it accepts them but raise an error since they are going to be processed as 1-Channel cv::Mat at the end. Is there a better (cleaner like directly from cv::Scalar or cv::VecYX) way than constructing a one element cv::Mat like this?

cv::Vec3b covert_1_pixel_to_lab(cv::Vec3b const& src){
    cv::Vec3b src(b,g,r);
    cv::Mat src_mat(1, 1, CV_8UC3);
    src_mat.ptr<uchar>(0)[0] = src(0);
    src_mat.ptr<uchar>(0)[1] = src(1);
    src_mat.ptr<uchar>(0)[2] = src(2);
    cv::Mat dst_mat;
    cv::cvtColor(src_mat, dst_mat, cv::COLOR_BGR2Lab);
    return cv::Vec3b(dst_mat.ptr<uchar>(0)[0],
        dst_mat.ptr<uchar>(0)[1],
        dst_mat.ptr<uchar>(0)[2]);
}

Before marking as a dupe, check if [this](http://stackoverflow.com/q/35737032/5008845) helps — Miki, Mar 03 '16 at 08:06
@miki I swear I searched million time but did not find that question :D. thanks :) — Humam Helfawi, Mar 03 '16 at 08:07

score 1 · Answer 1 · answered Mar 03 '16 at 07:37

1

You can use ROI via Rects:

Rect r=Rect(x,y,1,1);
Mat img2=img(r);
cvtColor(img2,img2,CV_BGR2Luv);//or any other color space

This may make the change on img as well

answered Mar 03 '16 at 07:37

Saransh Kejriwal

2,467
5
15
39

1

Thanks but I have the value as cv::Vec3b not as cv::Mat.. It is not part of any image – Humam Helfawi Mar 03 '16 at 07:37

Convert one pixel from color space to another

1 Answers1