Blending a color image with a greyscale image in OpenCV 2

Question

I want to blend a color (RGB) image with a greyscale image in OpenCV 2. I am currently getting runtime errors and the cause seems to be that I am using different types for each image pixel. e.g. the color image is CV_8U. My code:

cv::Mat copy;
    image.copyTo(copy);
    cv::cvtColor(copy, copy, CV_BGR2GRAY);
    threshold(copy, copy, 0, 255,3 );
    addWeighted( image, 0.5f, copy, 0.5f, 0.0,image);

The error is in the addWeighted function. I am unsure how to blend these two images.

Answer 1

After cvtcolor, your grayscale image is in one channel. Change it back to three channel after you have performed threshold. So, between threshold and addWeighted, add the statement:

cv::cvtColor ( copy, copy, CV_GRAY2BGR );

Also, I am not sure what you want to achieve. If you want to just extract the regions that are white, you are better off using the cv::bitwise_and.