如何更改cv :: Mat中所有像素的值

Question

I have a simple function that attempts to loop through all the pixels in a single channel cv::Mat. Its not functioning correctly. I'm running this in xcode on ios sim.

cv::Mat fillEdge(cv::Mat floated) {
    float currentColor = 255.0;
    cv::Size shape = floated.size();
    int h = shape.height;
    int w = shape.width;

    int count = 1;

    for(int y = 0; y!= h; y++) {
        for(int x = 0; x!= w; x++) {
            cv::Point2i p(y, x);
            floated.at<int>(p) = currentColor;
        }
    }
    std::cout << floated.channels() << std::endl;
    // prints 1


    std::cout << floated << std::endl;
    return floated;
}

For some reason it prints a striped image.

Here is what the output of the cv::Mat looks like before the function returns

[255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,
0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,
0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,
0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   0, 255,   0,   0,   ...

Answer 1

You should use setTo :

cv::Mat fillEdge(cv::Mat floated) {
    float currentColor = 255.0;
    floated.setTo(cv::Scalar(currentColor));
    return floated;
}

Answer 2

Ok, I changed your for loops condition check, changed the definition of your Point2i and also changed the template type of your at method from int to float , to maintain type integrity.

This should work now:

cv::Mat fillEdge(cv::Mat floated) {
    float currentColor = 255.0;
    cv::Size shape = floated.size();
    int h = shape.height;
    int w = shape.width;

    int count = 1;

    for(int y = 0; y < h; y++) {
        for(int x = 0; x < w; x++) {
            cv:Point2i p = cv:Point2i(x,y);
            floated.at<float>(p) = currentColor;
            //floated.at<float>(y,x) = currentColor; //You could also replace the two lines above with direct indexing (be careful with the order of the axis, as pointed by @Micka in the comments)
        }
    }
    std::cout << floated.channels() << std::endl;
    // prints 1


    std::cout << floated << std::endl;
    return floated;
}