`cv::findContours` method doesn't work properly when detect text regions on white background. (OpenCV)

问题

What problem I face is that when I run the opencv code to detect contours in an image,I can't get inside the boundary of the image and thus the program gets me a contour on the boundary of the image.

 Mat3b xyres;
cvtColor(img, xyres, COLOR_GRAY2BGR);
for (int i = 0; i < rects.size(); ++i)
{
    rectangle(xyres, rects[i], Scalar(0, 0, 255), 2);
}

Size size2(700, 800);
        resize(xyres, xyres, size2);
imshow("XY-Cut Result", xyres);

waitKey();

The image output looks something like this:

I need something like this:

回答1:

We do findContours for white objects on black background.

While your binary image is black chars on white background, you should threshold it with flag THRESH_BINARY_INV to get white on black. Then do findContours.

来源：https://stackoverflow.com/questions/48314605/cvfindcontours-method-doesnt-work-properly-when-detect-text-regions-on-whit