I am trying to detect two vertical lines shown in the attached images using some image processing methods. The line are in low contrast.
The location is shown in the first image with yellow arrows. The original image is also attached.
I tried using adaptiveThresholding and normal thresholding using maximum and minimum at local windows. But I can't detect the lines.
Any ideas how to detect the two vertical lines in image processing?
There is some trick when contrast is low in bright pixels. There is thresholding method - otsu thresholding (https://en.wikipedia.org/wiki/Otsu%27s_method), which can be used to detect bright side of histogram. After that, you can normalize that part of histogram to (0,255) and set 0 to darker pixels as in code below:
cv::Mat img = cv::imread("E:\\Workspace\\KS\\excercise\\sjB8q.jpg", 0);
cv::Mat work;
for (int i = 0; i < 4; i++) // number of iterations has to be adjusted
{
cv::threshold(img, work, 30, 255, CV_THRESH_OTSU);
cv::bitwise_and(img, work,img);
cv::normalize(img, img, 0, 255, cv::NORM_MINMAX, -1, work);
}
Then your contrast will be better like in pictures below (for different iterations):
i=2:
i=4:
i =6:
After that preprocessing detecting dark lines should be easier. That answer is just explanation of idea. If you want to know more just ask in comment.
