Improve the quality by applying adaptive threshold in javacv/opencv ?

Question

I'm try to improve my image quality by applying following shareholding to input image.

        CvSize sz = cvSize(img.width(), img.height());
        IplImage gry = cvCreateImage(sz, img.depth(), 1);
        cvCvtColor(img, gry, CV_BGR2GRAY);
        cvAdaptiveThreshold(gry, gry, 255, CV_ADAPTIVE_THRESH_MEAN_C, CV_THRESH_BINARY_INV, 5, 4);

This is my input file

by applying threshold I need to draw all the lines in white and all other areas in black but in my out put there are some missing lines. So please can some one explain how to overcome with this problem ?

This is my out put after applying above threshold.

Answer 1

you should do erosion (cvErode() in opencv) and then dilate (cvDilate()) to get rid of the small speckles. Hope this helps

Answer 2

I hope you've already found the answer, if not.... Try some gaussian blur before you threshold:

Mat image = imread("mX5h6.jpg", IMREAD_GRAYSCALE);
GaussianBlur(image, image, Size(3, 3), 0, 0);
adaptiveThreshold(image, image, 255, CV_ADAPTIVE_THRESH_MEAN_C, CV_THRESH_BINARY_INV, 5, 4);
imshow("image", image);