Revision history [back]

Efficient way to remove holes in an object

Hello,

I would like to remove holes in an object after I apply threshold function. Right now, I am applying dilate function a few times, then the erode function. It does okay, but in some cases, it changes the shape of the object.

I also tried to use the MORPH_CLOSE, but I guess it is no good against big holes.

I tried with different element size and shape but none of them helped.

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;
using namespace std;

Mat src, srcGray, srcSmooth, srcThresh;

int morpho_elem = 1; // 0: MORPH_RECT, 1: MORPH_CROSS, 2: MORPH_ELLIPSE
int morpho_size = 3;
int morpho_qty = 9;

int const smooth_kernel = 11;

int main()
{   
    src = imread("source.png", 1);

    cvtColor(src, srcGray, CV_BGR2GRAY);

    for (int i = 1; i < smooth_kernel; i = i + 2)
    {
        medianBlur(srcGray, srcSmooth, i);
    }

    threshold(srcSmooth, srcThresh, 0, 255, CV_THRESH_BINARY | CV_THRESH_OTSU);

    int dilation_type;
    if (morpho_elem == 0){ dilation_type = MORPH_RECT; }
    else if (morpho_elem == 1){ dilation_type = MORPH_CROSS; }
    else if (morpho_elem == 2) { dilation_type = MORPH_ELLIPSE; }

    Mat dilationDst, erosionDst;

    Mat element = getStructuringElement(dilation_type,
        Size(2 * morpho_size + 1, 2 * morpho_size + 1),
        Point(morpho_size, morpho_size));

    // Apply the dilation operation
    dilate(srcThresh, dilationDst, element);
    for (int i = 1; i < morpho_qty; i++)
    {
        dilate(dilationDst, dilationDst, element);
    }

    // Apply the erosion operation
    erode(dilationDst, erosionDst, element);
    for (int i = 1; i < morpho_qty; i++)
    {
        erode(erosionDst, erosionDst, element);
    }

    imshow("Final", erosionDst);

    cvWaitKey(0);

    return 0;
}

Source image:

image description

Binary image with holes: image description

Output of my attempt: image description