Filling gaps in shape edges

Question

Is there an algorithm that would perform well in terms of filling holes like those on the sample image? Dilation doesn\'t work well, cause before I eventually manage to conn

Answer 1

This is an OpenCV, C++ implementation of Mark Setchell's algorithm. It is very straightforward, uses the same kernel and convolutes the input image via the cv::filter2D function. I've, optionally, inverted the input image so target pixels have a value of 255:

//Read input Image
cv::Mat inputImage = cv::imread( "C://opencvImages//blobs.png", cv::IMREAD_GRAYSCALE );

//Invert the image:
inputImage = 255 - inputImage;

//Threshold the image so that white pixels get a value of 0 and
//black pixels a value of 10:
cv::threshold( inputImage, inputImage, 128, 10, cv::THRESH_BINARY );

Now, setup the kernel and convolute the image, like this:

//Set up the end-point kernel:
cv::Mat kernel = ( cv::Mat_(3, 3) <<
  1, 1, 1,
  1, 10, 1,
  1, 1, 1
);

//Convolute image with kernel:
cv::filter2D( inputImage, inputImage, -1 , kernel, cv::Point( -1, -1 ), 0, cv::BORDER_DEFAULT );

The direct result of the convolution is this, pixels at the end points now have a value of 110, which can be seen (barely) in this output:

Let's threshold these pixels and overlay them on the original image. This is the result (pixels in red):

Additionally, the skeleton of the image can be computed at the beginning. The skeleton has a normalized line-width of 1 pixel. The function is part of the Extended Image Processing module of OpenCV:

#include 

//Compute the skeleton of the input:
cv::Mat skel;
int algorithmType = 1;
cv::ximgproc::thinning( inputImage, skel, algorithmType );