// Input image already converted to a matrix
Imgproc.cvtColor(matrixImage, matrixImage, Imgproc.COLOR_BGR2GRAY);

// Gaussian blur
Imgproc.GaussianBlur(matrixImage, matrixImage, new Size(7,7), 0);

Imgproc.threshold(matrixImage, matrixImage, 125, 255, Imgproc.THRESH_BINARY_INV);

// This is my current approach for removing noise. However, there is still
// a lot of random areas that can be removed.

// Remove specs from image
Mat morphingMatrix = Mat.ones(3,3, CV_8UC1);
Imgproc.morphologyEx(matrixImage, matrixImage, Imgproc.MORPH_OPEN, morphingMatrix);

// Image denoising
Photo.fastNlMeansDenoising(matrixImage, matrixImage);