Cartoons and comics always have both good and bad characters. With the right combination of edge filters, a scary image can be generated from the most innocent-looking people! The trick is to use a small-edge filter that will find many edges all over the image, then merge the edges using a small Median filter.
We will perform this on a grayscale image with some noise reduction, so the previous code for converting the original image to grayscale and applying a 7 x 7 Median filter should be used again (the first image in the following figure shows the output of the grayscale Median blur). Instead of following it with a Laplacian filter and Binary threshold, we can get a scarier look if we apply a 3 x 3 Scharr gradient filter along x and y (the second image in the figure), and then apply a binary threshold with a very low cutoff (the third image in the figure) and a 3 x 3 Median blur, producing the final "evil" mask (the fourth image in the figure):
Mat gray; cvtColor(srcColor, gray, CV_BGR2GRAY); const int MEDIAN_BLUR_FILTER_SIZE = 7; medianBlur(gray, gray, MEDIAN_BLUR_FILTER_SIZE); Mat edges, edges2; Scharr(srcGray, edges, CV_8U, 1, 0); Scharr(srcGray, edges2, CV_8U, 1, 0, -1); edges += edges2; // Combine the x & y edges together. const int EVIL_EDGE_THRESHOLD = 12; threshold(edges, mask, EVIL_EDGE_THRESHOLD, 255, THRESH_BINARY_INV); medianBlur(mask, mask, 3);
Now that we have an "evil" mask, we can overlay this mask onto the cartoonified "painting" image like we did with the regular "sketch" edge mask. The final result is shown on the right side of the following figure: