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 preceding code for converting the original image to grayscale and applying a 7 x 7 median filter should still be used (the first image in the following diagram 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 (second image in the diagram), then a binary threshold with a very low cutoff (third image in the diagram), and a 3 x 3 median blur, producing the final evil mask (fourth image in the diagram):
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)
The following diagram shows the evil effect applied in the fourth image:
Now that we have an evil mask, we can overlay this mask onto the cartoonified painting image as we did with the regular sketch edge mask. The final result is shown on the right-hand side of the following diagram:
