Applying an edge detection filter

Edge detection is an image processing technique that identifies regions where there is a significant change in the brightness of the image. It provides a way to detect the boundaries of objects and changes in the topology of the surface. It has applications in the field of computer vision, image processing, image analysis, and image pattern recognition. It can also be used to create some visually interesting effects. For example, it can make a 3D scene look similar to a 2D pencil sketch, as shown in the following image. To create this image, a teapot and torus were rendered normally, and then an edge detection filter was applied in a second pass:

The edge detection filter that we'll use here involves the use of a convolution filter, or convolution kernel (also called a filter kernel). A convolution filter is a matrix that defines how to transform a pixel by replacing it with the sum of the products between the values of nearby pixels and a set of pre-determined...