Sobel Filter demonstrated in Processing
https://en.wikipedia.org/wiki/Sobel_operator
Load an image when prompted, then move mouse over left hand side.
The calculated gradient of the image is stored as two sobel tests -the X axis test in the red channel and the Y axis test in the blue channel.
Given a point on the image and a direction, I can quickly calculate the slope of the gradient. That gradient is displayed to the user as dark (decreasing), grey (no slope), and light (increasing).
In real time I can easily display the gradient at every point on the image, using the direction from the center of the image to the user's cursor.
I wrote this for the weaving algorithm @ https://github.com/i-make-robots/weaving_algorithm