Edge Detection using MarvinJ JavaScript

Question

I am a beginner in Image Processing.I want to use MarvinJ javascript library to detect horizontal ,vertical and diagonal line (edge detection) given a image. I have came across a lot of code examples which told that using prewitt one can do edge detection,like the one below.

function clickExampleFiltersEdge(){
    imageProcessed.clear(0xFF000000);
    Marvin.prewitt(imageOriginal, imageProcessed);
    Marvin.invertColors(imageProcessed, imageProcessed);
    Marvin.thresholding(imageProcessed, imageProcessed, 150);
    repaint();
}