Edge Detection.

A high-pass filter sharpens an image. This program analyzes every pixel in an image in relation to the neighboring pixels to sharpen the image. This example is currently not accurate in JavaScript mode.

// The next line is needed if running in JavaScript Mode with Processing.js
/* @pjs preload="moon.jpg"; */

float[][] kernel = {{ -1, -1, -1}, 
                    { -1,  9, -1}, 
                    { -1, -1, -1}};
                    
PImage img;

void setup() { 
  size(640, 360);
  img = loadImage("moon.jpg"); // Load the original image
  noLoop();
}

void draw() {
  image(img, 0, 0); // Displays the image from point (0,0) 
  img.loadPixels();
  // Create an opaque image of the same size as the original
  PImage edgeImg = createImage(img.width, img.height, RGB);
  // Loop through every pixel in the image.
  for (int y = 1; y < img.height-1; y++) { // Skip top and bottom edges
    for (int x = 1; x < img.width-1; x++) { // Skip left and right edges
      float sum = 0; // Kernel sum for this pixel
      for (int ky = -1; ky <= 1; ky++) {
        for (int kx = -1; kx <= 1; kx++) {
          // Calculate the adjacent pixel for this kernel point
          int pos = (y + ky)*img.width + (x + kx);
          // Image is grayscale, red/green/blue are identical
          float val = red(img.pixels[pos]);
          // Multiply adjacent pixels based on the kernel values
          sum += kernel[ky+1][kx+1] * val;
        }
      }
      // For this pixel in the new image, set the gray value
      // based on the sum from the kernel
      edgeImg.pixels[y*img.width + x] = color(sum, sum, sum);
    }
  }
  // State that there are changes to edgeImg.pixels[]
  edgeImg.updatePixels();
  image(edgeImg, width/2, 0); // Draw the new image
}