// Edge Detection 
// by REAS <http://reas.com> 

size(200, 200); 
PImage a;                    // Declare variable 'a' of type PImage 
a = loadImage("house.jpg");  // Load the images into the program 
image(a, 0, 0);              // Displays the image from point (0,0) 
 
// A new array to store the modified image 
int[][] output = new int[width/2][height]; 
 
int n2 = 3/2; 
int m2 = 3/2; 
float[][] kernel = { {-1, -1, -1}, 
                     {-1,  6, -1},                                        
                     {-1, -1, -1} }; 
 
// Convolve the image 
for(int y=0; y<height; y++) { 
  for(int x=0; x<width/2; x++) { 
    float sum = 0; 
    for(int k=-n2; k<n2; k++) { 
      for(int j=-m2; j<m2; j++) { 
        // Reflect x-j to not exceed array boundary 
        int xp = x-j; 
        int yp = y-k; 
        if (xp < 0) { 
          xp = xp + width; 
        } else if (x-j >= width) { 
          xp = xp - width; 
        } 
        // Reflect y-k to not exceed array boundary 
        if (yp < 0) { 
          yp = yp + height; 
        } else if (yp >= height) { 
          yp = yp - height; 
        } 
        sum = sum + kernel[j+m2][k+n2] * red(get(xp, yp)); 
      } 
    } 
    output[x][y] = int(sum);    
  } 
} 
 
// Display the result of the convolution 
// by copying new data into the pixel buffer 
loadPixels(); 
for(int i=0; i<height; i++) { 
  for(int j=0; j<width/2; j++) { 
    pixels[i*width + j] = color(output[j][i], output[j][i], output[j][i]); 
  } 
} 
updatePixels();