/** * Convolution * by Daniel Shiffman.   *  * Applies a convolution matrix to a portion of the index.   * Move mouse to apply filter to different parts of the image.  */PImage img;int w = 80;// It's possible to convolve the image with // many different matrices  float[][] matrix = { { -1, -1, -1 },                       { -1,  9, -1 },                       { -1, -1, -1 } }; void setup() {  size(200, 200);  frameRate(30);  img = loadImage("end.jpg");}void draw() {  // We're only going to process a portion of the image  // so let's set the whole image as the background first  image(img,0,0);  // Where is the small rectangle we will process  int xstart = constrain(mouseX-w/2,0,img.width);  int ystart = constrain(mouseY-w/2,0,img.height);  int xend = constrain(mouseX+w/2,0,img.width);  int yend = constrain(mouseY+w/2,0,img.height);  int matrixsize = 3;  loadPixels();  // Begin our loop for every pixel  for (int x = xstart; x < xend; x++) {    for (int y = ystart; y < yend; y++ ) {      color c = convolution(x,y,matrix,matrixsize,img);      int loc = x + y*img.width;      pixels[loc] = c;    }  }  updatePixels();}color convolution(int x, int y, float[][] matrix,int matrixsize, PImage img){  float rtotal = 0.0;  float gtotal = 0.0;  float btotal = 0.0;  int offset = matrixsize / 2;  for (int i = 0; i < matrixsize; i++){    for (int j= 0; j < matrixsize; j++){      // What pixel are we testing      int xloc = x+i-offset;      int yloc = y+j-offset;      int loc = xloc + img.width*yloc;      // Make sure we haven't walked off our image, we could do better here      loc = constrain(loc,0,img.pixels.length-1);      // Calculate the convolution      rtotal += (red(img.pixels[loc]) * matrix[i][j]);      gtotal += (green(img.pixels[loc]) * matrix[i][j]);      btotal += (blue(img.pixels[loc]) * matrix[i][j]);    }  }  // Make sure RGB is within range  rtotal = constrain(rtotal,0,255);  gtotal = constrain(gtotal,0,255);  btotal = constrain(btotal,0,255);  // Return the resulting color  return color(rtotal,gtotal,btotal);}