* Image Stitching (scale & translate)

 *

 * Keith O'Hara <kohara2@swarthmore.edu>

 * revised for p5 & mljs (Feb 2024)

 */

​

let cap;     // webcam capture

let p1 = []; // clicked points

let p2 = []; // window corners

​

let homography = ML.Matrix.eye(3, 3);

​

function setup() {

  createCanvas(640, 480);

  cap = createCapture(VIDEO);

  cap.size(width, height);

  cap.hide();

​

  p2.push(new p5.Vector(0, 0, 1));

  //p2.push(new p5.Vector(cap.width, 0, 1));

  p2.push(new p5.Vector(cap.width, cap.height, 1));

  //p2.push(new p5.Vector(0, cap.height, 1));

  pixelDensity(1);

  print(homography);

}

​

function estimate(p1, p2) {

  let H = ML.Matrix.eye(3, 3);

​

  if (p1.length == p2.length) {

    let as = [];

    let bs = [];

    // Creates the estimation matrix

    for (let i =0; i < p1.length; i++) {

      as.push([p2[i].x, 1, 0]);

      as.push([p2[i].y, 0, 1]);

      bs.push([p1[i].x]);

      bs.push([p1[i].y]);

    }

​

    let mls_a = new ML.Matrix(as);

    let mls_b = new ML.Matrix(bs);

    let mls_x = ML.MatrixLib.solve(mls_a, mls_b);

    let s = mls_x.data[0][0];

    let t_x =  mls_x.data[1][0];

    let t_y = mls_x.data[2][0];

​

    H.data[0][0] = s;

    H.data[1][1] = s;

    H.data[0][2] = t_x;

    H.data[1][2] = t_y;

  }    

  print(H.data);

  return H;

}

​

function mousePressed() {

  if (p1.length >= p2.length) p1 = [];

  let v = new p5.Vector(mouseX, mouseY, 1);

  p1.push(v);

​

  if (p1.length == p2.length) {

    homography = estimate(p1, p2);

  }

}

​

function draw() {

  background(0);

  cap.loadPixels();

  loadPixels();

  // perform forward warping

  for (let x = 0; x < cap.width; x++) {

    for (let y = 0; y < cap.height; y++) {

      let idx = (y * cap.width + x) * 4;

​

      let v = new ML.Matrix([[x], [y], [1]]);

      let tv = homography.mmul(v);

      let x1 = Math.round(tv.get(0, 0) / tv.get(2, 0));

      let y1 = Math.round(tv.get(1, 0) / tv.get(2, 0));

      if (x1 >= 0 && x1 < width && y1 >= 0 && y1 < height) {

        let idx1 = (y1 * width + x1) * 4;

        pixels[idx1] = cap.pixels[idx];

        pixels[idx1 + 1] = cap.pixels[idx + 1];

        pixels[idx1 + 2] = cap.pixels[idx + 2];

        pixels[idx1 + 3] = cap.pixels[idx + 3];

      }

    }

  }

  updatePixels();

​

  fill(255, 255, 0);

  // draw the selected points

  for (let i = 0; i < p1.length; i++) {

    ellipse(p1[i].x, p1[i].y, 2, 2);

    text(str(i), p1[i].x, p1[i].y);

  }

}

​