尝试自定义屏幕

<h1>green screen web page</h1>

<script src="https://www.dukelearntoprogram.com/course1/common/js/image/simpleimage.js"> </script>

<canvas id="can1"></canvas>
<canvas id="can2"></canvas>

<p>
foreground: <input type="file" multiple="false" accept="image/*" id="fgfile" onchange="loadforegroundimage()">
</p>

<p>
background: <input type="file" multiple="false" accept="image/*" id="bgfile" onchange="loadbackgroundimage()">
</p>

<input type="button" id="button" value="create composite" onclick="dogreenscreen()">

<input type="button" id="button" value="clear canvas" onclick="clearcanvas()">

h1 {
  font-size: 20pt;
  font-family: arial;
  color: #4b0082;
}

body {
  background-color: #faebd7;
}

p {
  font-size: 13pt;
}

canvas {
  width: 380px;
  background-color: #7b68ee;
  border: 2px solid #a9a9a9;
}

input {
  font-size: 12pt;
}

var fgimage = null;
var bgimage = null;
var can1 = null;
var can2 = null;

function loadForegroundImage(){
  can1 = document.getElementById("can1");
  var imgFile = document.getElementById("fgfile");
  fgimage = new SimpleImage(imgFile);
  fgimage.drawTo(can1);
}

function loadBackgroundImage(){
  can2 = document.getElementById("can2");
  var imgFile = document.getElementById("bgfile");
  bgimage = new SimpleImage(imgFile);
  bgimage.drawTo(can2);
}

function doGreenScreen(){
  if (fgimage==null || !fgimage.complete()) {
    alert("Foreground not loaded");
    return;
  }
  if (bgimage==null || !bgimage.complete()) {
    alert("Background not loaded");
    return;
  }
  clearCanvas();

  var output = new SimpleImage(fgimage.getWidth(), fgimage.getHeight());

  for (var pixel of fgimage.values()) {
    if (pixel.getGreen()> pixel.getRed() + pixel.getBlue()) {
      var x = pixel.getX();
      var y = pixel.getY();
      var bgpixel = bgimage.getPixel(x, y);
      output.setPixel(x, y, bgpixel);
    }
    else {
      output.setPixel(pixel.getX(), pixel.getY(), pixel);
    }
  }
  output.drawTo(can1);
}

function clearCanvas(){
  can1 = document.getElementById("can1");
  can2 = document.getElementById("can2");

  var context1 = can1.getContext("2d");
  var context2 = can2.getContext("2d");
  context1.clearRect(0,0,can1.width,can1.height);
  context2.clearRect(0,0,can2.width,can2.height);
}