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Implement green screen algorithms using JavaScript

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2023-09-23 11:57:051023browse

使用 JavaScript 实现绿屏算法

The green background image has been changed and replaced with any effects or other images that use green Screen algorithm, also known as chroma key algorithm. In short, what we are doing is Swap all green pixels in the forward image with their matching counterparts in the backward image Background picture.

Also, we need to remember that the size of the output image should match the size of the output image forward image. In the next step, copy the pixels from the forward image into the new image image. Use matching pixels from the background image instead of copying green pixels.

Don’t miss to include the following source files into your HTML code before applying the following Code -

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

The JavaScript code required to implement this algorithm is provided below. To use it you must create Write your own HTML code.

HTML source code

You must add this HTML code to an element of your HTML document. 

<h1>Green Screen Algorithm Implementation using JavaScript with TutorialsPoint </h1>
<canvas id="image1"></canvas>
<canvas id="image2"></canvas>
<br />
<p>
   First Image: <input type="file"
   id="myImageFile" multiple="false"
   onChange="frontimg()">
</p>
<p>
   Background Image: <input type="file"
   id="bgImageFile" multiple="false"
   onChange="backimg()">
</p>
<input type="button" value="Merge Image" onClick="merge()">

CSS source code

Next, the CSS code in the HTML document

<style>
   canvas {
      background: rgb(214, 235, 176);
      border: 1px solid rgb(13, 109, 160);
      width: 420px;
      height: 290px;
      margin: 30px;
   }
   h1{
      color: rgb(13, 109, 160);
   }
   body {
      background-color: #bbb6ab;
   }
</style>

JavaScript Source Code

You must add the following JavaScript code<script> in the </script>

tag of your HTML document 
<script type="text/javascript">
   let forwdImage = null;
   let secImage = null;
   
   // This function accepts an input of a forward picture
   function frontimg() {
      let fileInput = document.getElementById("myImageFile");
      let canvas = document.getElementById("image1");
      forwdImage = new SimpleImage(fileInput);
      forwdImage.drawTo(canvas);
   }
   
   // Background picture is output from this function
   function backimg() {
      let fileInput = document.getElementById("bgImageFile");
      let canvas = document.getElementById("image2");
      secImage = new SimpleImage(fileInput);
      secImage.drawTo(canvas);
   }
   
   // This function combines the two images and outputs the
   // merged image as the final result. The Green Screen
   // Algorithm is implemented
   function merge() {
      clear();
      let image1 = document.getElementById("image1");
      let outputImage = new SimpleImage(
         forwdImage.width, forwdImage.height);
      for (let pixel of forwdImage.values()) {
         if (pixel.getGreen() > pixel.getRed() +
            pixel.getBlue()) {
            let x = pixel.getX();
            let y = pixel.getY();
            let newPixel = secImage.getPixel(x, y);
            outputImage.setPixel(x, y, newPixel);
         } else {
            outputImage.setPixel(pixel.getX(),
               pixel.getY(), pixel);
         }
      }
      outputImage.drawTo(image1);
   }
   
   // The output and input from earlier
   // fetches are cleared by this function.
   function clear() {
      let image1 = document.getElementById("image1");
      let image2 = document.getElementById("image2");
      let context = image1.getContext("2d");
      context.clearRect(0, 0, image1.width, image1.height);
      context = image2.getContext("2d");
      context.clearRect(0, 0, image2.width, image2.height);
   }
</script>

Example

Now let us check the complete code and output in the following code. 

<!DOCTYPE html>
<html>
<title>Implement Green Screen Algorithm using JavaScript - TutorialsPoint</title>
<head>
   <meta charset="UTF-8">
   <meta http-equiv="X-UA-Compatible" content="IE=edge">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <script src="https://www.dukelearntoprogram.com/course1/common/js/image/SimpleImage.js"></script>
   <style>
      canvas {
         background: rgb(214, 235, 176);
         border: 1px solid rgb(13, 109, 160);
         width: 420px;
         height: 290px;
         margin: 30px;
      }

      h1 {
         color: rgb(13, 109, 160);
      }

      body {
         background-color: #bbb6ab;
      }
   </style>
</head>
<body>
   <h1>Green Screen Algorithm Implementation using JavaScript with TutorialsPoint </h1>
   <canvas id="image1"></canvas>
   <canvas id="image2"></canvas>
   <br />
   <p>
      First Image: <input type="file" id="myImageFile" multiple="false" onChange="frontimg()">
   </p>
   <p>
      Background Image: <input type="file" id="bgImageFile" multiple="false" onChange="backimg()">
   </p>
   <input type="button" value="Merge Image" onClick="merge()">
   <script type="text/javascript">
      let forwdImage = null;
      let secImage = null;
      
      // This function accepts an input of a forward picture
      function frontimg() {
         let fileInput = document.getElementById("myImageFile");
         let canvas = document.getElementById("image1");
         forwdImage = new SimpleImage(fileInput);
         forwdImage.drawTo(canvas);
      }
      
      // Background picture is output from this function
      function backimg() {
         let fileInput = document.getElementById("bgImageFile");
         let canvas = document.getElementById("image2");
         secImage = new SimpleImage(fileInput);
         secImage.drawTo(canvas);
      }
      
      // This function combines the two images and outputs the
      // merged image as the final result. The Green Screen
      // Algorithm is implemented
      function merge() {
         clear();
         let image1 = document.getElementById("image1");
         let outputImage = new SimpleImage(
            forwdImage.width, forwdImage.height);
         for (let pixel of forwdImage.values()) {
            if (pixel.getGreen() > pixel.getRed() +
               pixel.getBlue()) {
               let x = pixel.getX();
               let y = pixel.getY();
               let newPixel = secImage.getPixel(x, y);
               outputImage.setPixel(x, y, newPixel);
            } else {
               outputImage.setPixel(pixel.getX(),
                  pixel.getY(), pixel);
            }
         }
         outputImage.drawTo(image1);
      }
      
      // The output and input from earlier
      // fetches are cleared by this function.
      function clear() {
         let image1 = document.getElementById("image1");
         let image2 = document.getElementById("image2");
         let context = image1.getContext("2d");
         context.clearRect(0, 0, image1.width, image1.height);
         context = image2.getContext("2d");
         context.clearRect(0, 0, image2.width, image2.height);
      }
   </script>
</body>
</html>

You will see this output screen without adding any images.

Next, after adding the "First Image" and "Background Image" images, you will see this output screen.

Now you will see the final output after clicking the "Merge Images" button. Both pictures are The combination is shown below.

Two pictures are used as input to the algorithm. The first one is the first image with the background green, the second one is the background image that should be used instead of green background.

JavaScript combines two images after receiving them as input; therefore, the lagging The image replaces the green background of the forward image. In order to implement the green Screening algorithm, code is provided above.

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