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How to get Pixel from HTML Canvas ?

  • Last Updated : 22 Nov, 2019

To get the pixel of any specific portion from HTML canvas you can use the HTML canvas getImageData() Method. The getImageData() method usually returns an ImageData object that contains the pixel information of the specified object on the HTML canvas.

Example 1: This example will display each pixel value of the square box. The boxes color is linear gradient so the pixels will change the color value that will change simultaneously.

  • Program:




    <!DOCTYPE html>
    <html>
      
    <head>
        <title>
            Getting pixel information
            from html canvas.
        </title>
    </head>
      
    <body>
        <center>
            <h1 style="color:green;">
                GeeksfoGeeks
            </h1>
              
            <h3>
                Getting pixel information
                from html canvas
            </h3>
      
            <canvas id="GFG" width="190" height="100"
                    style="border:1px solid black;">
            </canvas>
      
            <script>
              
                /* Retrieve canvas with id GFG,
                    and store it in a */
                var a = document.getElementById("GFG");
      
                /* Retrieve a 2D context for the canvas */
                var gfg = a.getContext("2d");
      
      
                var geeks = 
                    gfg.createLinearGradient(0, 0, 200, 0);
                  
                geeks.addColorStop(0, "green");
                geeks.addColorStop(1, "yellow");
      
                gfg.fillStyle = geeks;
                gfg.fillRect(20, 20, 150, 150);
      
                /* Define a function find(), that prints
                the array containing pixel information
                returned by the getImageData() method */
                function find() {
      
                    /* Store the pixel information of
                    the canvas at (x,y) coordinate of
                    (20,20) */
                    var ImageData = 
                        gfg.getImageData(20, 20, 60, 60);
      
                    /* Print the array on console */
                    console.log(ImageData);
                }
                  
                find();
            </script>
        </center>
    </body>
      
    </html>
  • Output:

Example 2: Code for getting color/alpha information of the first pixel. After running the code you can check by changing the color from the line 36.




<!DOCTYPE html>
<html>
  
<head>
    <title>
        Getting pixel information
        from html canvas.
    </title>
</head>
  
<body>
    <center>
        <h1 style="color:green;">
            GeeksfoGeeks
        </h1>
          
        <h3>
            Getting pixel information
            from html canvas
        </h3>
  
        <canvas id="GFG" width="100" height="100"
            style="border:1px solid black;">
        </canvas>
  
        <script>
              
            // Retrieve canvas with id GFG,
            // and store it in a 
            var a = document.getElementById("GFG");
  
            // Retrieve a 2D context for the canvas
            var geeks = a.getContext("2d");
  
            // Set the filling style to red colour
            geeks.fillStyle = "blue";
  
            /* Move the cursor to the (x,y) coordinate
            of (20,20) and then create a rectangle of
            height and width 60 */
            geeks.fillRect(20, 20, 60, 60);
  
            /* Define a function find(), that prints
            the colour/alpha information of of the
            first pixel returned by getImageData()
            method */
            function find() {
                  
                var ImageData = 
                    geeks.getImageData(20, 20, 60, 60);
  
                /* Stores the red color information of 
                the first pixel */
                red = ImageData.data[0];
  
                /* Stores the green color information of 
                the first pixel */
                green = ImageData.data[1];
  
                /* Stores the blue color information of 
                the first pixel */
                blue = ImageData.data[2];
  
                /* Stores the opacity of the first pixel */
                alpha = ImageData.data[3];
                console.log(red);
                console.log(green);
                console.log(blue);
                console.log(alpha);
            }
            find();
        </script>
    </center>
</body>
  
</html>     

Output:




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