ImageProcessing Object

Provides support for image processing on a HTML5 ImageData.

Syntax

JavaScript

function Leadtools.ImageProcessing()

Remarks

The LEADTOOLS JavaScript ImageProcessing class allows you to perform various image processing commands on an HTML5 ImageData object.

ImageProcessing uses HTML5 a web worker to run the command in a separate thread. If the browser does not support web workers, then the work is emulated in the same thread. The RunInMainThread property can be used to force the command to not use a web worker and run the command in the current thread.

The nature of web workers dictate that the code behind is stored in a separate JavaScript file. This file does not have to be part of your page script; instead it is loaded dynamically when the command is run.

Follow these steps to run an image processing command:

Create a new instance of ImageProcessing
Set the JavaScript file name to use in the JSFilePath property. For a list of supported file names, refer to LEADTOOLS JavaScript Image Processing
Set the desired command name in Command and any required arguments. Refer to the topic above for a list of supported command names and their arguments
Set the source HTML5 canvas ImageData object in the ImageData property. The image data can be obtained from the drawing context of any canvas in your application or from LEADTOOLS Image Viewer.
Subscribe to the Completed event. This is not optional since web workers do not allow changing the source data (in this case, the source image data). The event will contain the updated image data. If the command contains out parameters, you can query them from the event data as well
Optionally, subscribe to the Progress event to obtain a progress report
Call the Run method
When the command finishes, the Completed event fires, set the image data back into the drawing context. If the command contains out parameters, you can query them from the event data as well
Finally, at anytime after the Run is called, you can call Abort to abort the current operation. The original data will not be affected

During any of the above, if an error occurs, the Error event fires with Error containing the error object.

Example

This example shows how to perform image processing on a canvas.

JavaScript

<!DOCTYPE html>
<html>
<head>
   <title>Image Processing Test</title>
   <meta http-equiv="content-type" content="text/html; charset=utf-8" />
   <script type="text/javascript" src="Scripts/mscorlib.debug.js"></script>
   <script type="text/javascript" src="Scripts/Leadtools.js"></script>
   <script type="text/javascript">
      (function () {
         var imageLoaded = false;
         var imageProcessing;

         function updateUIState() {
            document.getElementById("resetButton").disabled = !imageLoaded;
            document.getElementById("runButton").disabled = !imageLoaded;
         }

         function loadImage() {

            // Load the image
            var imgElement = document.createElement("img");
            var load = null;
            imageLoaded = false;

            load = function () {
               imgElement.removeEventListener("load", load, false);

               // Draw the image on canvas
               var myCanvas = document.getElementById("myCanvas");
               myCanvas.width = imgElement.naturalWidth;
               myCanvas.height = imgElement.naturalHeight;
               var context = myCanvas.getContext("2d");
               context.drawImage(imgElement, 0, 0);

               imageLoaded = true;
               updateUIState();
            };

            imgElement.addEventListener("load", load, false);

            imgElement.src = "Images/24.png";
            updateUIState();
         }

         function runImageProcessing() {

            // If we are running, abort
            if (imageProcessing.get_isRunning()) {
               imageProcessing.abort();
               document.getElementById("runButton").value = "Run";
               return;
            }

            // Run the command

            // Get the name of the command
            var ipSelect = document.getElementById("ipSelect");
            var index = ipSelect.selectedIndex;
            var command = ipSelect.options[index].text;

            // Get the source canvas image data
            var myCanvas = document.getElementById("myCanvas");
            var context = myCanvas.getContext("2d");
            var imgData = context.getImageData(0, 0, myCanvas.width, myCanvas.height);

            // Set the command
            imageProcessing.set_command(command);

            // The source image data
            imageProcessing.set_imageData(imgData);

            // Set the arguments
            var arguments = imageProcessing.get_arguments();

            // If this is the fill command, then set the color
            if (command == "Fill") {
               // Set the fill color, dark red in this case, the format is 0x AA RR GG BB
               arguments["color"] = 0xFF7F0000;
            } else {
               // No, clear the arguments.
               Object.clearKeys(arguments);
            }

            // Run the command
            document.getElementById("runButton").value = "Abort";

            imageProcessing.run();
         }

         function imageProcessing_Progress(sender, e) {
            // Update the progress label
            var progressLabel = document.getElementById("progressLabel");
            var percentage = e.get_percentage();
            progressLabel.textContent = percentage + "%";
         }

         function imageProcessing_Completed(sender, e) {
            // Get the result and update the canvas
            var imgData = e.get_imageData();
            var myCanvas = document.getElementById("myCanvas");
            var context = myCanvas.getContext("2d");
            context.putImageData(imgData, 0, 0);

            document.getElementById("runButton").value = "Run";
         }

         function updateProgress() {
            if (document.getElementById("progressCheckBox").checked) {
               // Hook to the Progress and Completed events
               if (lt.LTHelper.supportsWebWorker) {
                  imageProcessing.add_progress(imageProcessing_Progress);
               }
               else {
                  alert("Web workers are not supported by this browser. Callbacks will be disabled");
               }
            } else {
               imageProcessing.remove_progress(imageProcessing_Progress);
            }
         }

         function runDemo() {
            window.onload = function () {
               // Add the button handlers
               document.getElementById("resetButton").addEventListener("click", loadImage, false);
               document.getElementById("runButton").addEventListener("click", runImageProcessing, false);
               document.getElementById("progressCheckBox").addEventListener("click", updateProgress, false);

               // Initialize the LEADTOOLS Image Processing class
               imageProcessing = new lt.ImageProcessing();
               imageProcessing.set_jsFilePath("Scripts/Leadtools.ImageProcessing.Main.js");

               // Hook to the Completed and (optionally) Progress event
               imageProcessing.add_completed(imageProcessing_Completed);
               updateProgress();

               // Load the image
               loadImage();
            }
         }

         runDemo();
      })();
   </script>
</head>
<body>
   <div>
      <input type="button" id="resetButton" value="Reset" />
      <label for="ipSelect">Image Processing:</label>
      <select id="ipSelect">
         <option>Flip</option>
         <option>Reverse</option>
         <option>Fill</option>
      </select>
      <label for="progressCheckBox">Use progress</label>
      <input type="checkbox" id="progressCheckBox" checked="checked"/>
      <input type="button" id="runButton" value="Run" />
      <label id="progressLabel">0%</label>
   </div>
   <div>
      <canvas id="myCanvas" />
   </div>
</body>
</html>

ImageProcessing Object

Reference