Windows Dev Center

Information
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

How to decode an image (HTML)

We show you how to load an image from a file, display it using the <img> tag, and create a BitmapDecoder object from it. A BitmapDecoder lets you access metadata and get pixel data from images.

What you need to know

Technologies

Prerequisites

Instructions

Step 1: Add a placeholder image

Add a <img> tag to your HTML file.


<img id="myImage" src="" />

You will later load the image file into the myImage object.

Step 2: Use the file picker to pick an image file

Create a new FileOpenPicker object to let the user select a file to be opened. Set the file extension to filter for JPEG images. Then, display the picker.


function DecodeImage() {
    var picker = new Windows.Storage.Pickers.FileOpenPicker();
    picker.fileTypeFilter.append(".jpg");
    picker.pickSingleFileAsync().then(function (file) {
        if (!file) {


Note  You can get a list of all the file extensions supported by the codecs installed on the system by using Windows.Graphics.Imaging.BitmapDecoder.getDecoderInformationEnumerator.
Note  If the user cancels, the pickSingleFileAsync method returns a null object.

Step 3: Display the image in the Image element

Create an object URL for the file and set it as the source of the Image element.

The createObjectURL method creates a URL that is backed by data from an object such as StorageFile.


            var objectURL = window.URL.createObjectURL(file, { oneTimeOnly: true });
            document.getElementById("myImage").src = objectURL;


Step 4: Create the decoder object

Open the file using the Read access mode to get an IRandomAccessStream. Then create a BitmapDecoder object on the stream.


    }).then(function (stream) {
        return Windows.Graphics.Imaging.BitmapDecoder.createAsync(stream);
    }).done(function (decoder) {
        // BitmapDecoder is ready for use.
    });
}


Remarks

Now that you have a decoder object you can use it to:

Related topics

How to read image metadata
How to get pixel data
How to encode an image
Windows.Graphics.Imaging

 

 

Show:
© 2015 Microsoft