Image Decoding

Image decoding refers to the process of decoding an archived image in a supported format into a pixel map for image display or processing. Currently, the following image formats are supported: JPEG, PNG, GIF, RAW, WebP, BMP, and SVG.

How to Develop

Read Image for APIs related to image decoding.

1. Import the image module.

   import image from '@ohos.multimedia.image';
   

2. Obtain an image.

   • Method 1: Obtain the sandbox path. For details about how to obtain the sandbox path, see Obtaining Application File Paths. For details about the application sandbox and how to push files to the application sandbox, see File Management.

     // Code on the stage model
     const context : Context = getContext(this);
     const filePath : string = context.cacheDir + '/test.jpg';
     

     // Code on the FA model
     import featureAbility from '@ohos.ability.featureAbility';
     
     const context = featureAbility.getContext();
     const filePath = context.getCacheDir() + "/test.jpg";
     

   • Method 2: Obtain the file descriptor of the image through the sandbox path. For details, see [file.fs API Reference] (../reference/apis/js-apis-file-fs.md). To use this method, you must import the @ohos.file.fs module first.

     import fs from '@ohos.file.fs';
     

     Then call fs.openSync() to obtain the file descriptor.

     // Code on the stage model
     const context = getContext(this);
     const filePath = context.cacheDir + '/test.jpg';
     const file : fs.File = fs.openSync(filePath, fs.OpenMode.READ_WRITE);
     const fd : number = file?.fd;
     

     // Code on the FA model
     import featureAbility from '@ohos.ability.featureAbility';
     
     const context = featureAbility.getContext();
     const filePath = context.getCacheDir() + "/test.jpg";
     const file : fs.File = fs.openSync(filePath, fs.OpenMode.READ_WRITE);
     const fd : number = file?.fd;
     

   • Method 3: Obtain the array buffer of the resource file through the resource manager. For details, see ResourceManager API Reference.

     // Code on the stage model
     const context : Context = getContext(this);
     // Obtain a resource manager.
     const resourceMgr : resourceManager.ResourceManager = context.resourceManager;
     

     // Code on the FA model
     // Import the resourceManager module.
     import resourceManager from '@ohos.resourceManager';
     const resourceMgr = await resourceManager.getResourceManager();
     

     The method of obtaining the resource manager varies according to the application model. After obtaining the resource manager, call resourceMgr.getRawFileContent() to obtain the array buffer of the resource file.

     const fileData : Uint8Array = await resourceMgr.getRawFileContent('test.jpg');
     // Obtain the array buffer of the image.
     const buffer = fileData.buffer;
     

3. Create an ImageSource instance.

   • Method 1: Create an ImageSource instance using the sandbox path. The sandbox path can be obtained by using method 1 in step 2.

     // path indicates the obtained sandbox path.
     const imageSource : image.ImageSource = image.createImageSource(filePath);
     

   • Method 2: Create an ImageSource instance using the file descriptor. The file descriptor can be obtained by using method 2 in step 2.

     // fd is the obtained file descriptor.
     const imageSource : image.ImageSource = image.createImageSource(fd);
     

   • Method 3: Create an ImageSource instance using a buffer array. The buffer array can be obtained by using method 3 in step 2.

     const imageSource : image.ImageSource = image.createImageSource(buffer);
     

4. Set DecodingOptions and decode the image to obtain a pixel map.

   let decodingOptions : image.DecodingOptions = {
       editable: true,
       desiredPixelFormat: 3,
   }
   // Create a pixel map and perform rotation and scaling on it.
   const pixelMap : image.PixelMap = await imageSource.createPixelMap(decodingOptions);
   

   After the decoding is complete and the pixel map is obtained, you can perform subsequent image processing.

5. Release the PixelMap instance.

   pixelMap.release();
   

Sample Code - Decoding an Image in Resource Files

1. Obtain a resource manager.

   const context : Context = getContext(this);
   // Obtain a resourceManager instance.
   const resourceMgr : resourceManager.ResourceManager = context.resourceManager;
   

2. Obtain the array buffer of the test.jpg file in the rawfile folder.

   const fileData : Uint8Array = await resourceMgr.getRawFileContent('test.jpg');
   // Obtain the array buffer of the image.
   const buffer = fileData.buffer;
   

3. Create an ImageSource instance.

   const imageSource : image.ImageSource = image.createImageSource(buffer);
   

4. Create a PixelMap instance.

   const pixelMap : image.PixelMap = await imageSource.createPixelMap();
   

5. Release the PixelMap instance.

   pixelMap.release();