OSS Image Processing (IMG) lets you resize, crop, rotate, and otherwise transform images stored in OSS buckets on the fly, using standard HTTP GET requests. IMG parameters are passed in the query string of an image object URL.
If the access control list (ACL) of an image object is private, only authorized users can access it.
Prerequisites
Before you begin, ensure that you have:
An OSS bucket with at least one image object uploaded
The OSS iOS SDK installed and configured in your project
Apply image processing when downloading an image
Anonymous access
Use presignPublicURLWithBucketName:withObjectKey:withParameters: to generate a public URL that includes IMG parameters. This approach works only for objects with public-read ACL.
OSSTask *task = [client presignPublicURLWithBucketName:@"examplebucket"
withObjectKey:@"exampledir/example.jpg"
withParameters:@{@"x-oss-process": @"image/resize,w_50"}];
[task continueWithBlock:^id(OSSTask *task) {
if (!task.error) {
NSLog(@"download image success!");
OSSGetObjectResult *getResult = task.result;
NSLog(@"download image data: %@", getResult.downloadedData);
} else {
NSLog(@"download object failed, error: %@", task.error);
}
return nil;
}];The x-oss-process parameter value follows the format image/<action>,<key>_<value>. For example, image/resize,w_50 resizes the image to 50 pixels wide.
Authorized access
For objects with private ACL, set request.xOssProcess on an OSSGetObjectRequest to apply IMG parameters when downloading.
OSSGetObjectRequest *request = [OSSGetObjectRequest new];
// Bucket that contains the image
request.bucketName = @"examplebucket";
// Full path to the image. If the image is in the bucket root, omit the directory prefix.
request.objectKey = @"exampledir/example.jpg";
// image/resize,m_lfit,w_100,h_100
// m_lfit → fit the image within the bounding box, preserving aspect ratio
// w_100 → maximum width: 100 px
// h_100 → maximum height: 100 px
request.xOssProcess = @"image/resize,m_lfit,w_100,h_100";
OSSTask *getTask = [client getObject:request];
[getTask continueWithBlock:^id(OSSTask *task) {
if (!task.error) {
NSLog(@"download image success!");
OSSGetObjectResult *getResult = task.result;
NSLog(@"download image data: %@", getResult.downloadedData);
} else {
NSLog(@"download object failed, error: %@", task.error);
}
return nil;
}];
// Block the calling thread until the download completes (optional):
// [getTask waitUntilFinished];
// Cancel an in-progress download (optional):
// [request cancel];Save a processed image to a bucket
Use OSSImagePersistRequest to apply an IMG operation and write the result directly to a destination bucket, without downloading the image locally.
The destination bucket (toBucket) must be in the same region as the source bucket (fromBucket).
OSSImagePersistRequest *request = [OSSImagePersistRequest new];
// Source image
request.fromBucket = @"srcbucket";
request.fromObject = @"exampledir/src.jpg"; // Full path, or just "src.jpg" if in the bucket root
// Destination for the processed image (must be in the same region as fromBucket)
request.toBucket = @"destbucket";
request.toObject = @"exampledir/dest.jpg";
// image/resize,w_100 → resize to 100 px wide, preserving aspect ratio
request.action = @"image/resize,w_100";
// request.action = @"resize,w_100";
OSSTask *task = [client imageActionPersist:request];
[task continueWithBlock:^id _Nullable(OSSTask * _Nonnull task) {
if (!task.error) {
NSLog(@"image saved successfully");
} else {
NSLog(@"failed to save image, error: %@", task.error);
}
return nil;
}];Generate a signed URL with IMG parameters
For private image objects, IMG parameters must be included in the URL signature—you cannot append them to an already-signed URL. Use presignConstrainURLWithBucketName:withObjectKey:withExpirationInterval:withParameters: to generate a signed URL that embeds the processing parameters.
NSString *bucketName = @"examplebucket";
NSString *objectKey = @"exampledir/example.jpg";
// Generate a signed URL valid for 1,800 seconds (30 minutes)
// that resizes the image to 50 px wide (image/resize,w_50)
OSSTask *task = [_client presignConstrainURLWithBucketName:bucketName
withObjectKey:objectKey
withExpirationInterval:30 * 60
withParameters:@{@"x-oss-process": @"image/resize,w_50"}];
NSLog(@"url: %@", task.result);What's next
For the full list of supported IMG operations and parameter syntax, see IMG parameters.