Use the OSS API to process images - Object Storage Service

Image Processing (IMG) is a secure, cost-effective, and highly reliable image processing service that is provided by Object Storage Service (OSS) to help you process large amounts of data. After you upload source images to OSS, you can call RESTful API operations to process the images on a device that is connected to the Internet anytime, anywhere.

Usage notes

In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions and endpoints.
In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Initialization.

Use IMG parameters to process an image

Use a single IMG parameter to process an image and save the image to your local computer

using System;
using System.IO;
using Aliyun.OSS;
using Aliyun.OSS.Common;
using Aliyun.OSS.Util;

namespace Samples
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
            var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.  
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the name of the bucket in which the source image is stored. Example: examplebucket. 
            var bucketName = "examplebucket";
            // Specify the name of the source image. If the source image is not stored in the root directory of the bucket, you must specify the full path of the image object. Example: exampledir/example.jpg. 
            var objectName = "exampledir/example.jpg";
            // Specify the local path of the source image. 
            var localImageFilename = "D:\\localpath\\example.jpg";
            // Create an OSSClient instance. 
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
            try
            {
                // Resize the image to 100 × 100 pixels. 
                var process = "image/resize,m_fixed,w_100,h_100";
                var ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                // Specify the name of the processed image. 
                WriteToFile(localImageFilename, ossObject.Content);
            }
            catch (OssException ex)
            {
                Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
                    ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed with error info: {0}", ex.Message);
            }
        }
        private static void WriteToFile(string filePath, Stream stream)
        {
            using (var requestStream = stream)
            {
                using (var fs = File.Open(filePath, FileMode.OpenOrCreate))
                {
                    IoUtils.WriteTo(stream, fs);
                }
            }
        }
    }
}

Use different IMG parameters to process an image and separately save the images to your local computer

using System;
using System.IO;
using Aliyun.OSS;
using Aliyun.OSS.Common;
using Aliyun.OSS.Util;
namespace Samples
{
    public class Program
    {
        public static void Main(string[] args)
        {
            // Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
            var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.  
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the name of the bucket in which the source image is stored. Example: examplebucket. 
            var bucketName = "examplebucket";
            // Specify the name of the source image. If the source image is not stored in the root directory of the bucket, you must specify the full path of the image object. Example: exampledir/example.jpg. 
            var objectName = "exampledir/example.jpg";
            // Specify the local path of the source image. 
            var localImageFilename = "D:\\localpath\\example.jpg";
       
            // Create an OSSClient instance. 
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
            try
            {
                // If the image does not exist in the specified bucket, upload the image to the bucket.    
                // client.PutObject(bucketName, objectName, localImageFilename);
                // Resize the image to 100 × 100 pixels. 
                var process = "image/resize,m_fixed,w_100,h_100";
                var ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                // Specify the name of the processed image. 
                WriteToFile(localImageFilename, ossObject.Content);
                // Crop the image to 100 × 100 pixels starting from the position specified by coordinate pair (100, 100). 
                process = "image/crop,w_100,h_100,x_100,y_100";
                ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                WriteToFile(localImageFilename , ossObject.Content);
                // Rotate the image 90 degrees. 
                process = "image/rotate,90";
                ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                WriteToFile(localImageFilename , ossObject.Content);
            }
            catch (OssException ex)
            {
                Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
                    ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed with error info: {0}", ex.Message);
            }
        }
        private static void WriteToFile(string filePath, Stream stream)
        {
            using (var requestStream = stream)
            {
                using (var fs = File.Open(filePath, FileMode.OpenOrCreate))
                {
                    IoUtils.WriteTo(stream, fs);
                }
            }
        }
    }
}

Use multiple IMG parameters to process an image and save the image to your local computer

The following code provides an example on how to use multiple IMG parameters to process an image. The IMG parameters are separated by forward slashes (/).

using System;
using System.IO;
using Aliyun.OSS;
using Aliyun.OSS.Common;
using Aliyun.OSS.Util;
namespace ImageProcessCascade
{
    class Program
    {
        static void Main(string[] args)
        {
            Program.ImageProcessCascade();
            Console.ReadKey();
        }
        public static void ImageProcessCascade()
        {
            // Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
            var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.  
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the name of the bucket in which the source image is stored. Example: examplebucket. 
            var bucketName = "examplebucket";
            // Specify the name of the source image. If the source image is not stored in the root directory of the bucket, you must specify the full path of the image object. Example: exampledir/example.jpg. 
            var objectName = "exampledir/example.jpg";
            // Specify the local path of the source image. 
           var localImageFilename = "D:\\localpath\\example.jpg";
            // Create an OSSClient instance. 
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
            try
            {
                // If the source image does not exist in the specified bucket, upload the image to the bucket.    
                // client.PutObject(bucketName, objectName, localImageFilename);
                // After you resize the image to 100 × 100 pixels, rotate the image 90 degrees. 
                var process = "image/resize,m_fixed,w_100,h_100/rotate,90";
                var ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                // Specify the name of the processed image. 
                WriteToFile(localImageFilename, ossObject.Content);
                Console.WriteLine("Get Object:{0} with process:{1} succeeded ", objectName, process);
            }
            catch (OssException ex)
            {
                Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
                    ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed with error info: {0}", ex.Message);
            }
        }
        private static void WriteToFile(string filePath, Stream stream)
        {
            using (var requestStream = stream)
            {
                using (var fs = File.Open(filePath, FileMode.OpenOrCreate))
                {
                    IoUtils.WriteTo(stream, fs);
                }
            }
        }
    }
}

Use an image style to process an image

You can encapsulate multiple IMG parameters within a style and then use the style to process an image. For more information, see Image styles. The following code provides an example on how to use an image style to process an image:

using System;
using System.IO;
using Aliyun.OSS;
using Aliyun.OSS.Common;
using Aliyun.OSS.Util;
namespace ImageProcessCustom
{
    class Program
    {
        static void Main(string[] args)
        {
            Program.ImageProcessCustomStyle();
            Console.ReadKey();
        }
        public static void ImageProcessCustomStyle()
        {
            // Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
            var endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.  
            var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID");
            var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
            // Specify the name of the bucket in which the source image is stored. Example: examplebucket. 
            var bucketName = "examplebucket";
            // Specify the name of the source image. If the source image is not stored in the root directory of the bucket, you must specify the full path of the image object. Example: exampledir/example.jpg. 
            var objectName = "exampledir/example.jpg";
            // Specify the local path of the source image. 
            var localImageFilename = "D:\\localpath\\example.jpg";
            // Create an OSSClient instance. 
            var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
            try
            {
                // If the source image does not exist in the specified bucket, upload the image to the bucket.    
                // client.PutObject(bucketName, objectName, localImageFilename);
                // Use the image style to process the image. In this example, replace yourCustomStyleName with the name of the image style that you created in the OSS console. 
                var process = "style/yourCustomStyleName";
                var ossObject = client.GetObject(new GetObjectRequest(bucketName, objectName, process));
                // Specify the name of the processed image.             
                WriteToFile(localImageFilename, ossObject.Content);
                Console.WriteLine("Get Object:{0} with process:{1} succeeded ", objectName, process);
            }
            catch (OssException ex)
            {
                Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
                    ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Failed with error info: {0}", ex.Message);
            }
        }
        private static void WriteToFile(string filePath, Stream stream)
        {
            using (var requestStream = stream)
            {
                using (var fs = File.Open(filePath, FileMode.OpenOrCreate))
                {
                    IoUtils.WriteTo(stream, fs);
                }
            }
        }
    }
}

Generate a signed object URL that includes IMG parameters

URLs of private objects must be signed. IMG parameters cannot be directly added to the end of a signed URL. If you want to process a private image object, add IMG parameters to the signature. The following code provides an example on how to add IMG parameters to a signature:

using Aliyun.OSS;
using Aliyun.OSS.Common;

// Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
var endpoint = "yourEndpoint";
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.  
var accessKeyId = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_ID"); 
var accessKeySecret = Environment.GetEnvironmentVariable("OSS_ACCESS_KEY_SECRET");
// Specify the name of the bucket in which the source image is stored. Example: examplebucket. 
var bucketName = "examplebucket";
// Specify the name of the source image. If the image is not stored in the root directory of the bucket, you must specify the full path of the image. Example: exampledir/example.jpg. 
var objectName = "exampledir/exampledir.jpg";
// Create an OSSClient instance. 
var client = new OssClient(endpoint, accessKeyId, accessKeySecret);
try
{
    // Resize the image to 100 × 100 pixels. 
    var process = "image/resize,m_fixed,w_100,h_100";
    var req = new GeneratePresignedUriRequest(bucketName, objectName, SignHttpMethod.Get)
    {
        Expiration = DateTime.Now.AddHours(1),
        Process = process
    };
    // Generate a signed URL. 
    var uri = client.GeneratePresignedUri(req);
    Console.WriteLine("Generate Presigned Uri:{0} with process:{1} succeeded ", uri, process);
}
catch (OssException ex)
{
    Console.WriteLine("Failed with error code: {0}; Error info: {1}. \nRequestID:{2}\tHostID:{3}",
        ex.ErrorCode, ex.Message, ex.RequestId, ex.HostId);
}
catch (Exception ex)
{
    Console.WriteLine("Failed with error info: {0}", ex.Message);
}

References

For the complete sample code of IMG, visit GitHub.
For more information about supported IMG parameters, see IMG parameters.