将图像转换为base64，反之亦然

Question

我想将图像转换为base64并再次转换为图像。 这是我到目前为止的代码，也是错误。有什么建议吗？

public void Base64ToImage(string coded) 
{ 
    System.Drawing.Image finalImage; 
    MemoryStream ms = new MemoryStream(); 
    byte[] imageBytes = Convert.FromBase64String(coded); 
    ms.Read(imageBytes, 0, imageBytes.Length); 
    ms.Seek(0, SeekOrigin.Begin); 
    finalImage = System.Drawing.Image.FromStream(ms); 

    Response.ContentType = "image/jpeg"; 
    Response.AppendHeader("Content-Disposition", "attachment; filename=LeftCorner.jpg"); 
    finalImage.Save(Response.OutputStream, ImageFormat.Jpeg); 
} 

错误是：

Parameter is not valid.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: Parameter is not valid.

Source Error:

Line 34:    ms.Read(imageBytes, 0, imageBytes.Length); 
Line 35:    ms.Seek(0, SeekOrigin.Begin); 
Line 36:    finalImage = System.Drawing.Image.FromStream(ms); 
Line 37:   
Line 38:   Response.ContentType = "image/jpeg"; 

Source File: e:\Practice Projects\FaceDetection\Default.aspx.cs Line: 36

Answer 1

您是读取从空流，而不是加载现有数据（imageBytes）到流中。尝试：

byte[] imageBytes = Convert.FromBase64String(coded); 
using(var ms = new MemoryStream(imageBytes)) { 
    finalImage = System.Drawing.Image.FromStream(ms); 
} 

此外，你应该努力确保finalImage配置;我建议：

System.Drawing.Image finalImage = null; 
try { 
    // the existing code that may (or may not) successfully create an image 
    // and assign to finalImage 
} finally { 
    if(finalImage != null) finalImage.Dispose(); 
} 

最后，注意System.Drawing中is not supported在ASP.NET;因人而异。

Caution

Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions. For a supported alternative, see Windows Imaging Components.

Answer 2

MemoryStream.Read Method的读取从MemoryStream字节到指定的字节数组。

如果你想要写的字节数组MemoryStream，使用MemoryStream.Write Method：

ms.Write(imageBytes, 0, imageBytes.Length); 
ms.Seek(0, SeekOrigin.Begin); 

或者，你可以简单地包裹在MemoryStream字节数组：

MemoryStream ms = new MemoryStream(imageBytes);