.net Image調整內存泄漏大小

Question

我正嘗試調整批處理作業中的圖像大小。當我使用.Net提供的類時，內存未正確釋放，因此引發OutOfMemoryException。我想我正確地使用了陳述。代碼如下：

private static byte[] Resize(byte[] imageBytes, int width, int height) 
    { 
      using (var img = Image.FromStream(new MemoryStream(imageBytes))) 
      { 
       using (var outStream = new MemoryStream()) 
       { 
        double y = img.Height; 
        double x = img.Width; 

        double factor = 1; 
        if (width > 0) 
         factor = width/x; 
        else if (height > 0) 
         factor = height/y; 

        var imgOut = new Bitmap((int)(x * factor), (int)(y * factor)); 
        var g = Graphics.FromImage(imgOut); 
        g.Clear(Color.White); 
        g.DrawImage(img, new Rectangle(0, 0, (int)(factor * x), 
                (int)(factor * y)), 
           new Rectangle(0, 0, (int)x, (int)y), GraphicsUnit.Pixel); 

        imgOut.Save(outStream, ImageFormat.Jpeg); 

        return outStream.ToArray(); 
       } 
      } 
     } 

對此可替代的代碼是使用的FreeImage庫。當我使用FreeImage時，沒有內存問題。代碼的FreeImage：

private static byte[] Resize(byte[] imageBytes, int width, int height) 
    { 
     var img = new FIBITMAP(); 
     var rescaled = new FIBITMAP(); 
     try 
     { 
      using (var inStream = new MemoryStream(imageBytes)) 
      { 
       img = FreeImage.LoadFromStream(inStream); 
       rescaled = FreeImage.Rescale(img, width, height, FREE_IMAGE_FILTER.FILTER_BICUBIC); 

       using (var outStream = new MemoryStream()) 
       { 
        FreeImage.SaveToStream(rescaled, outStream, FREE_IMAGE_FORMAT.FIF_JPEG); 
        return outStream.ToArray(); 
       } 
      } 
     } 
     finally 
     { 
      if (!img.IsNull) 
       FreeImage.Unload(img); 

      img.SetNull(); 

      if (!rescaled.IsNull) 
       FreeImage.Unload(rescaled); 

      rescaled.SetNull(); 
     } 
    } 

缺什麼在我的第一個代碼？

Answer 1

我相信你的泄漏是以下兩行：

var imgOut = new Bitmap((int)(x * factor), (int)(y * factor)); 
var g = Graphics.FromImage(imgOut); 

兩個Bitmap和Graphics實施IDisposable，當你使用完，因此應設置。

我建議在using塊包裹他們兩個：

using(imgOut = new Bitmap((int)(x * factor), (int)(y * factor))) 
{ 
    using(var g = Graphics.FromImage(imgOut)) 
    { 
     //rest of code... 
    } 
} 

Here is a list of GDI objects保留一隻眼睛，一定要清除它們正確，如果你使用它們。

Answer 2

一個比較正確的做法：

private static byte[] Resize(byte[] imageBytes, int width, int height) 
    { 
     using (var imagestream = new MemoryStream(imageBytes)) 
     { 
      using (var img = Image.FromStream(imagestream)) 
      { 
       using (var outStream = new MemoryStream()) 
       { 
        double y = img.Height; 
        double x = img.Width; 

        double factor = 1; 
        if (width > 0) 
         factor = width/x; 
        else if (height > 0) 
         factor = height/y; 

        using (var imgOut = new Bitmap((int)(x * factor), (int)(y * factor))) 
        { 
         using (var g = Graphics.FromImage(imgOut)) 
         { 
          g.Clear(Color.White); 
          g.DrawImage(img, new Rectangle(0, 0, (int)(factor * x), 
                (int)(factor * y)), 
           new Rectangle(0, 0, (int)x, (int)y), GraphicsUnit.Pixel); 
         } 

         imgOut.Save(outStream, ImageFormat.Jpeg); 
        } 

        return outStream.ToArray(); 
       } 
      } 
     } 

} 

您還需要非常小心分配和釋放較大的物體時（那些> = 85000個字節）......因爲他們去蕙（大對象堆），並有可能將其分段，然後以超出預期的速度運行內存（如果遇到該問題，可以使用各種技術來解決問題）。

• http://msdn.microsoft.com/en-us/magazine/cc534993.aspx