c# - .Net 图像调整大小内存泄漏

Question

我正在尝试在批处理作业中调整图像大小。当我使用 .Net 提供的类时，内存未正确释放，因此抛出 OutOfMemoryException。我想我正确地使用了 using 语句。代码如下:

    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();
                }
            }
      }

此代码的替代方法是使用 FreeImage 库。当我使用 FreeImage 时，没有内存问题。使用 FreeImage 的代码:

   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();
        }
   }

我的第一个代码中缺少什么？

Answer 1

我相信您的泄漏是由于以下两行:

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

Bitmap 和 Graphics 都实现了 IDisposable，因此在您使用完它们后应该将其丢弃。

我建议将它们都包装在 using block 中:

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请注意，如果您使用它们，请确保正确清理它们。