Image ReducedImage;
using( System.IO.Stream stream = System.IO.File.OpenRead(resourceFile))
{
  ReducedImage = Image.FromStream(stream);
  Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);
  if ((ResourceImage.Width / ResourceImage.Height) >= 1)
  {
    ImageWidth = maxSize;
    ImageHeight = (ResourceImage.Height) * ImageWidth / ResourceImage.Width;//等比例缩放
  }
  else
  {
    ImageHeight = maxSize;
    ImageWidth = (ResourceImage.Width) * ImageHeight / ResourceImage.Height;//等比例缩放
  }
  ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);
  ReducedImage.Save(targetFilePath, ImageFormat.Jpeg);
  ReducedImage.Dispose();
}
  return true;