Asp.net，Jcrop价值问题

我试图让 Jcrop 与 Asp.net 一起工作，但我认为我有一个问题：

Convert.ToInt32(W.Value);

我在 aspx 页中使用隐藏字段。我尝试使用常规输入字段，然后编写一个请求表单来获取所有值，这奏效了。但是我无法让它与隐藏字段和 Convert.ToInt32（W.Value） 一起使用。当我尝试这样做时，似乎该值始终为空。我得到消息：输入格式不正确。

我的后台代码如下所示：

protected void btnCrop_Click(object sender, EventArgs e)
{
    string ImageName = Request.QueryString["upload"];
    String path = "~/Members/TemporaryProfilePhotos/";
    int w = Convert.ToInt32(W.Value);
    int h = Convert.ToInt32(H.Value);
    int x = Convert.ToInt32(X.Value);
    int y = Convert.ToInt32(Y.Value);
    byte[] CropImage = Crop(path + ImageName, w, h, x, y);
    using (MemoryStream ms = new MemoryStream(CropImage, 0, CropImage.Length))
    {
        ms.Write(CropImage, 0, CropImage.Length);
        using (SD.Image CroppedImage = SD.Image.FromStream(ms, true))
        {
            string SaveTo = path + "crop" + ImageName;
            CroppedImage.Save(SaveTo, CroppedImage.RawFormat);
        }
    }
}
static byte[] Crop(string Img, int Width, int Height, int X, int Y)
{
  try {
    using (SD.Image OriginalImage = SD.Image.FromFile(Img)) {
      using (SD.Bitmap bmp = new SD.Bitmap(Width, Height)) {
        bmp.SetResolution(OriginalImage.HorizontalResolution,
          OriginalImage.VerticalResolution);
        using (SD.Graphics Graphic = SD.Graphics.FromImage(bmp)) {
          Graphic.SmoothingMode = SmoothingMode.AntiAlias;
          Graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;
          Graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;
          Graphic.DrawImage(OriginalImage,
            new SD.Rectangle(0, 0, Width, Height),
            X, Y, Width, Height, SD.GraphicsUnit.Pixel);
          MemoryStream ms = new MemoryStream();
          bmp.Save(ms, OriginalImage.RawFormat);
          return ms.GetBuffer();
        }
      }
    }
  }
  catch (Exception Ex) {
    throw (Ex);
  }
}