C#合并保存多个图片Image

/// <summary>
/// 打开图片列表，存放在列表里
/// </summary>
private void OpenImage()
{
fileDialog.RestoreDirectory = true;
fileDialog.Multiselect = true;
fileDialog.Filter = "JPG文件(*.jpg)|*.jpg|BMP文件(*.bmp)|*.bmp|TFT文件(*.tft)|*.tft|所有文件(*.*)|*.*";
if (fileDialog.ShowDialog() == DialogResult.OK)
{
foreach (string s in fileDialog.FileNames)
{
this.listView1.Items.Add(s);
}
}
}

Image MergedImage = default(Image);
string savePath;
string saveImgPath;

/// <summary>
/// 合并保存图片
/// </summary>
/// <param name="img1"></param>
/// <param name="img2"></param>
private void HorizontalMergeImages(Image img1, Image img2)
{
Int32 Wide = 0;
Int32 High = 0;

High = img1.Height + img2.Height;//設定高度

if (img1.Width >= img2.Width)
{
Wide = img1.Width;
}
else
{
Wide = img2.Width;
}
Bitmap mybmp = new Bitmap(Wide / 2, High / 2);
Graphics gr = Graphics.FromImage(mybmp);
gr.DrawImage(img1, new Rectangle(0, 0, img1.Width / 2, img1.Height / 2));
gr.DrawImage(img2, new Rectangle(0, img1.Height / 2, img2.Width / 2, img2.Height / 2));

MergedImage = mybmp;
saveImgPath = savePath + "\\" + DateTime.Now.ToString("yyyyMMHHmmffffff") + ".jpg";
textBox1.Text = saveImgPath;
MergedImage.Save(saveImgPath);

gr.Dispose();
mybmp.Dispose();
}

/// <summary>
/// 从列表里保存图片
/// </summary>
public void MerAndSave()
{
if (savePath == null)
{
MessageBox.Show("请先设置图片的保存路径!");
return;
}
stw.Start();
this.ProgressSpeed.Value = 0;
this.ProgressSpeed.Maximum = listView1.Items.Count;
Image img1;
Image img2 = pictureBox2.Image;
for (int i = 0; i < listView1.Items.Count; i++)
{
Application.DoEvents();
img1 = Image.FromFile(listView1.Items[i].Text.ToString());
HorizontalMergeImages(img1, img2);
this.ProgressSpeed.Value = i + 1;
img1.Dispose();
}
stw.Stop();
labelTime.Text = "一共使用时间" + stw.Elapsed.Seconds.ToString() + "秒";
MessageBox.Show("合成图片成功");
this.ProgressSpeed.Value = 0;
}