我使用WinForms。在我的表单中，我有一个显示图像文档的图片框。这些图像文档具有许多页。我的窗体上有一个打开、下一个和上一个按钮。在图片框中打开的文档中，下一个按钮前进一页，上一个按钮后退一页。我的表单上还有一些标签，用于指示有多少页面，以及用户当前正在查看的页面。
我的代码的问题是，当我打开大的图像文件到我的图片框，例如有1200页的文档，并单击下一步。页面加载缓慢。我想提高代码的性能。
我怎样才能使查看图像文档更快或我的代码更好？
我提供了一个tif文档来测试：http://www.filedropper.com/sampletifdocument5pages

private int int_Current_Page = 0;

    private void btnNextImage_Click_1(object sender, EventArgs e)
    {
        Image image2;
        try
        {
            if (int_Current_Page == Convert.ToInt32(lblNumPages.Text)) // if you have reached the last page it ends here
                                                                  // the "-1" should be there for normalizing the number of pages
            { int_Current_Page = Convert.ToInt32(lblNumPages.Text); }
            else
            {                   
                int_Current_Page++; //page increment

                using (FileStream stream = new FileStream(@"C:\my_Image_document", FileMode.Open, FileAccess.Read))
                {
                    image2 = Image.FromStream(stream);
                    Refresh_Image();
                } 
            }
        }
        catch(Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    private void btnPrevImage_Click_1(object sender, EventArgs e)
    {
        if (int_Current_Page == 0) // it stops here if you reached the bottom, the first page of the tiff
        { int_Current_Page = 0; }
        else
        {
            int_Current_Page--; // if its not the first page, then go to the previous page
            Refresh_Image(); // refresh the image on the selected page
        }
    }

    private void openButton_Click_1(object sender, EventArgs e)
    {
        Refresh_Image(); //Opens the large image document
    }

    private void Refresh_Image()
    {
        Image myImg; // setting the selected tiff
        Image myBmp; // a new occurance of Image for viewing

        using (FileStream stream = new FileStream(@"C:\my_Image_document", FileMode.Open, FileAccess.Read))
        {
            myImg = Image.FromStream(stream);

            int intPages = myImg.GetFrameCount(System.Drawing.Imaging.FrameDimension.Page); // getting the number of pages of this tiff
            intPages--; // the first page is 0 so we must correct the number of pages to -1
            lblNumPages.Text = Convert.ToString(intPages); // showing the number of pages
            lblCurrPage.Text = Convert.ToString(int_Current_Page); // showing the number of page on which we're on

            myImg.SelectActiveFrame(System.Drawing.Imaging.FrameDimension.Page, int_Current_Page); // going to the selected page

            myBmp = new Bitmap(myImg, pictureBox1.Width, pictureBox1.Height);

            pictureBox1.Image = myBmp; // showing the page in the pictureBox1  
        }
    }