c# pictureBox控件

我使用控件时控件的宽和高小于图片的长和宽
所以我添加了滚动条来调节图片的位置
但是没有成功！！请高手帮忙
pictureBox1.Image = Image.FromFile("C:\\Documents and Settings\\Owner\\桌面\\078_001.tif");
vScrollBar1.Maximum =pictureBox1.Image.Height -pictureBox1.Height;
hScrollBar1.Maximum = pictureBox1.Image.Width - pictureBox1.Width;
pictureBox1.SizeMode = PictureBoxSizeMode.CenterImage;
SetScrollBarValue();
}
private void SetScrollBarValue() //根据图片的长和宽来判断滚动条的现实情况
{
if (pictureBox1.Width > pictureBox1.Image.Width)
{
hScrollBar1.Visible = true;
}
else
{
hScrollBar1.Visible = false;
}
if (pictureBox1.Height > pictureBox1.Image.Height)
{
vScrollBar1.Visible = true;
}