Image类
Image主要实现读取图片文件（Image.FromFile）和保存图像文件（Image.Save）。
只要将图片转为Image类之后，就可以用.Net里面强大的GDI+功能
GDI+必须先要创建Graphics，一般的创建方法有Panel1.CreateGraphics
Graphics的DrawLine，DrawString，DrawImage都是十分常用的方法。
例如：
代码
1 Dim oImg As Image = Image.FromFile(a.FileName)
2
3 Dim x As Integer = oImg.Width / 4
4 Dim y As Integer = oImg.Height / 4
5 Dim w As Integer = oImg.Width / 2
6 Dim h As Integer = oImg.Height / 2
7 Dim oSaveImg As Image = New Bitmap(w, h)
8
9 Dim g As Graphics = Graphics.FromImage(oSaveImg)
10
11 g.DrawImage(oImg, 0, 0, New Rectangle(x, y, w, h), GraphicsUnit.Pixel)
12 g.Dispose()
13
14 oSaveImg.Save("D:\Test.jpg", Imaging.ImageFormat.Jpeg)
15
16 Me.PictureBox1.Image = oSaveImg
2
3 Dim x As Integer = oImg.Width / 4
4 Dim y As Integer = oImg.Height / 4
5 Dim w As Integer = oImg.Width / 2
6 Dim h As Integer = oImg.Height / 2
7 Dim oSaveImg As Image = New Bitmap(w, h)
8
9 Dim g As Graphics = Graphics.FromImage(oSaveImg)
10
11 g.DrawImage(oImg, 0, 0, New Rectangle(x, y, w, h), GraphicsUnit.Pixel)
12 g.Dispose()
13
14 oSaveImg.Save("D:\Test.jpg", Imaging.ImageFormat.Jpeg)
15
16 Me.PictureBox1.Image = oSaveImg
就能实现图片的截取。
