[VB.NET] Kako shraniti modificirano sliko iz PictureBoxa v datoteko?

V pictureBoxu imam naložen čisto bel BMP. Potem na ta picturebox z ukazi DrawString, Drawline in ostalimi rišem različne oblike.

Problem je, da nikakor ne morem shranit tega PictureBox-a z dodano grafiko v datoteko.

Ukaz PictureBox.Image.Save("imedatoteke.bmp") namreč shrani samo prvotno nemodoficirano datoteko. Kako shranit vse skupaj? Se to sploh da? Namreč tudi če program minimiram in spet nazaj odprem, je picturebox spet prazen.

Pa še delček kode s točnim prikazom risanja na picturebox:

Public grafika As Graphics
Public black_pen As New Pen(Color.Black)
Public img As Image

Private Sub Zacni_Animacijo(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Button1.Hide()

Dim axis_x_name As [String] = "t/s"
Dim axis_y_name As [String] = "h/m"
Dim font_axis As New Font("Arial", 10, FontStyle.Bold)
Dim draw_pen As New SolidBrush(Color.Black)


grafika = PictureBox2.CreateGraphics
grafika.DrawLine(black_pen, 40, 5, 40, 300)
grafika.DrawLine(black_pen, 30, 295, 667, 295)
grafika.DrawString(axis_x_name, font_axis, draw_pen, 650, 298)
grafika.DrawString(axis_y_name, font_axis, draw_pen, 10, 5)


Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
img = PictureBox2.Image
img.Save("test.bmp")
End Sub