Difference between .Backgroundimage and .Image paint behavior Form vs Picturebox.

Question

In this code when I copy the image to picturebox1.background image the form does not paint the controls on startup and the paint event keeps firing repeatedly. When copy image to picturebox1.image the form starts properly and the paint event does not fire
(unless needed).
What is the difference between the .backgroundimage and .image that makes the form not paint the controls but repeatedly fire the form paint event?
Same behaviour if a form backgroundimage is used, but it does not have image property so it cant be stopped if copying to a form background?
Thanks.
Public Class Form6
Private Sub Form6_Paint(sender As Object, e As PaintEventArgs) Handles Me.Paint
Static t As Integer
t += 1
Me.Text = t.ToString
Using bmp As New Bitmap(400, 400)
Using g As Graphics = Graphics.FromImage(bmp)
g.Clear(Color.Red)
PictureBox1.Image = bmp.Clone
End Using
End Using
End Sub
Private Sub Form6_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.DoubleBuffered = True
End Sub
End Class
Copy to picturebox1.backgroundimages gives this startup without the controls painted and the form paint is continuously firing as can be seen in the form header text:
Copy to picturebox1.image and form startups up properly and does not keep firing form paint.
Edit: removed         Me.Location = New Point(200, 100)
That does not cause a problem.

Answer 1

Hey Tom,
 Well, i have been playing around monitoring the windows messages received by the form and the picturebox to see what was happening.  I found the messages start changing right after the picturebox receives it`s first Paint message. Here is where
they start changing.
Using Image Property these are all the massages received after its first paint message is received.
PictureBox - msg=0xf (WM_PAINT) hwnd=0x37037c wparam=0x0 lparam=0x0 result=0x0
Form - msg=0x14 (WM_ERASEBKGND) hwnd=0x1303c4 wparam=0xffffffffeb0108b7 lparam=0x0 result=0x1
Form - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x1303c4 wparam=0x0 lparam=0x0 result=0x5
Form - msg=0xd (WM_GETTEXT) hwnd=0x1303c4 wparam=0x6 lparam=0x342ee08 result=0x5
Form - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x1303c4 wparam=0x0 lparam=0x0 result=0x5
Form - msg=0xd (WM_GETTEXT) hwnd=0x1303c4 wparam=0x6 lparam=0x342ee08 result=0x5
Form - msg=0x318 (WM_PRINTCLIENT) hwnd=0x1303c4 wparam=0xffffffffeb0108b7 lparam=0x4 result=0x0
PictureBox - msg=0x14 (WM_ERASEBKGND) hwnd=0x37037c wparam=0x9010329 lparam=0x0 result=0x1
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x37037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x37037c wparam=0x1 lparam=0x342ede8 result=0x0
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x37037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x37037c wparam=0x1 lparam=0x342ede8 result=0x0
PictureBox - msg=0xf (WM_PAINT) hwnd=0x37037c wparam=0x0 lparam=0x0 result=0x0
 Using the BackgroundImage property these are the messages received after the first picturebox Paint message is received. The last 6 messages just keep repeating until the app is closed.
PictureBox - msg=0xf (WM_PAINT) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0x14 (WM_ERASEBKGND) hwnd=0x38037c wparam=0x9010329 lparam=0x0 result=0x1
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x38037c wparam=0x1 lparam=0x3430160 result=0x0
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x38037c wparam=0x1 lparam=0x3430160 result=0x0
PictureBox - msg=0xf (WM_PAINT) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0x14 (WM_ERASEBKGND) hwnd=0x38037c wparam=0x9010329 lparam=0x0 result=0x1
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x38037c wparam=0x1 lparam=0x3430160 result=0x0
PictureBox - msg=0xe (WM_GETTEXTLENGTH) hwnd=0x38037c wparam=0x0 lparam=0x0 result=0x0
PictureBox - msg=0xd (WM_GETTEXT) hwnd=0x38037c wparam=0x1 lparam=0x3430160 result=0x0
 So that made me wonder how they differed in the BackGroundImage and Image properties of the PictureBox class when being painted.  I looked at the .Net source code for the picturebox class HERE
and found that the PictureBox class is inherited from the Control base class and the Image property is a special property added to the picturebox class and is handled in its OnPaint event.  The BackgroundImage is a property of the Control base class that
the picturebox class inherits from.  So, that is handled in the base class somehow.
 I looked at the Control class code but, it is so much different than what i am use to looking at that i could not really follow what it was doing.  So, in the end i still don`t have an answer but, i can only guess that setting the BackgroundImage
inside the Paint event of the form is somehow stopping the Form from receiving the 6 messages shown in the first set of messages shown which is causing it to never finish painting itself.
 Maybe Crazypennie or someone with a deeper knowledge into the "behind the scenes" workings of it can say what the difference is. I figured that changing the backgroundimage was causing the form to receive a new paint message and was going
into an infinite loop but, according to the messages i was getting after the picturebox`s 1st paint message, the form never receives another message.
 I know this probably won`t help but, if you want to create a new backgroundimage for the picturebox and modify it each time the form is painted you could just assign the picturebox a new bitmap at Load and then use the graphics object of the PictureBox.BackgroundImage
to redraw it in the paint event instead of creating a new bitmap for it each time the form is painted.
Public Class Form1
Private bmp As New Bitmap(400, 400)
Private Sub Form6_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
Me.DoubleBuffered = True
PictureBox1.BackgroundImage = bmp
End Sub
Private Sub Form1_Paint(ByVal sender As Object, ByVal e As PaintEventArgs) Handles Me.Paint
Using g As Graphics = Graphics.FromImage(PictureBox1.BackgroundImage)
g.Clear(Color.Red)
End Using
End Sub
End Class
 Or i guess just use the Image property instead.  8)
If you say it can`t be done then i`ll try it