Saving a Drawing to a Bitmap File

Question

3.00/5 (2 votes)

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In VB 2010:
How do i save a drawing on a picturebox to a file on harddisk

VB

Imports System.Drawing.Imaging
Public Class Form1
       Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        myPictureBox.BackColor = Color.Yellow
        myPictureBox.Image = Image.FromFile("C:\TEMP\test.jpg")
    End Sub

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        myPictureBox.Image.Save("c:\Temp\MyPicture.jpg", ImageFormat.Jpeg)
    End Sub

    Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        Dim redPen As Pen = New Pen(Color.Red, 20)
        Dim point1 As Point = New Point(0, 0)
        Dim point2 As Point = New Point(130, 150)
        Dim G As Graphics
        G = myPictureBox.CreateGraphics
        G.DrawLine(redPen, point1, point2)
    End Sub
End Class

the save command ( Button1) did not work.
I got the mesage:
Use the New keyword to create the instance.

when I load an image in myPictureBox,
as I now did in the line:
myPictureBox.Image = Image.FromFile("C:\TEMP\test.jpg")

The Save command worked,but the result is not what I want.
I wanted the redline ON my image.
(What I am trying to do is making a program for a child to give color on an loaded bitmap,
and the possebility to store the colored bitmap)

[Edit - Added code block]

Posted 25-Feb-12 4:44am

geert vullings

Updated 27-Feb-12 9:04am

v4

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OriginalGriff · Answer 1 · 2012-02-25T04:52:00

Solution 1

Try:

VB

myPictureBox.Image.Save("D:\Temp\MyPicture.jpg", ImageFormat.Jpeg)

Posted 25-Feb-12 4:52am

OriginalGriff

Comments

geert vullings 26-Feb-12 3:04am

I became an error saying:
{"Object reference not set to an instance of an object."}

OriginalGriff 26-Feb-12 3:28am

Then you haven't set the Image property (in which case you have nothing to save) or you haven't changed "myPictureBox" to the name of your actual PictureBox!

geert vullings 27-Feb-12 13:57pm

the save command ( Button1) did not work
I got the mesage:
Use the New keyword to create the instance.
I have updated my question.

OriginalGriff 27-Feb-12 14:06pm

I have looked at your code, now you have posted it, and two things occur:
1) Whenever you call CreateGraphics to get a graphics context, you are responsible for calling Dispose on it - if you do not, you will have a problem as the supply of such graphics contexts is limited, and you will run out. At that point your program will fail - but it may not fail in your code! It can be very difficult to spot such problems.

2) You see to be under the illusion that drawing a line on the PictureBox changes the Image inside it - this is not the case.
You do no appear to allocate an Image to the PictureBox at all - which is why you get the "not set to an instance of an object" error, and you do not draw into the Image anyway - so it would not save your changes if you did.

Take a step back, think about what you are trying to do, and decide: do I want to draw a line on the screen? Or on a Image control which will be shown on the screen?

The two processes are very similar in execution, but they have profoundly different results.

geert vullings 27-Feb-12 15:05pm

when I load an image in myPictureBox,
as I now did in the line:
myPictureBox.Image = Image.FromFile("C:\TEMP\test.jpg")

The Save command worked,but the result is not what I want.
I wanted the redline ON my image.
(What I am trying to do is making a program for a child to give color on an loaded bitmap,
and the possebility to store the colored bitmap)

OriginalGriff 28-Feb-12 3:49am

Ok. This is what I meant by "The two processes are very similar in execution, but they have profoundly different results."

You are drawing on a Graphics context for the PictureBox - that does not affect the Image in any way.
You have two options:
1) Change it so that your code gets it's Graphics context from myPictureBox.Image.CreateGraphics instead of myPictureBox.CreateGraphics - That will mean that the Image will be affected and when you save it the changes will go to the file. But (and it's a big but) That is likely to mean that it won't affect the display! So you need to move the drawing out of the Paint event, and into some other event - a button click or similar, and then use Invalidate on the PictureBox. (You mustn't Invalidate the PictureBox from within the Form Paint event, or it will cause another Paint, which will Invalidate, which...you get the idea)

2) Move your drawing code into a separate method, which you hand a Graphics Context as a parameter. You draw your line(s) and it all is happy. In the Paint event, you hand it the PictureBox context. When you want to save, you hand it the Image context, and then save the modified image afterwards. This way is a little more complex, but it allows the child to "undo" his changes which the first method doesn't without reloading the image completely.

Sergey Alexandrovich Kryukov · Answer 2 · 2012-02-25T16:28:00

If you have a need to save an image of the PictureBox, the chances are, you misuse this class. Usually, you don't need it at all. It is good only to present some picture; in more complex cases it does not help, only adds some hassles.

I explained why and what to do instead in my past answers:
How do I clear a panel from old drawing[^],
draw a rectangle in C#[^].

Just in case, please review it.

—SA