Webcam donot capture when cam window is inactive

Question

hi

i am creating a project in vb.net 2005. i am using a timer to save images that is captured by webcam.

when i minimize the form . it save last captuerd image again and again.

Webcam donot capture when cam window is inactive

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Ali Usman

Answer 1

I would suggest you don't minimize the form. Maybe you should hide and unhide the form.

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You've taught me everything I know but not everything you know.

Answer 2

You could do something like this.

Option Strict On

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Timer1.Interval = 100
        Timer1.Start()
    End Sub


    Private Sub Form1_Minimized(sender As Object, e As EventArgs) Handles Me.Resize
        If Me.WindowState = FormWindowState.Minimized Then
            Me.WindowState = FormWindowState.Normal
            Me.Hide()
        End If
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        If My.Computer.Keyboard.AltKeyDown Then
            Me.Show()
        End If
    End Sub
End Class

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You've taught me everything I know but not everything you know.

Answer 3

Hi, It would help to see the code that is capturing the image and the code that is saving the image.

Answer 4

i am using this code

Public Class Form1
    Inherits DevComponents.DotNetBar.Office2007Form

    Dim fileno As Integer = 0
    Dim Data As IDataObject
    Dim Bmap As Image
    Dim str As String
    Private Sub OpenPreviewWindow()
        Dim iHeight As Integer = Me.PictureBox1.Height
        Dim iWidth As Integer = Me.PictureBox1.Width
       
        hHwnd = capCreateCaptureWindowA(iDevice, WS_VISIBLE Or WS_CHILD, 0, 0, 640, 480, PictureBox1.Handle.ToInt32, 0)
        If SendMessage(hHwnd, WM_Cap_Paki_CONNECT, iDevice, 0) Then
            SendMessage(hHwnd, WM_Cap_SET_SCALE, True, 0)
            SendMessage(hHwnd, WM_Cap_SET_PREVIEWRATE, 66, 0)
            SendMessage(hHwnd, WM_Cap_SET_PREVIEW, True, 0)
            SetWindowPos(hHwnd, HWND_BOTTOM, 0, 0, PictureBox1.Width, PictureBox1.Height, SWP_NOMOVE Or SWP_NOZORDER)
        Else
            DestroyWindow(hHwnd)
        End If
    End Sub

    Private Sub ClosePreviewWindow()
        SendMessage(hHwnd, WM_Cap_Paki_DISCONNECT, iDevice, 0)
        DestroyWindow(hHwnd)
    End Sub

    Private Sub FrmCamera_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Call OpenPreviewWindow()
        Button1.Focus()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
       
        SendMessage(hHwnd, WM_Cap_EDIT_COPY, 0, 0)
      
        Data = Clipboard.GetDataObject()
        If Data.GetDataPresent(GetType(System.Drawing.Bitmap)) Then
            Bmap = CType(Data.GetData(GetType(System.Drawing.Bitmap)), Image)
            PictureBox1.Image = Bmap
            PictureBox1.Image.Save("c:\test\Img" & fileno & ".jpg")
            fileno += 1

        End If
        PictureBox1.Image.Dispose()

        If My.Computer.Keyboard.AltKeyDown Then
            Me.Show()
        End If
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Timer1.Enabled = False
    End Sub

    Private Sub Form1_Minimized(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Resize
        If Me.WindowState = FormWindowState.Minimized Then
            Me.WindowState = FormWindowState.Normal
            Me.Hide()
        End If
    End Sub

    Private Sub ButtonX1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonX1.Click
        Me.Close()
    End Sub
End Class

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Ali Usman

Answer 5

Being that i did not see any constants or API functions in your code i could not tell how you had things working so here is a working copy of pretty much the same thing that captures the picture even if the window is minimized. To test it just create a new Form project with 1 Timer, 1 PictureBox, and 2 Buttons. (Button_Start) and (Button_Stop). You can change the directory and the picture name it is saved as inside the timer1_Tick event.

Public Class Form1
    Dim fileno As Integer = 0
    Dim tmppic As String = My.Application.Info.DirectoryPath & "\Temp.dib"
    Dim hHwnd As IntPtr = IntPtr.Zero
    Dim iDevice As Integer = 0 'This is the device number
    Dim CamFrameRate As Integer = 15  'This is the Frames Per Second (FPS)
    Dim OutputHeight As Integer = 240 'Height of the picture
    Dim OutputWidth As Integer = 360  'Width of the picture

    Private Const WS_CHILD As Integer = &H40000000
    Private Const WS_VISIBLE As Integer = &H10000000
    Private Const WM_USER As Integer = &H400
    Private Const WM_CAP_DRIVER_CONNECT As Integer = WM_USER + 10
    Private Const WM_CAP_DRIVER_DISCONNECT As Integer = WM_USER + 11
    Private Const WM_CAP_SET_PREVIEW As Integer = WM_USER + 50
    Private Const WM_CAP_SET_PREVIEWRATE As Integer = WM_USER + 52
    Private Const WM_CAP_SAVEDIB As Integer = WM_USER + 25
    Private Const WM_CAP_GRAB_FRAME_NOSTOP As Integer = WM_USER + 61

    Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As String) As IntPtr
    Private Declare Function capCreateCaptureWindowA Lib "avicap32.dll" (ByVal lpszWindowName As String, ByVal dwStyle As Integer, ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, ByVal nHeight As Short, ByVal hWndParent As IntPtr, ByVal nID As Integer) As IntPtr
    Private Declare Function DestroyWindow Lib "user32" (ByVal hndw As IntPtr) As Boolean

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        Timer1.Stop()
        SendMessage(hHwnd, WM_CAP_DRIVER_DISCONNECT, iDevice, vbNullString)
        DestroyWindow(hHwnd)
        If System.IO.File.Exists(tmppic) Then System.IO.File.Delete(tmppic)
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Button_Stop.Enabled = False
        hHwnd = capCreateCaptureWindowA(iDevice.ToString, WS_VISIBLE Or WS_CHILD, 0, 0, OutputWidth, CShort(OutputHeight), PictureBox1.Handle, 0)
        If Not SendMessage(hHwnd, WM_CAP_DRIVER_CONNECT, iDevice, vbNullString) = IntPtr.Zero Then
            SendMessage(hHwnd, WM_CAP_SET_PREVIEWRATE, CamFrameRate, vbNullString)
            SendMessage(hHwnd, WM_CAP_SET_PREVIEW, 1, vbNullString)
        Else
            MessageBox.Show("Error Connecting To Capture Device")
            Me.Close()
        End If
    End Sub

    Private Sub Button_Start_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Start.Click
        Timer1.Interval = 1000 'capture pic every 1 second
        Timer1.Start()
        Button_Start.Enabled = False
        Button_Stop.Enabled = True
    End Sub

    Private Sub Button_Stop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Stop.Click
        Timer1.Stop()
        Button_Start.Enabled = True
        Button_Stop.Enabled = False
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        SendMessage(hHwnd, WM_CAP_GRAB_FRAME_NOSTOP, 0, vbNullString)
        SendMessage(hHwnd, WM_CAP_SAVEDIB, 0, tmppic)
        Dim bmp As New Bitmap(tmppic)
        bmp.Save("c:\test\Img" & fileno & ".jpg", Imaging.ImageFormat.Jpeg)
        fileno += 1
        bmp.Dispose()
    End Sub
End Class

Answer 6

thanks the problem is solve.

can we set motion detection and brightness of preview window

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Ali Usman

Answer 7

Hi,

 I have not experimented enough with this to figure out a way to do ether of the new questions but, someone else may have an answer or some tips on doing them. Also if any of the posts here helped solve your original question then please mark them as the answers. It will help other people with the same question find an answer.  :)