What if you want to capture a single image from a webcam? It turns out that this is quite straight forward to do using a couple of Win32 api calls to the avicap32.dll library.
I encapsulated these api calls in a simple class.
To write a file called “snapshot.jpg” out to the desktop from a single webcam, simply declare the class and call a the TakePicture method.
Dim loSnap As New WebcamSnap
loSnap.TakePicture(0)
The devices collection shows a list of all webcam devices on your machine so you can populate a combo with them.
Note: This example has no decent error handling, which I suspect will be needed in the “real world” of multiple devices.
Here’s the WebcamSnap class:
Option Explicit On
Imports System.IO
Imports System.Runtime.InteropServices
''' <summary>
''' This class takes a snapshot from any or all attached webcams
''' </summary>
''' <remarks></remarks>
Public Class WebcamSnap
Const WM_CAP As Short = &H400S
Const WM_CAP_DRIVER_CONNECT As Integer = WM_CAP + 10
Const WM_CAP_DRIVER_DISCONNECT As Integer = WM_CAP + 11
Const WM_CAP_EDIT_COPY As Integer = WM_CAP + 30
Const WS_CHILD As Integer = &H40000000
Const WS_VISIBLE As Integer = &H10000000
Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
(ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, _
<MarshalAs(UnmanagedType.AsAny)> ByVal lParam As Object) As Integer
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 Integer, _
ByVal nID As Integer) As Integer
Declare Function capGetDriverDescriptionA Lib "avicap32.dll" (ByVal wDriver As Short, _
ByVal lpszName As String, ByVal cbName As Integer, ByVal lpszVer As String, _
ByVal cbVer As Integer) As Boolean
Public Devices As New List(Of String)
Public Height As Integer = 480
Public Width As Integer = 640
Public OutputPath As String = Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory)
Public FilenamePrefix As String = "snapshot"
Public Sub New()
mLoadDeviceList()
End Sub
Private Sub mLoadDeviceList()
Dim lsName As String = Space(100)
Dim lsVers As String = Space(100)
Dim lbReturn As Boolean
Dim x As Integer = 0
Do
' Get Driver name and version
lbReturn = capGetDriverDescriptionA(x, lsName, 100, lsVers, 100)
' If there was a device add device name to the list
If lbReturn Then Devices.Add(lsName.Trim)
x += 1
Loop Until lbReturn = False
End Sub
Public Sub TakePicture()
For i = 0 To Me.Devices.Count - 1
Dim lsFilename As String = Path.Combine(OutputPath, Me.FilenamePrefix & i & ".jpg")
TakePicture(i, lsFilename)
Next
End Sub
Public Sub TakePicture(ByVal iDevice As Integer)
Me.TakePicture(iDevice, Path.Combine(OutputPath, Me.FilenamePrefix & ".jpg"))
End Sub
Public Sub TakePicture(ByVal iDevice As Integer, ByVal filename As String)
Dim lhHwnd As Integer ' Handle to preview window
' Create a form to play with
Using loWindow As New System.Windows.Forms.Form
' Create capture window
lhHwnd = capCreateCaptureWindowA(iDevice, WS_VISIBLE Or WS_CHILD, 0, 0, Me.Width, _
Me.Height, loWindow.Handle.ToInt32, 0)
' Hook up the device
SendMessage(lhHwnd, WM_CAP_DRIVER_CONNECT, iDevice, 0)
' Allow the webcam apeture to let enough light in
For i = 1 To 10
Application.DoEvents()
Next
' Copy image to clipboard
SendMessage(lhHwnd, WM_CAP_EDIT_COPY, 0, 0)
' Get image from clipboard and convert it to a bitmap
Dim loData As IDataObject = Clipboard.GetDataObject()
If loData.GetDataPresent(GetType(System.Drawing.Bitmap)) Then
Using loBitmap As Image = CType(loData.GetData(GetType(System.Drawing.Bitmap)), Image)
loBitmap.Save(filename, Imaging.ImageFormat.Jpeg)
End Using
End If
SendMessage(lhHwnd, WM_CAP_DRIVER_DISCONNECT, iDevice, 0)
End Using
End Sub
End Class
Links
I found the original code sample here:
http://www.experts-exchange.com/Programming/Languages/.NET/Visual_Basic.NET/Q_22482234.html
(Although I’ve seen it all over the web in various guises)
An Original Idea 