HOWTO: Retrieving Bitmap from access and Displaying In Web Page
-------------------------------------------------------------------------------- The information in this article applies to:
Active Server Pages Microsoft Visual Basic PRofessional and Enterprise Editions for Windows, versions 5.0, 6.0 ActiveX Data Objects (ADO), versions 1.0, 1.5, 2.0, 2.1 SP2, 2.5 Microsoft Internet Information Server versions 4.0, 5.0 Microsoft Data Access Components version 2.5
SUMMARY This article shows by example how to extract the bitmap photos in the Microsoft Access 97 Northwind.mdb database, and view them from a Web browser using Active Server Pages (asp). In order to accomplish this task, an ActiveX DLL must be created that strips the Access and OLE headers from the field. This article shows how to create this ActiveX DLL, and how to implement it.
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This article demonstrates how to use Visual Basic to retrieve a bitmap stored in an OLE Object field. Because the definition of OLE object storage is not documented, the following code searches the object's OLE header for characters consistent with the start of the graphic. This method may not work in all circumstances.
Be aware that Internet Explorer 3.0 is unable to display true color bitmaps. For this reason, the bitmaps stored in the Access database should be no higher than 256 colors.
Step-by-Step Example to Extract the Photos Create a new project in Visual Basic and make the project an ActiveX DLL.
Add a reference to ActiveX Data Objects (ADO) by clicking the Project menu and selecting References. Select "Microsoft OLE DB ActiveX Data Objects 1.0 Library" and click OK.
Add a new module to the project by selecting the Project menu and clicking Add Module. Select Module and click Open.
Place the following code in the (general) (declarations) section of MODULE1.BAS:
' Enter the following Declare statement as one single line: Public Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (lpvDest As Any, lpvSource As Any, ByVal cbCopy As Long)
Type PT Width As Integer Height As Integer End Type
Type OBJECTHEADER Signature As Integer HeaderSize As Integer ObjectType As Long NameLen As Integer ClassLen As Integer NameOffset As Integer ClassOFfset As Integer ObjectSize As PT OleInfo As String * 256 End Type
Place the following code in the (general) (declarations) section of CLASS1.CLS:
Function DisplayBitmap(ByVal OleField As Variant) Dim Arr() As Byte Dim ObjHeader As OBJECTHEADER Dim Buffer As String Dim ObjectOffset As Long Dim BitmapOffset As Long Dim BitmapHeaderOffset As Integer Dim ArrBmp() As Byte Dim i As Long
'Resize the array, then fill it with 'the entire contents of the field ReDim Arr(OleField.ActualSize) Arr() = OleField.GetChunk(OleField.ActualSize)
'Copy the first 19 bytes into a variable 'of the OBJECTHEADER user defined type. CopyMemory ObjHeader, Arr(0), 19
'Determine where the Access Header ends. ObjectOffset = ObjHeader.HeaderSize + 1
'Grab enough bytes after the OLE header to get the bitmap header. Buffer = "" For i = ObjectOffset To ObjectOffset + 512 Buffer = Buffer & Chr(Arr(i)) Next i
'Make sure the class of the object is a Paint Brush object If Mid(Buffer, 12, 6) = "PBrush" Then BitmapHeaderOffset = InStr(Buffer, "BM") If BitmapHeaderOffset > 0 Then
'Calculate the beginning of the bitmap BitmapOffset = ObjectOffset + BitmapHeaderOffset - 1
'Move the bitmap into its own array ReDim ArrBmp(UBound(Arr) - BitmapOffset) CopyMemory ArrBmp(0), Arr(BitmapOffset), UBound(Arr) - BitmapOffset + 1
'Return the bitmap DisplayBitmap = ArrBmp End If End If End Function
Rename the Project by selecting the Project menu, and clicking on "Project1 Properties" and type your new name in the "Project Name" field. This example assumes that you named the project "MyProject" and will refer to that name in future steps.
Make the project Apartment Model Threaded by selecting the "Unattended Execution" check box. Click OK.
Rename the Class in the Property Pane. This example assumes that you named the class "MyClass" and refers to that name in future steps.
Compile the DLL by clicking the File menu and selecting "Make MyProject.dll."
Create an ASP page named "bitmap.asp" that contains the following code:
<%@ LANGUAGE="VBSCRIPT" %> <% ' You need to set up a System DSN named 'NWind' that points to ' the Northwind.mdb database Set DataConn = Server.CreateObject("ADODB.Connection") DataConn.Open "DSN=NWind", "admin", "" Set cmdTemp = Server.CreateObject("ADODB.Command") Set RS = Server.CreateObject("ADODB.Recordset") cmdTemp.CommandText = "SELECT Photo FROM Employees WHERE EmployeeID = 1" cmdTemp.CommandType = 1 Set cmdTemp.ActiveConnection = DataConn RS.Open cmdTemp, , 0, 1 Response.ContentType = "image/bmp" Set Bitmap = Server.CreateObject("MyProject.MyClass") Response.BinaryWrite Bitmap.DisplayBitmap(RS("Photo")) RS.Close %>
Create an HTML page named "BitmapTest.htm" that contains the following code:
