HOWTO: Retrieving Bitmap from Access and Displaying In Web Page

• Microsoft Visual InterDev, version 1.0
• Microsoft Active Server Pages, version 1.0b
• Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0

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.

MORE INFORMATION

WARNING: ANY USE BY YOU OF THE CODE PROVIDED IN THIS ARTICLE IS AT YOUR OWN RISK. Microsoft provides this code "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

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

1. Create a new project in Visual Basic and make the project an ActiveX DLL.

2. 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.

3. Add a new module to the project by selecting the Project menu and clicking Add Module. Select Module and click Open.

4. 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
   
   

5. Place the following code in the (general) (declarations) section of CLASS1.CLS:

         Function DisplayBitmap(ByVal OleField As ADODB.Field)
            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
   
   

6. 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.

7. Make the project Apartment Model Threaded by selecting the "Unattended Execution" check box. Click OK.

8. Rename the Class in the Property Pane. This example assumes that you named the class "MyClass" and refers to that name in future steps.

9. Compile the DLL by clicking the File menu and selecting "Make MyProject.dll."

10. 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
          %>
    
    

11. Create an HTML page named "BitmapTest.htm" that contains the following code:

          <HTML>
          <HEAD>
          <TITLE>Bitmap Test</TITLE>
          </HEAD>
          <BODY>
          <HR>
          <img src="Bitmap.asp">
          <HR>
          </BODY>
          </HTML>
    

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q173308
   TITLE     : HOWTO: Displaying Images Stored in a BLOB Field

   http://support.microsoft.com/support/vinterdev/

Keywords          : AXSFMisc kbcode
Technology        : kbInetDev
Version           : WINDOWS:1.0,5.0; WINNT:1.0b
Platform          : WINDOWS winnt
Issue type        : kbhowto