using FreeImage_OpenMemory to access BLOB

[Steve Murphy]

Some time ago I wanted to find out how to read image data stored in a database
BLOB column into Freeimage without having to save the BLOB as a temporary file
on disk first. It seemed pretty obvious that using FreeImage_OpenMemory was
the way to go but nobody else had been able to get any help with it here so I
gave up as I was short of time. I've now had time to revisit the issue and
thought it would be a good idea to to post some simple sample code to
demonstrate the process.

    Dim rsWork As New cRecordset
    Dim byBlobData() As Byte
    Dim lngMem As Long
    Dim fifMem As FREE_IMAGE_FORMAT
    Dim fibImage As Long

    cnnDB.OpenDB mstrDBFile

    Set rsWork = cnnDB.OpenRecordset("SELECT Image_Len, ImageData FROM Medications")

    byBlobData = rsWork.Fields("ImageData").value

    ' Note that we just pass in the the first item of the array as VB handles
    ' turning it into an appropriate pointer
    lngMem = FreeImage_OpenMemory(byBlobData(0), rsWork!Image_Len)

    fifMem = FreeImage_GetFileTypeFromMemory(lngMem)

    fibImage = FreeImage_LoadFromMemory(fifMem, lngMem, 0)

    FreeImage_PaintDC Me.hdc, fibImage
    FreeImage_Unload fibImage
    FreeImage_CloseMemory lngMem

    Set rsWork = Nothing
End Sub

[Carsten Klein]

Hi Crunchy Frog,

you could do this even more easily by using wrapper method
FreeImage_LoadFromMemoryEx, which takes a VB-style Byte array as its first
parameter. Have a look at this modified version of your code.

Dim rsWork As New cRecordset
Dim byBlobData() As Byte
Dim fifMem As FREE_IMAGE_FORMAT
Dim fibImage As Long

   cnnDB.OpenDB mstrDBFile
   Set rsWork = cnnDB.OpenRecordset("SELECT Image_Len, ImageData FROM Medications")
   byBlobData = rsWork.Fields("ImageData").Value

   ' If you need the image type, add fifMem as the last ByRef parameter, which will contain the image's type
   ' after the function returns.
   fibImage = FreeImage_LoadFromMemoryEx(byBlobData, , , fifMem)
   ' Use this line instead, if you do not need the image type.
   'fibImage = FreeImage_LoadFromMemoryEx(byBlobData)

   ' Now, paint the image.
   FreeImage_PaintDC Me.hDC, fibImage

   ' Unload the FreeImage bitmap from memory.
   FreeImage_Unload fibImage

   Set rsWork = Nothing

However, FreeImage_LoadFromMemoryEx only works with explicitly declared VB-
style arrays so, you always need to assign your recordset field's value to a
(Byte in this case) array. Although it seems obvious, doing this even shorter
like

   fibImage = FreeImage_LoadFromMemoryEx(rsWork.Fields("ImageData").Value)

does not work.

Carsten

[Steve Murphy]

Thanks for the follow-up Carsten. I'll revisit my working code as you
recommend.

Regards

Steve Murphy

[Wolfgang Fürtbauer]

Carsten,
I tried your code, but FreeImage_LoadFromMemoryEx returns 0
Running step by step through the code, I found out that FreeImage_GetFileTypeFromMemory(hStream) returns -1 (unknown) ?

Could you please help?

Here's what i did:

public function test()

dim rs as recordset
dim data() as byte
dim dib as long

' "bild" is the memo/blob field containing the binary data

set rs = currentdb().openrecordset("select * from tabelle1")
rs.edit
rs!bild = readbitmap("C:\temp\test.bmp")
rs.update
rs.Requery
' now we have the binaray data in the memo field
data = rs!bild

dib = FreeImage_LoadFromMemoryEx(data, , , FIF_BMP)
' dib is 0 ???

end function

Public Function readbmp(pfad As String) As String
Dim content As String
Open pfad For Binary Access Read As #1
content = Space(LOF(1))
Get #1, , content
readbmp = content
Close #1
End Function

[Carsten Klein]

Hi,

have you had a look at the data array after that line? Does is contain the same bytes that you see when you view the file C:\temp\test.bmp with a HEX editor?

Currently I'm on vacation (St. Peter Ording) and only have a Linux box with me, so I'm not really able to figure out things about VBA and Access. But I guess that something with loading /storing / requerying of the image file's
bytes goes wrong.

Maybe you should not load the image file into a String variable in function readbmp. Try it with a byte array. Make the function return Byte() and turn variable content into a byte array. Then use

ReDim content(LOF(1) - 1)

instead of the Space() function.

Carsten