Code

bool GdiPlusEngine::saveBitmap(
	const wchar_t* fileName, HBITMAP bitmapHandle)
{
	// create GDI+ image for the bitmap handle
	Gdiplus::Bitmap image(bitmapHandle, 0);

	// determine which encoder to use from the fileName extension
	CLSID clsid;
	if (getEncoderClsidForFileName(fileName, &clsid))
	{
		if (image.Save(fileName, &clsid, 0) == Gdiplus::Ok)
			return true;
	}

	return false;
} 

Code

Private Function pvGetEncoderClsID(strMimeType As String, ClassID() As Long) As Long
  Dim Num      As Long
  Dim Size     As Long
  Dim lIdx     As Long
  Dim ICI()    As ImageCodecInfo
  Dim Buffer() As Byte

    pvGetEncoderClsID = -1 ' Failure flag

    Call GdipGetImageEncodersSize(Num, Size)
    If (Size = 0&) Then Exit Function ' Failed!

    ReDim ICI(1 To Num) As ImageCodecInfo
    ReDim Buffer(1 To Size) As Byte

    Call GdipGetImageEncoders(Num, Size, Buffer(1))
    Call CopyMemory(ICI(1), Buffer(1), (Len(ICI(1)) * Num))

    For lIdx = 1& To Num
        If (StrComp(pvPtrToStrW(ICI(lIdx).MimeType), strMimeType, vbTextCompare) = 0) Then
            CopyMemory ClassID(0), ICI(lIdx).ClassID(0), 16& ' Save the Class ID
            pvGetEncoderClsID = lIdx      ' Return the index number for success
            Exit For
        End If
    Next lIdx
    Erase ICI
    Erase Buffer
End Function

Private Function pvPtrToStrW(ByVal lpsz As Long) As String
String Pointer to String
  Dim sOut As String
  Dim lLen As Long

    lLen = lstrlenW(lpsz)

    If (lLen > 0&) Then
        sOut = StrConv(String$(lLen, vbNullChar), vbUnicode)
        Call CopyMemory(ByVal sOut, ByVal lpsz, lLen * 2&)
        pvPtrToStrW = StrConv(sOut, vbFromUnicode)
    End If

End Function

Public Function ConvertToPng(FileName As String) As String

   Dim hStatus As Long
   Dim token As Long
   Dim StartupInput As GdiplusStartupInput
   Dim EncoderClsid As String
   Dim pImage As Long
   Dim nWidth As Long
   Dim nHeight As Long
   Dim transformation As Long
   Dim strFileName As String
   Dim ClassID() As Long
   ReDim ClassID(0 To 3) As Long

   StartupInput.GdiplusVersion = 1
   hStatus = GdiplusStartup(token, StartupInput)
   If hStatus Then
      PutToLog 0, "Error initializing GDI+", ""
      Exit Function
   End If

   hStatus = GdipLoadImageFromFile(StrPtr(FileName), pImage)

   EncoderClsid = pvGetEncoderClsID("image/png", ClassID)

   strFileName = GetPath(FileName) & GetFileNameWithoutExtention(FileName) & ".png"
   hStatus = GdipSaveImageToFile(pImage, StrPtr(strFileName), ClassID(0&), 0)
   If hStatus = 0 Then
   Else
      PutToLog 0, "Error:", CStr(hStatus) & " ---- " & CStr(Err.LastDllError)
   End If

   If pImage Then GdipDisposeImage (pImage)
   ConvertToPng = strFileName

   GdiplusShutdown token

End Function