scanning under windows WIA with custom settings (dpi / etc )

[News123]

Hi,

I'm trying to scan a document from a python 2.6 script without user
interaction.

I found  a code snippet, that allows me to scan under Vista, but that
doesn't allow me to select the dpi / color mode / etc.

The snippet uses win32com.client

# ##################### script start
import win32com.client,os

WIA_IMG_FORMAT_PNG       = "{B96B3CAF-0728-11D3-9D7B-0000F81EF32E}"
WIA_COMMAND_TAKE_PICTURE = "{AF933CAC-ACAD-11D2-A093-00C04F72DC3C}"

os.chdir('c:/temp')
wia = win32com.client.Dispatch("WIA.CommonDialog")
dev = wia.ShowSelectDevice()
for command in dev.Commands:
    if command.CommandID==WIA_COMMAND_TAKE_PICTURE:
        foo=dev.ExecuteCommand(WIA_COMMAND_TAKE_PICTURE)
i=1
for item in dev.Items:
    if i==dev.Items.Count:
        image=item.Transfer(WIA_IMG_FORMAT_PNG)
        break
    i=i+1

image.SaveFile("test.png")
######################### script end


My problems are:

- This script works fine for me under Windows 7, however I'm
  unable to   specify additional parameters, like dpi and
  color mode.

- The script doesn't work under windows XP, though the scanner driver is
installed. (Gimp finds the scanner (as WIA scanner)).
Perhaps 'WIA.CommonDialig' has another name or I need to install some DLL.
The error message is:
--------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\work\python\minidemos\wia_get_simple.py", line 7, in <module>
    wia = win32com.client.Dispatch("WIA.CommonDialog")
  File "C:\Python26\lib\site-packages\win32com\client\__init__.py", line
95, in Dispatch
    dispatch, userName =
dynamic._GetGoodDispatchAndUserName(dispatch,userName,clsctx)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line
104, in _GetGoodDispatchAndUserName
    return (_GetGoodDispatch(IDispatch, clsctx), userName)
  File "C:\Python26\lib\site-packages\win32com\client\dynamic.py", line
84, in _GetGoodDispatch
    IDispatch = pythoncom.CoCreateInstance(IDispatch, None, clsctx,
pythoncom.IID_IDispatch)
com_error: (-2147221005, 'Invalid class string', None, None)
---------------------------------------------------------------------


As I have no knowledge of Win32com and WIA I would appreciate some help
or good documentation about wincom32 / WIA with python



thanks for your help and bye


N