public void ChangeSource(int index)
{
_twain32.ChangeSource(index);
if (_twain32.ChangeSourceResp != null)
{
throw new Exception(_twain32.ChangeSourceResp);
}
var currentSource = _twain32.GetSourceProduct(_twain32.SourceIndex);
_currentSource = new TwainSource(currentSource, _twain32, index);
}