Help me about BITMAP in MFC application

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MFC

I have a project for example about some image processing algorithm.
I open a bitmap file by using

BOOL CImageProc_1Doc::OnOpenDocument(LPCTSTR lpszPathName)
{
	if (!CDocument::OnOpenDocument(lpszPathName))
		return FALSE;


	// TODO:  Add your specialized creation code here

hBitmap=(HBITMAP)::LoadImage (AfxGetInstanceHandle(), lpszPathName,IMAGE_BITMAP,0,0,LR_LOADFROMFILE | LR_CREATEDIBSECTION);
	if(m_bmBitmap.DeleteObject ()) m_bmBitmap.Detach ();
	m_bmBitmap.Attach (hBitmap);
}

I draw the image using this code

void CImageProc_1View::OnDraw(CDC*pDC)
{
	CImageProc_1Doc* pDoc = GetDocument();
	ASSERT_VALID(pDoc);
	if (!pDoc)
		return;
	
	// TODO: add draw code for native data here

	if  (pDoc->m_bmBitmap.m_hObject ==NULL )	return;
	BITMAP bm;
	pDoc->m_bmBitmap.GetBitmap (&bm);
	CDC dcMem;
	dcMem.CreateCompatibleDC (pDC);
    	dcMem.SelectObject (pDoc->m_bmBitmap );
	::SetDIBColorTable(dcMem,0,256,pDoc->rgb);
	pDC->StretchBlt(0,0,bm .bmWidth ,bm.bmHeight ,&dcMem,0,0,bm.bmWidth ,bm.bmHeight ,SRCCOPY);
}

Now I process the bitmap data (store in bm.bmBits pointer) , I store the result in a other newBit pointer and try this code :

dw=::SetBitmapBits(pDlgDoc->hBitmap,bm.bmHeight*bm.bmWidthBytes,newBit);

It's only work well when the bitmap has no padding buffer although the newBit has padding bytes.
When the bitmap has padding , the bitmap is drawn in wrong way like THIS
Please help me solve this problem , Thanks all!