C++ 处理图片像素时无法读取内存

CImage* CCatchScreenDlg::LoadCImage( UINT nID, LPCTSTR lpszType, HINSTANCE hInstance )
{
CImage* pImage = NULL;

hInstance = ( NULL == hInstance ) ? ::AfxGetResourceHandle() : hInstance;

if( RT_BITMAP == lpszType )
{
    pImage = new CImage();
    pImage->LoadFromResource( hInstance, nID );
    if ( !pImage->IsNull() )
    {
        return pImage;
    }
    else
    {
        WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]CImage::LoadFromResource失败") );

        delete pImage;
        pImage = NULL;
        return NULL;
    }
}   

CString strLog;
HRSRC hRsrc = ::FindResource( hInstance, MAKEINTRESOURCE(nID), lpszType ); 
ASSERT( hRsrc != NULL );
if ( NULL == hRsrc ) 
{
    WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]::FindResource失败") );
    return NULL;
}

DWORD dwSize = ::SizeofResource( hInstance, hRsrc);
LPBYTE lpRsrc = (LPBYTE)::LoadResource( hInstance, hRsrc);
ASSERT( lpRsrc != NULL );
if ( NULL == hRsrc ) 
{
    WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]::LoadResource失败") );
    return NULL;
}

HGLOBAL hMem = ::GlobalAlloc( GMEM_FIXED, dwSize );
if ( NULL == hMem ) 
{
    WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]::GlobalAlloc失败") );

    ::FreeResource( lpRsrc );
    return NULL;
}

LPBYTE pMem = (LPBYTE)::GlobalLock( hMem );
if ( NULL == pMem ) 
{
    WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]::GlobalLock失败") );

    ::GlobalUnlock( hMem );
    ::GlobalFree( hMem );
    ::FreeResource( lpRsrc );
    return NULL;
}

memcpy( pMem, lpRsrc, dwSize );
IStream * pStream = NULL;
HRESULT hr = ::CreateStreamOnHGlobal( hMem, FALSE, &pStream );
if ( pStream != NULL && hr == S_OK ) 
{
    pImage = new CImage();
    HRESULT hrs = pImage->Load( pStream );

    pStream->Release();

    //释放
    ::GlobalUnlock( hMem );
    ::GlobalFree( hMem );
    ::FreeResource( lpRsrc );

    if ( hrs == S_OK )
    {
        if ( pImage->GetBPP() == 32 )
        {
            for(int i = 0; i < pImage->GetWidth(); i++)   
            {   
                for(int j = 0; j < pImage->GetHeight(); j++)   
                {   
                    unsigned char* pucColor = reinterpret_cast<unsigned char *>(pImage->GetPixelAddress(i , j));   
                    pucColor[0] = pucColor[0] * pucColor[3] / 255;   
                    pucColor[1] = pucColor[1] * pucColor[3] / 255;   
                    pucColor[2] = pucColor[2] * pucColor[3] / 255;   
                }   
            }
        }

        return pImage;
    }
    else
    {
        delete pImage;
        pImage = NULL;
        return NULL;
    }
}
else
{
    WriteScreenCatchLog( _T("[CCatchScreenDlg::LoadCImage]::CreateStreamOnHGlobal失败") );

    ::GlobalUnlock( hMem );
    ::GlobalFree( hMem );
    ::FreeResource( lpRsrc );
    return NULL;
}
}