MFC GDI+ Text rendering issue

I'm currently using 5MP Camera, so I convert BYTE* to GDI+ Bitmap object and uses Graphics object to draw on picture control (all GDI+ objects)

and I want to draw a string on it and when I do so, resolution (quality or whatsoever) gets strange. here're the images.

this is the original image

this is the image with the text on it

And here's my code. it uses MFC's WM_MOUSEMOVE. and when mouse pointer gets on CRect(dispRC[array]), it renders string "aa" on the Bitmap object.

and when I do so, quality of image gets lower or I don't exactly know it changes the IMAGE. (You might not notice because those are captured images, but latter image's quality gets lower.)

void CSmall_StudioDlg::OnMouseMove(UINT nFlags, CPoint point)
{
    CPoint insidePoint;
// MAXCAM is the number of bitmap objects.
    for (int i = 0; i < MAXCAM; i++)
    {
// m_pBitmap[MAXCAM] is array of Bitmap* which contains address of Gdiplus::Bitmap objects.
        if (m_pBitmap[i] != NULL)
        {
// m_rcDisp[MAXCAM] are CRect objects which has information of picture control.
// i.e. GetDlgItem(IDC_BIN_DISP)->GetWindowRect(m_rcDisp[BINARY_VID]);
            if (point.x > m_rcDisp[i].TopLeft().x && point.y > m_rcDisp[i].TopLeft().y)
            {
                if (point.x < m_rcDisp[i].BottomRight().x && point.y < m_rcDisp[i].BottomRight().y)
                {
                    StringFormat SF;

                    insidePoint.x = point.x - m_rcDisp[i].TopLeft().x;
                    insidePoint.y = point.y - m_rcDisp[i].TopLeft().y;

                    Graphics textG(m_pBitmap[i]);
                    textG.SetTextRenderingHint(TextRenderingHintSingleBitPerPixel);
                    Gdiplus::Font F(L"Palatino Linotype Bold", 10, FontStyleBold, UnitPixel);
                    RectF R(insidePoint.x, insidePoint.y, 20, 100);

                    SF.SetAlignment(StringAlignmentCenter);
                    SF.SetLineAlignment(StringAlignmentCenter);

                    SolidBrush B(Color(0, 0, 0));

                    textG.DrawString(_T("aa"), -1, &F, R, &SF, &B);
// m_pGraphics[MAXCAM] is made like this
// i.e.
// static CClientDC roiDc(GetDlgItem(IDC_ROI_DISP));
// m_hDC[ROI_VID] = roiDc.GetSafeHdc();
// m_pGraphics[ROI_VID] = Graphics::FromHDC(m_hDC[ROI_VID]);
                    m_pGraphics[i]->DrawImage(m_pBitmap[i], 0, 0, m_vidwidth[i], m_vidheight[i]);
                }
            }
        }

        
    }

    CDialogEx::OnMouseMove(nFlags, point);
}

Hope I get a helpful answer.

Thanks!