public void Zmien_obraz()
        {
            System.Drawing.Color pixel;
            int r, g, b;
            int jasnosc, jasnosc_pixel;
            int n = 50;
            pixel = m_obraz_w_pamieci.GetPixel(128, 128);
            r = pixel.R;
            g = pixel.G;
            b = pixel.B;
            jasnosc = (r + g + b) / 3;

            for (int j = 1; j <= L; j++)
                for (int i = 1; i <= K; i++)
                {
                    pixel = m_obraz_w_pamieci.GetPixel(i - 1, j - 1);

                        r = pixel.R;
                        b = pixel.B;
                        g = pixel.G;
                    jasnosc_pixel = (r + g + b) / 3;
                    if (jasnosc >= jasnosc_pixel)
                    {

                        r = r - n;
                        if (r <= 0)
                            r = 0;

                        b = b - n;
                        if (b <= 0)
                            b = 0;

                        g = g - n;
                        if (g <= 0)
                            g = 0;
                    }
                    else
                    {
                        r = r + n;
                        if (r >= 255)
                            r = 255;
                        b = b + n;
                        if (b >= 255)
                            b = 255;
                        g = g + n;
                        if (g >= 255)
                            g = 255;
                    }


                        pixel = System.Drawing.Color.FromArgb(r, g, b);
                        m_ekran.SetPixel(i - 1, j - 1, pixel);



                        //--------------------------------------//


                    }


                    SetBitMap(ref m_ekran);
        }