private void button7_Click(object sender, EventArgs e)
        {
            Bitmap b1 = (Bitmap)pictureBox1.Image;
            Bitmap b2 = (Bitmap)pictureBox2.Image;
            Color k;
            int r, g, b;
            for (int x = 0; x < szer; x++)
            {
                for (int y = 0; y < wys; y++)
                {
                    k = b1.GetPixel(x, y);
                    r = k.R/3;
                    g = k.G/3;
                    b = k.B/3;
                    int a = (r + g + b);
                    
                    b2.SetPixel(x, y, Color.FromArgb(a,a,a));

                }
            }
            pictureBox2.Refresh();
        }