Image Processing Brightness

Brightness

private void button1_Click(object sender, EventArgs e)
        {
            Bitmap bmp = new Bitmap(pictureBox1.Image);
            Bitmap bmp2 = new Bitmap(pictureBox1.Image);
            int r, g, b;
            Color c;
            int val = (int)Convert.ToInt16(textBox1.Text);
            Cursor = Cursors.WaitCursor;
            for(int i=0; i < bmp.Width; i++)
            {
                for (int j = 0; j < bmp.Height; j++)
                {
                    c = bmp.GetPixel(i, j);
                    r = c.R + val;
                    g = c.G + val;
                    b = c.B + val;
                    if (r > 255) r = 255;
                    if (g > 255) g = 255;
                    if (b > 255) b = 255;
                    if (r < 0) r = 0;
                    if (g < 0) g = 0;
                    if (b < 0) b = 0;
                    bmp2.SetPixel(i, j, Color.FromArgb(r, g, b));
                }
            }
            pictureBox2.Image = bmp2;
            Cursor = Cursors.Default;
        }