C# 处理透明问题[通俗易懂]

private void pictureBox1_Click(object sender, EventArgs e)
        {
            Image Imageimage;
            Imageimage = System.Drawing.Image.FromFile(@"D:\black.png");            
            Bitmap bitmap = new Bitmap(Imageimage);
            bitmap.MakeTransparent(Color.White);

            Imageimage = System.Drawing.Image.FromFile(@"D:\white.png");            
            Bitmap bitmap1 = new Bitmap(Imageimage);
            bitmap1.MakeTransparent(Color.Black);
            
            Graphics g = pictureBox1.CreateGraphics();
            g.Clear(pictureBox1.BackColor);
            for (int j = 0; j < 4; j++)
                for (int i = 0; i < 5; i++)
                {
                    Image x;
                    Random random = new Random();
                    int n = random.Next(1, 3);
                    if (n==1)
                    { 
                        
                        x = bitmap;
                        g.DrawImage(x, new Point(i * 100, j * 100));
                    }
                        
                    if(n==2)
                    { 
                        x = bitmap1;
                        g.DrawImage(x, new Point(i * 100, j * 100));
                    }
                }
                

            //pictureBox1.Image = bitmap;
        }