（1）

        public static Bitmap RotateImage(Image image, float angle)
        {
            if (image == null)
                throw new ArgumentNullException("image");
            float dx = image.Width / 2.0f;
            float dy = image.Height / 2.0f;

            Bitmap rotatedBmp = new Bitmap(image.Width, image.Height);
            rotatedBmp.SetResolution(image.HorizontalResolution, image.VerticalResolution);
            Graphics g = Graphics.FromImage(rotatedBmp);
            g.TranslateTransform(dx, dy);
            g.RotateTransform(angle);
            g.TranslateTransform(-dx, -dy);
            g.DrawImage(image, new PointF(0, 0));
            return rotatedBmp;
        }

        void tm_Elapsed(object sender, EventArgs e)
        {
            if (isStart)
            {
                angle += 5;
                if (angle >= 359) angle = 0;
                RotateImage(pic1, Properties.Resources._1, angle);
            }
        }

        private void RotateImage(PictureBox pb, Image img, float angle)
        {
            if (img == null || pb.Image == null)
                return;
            Image oldImage = pb.Image;
            pb.Image = Utilities.RotateImage(img, angle);
            if (oldImage != null)
            {
                oldImage.Dispose();
            }
        }
 

（2）

        //任意角度旋轉
        private void RotateTransformButton_Click(object sender, EventArgs e)
        {
            try
            {
                Bitmap a = new Bitmap(pictureBox1.Image);//得到圖片框中的圖片
                pictureBox1.Image = Rotate(a, Convert.ToInt32(textBox1.Text));
                pictureBox1.SizeMode = PictureBoxSizeMode.AutoSize;
                pictureBox1.Location = panel1.Location;
                pictureBox1.Refresh();//最後重新整理圖片框
            }
            catch { }
        }
 
        #region 圖片旋轉函式
        /// <summary>
        /// 以逆時針為方向對影象進行旋轉
        /// </summary>
        /// <param name="b">點陣圖流</param>
        /// <param name="angle">旋轉角度[0,360](前臺給的)</param>
        /// <returns></returns>
        public Bitmap Rotate(Bitmap b, int angle)
        {
            angle = angle % 360;
 
            //弧度轉換
            double radian = angle * Math.PI / 180.0;
            double cos = Math.Cos(radian);
            double sin = Math.Sin(radian);
 
            //原圖的寬和高
            int w = b.Width;
            int h = b.Height;
            int W = (int)(Math.Max(Math.Abs(w * cos - h * sin), Math.Abs(w * cos + h * sin)));
            int H = (int)(Math.Max(Math.Abs(w * sin - h * cos), Math.Abs(w * sin + h * cos)));
 
            //目標點陣圖
            Bitmap dsImage = new Bitmap(W, H);
            Graphics g = Graphics.FromImage(dsImage);            
 
            g.InterpolationMode = InterpolationMode.Bilinear;
 
            g.SmoothingMode = SmoothingMode.HighQuality;
 
            //計算偏移量
            Point Offset = new Point((W - w) / 2, (H - h) / 2);
 
            //構造影象顯示區域：讓影象的中心與視窗的中心點一致
            Rectangle rect = new Rectangle(Offset.X, Offset.Y, w, h);
            Point center = new Point(rect.X + rect.Width / 2, rect.Y + rect.Height / 2);
            g.TranslateTransform(center.X, center.Y);
            g.RotateTransform(360 - angle);
 
            //恢復影象在水平和垂直方向的平移
            g.TranslateTransform(-center.X, -center.Y);
            g.DrawImage(b, rect);
 
            //重至繪圖的所有變換
            g.ResetTransform();
 
            g.Save();
            g.Dispose();
            return dsImage;
        }
        #endregion 圖片旋轉函式