ImageHelper

    public class ImagesHelper
    {
        /// <summary>
        /// 缩略图1:生成等比例高清缩略图，图片比较大
        /// </summary>
        /// <param name="phyPath">原图片的路径</param>
        /// <param name="width">缩略图宽</param>
        /// <param name="height">缩略图高</param>
        /// <returns></returns>
        public static System.Drawing.Image GetThumbnailImage(System.Drawing.Image image, int width, int height)
        {
            Bitmap bmp = new Bitmap(width, height);
            //从Bitmap创建一个System.Drawing.Graphics
            System.Drawing.Graphics gr = System.Drawing.Graphics.FromImage(bmp);
            //设置 
            gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //设成高质量
            gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            //设成High
            gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            //把原始图像绘制成上面所设置宽高的缩小图
            System.Drawing.Rectangle rectDestination = new System.Drawing.Rectangle(0, 0, width, height);

            gr.DrawImage(image, rectDestination, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel);
            return bmp;
        }

        /// <summary>
        /// 缩略图2：得到指定像素缩略图，图片比较小
        /// </summary>
        /// <param name="Image"></param>
        /// <param name="newFile"></param>
        /// <param name="maxHeight"></param>
        /// <param name="maxWidth"></param>
        /// <param name="qualityNum">图片质量1-100</param>
        /// <param name="mode">缩放模式，CUT裁剪不失真，HW定宽高有可能变形，W定宽，H定高</param>
        public static void GetSmallImage(Image img, string newFile, int maxHeight, int maxWidth, long qualityNum, string mode)
        {
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;
            int towidth = maxWidth;
            int toheight = maxHeight;
            int x = 0;
            int y = 0;
            int ow = img.Width;
            int oh = img.Height;
            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形）                
                    break;
                case "W"://指定宽，高按比例                    
                    toheight = img.Height * maxWidth / img.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = img.Width * maxHeight / img.Height;
                    break;
                case "CUT"://指定高宽裁减（不变形）                
                    if ((double)img.Width / (double)img.Height > (double)towidth / (double)toheight)
                    {
                        oh = img.Height;
                        ow = img.Height * towidth / toheight;
                        y = 0;
                        x = (img.Width - ow) / 2;
                    }
                    else
                    {
                        ow = img.Width;
                        oh = img.Width * maxHeight / towidth;
                        x = 0;
                        y = (img.Height - oh) / 2;
                    }
                    break;
                default:
                    break;
            }
            Bitmap outBmp = new Bitmap(towidth, toheight);
            Graphics g = Graphics.FromImage(outBmp);
            // 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(img, new Rectangle(0, 0, towidth, toheight), x, y, ow, oh, GraphicsUnit.Pixel);
            g.Dispose();
            // 以下代码为保存图片时,设置压缩质量
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = qualityNum;//图片质量1-100
            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;
            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象.
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo jpegICI = null;
            for (int index = 0; index < arrayICI.Length; index++)
            {
                if (arrayICI[index].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[index];
                    //设置JPEG编码
                    break;
                }
            }
            if (jpegICI != null)
            {
                outBmp.Save(newFile, jpegICI, encoderParams);
            }
            else
            {
                outBmp.Save(newFile, thisFormat);
            }
            img.Dispose();
            outBmp.Dispose();
        }

        #region 图片旋转函数

        /// <summary>
        /// 以逆时针或顺时针方向对图像进行旋转
        /// </summary>
        /// <param name="imgFilePath">图片的物理路基</param>
        /// <param name="angle">1-360刻度</param>
        /// <returns></returns>
        public static Bitmap Rotate(string imgFilePath, int angle)
        {
            var b = new Bitmap(imgFilePath);
            return Rotate(b, angle, imgFilePath);
        }

        /// <summary>
        /// 图片向左旋转90度
        /// </summary>
        /// <param name="imgFilePath">图片物理路径</param>
        /// <param name="angle">旋转度数</param>
        /// <returns>成功返回true，失败返回false</returns>
        public static bool RotateLeft(string imgFilePath, int angle = 90)
        {
            try
            {
                Rotate(imgFilePath, angle);
            }
            catch (Exception)
            {
                return false;
            }
            return true;
        }

        /// <summary>
        /// 图片向右旋转90度
        /// </summary>
        /// <param name="imgFilePath">图片物理路径</param>
        /// <param name="angle">旋转度数</param>
        /// <returns>成功返回true，失败返回false</returns>
        public static bool RotateRight(string imgFilePath, int angle = 270)
        {
            try
            {
                Rotate(imgFilePath, angle);
            }
            catch (Exception)
            {
                return false;
            }
            return true;
        }

        /// <summary>
        /// 以逆时针或顺时针方向对图像进行旋转
        /// </summary>
        /// <param name="bitmap">Bitmap图片类型</param>
        /// <param name="angle">1-360刻度</param>
        /// <param name="imgFilePath">保存图片路径,可选项</param>
        /// <returns></returns>
        private static Bitmap Rotate(Image bitmap, int angle, string imgFilePath = "")
        {
            angle = angle > 0 ? angle : angle + 360;
            angle = angle % 360;            //弧度转换
            var radian = angle * Math.PI / 180.0;
            var cos = Math.Cos(radian);
            var sin = Math.Sin(radian);
            //原图的宽和高
            var w = bitmap.Width;
            var h = bitmap.Height;
            var W = (int)(Math.Max(Math.Abs(w * cos - h * sin), Math.Abs(w * cos + h * sin)));
            var H = (int)(Math.Max(Math.Abs(w * sin - h * cos), Math.Abs(w * sin + h * cos)));
            //目标位图
            var dsImage = new Bitmap(W, H);
            var g = Graphics.FromImage(dsImage);
            g.InterpolationMode = InterpolationMode.Bilinear;
            g.SmoothingMode = SmoothingMode.HighQuality;
            //计算偏移量
            var offset = new Point((W - w) / 2, (H - h) / 2);
            //构造图像显示区域：让图像的中心与窗口的中心点一致
            var rect = new Rectangle(offset.X, offset.Y, w, h);
            var center = new Point(rect.X + rect.Width / 2, rect.Y + rect.Height / 2);
            g.TranslateTransform(center.X, center.Y);
            g.RotateTransform(360 - angle);
            //恢复图像在水平和垂直方向的平移
            g.TranslateTransform(-center.X, -center.Y);
            g.DrawImage(bitmap, rect);
            //重至绘图的所有变换
            g.ResetTransform();
            g.Save();
            g.Dispose();
            bitmap.Dispose();
            if (imgFilePath != "")
                dsImage.Save(imgFilePath);
            return dsImage;
        }
        #endregion 图片旋转函数


        /// <summary>
        /// 向图片中添加水印
        /// </summary>
        /// <param name="image">上传图片对象</param>
        /// <param name="waterFilePath">水印图片物理路径</param>
        public static Image AddWater(Image image, string waterFilePath)
        {
            if (image == null) return null;
            var waterImage = Image.FromFile(waterFilePath, false);
            if (image.Width <= waterImage.Width)
            {
                return image;
            }
            //Imaging.Encoder.Quality 默认为60 指定的数字越小，压缩的级别就越高 最大为100L 质量最佳
            var g = Graphics.FromImage(image);
            //设置高质量插值法
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            //设置高质量,低速度呈现平滑程度
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.DrawImage(waterImage, new Rectangle((image.Width - waterImage.Width) - 10, (image.Height - waterImage.Height) - 10, waterImage.Width, waterImage.Height), 0, 0, waterImage.Width, waterImage.Height, GraphicsUnit.Pixel);
            g.Dispose();
            return image;
        }
    }