压缩图片

 public class ImageHelper
    {
        private static Bitmap bmp = null;
        private static ImageCodecInfo ici = null;
        private static System.Drawing.Imaging.Encoder ecd = null;
        private static EncoderParameter ept = null;
        private static EncoderParameters eptS = null;

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">源图路径（物理路径）</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">生成缩略图的方式</param>
        public static string MakeThumbnail(string originalImagePath, int width, int height, string mode)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);
            string thumbnailPath = App.localStore.Store_SendImage();
            string type = originalImagePath.Substring(originalImagePath.LastIndexOf('.') + 1).ToUpper();
            int towidth = width;
            int toheight = height;
            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.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 = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减（不变形）
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                case "DB"://等比缩放（不变形，如果高大按高，宽大按宽缩放）
                    if ((double)originalImage.Width / (double)towidth < (double)originalImage.Height / (double)toheight)
                    {
                        toheight = height;
                        towidth = originalImage.Width * height / originalImage.Height;
                    }
                    else
                    {
                        towidth = width;
                        toheight = originalImage.Height * width / originalImage.Width;
                    }
                    break;
                default:
                    break;
            }
            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //新建一个画板
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            //设置高质量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //设置高质量,低速度呈现平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清空画布并以透明背景色填充
            g.Clear(System.Drawing.Color.Transparent);
            //在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
            new System.Drawing.Rectangle(x, y, ow, oh),
            System.Drawing.GraphicsUnit.Pixel);
            try
            {
                //保存缩略图
                if (type == "JPG")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
                if (type == "BMP")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);
                }
                if (type == "GIF")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                }
                if (type == "PNG")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);
                }
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
            return thumbnailPath;
        }
        /// <summary>
        /// 限制图片大小
        /// </summary>
        /// <param name="strOldPic">原图路径</param>
        /// <param name="intWidth">图片设置宽度</param>
        public static string SmallPicWidth(string strOldPic, double intWidth)
        {
            string strNewPic = App.localStore.Store_SendImage();
            Bitmap objPic, objNewPic;
            try
            {
                objPic = new Bitmap(strOldPic);
                double intHeight = (intWidth / Convert.ToDouble(objPic.Width)) * objPic.Height;
                objNewPic = new Bitmap(objPic, Convert.ToInt32(intWidth), Convert.ToInt32(intHeight));
                objNewPic.Save(strNewPic);
            }
            catch (Exception exp) { throw exp; }
            finally
            {
                objPic = null;
                objNewPic = null;
            }
            return strNewPic;
        }

        /// <summary>
        /// 压缩图片（无损）
        /// </summary>
        /// <param name="newbmp"></param>
        /// <returns></returns>
        public static string ToZipImage(Bitmap newbmp)
        {
            string filePath_ystp = App.localStore.Store_SendImage();
            try
            {
                bmp = newbmp;
                ici = getImageCoderInfo(@"image/png");
                ecd = System.Drawing.Imaging.Encoder.Quality;
                eptS = new EncoderParameters(1);
                ept = new EncoderParameter(ecd, 10L);
                eptS.Param[0] = ept;
                bmp.Save(filePath_ystp, ici, eptS);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
            finally
            {
                bmp.Dispose();
                ept.Dispose();
                eptS.Dispose();
            }

            return filePath_ystp;
        }
        /// <summary>
        /// 压缩图片（无损）
        /// </summary>
        /// <param name="newbmp"></param>
        /// <returns></returns>
        public static string ToZipImage(string filePath) //压缩本地图片
        {
            string filePath_ystp = App.localStore.Store_SendImage();
            try
            {
                using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
                {
                    bmp = new Bitmap(fs);
                    switch (filePath.Substring(filePath.LastIndexOf('.') + 1).ToLower())
                    {
                        case "jpeg":
                        case "jpg":
                            ici = getImageCoderInfo(@"image/jpeg");
                            break;
                        case "bmp":
                             ici = getImageCoderInfo(@"image/bmp");
                            break;
                        case "png":
                            ici = getImageCoderInfo(@"image/png");
                            break;
                        case "ico":
                            ici = getImageCoderInfo(@"image/icon");
                            break;
                    }
                    ecd = System.Drawing.Imaging.Encoder.Quality;
                    eptS = new EncoderParameters(1);
                    ept = new EncoderParameter(ecd, 10L);
                    eptS.Param[0] = ept;
                    bmp.Save(filePath_ystp, ici, eptS);
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
            finally
            {
                bmp.Dispose();
                ept.Dispose();
                eptS.Dispose();
            }
            return filePath_ystp;
        }

        private static ImageCodecInfo getImageCoderInfo(string coderType)// 获取图片编码类型信息
        {
            ImageCodecInfo[] iciS = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo retIci = null;

            foreach (ImageCodecInfo ici in iciS)
            {
                if (ici.MimeType.Equals(coderType))
                    retIci = ici;
            }

            return retIci;
        }