記錄一個圖片處理類，分享給你們參考

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
namespace  Common
{
    /// <summary>
    /// 圖片處理    
    /// </summary>
    public class Image
    {
        public static bool Thumb(string srcImage, string thumbImage, int maxWidth = 200, int maxHeight = 50, int x = 0, int y = 0)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(Tool.GetMapPath(srcImage));
            ImageFormat originalFormat = originalImage.RawFormat;
            string ext = System.IO.Path.GetExtension(srcImage).ToLower();
            int width = 0;
            int height = 0;

            int srcWidth = originalImage.Width;    //原始圖片的寬度
            int srcHeight = originalImage.Height;  //原始圖片的高度

            double scale = Math.Min((double)maxWidth / (double)srcWidth, (double)maxHeight / (double)srcHeight);
            if (scale >= 1)
            {
                width = srcWidth;
                height = srcHeight;    //縮略圖的高度
            }
            else
            {
                width = (int)(srcWidth * scale);
                height = (int)(srcHeight * scale);
            }

         

            //新建一個bmp圖片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(width, height);

            //新建一個畫板
            System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(bitmap);

            //呈現質量
            graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

            //設置高質量，低速度呈現平滑程度
            graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //設置高質量查值法
            graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //清空畫布並以透明背景色填充
            graphic.Clear(System.Drawing.Color.Transparent);

            //在指定位置而且按指定大小繪製原圖片的指定部分
            graphic.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(x, y, srcWidth, srcHeight), System.Drawing.GraphicsUnit.Pixel);
            
            //如下代碼爲保存圖片時，設置壓縮質量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = 100;
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                switch (ext)
                {
                    case ".jpeg":                        
                    case ".jpg":
                        ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                        ImageCodecInfo jpegICIinfo = null;
                        for (int i = 0; i < arrayICI.Length; i++)
                        {
                            if (arrayICI[i].FormatDescription.Equals("JPEG"))
                            {
                                jpegICIinfo = arrayICI[i];
                                break;
                            }
                        }
                        if (jpegICIinfo != null)
                        {
                            bitmap.Save(Tool.GetMapPath(thumbImage), jpegICIinfo, ep); //thumNailPath是壓縮後的新路徑
                        }
                        else
                        {
                            bitmap.Save(Tool.GetMapPath(thumbImage), originalFormat);
                        }
                        break;
                    case ".png":
                        bitmap.Save(Tool.GetMapPath(thumbImage), System.Drawing.Imaging.ImageFormat.Png);
                        break;
                    case ".gif":
                        bitmap.Save(Tool.GetMapPath(thumbImage), System.Drawing.Imaging.ImageFormat.Gif);
                        break;
                    default:
                        bitmap.Save(Tool.GetMapPath(thumbImage), originalFormat);
                        break;
                }                
            }
            catch
            {
                return false;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                graphic.Dispose();
            }
            return true;
        }

        public static bool Crop(string srcImage, string thumbImage, int x, int y, int width, int height)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(Tool.GetMapPath(srcImage));
            ImageFormat originalFormat = originalImage.RawFormat;
            string ext = System.IO.Path.GetExtension(srcImage).ToLower();

            int srcWidth = originalImage.Width;    //原始圖片的寬度
            int srcHeight = originalImage.Height;  //原始圖片的高度


            //新建一個bmp圖片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(width, height);

            //新建一個畫板
            System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(bitmap);

            //呈現質量
            graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;

            //設置高質量，低速度呈現平滑程度
            graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //設置高質量查值法
            graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            //清空畫布並以透明背景色填充
            graphic.Clear(System.Drawing.Color.Transparent);

            //在指定位置而且按指定大小繪製原圖片的指定部分
            graphic.DrawImage(originalImage, new System.Drawing.Rectangle(x, y, width, height), new System.Drawing.Rectangle(x, y, srcWidth, srcHeight), System.Drawing.GraphicsUnit.Pixel);

            //如下代碼爲保存圖片時，設置壓縮質量
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = 100;
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                switch (ext)
                {
                    case ".jpeg":
                    case ".jpg":
                        ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                        ImageCodecInfo jpegICIinfo = null;
                        for (int i = 0; i < arrayICI.Length; i++)
                        {
                            if (arrayICI[i].FormatDescription.Equals("JPEG"))
                            {
                                jpegICIinfo = arrayICI[i];
                                break;
                            }
                        }
                        if (jpegICIinfo != null)
                        {
                            bitmap.Save(Tool.GetMapPath(thumbImage), jpegICIinfo, ep); //thumNailPath是壓縮後的新路徑
                        }
                        else
                        {
                            bitmap.Save(Tool.GetMapPath(thumbImage), originalFormat);
                        }
                        break;
                    case ".png":
                        bitmap.Save(Tool.GetMapPath(thumbImage), System.Drawing.Imaging.ImageFormat.Png);
                        break;
                    case ".gif":
                        bitmap.Save(Tool.GetMapPath(thumbImage), System.Drawing.Imaging.ImageFormat.Gif);
                        break;
                    default:
                        bitmap.Save(Tool.GetMapPath(thumbImage), originalFormat);
                        break;
                }
            }
            catch
            {
                return false;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                graphic.Dispose();
            }
            return true;
        }


        #region 正方型裁剪並縮放
        /// <summary>
        /// 正方型裁剪
        /// 以圖片中心爲軸心，截取正方型，而後等比縮放
        /// 用於頭像處理
        /// </summary>
        /// <remarks>吳劍 2012-08-08</remarks>
        /// <param name="fromFile">原圖Stream對象</param>
        /// <param name="fileSaveUrl">縮略圖存放地址</param>
        /// <param name="side">指定的邊長（正方型）</param>
        /// <param name="quality">質量（範圍0-100）</param>
        public static void CutForSquare(System.IO.Stream fromFile, string fileSaveUrl, int side, int quality)
        {
            //建立目錄
            string dir = Path.GetDirectoryName(fileSaveUrl);
            if (!Directory.Exists(dir))
                Directory.CreateDirectory(dir);

            //原始圖片（獲取原始圖片建立對象，並使用流中嵌入的顏色管理信息）
            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);

            //原圖寬高均小於模版，不做處理，直接保存
            if (initImage.Width <= side && initImage.Height <= side)
            {
                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            else
            {
                //原始圖片的寬、高
                int initWidth = initImage.Width;
                int initHeight = initImage.Height;

                //非正方型先裁剪爲正方型
                if (initWidth != initHeight)
                {
                    //截圖對象
                    System.Drawing.Image pickedImage = null;
                    System.Drawing.Graphics pickedG = null;

                    //寬大於高的橫圖
                    if (initWidth > initHeight)
                    {
                        //對象實例化
                        pickedImage = new System.Drawing.Bitmap(initHeight, initHeight);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //設置質量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle((initWidth - initHeight) / 2, 0, initHeight, initHeight);
                        Rectangle toR = new Rectangle(0, 0, initHeight, initHeight);
                        //畫圖
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置寬
                        initWidth = initHeight;
                    }
                    //高大於寬的豎圖
                    else
                    {
                        //對象實例化
                        pickedImage = new System.Drawing.Bitmap(initWidth, initWidth);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //設置質量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle(0, (initHeight - initWidth) / 2, initWidth, initWidth);
                        Rectangle toR = new Rectangle(0, 0, initWidth, initWidth);
                        //畫圖
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置高
                        initHeight = initWidth;
                    }

                    //將截圖對象賦給原圖
                    initImage = (System.Drawing.Image)pickedImage.Clone();
                    //釋放截圖資源
                    pickedG.Dispose();
                    pickedImage.Dispose();
                }

                //縮略圖對象
                System.Drawing.Image resultImage = new System.Drawing.Bitmap(side, side);
                System.Drawing.Graphics resultG = System.Drawing.Graphics.FromImage(resultImage);
                //設置質量
                resultG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                resultG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                //用指定背景色清空畫布
                resultG.Clear(Color.White);
                //繪製縮略圖
                resultG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, side, side), new System.Drawing.Rectangle(0, 0, initWidth, initHeight), System.Drawing.GraphicsUnit.Pixel);

                //關鍵質量控制
                //獲取系統編碼類型數組,包含了jpeg,bmp,png,gif,tiff
                ImageCodecInfo[] icis = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo ici = null;
                foreach (ImageCodecInfo i in icis)
                {
                    if (i.MimeType == "image/jpeg" || i.MimeType == "image/bmp" || i.MimeType == "image/png" || i.MimeType == "image/gif")
                    {
                        ici = i;
                    }
                }
                EncoderParameters ep = new EncoderParameters(1);
                ep.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);

                //保存縮略圖
                resultImage.Save(fileSaveUrl, ici, ep);

                //釋放關鍵質量控制所用資源
                ep.Dispose();

                //釋放縮略圖資源
                resultG.Dispose();
                resultImage.Dispose();

                //釋放原始圖片資源
                initImage.Dispose();
            }
        }

        #endregion

        #region 自定義裁剪並縮放

        /// <summary>
        /// 指定長寬裁剪
        /// 按模版比例最大範圍的裁剪圖片並縮放至模版尺寸
        /// </summary>
        /// <remarks>吳劍 2012-08-08</remarks>
        /// <param name="fromFile">原圖Stream對象</param>
        /// <param name="fileSaveUrl">保存路徑</param>
        /// <param name="maxWidth">最大寬(單位:px)</param>
        /// <param name="maxHeight">最大高(單位:px)</param>
        /// <param name="quality">質量（範圍0-100）</param>
        public static void CutForCustom(System.IO.Stream fromFile, string fileSaveUrl, int maxWidth, int maxHeight, int quality)
        {
            //從文件獲取原始圖片，並使用流中嵌入的顏色管理信息
            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);

            //原圖寬高均小於模版，不做處理，直接保存
            if (initImage.Width <= maxWidth && initImage.Height <= maxHeight)
            {
                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            else
            {
                //模版的寬高比例
                double templateRate = (double)maxWidth / maxHeight;
                //原圖片的寬高比例
                double initRate = (double)initImage.Width / initImage.Height;

                //原圖與模版比例相等，直接縮放
                if (templateRate == initRate)
                {
                    //按模版大小生成最終圖片
                    System.Drawing.Image templateImage = new System.Drawing.Bitmap(maxWidth, maxHeight);
                    System.Drawing.Graphics templateG = System.Drawing.Graphics.FromImage(templateImage);
                    templateG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                    templateG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    templateG.Clear(Color.White);
                    templateG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, maxWidth, maxHeight), new System.Drawing.Rectangle(0, 0, initImage.Width, initImage.Height), System.Drawing.GraphicsUnit.Pixel);
                    templateImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
                //原圖與模版比例不等，裁剪後縮放
                else
                {
                    //裁剪對象
                    System.Drawing.Image pickedImage = null;
                    System.Drawing.Graphics pickedG = null;

                    //定位
                    Rectangle fromR = new Rectangle(0, 0, 0, 0);//原圖裁剪定位
                    Rectangle toR = new Rectangle(0, 0, 0, 0);//目標定位

                    //寬爲標準進行裁剪
                    if (templateRate > initRate)
                    {
                        //裁剪對象實例化
                        pickedImage = new System.Drawing.Bitmap(initImage.Width, (int)System.Math.Floor(initImage.Width / templateRate));
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);

                        //裁剪源定位
                        fromR.X = 0;
                        fromR.Y = (int)System.Math.Floor((initImage.Height - initImage.Width / templateRate) / 2);
                        fromR.Width = initImage.Width;
                        fromR.Height = (int)System.Math.Floor(initImage.Width / templateRate);

                        //裁剪目標定位
                        toR.X = 0;
                        toR.Y = 0;
                        toR.Width = initImage.Width;
                        toR.Height = (int)System.Math.Floor(initImage.Width / templateRate);
                    }
                    //高爲標準進行裁剪
                    else
                    {
                        pickedImage = new System.Drawing.Bitmap((int)System.Math.Floor(initImage.Height * templateRate), initImage.Height);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);

                        fromR.X = (int)System.Math.Floor((initImage.Width - initImage.Height * templateRate) / 2);
                        fromR.Y = 0;
                        fromR.Width = (int)System.Math.Floor(initImage.Height * templateRate);
                        fromR.Height = initImage.Height;

                        toR.X = 0;
                        toR.Y = 0;
                        toR.Width = (int)System.Math.Floor(initImage.Height * templateRate);
                        toR.Height = initImage.Height;
                    }

                    //設置質量
                    pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                    pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

                    //裁剪
                    pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);

                    //按模版大小生成最終圖片
                    System.Drawing.Image templateImage = new System.Drawing.Bitmap(maxWidth, maxHeight);
                    System.Drawing.Graphics templateG = System.Drawing.Graphics.FromImage(templateImage);
                    templateG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                    templateG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                    templateG.Clear(Color.White);
                    templateG.DrawImage(pickedImage, new System.Drawing.Rectangle(0, 0, maxWidth, maxHeight), new System.Drawing.Rectangle(0, 0, pickedImage.Width, pickedImage.Height), System.Drawing.GraphicsUnit.Pixel);

                    //關鍵質量控制
                    //獲取系統編碼類型數組,包含了jpeg,bmp,png,gif,tiff
                    ImageCodecInfo[] icis = ImageCodecInfo.GetImageEncoders();
                    ImageCodecInfo ici = null;
                    foreach (ImageCodecInfo i in icis)
                    {
                        if (i.MimeType == "image/jpeg" || i.MimeType == "image/bmp" || i.MimeType == "image/png" || i.MimeType == "image/gif")
                        {
                            ici = i;
                        }
                    }
                    EncoderParameters ep = new EncoderParameters(1);
                    ep.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);

                    //保存縮略圖
                    templateImage.Save(fileSaveUrl, ici, ep);
                    //templateImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);

                    //釋放資源
                    templateG.Dispose();
                    templateImage.Dispose();

                    pickedG.Dispose();
                    pickedImage.Dispose();
                }
            }

            //釋放資源
            initImage.Dispose();
        }
        #endregion

        #region 等比縮放

        /// <summary>
        /// 圖片等比縮放
        /// </summary>
        /// <remarks>吳劍 2012-08-08</remarks>
        /// <param name="fromFile">原圖Stream對象</param>
        /// <param name="savePath">縮略圖存放地址</param>
        /// <param name="targetWidth">指定的最大寬度</param>
        /// <param name="targetHeight">指定的最大高度</param>
        /// <param name="watermarkText">水印文字(爲""表示不使用水印)</param>
        /// <param name="watermarkImage">水印圖片路徑(爲""表示不使用水印)</param>
        public static void ZoomAuto(System.IO.Stream fromFile, string savePath, System.Double targetWidth, System.Double targetHeight, string watermarkText, string watermarkImage)
        {
            //建立目錄
            string dir = Path.GetDirectoryName(savePath);
            if (!Directory.Exists(dir))
                Directory.CreateDirectory(dir);

            //原始圖片（獲取原始圖片建立對象，並使用流中嵌入的顏色管理信息）
            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);

            //原圖寬高均小於模版，不做處理，直接保存
            if (initImage.Width <= targetWidth && initImage.Height <= targetHeight)
            {
                //文字水印
                if (watermarkText != "")
                {
                    using (System.Drawing.Graphics gWater = System.Drawing.Graphics.FromImage(initImage))
                    {
                        System.Drawing.Font fontWater = new Font("黑體", 10);
                        System.Drawing.Brush brushWater = new SolidBrush(Color.White);
                        gWater.DrawString(watermarkText, fontWater, brushWater, 10, 10);
                        gWater.Dispose();
                    }
                }

                //透明圖片水印
                if (watermarkImage != "")
                {
                    if (File.Exists(watermarkImage))
                    {
                        //獲取水印圖片
                        using (System.Drawing.Image wrImage = System.Drawing.Image.FromFile(watermarkImage))
                        {
                            //水印繪製條件：原始圖片寬高均大於或等於水印圖片
                            if (initImage.Width >= wrImage.Width && initImage.Height >= wrImage.Height)
                            {
                                Graphics gWater = Graphics.FromImage(initImage);

                                //透明屬性
                                ImageAttributes imgAttributes = new ImageAttributes();
                                ColorMap colorMap = new ColorMap();
                                colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
                                colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
                                ColorMap[] remapTable = { colorMap };
                                imgAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

                                float[][] colorMatrixElements = { 
                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
                                };

                                ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);
                                imgAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
                                gWater.DrawImage(wrImage, new Rectangle(initImage.Width - wrImage.Width, initImage.Height - wrImage.Height, wrImage.Width, wrImage.Height), 0, 0, wrImage.Width, wrImage.Height, GraphicsUnit.Pixel, imgAttributes);

                                gWater.Dispose();
                            }
                            wrImage.Dispose();
                        }
                    }
                }

                //保存
                initImage.Save(savePath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            else
            {
                //縮略圖寬、高計算
                double newWidth = initImage.Width;
                double newHeight = initImage.Height;

                //寬大於高或寬等於高（橫圖或正方）
                if (initImage.Width > initImage.Height || initImage.Width == initImage.Height)
                {
                    //若是寬大於模版
                    if (initImage.Width > targetWidth)
                    {
                        //寬按模版，高按比例縮放
                        newWidth = targetWidth;
                        newHeight = initImage.Height * (targetWidth / initImage.Width);
                    }
                }
                //高大於寬（豎圖）
                else
                {
                    //若是高大於模版
                    if (initImage.Height > targetHeight)
                    {
                        //高按模版，寬按比例縮放
                        newHeight = targetHeight;
                        newWidth = initImage.Width * (targetHeight / initImage.Height);
                    }
                }

                //生成新圖
                //新建一個bmp圖片
                System.Drawing.Image newImage = new System.Drawing.Bitmap((int)newWidth, (int)newHeight);
                //新建一個畫板
                System.Drawing.Graphics newG = System.Drawing.Graphics.FromImage(newImage);

                //設置質量
                newG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                newG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

                //置背景色
                newG.Clear(Color.White);
                //畫圖
                newG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, newImage.Width, newImage.Height), new System.Drawing.Rectangle(0, 0, initImage.Width, initImage.Height), System.Drawing.GraphicsUnit.Pixel);

                //文字水印
                if (watermarkText != "")
                {
                    using (System.Drawing.Graphics gWater = System.Drawing.Graphics.FromImage(newImage))
                    {
                        System.Drawing.Font fontWater = new Font("宋體", 10);
                        System.Drawing.Brush brushWater = new SolidBrush(Color.White);
                        gWater.DrawString(watermarkText, fontWater, brushWater, 10, 10);
                        gWater.Dispose();
                    }
                }

                //透明圖片水印
                if (watermarkImage != "")
                {
                    if (File.Exists(watermarkImage))
                    {
                        //獲取水印圖片
                        using (System.Drawing.Image wrImage = System.Drawing.Image.FromFile(watermarkImage))
                        {
                            //水印繪製條件：原始圖片寬高均大於或等於水印圖片
                            if (newImage.Width >= wrImage.Width && newImage.Height >= wrImage.Height)
                            {
                                Graphics gWater = Graphics.FromImage(newImage);

                                //透明屬性
                                ImageAttributes imgAttributes = new ImageAttributes();
                                ColorMap colorMap = new ColorMap();
                                colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
                                colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
                                ColorMap[] remapTable = { colorMap };
                                imgAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

                                float[][] colorMatrixElements = { 
                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
                                };

                                ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);
                                imgAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
                                gWater.DrawImage(wrImage, new Rectangle(newImage.Width - wrImage.Width, newImage.Height - wrImage.Height, wrImage.Width, wrImage.Height), 0, 0, wrImage.Width, wrImage.Height, GraphicsUnit.Pixel, imgAttributes);
                                gWater.Dispose();
                            }
                            wrImage.Dispose();
                        }
                    }
                }

                //保存縮略圖
                newImage.Save(savePath, System.Drawing.Imaging.ImageFormat.Jpeg);

                //釋放資源
                newG.Dispose();
                newImage.Dispose();
                initImage.Dispose();
            }
        }

        #endregion

        #region 其它

        /// <summary>
        /// 判斷文件類型是否爲WEB格式圖片
        /// (注：JPG,GIF,BMP,PNG)
        /// </summary>
        /// <param name="contentType">HttpPostedFile.ContentType</param>
        /// <returns></returns>
        public static bool IsWebImage(string contentType)
        {
            if (contentType == "image/pjpeg" || contentType == "image/jpeg" || contentType == "image/gif" || contentType == "image/bmp" || contentType == "image/png")
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        #endregion

        /// <summary>
        /// 剪裁 -- 用GDI+
        /// </summary>
        /// <param name="b">原始Bitmap</param>
        /// <param name="StartX">開始座標X</param>
        /// <param name="StartY">開始座標Y</param>
        /// <param name="iWidth">寬度</param>
        /// <param name="iHeight">高度</param>
        /// <returns>剪裁後的Bitmap</returns>
        public static bool KiCut(string source, string newpic, int X, int Y, int Width, int Height)
        {
            Bitmap b = new Bitmap(source);
            if (b == null)
            {
                return false;
            }

            int w = b.Width;
            int h = b.Height;

            if (X >= w || Y >= h)
            {
                return false;
            }

            if (X + Width > w)
            {
                Width = w - X;
            }

            if (Y + Height > h)
            {
                Height = h - Y;
            }

            try
            {
                Bitmap bmpOut = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);

                Graphics g = Graphics.FromImage(bmpOut);
                g.DrawImage(b, new Rectangle(0, 0, Width, Height), new Rectangle(X, Y, Width, Height), GraphicsUnit.Pixel);
                g.Dispose();

                bmpOut.Save(newpic);
                return true;
            }
            catch
            {
                return false;
            }
        }

    }//end class


    public class ImageCut
    {
        /// <summary>
        /// 剪裁 -- 用GDI+
        /// </summary>
        /// <param name="b">原始Bitmap</param>
        /// <param name="StartX">開始座標X</param>
        /// <param name="StartY">開始座標Y</param>
        /// <param name="iWidth">寬度</param>
        /// <param name="iHeight">高度</param>
        /// <returns>剪裁後的Bitmap</returns>
        public Bitmap KiCut(Bitmap b)
        {
            if (b == null)
            {
                return null;
            }

            int w = b.Width;
            int h = b.Height;

            if (X >= w || Y >= h)
            {
                return null;
            }

            if (X + Width > w)
            {
                Width = w - X;
            }

            if (Y + Height > h)
            {
                Height = h - Y;
            }

            try
            {
                Bitmap bmpOut = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);

                Graphics g = Graphics.FromImage(bmpOut);
                g.DrawImage(b, new Rectangle(0, 0, Width, Height), new Rectangle(X, Y, Width, Height), GraphicsUnit.Pixel);
                g.Dispose();

                return bmpOut;
            }
            catch
            {
                return null;
            }
        }

        public int X = 0;
        public int Y = 0;
        public int Width = 120;
        public int Height = 120;
        public ImageCut(int x, int y, int width, int heigth)
        {
            X = x;
            Y = y;
            Width = width;
            Height = heigth;
        }
    }
}