C#图片处理示例(裁剪,缩放,清晰度,水印)

前言

需求源自项目中的一些应用，比如相册功能，通常用户上传相片后我们都会针对该相片再生成一张缩略图，用于其它页面上的列表显示。随便看一下，大部分网站基本都是将原图等比缩放来生成缩略图。但完美主义者会发现一些问题，比如显示排版时想让相片缩略图列表非常统一、整齐、和美观，比如要求每张缩略图大小固定为120 x 90且不拉伸变形怎么办？再比如用户头像如何让缩略图比原图更清晰？或是如何在上传的图片下加一个半透明的LOGO水印？

OK，本文根据自己的项目代码描述以上问题的解决方案，全部基于.Net Framework类库完成，代码中包含了C#图片处理的一些基础知识.

提高缩略图清晰度

(原图200*200,12.3k)(处理后80*80,17.7k)

之前一直认为缩略图不可能比原图清晰，直到某天一位产品的同事给我看某网站的效果。于是开始寻找.NET下实现代码，仔细观察缩略图确实比原图更清晰了一些，但代价是缩略图文件比原图更大，所以如果你想让一张占满显示器屏幕的超大图片更清晰，那么图片占用空间和网络流量就必需考虑了，如果是互联网应用，建议缩略图在200像素以内的使用该方法。当然如果哪位有更好的代码即能让图片文件大小变化不大又让图片更清晰还请分享。

吴剑 http://www.cnblogs.com/wu-jian

图片裁剪

(原图256*192)(裁剪要求100*100)

(原图256*192)(裁剪要求90*120)

(原图256*192)(裁剪要求120*90)

(原图146*256)(裁剪要求100*100)

(原图146*256)(裁剪要求90*120)

(原图146*256)(裁剪要求120*90)

算法：以原图中心作为裁剪中心，最大范围的对原图进行裁剪，然后对裁剪结果等比缩放。

吴剑 http://www.cnblogs.com/wu-jian

图片水印

仅演示了效果，如需要变更字体、水印透明度、位置等可自行在代码或方法中扩展。

代码

封装了几个通用的方法，如发现有BUG或漏洞还请及时指正。

1using System;
2using System.Collections.Generic;
3using System.Text;
4using System.IO;
5using System.Drawing;
6using System.Drawing.Drawing2D;
7using System.Drawing.Imaging;
8
9namespace WuJian.Common
10{
11    /// <summary>
12    /// 图片处理
13    /// http://www.cnblogs.com/wu-jian/
14    /// 
15    /// 吴剑 2011-02-20 创建
16    /// 吴剑 2012-08-08 修改
17    /// </summary>
18    public class Image
19    {
20        #region 正方型裁剪并缩放
21
22        /// <summary>
23        /// 正方型裁剪
24        /// 以图片中心为轴心，截取正方型，然后等比缩放
25        /// 用于头像处理
26        /// </summary>
27        /// <remarks>吴剑 2012-08-08</remarks>
28        /// <param name="fromFile">原图Stream对象</param>
29        /// <param name="fileSaveUrl">缩略图存放地址</param>
30        /// <param name="side">指定的边长（正方型）</param>
31        /// <param name="quality">质量（范围0-100）</param>
32        public static void CutForSquare(System.IO.Stream fromFile, string fileSaveUrl, int side, int quality)
33        {
34            //创建目录
35            string dir = Path.GetDirectoryName(fileSaveUrl);
36            if (!Directory.Exists(dir))
37                Directory.CreateDirectory(dir);
38
39            //原始图片（获取原始图片创建对象，并使用流中嵌入的颜色管理信息）
40            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);
41
42            //原图宽高均小于模版，不作处理，直接保存
43            if (initImage.Width <= side && initImage.Height <= side)
44            {
45                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
46            }
47            else
48            {
49                //原始图片的宽、高
50                int initWidth = initImage.Width;
51                int initHeight = initImage.Height;
52
53                //非正方型先裁剪为正方型
54                if (initWidth != initHeight)
55                {
56                    //截图对象
57                    System.Drawing.Image pickedImage = null;
58                    System.Drawing.Graphics pickedG = null;
59
60                    //宽大于高的横图
61                    if (initWidth > initHeight)
62                    {
63                        //对象实例化
64                        pickedImage = new System.Drawing.Bitmap(initHeight, initHeight);
65                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
66                        //设置质量
67                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
68                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
69                        //定位
70                        Rectangle fromR = new Rectangle((initWidth - initHeight) / 2, 0, initHeight, initHeight);
71                        Rectangle toR = new Rectangle(0, 0, initHeight, initHeight);
72                        //画图
73                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
74                        //重置宽
75                        initWidth = initHeight;
76                    }
77                    //高大于宽的竖图
78                    else
79                    {
80                        //对象实例化
81                        pickedImage = new System.Drawing.Bitmap(initWidth, initWidth);
82                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
83                        //设置质量
84                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
85                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
86                        //定位
87                        Rectangle fromR = new Rectangle(0, (initHeight - initWidth) / 2, initWidth, initWidth);
88                        Rectangle toR = new Rectangle(0, 0, initWidth, initWidth);
89                        //画图
90                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
91                        //重置高
92                        initHeight = initWidth;
93                    }
94
95                    //将截图对象赋给原图
96                    initImage = (System.Drawing.Image)pickedImage.Clone();
97                    //释放截图资源
98                    pickedG.Dispose();
99                    pickedImage.Dispose();
100                }
101
102                //缩略图对象
103                System.Drawing.Image resultImage = new System.Drawing.Bitmap(side, side);
104                System.Drawing.Graphics resultG = System.Drawing.Graphics.FromImage(resultImage);
105                //设置质量
106                resultG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
107                resultG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
108                //用指定背景色清空画布
109                resultG.Clear(Color.White);
110                //绘制缩略图
111                resultG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, side, side), new System.Drawing.Rectangle(0, 0, initWidth, initHeight), System.Drawing.GraphicsUnit.Pixel);
112
113                //关键质量控制
114                //获取系统编码类型数组,包含了jpeg,bmp,png,gif,tiff
115                ImageCodecInfo[] icis = ImageCodecInfo.GetImageEncoders();
116                ImageCodecInfo ici = null;
117                foreach (ImageCodecInfo i in icis)
118                {
119                    if (i.MimeType == "image/jpeg" || i.MimeType == "image/bmp" || i.MimeType == "image/png" || i.MimeType == "image/gif")
120                    {
121                        ici = i;
122                    }
123                }
124                EncoderParameters ep = new EncoderParameters(1);
125                ep.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);
126
127                //保存缩略图
128                resultImage.Save(fileSaveUrl, ici, ep);
129
130                //释放关键质量控制所用资源
131                ep.Dispose();
132
133                //释放缩略图资源
134                resultG.Dispose();
135                resultImage.Dispose();
136
137                //释放原始图片资源
138                initImage.Dispose();
139            }
140        }
141
142        #endregion
143
144        #region 自定义裁剪并缩放
145
146        /// <summary>
147        /// 指定长宽裁剪
148        /// 按模版比例最大范围的裁剪图片并缩放至模版尺寸
149        /// </summary>
150        /// <remarks>吴剑 2012-08-08</remarks>
151        /// <param name="fromFile">原图Stream对象</param>
152        /// <param name="fileSaveUrl">保存路径</param>
153        /// <param name="maxWidth">最大宽(单位:px)</param>
154        /// <param name="maxHeight">最大高(单位:px)</param>
155        /// <param name="quality">质量（范围0-100）</param>
156        public static void CutForCustom(System.IO.Stream fromFile, string fileSaveUrl, int maxWidth, int maxHeight, int quality)
157        {
158            //从文件获取原始图片，并使用流中嵌入的颜色管理信息
159            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);
160
161            //原图宽高均小于模版，不作处理，直接保存
162            if (initImage.Width <= maxWidth && initImage.Height <= maxHeight)
163            {
164                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
165            }
166            else
167            {
168                //模版的宽高比例
169                double templateRate = (double)maxWidth / maxHeight;
170                //原图片的宽高比例
171                double initRate = (double)initImage.Width / initImage.Height;
172
173                //原图与模版比例相等，直接缩放
174                if (templateRate == initRate)
175                {
176                    //按模版大小生成最终图片
177                    System.Drawing.Image templateImage = new System.Drawing.Bitmap(maxWidth, maxHeight);
178                    System.Drawing.Graphics templateG = System.Drawing.Graphics.FromImage(templateImage);
179                    templateG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
180                    templateG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
181                    templateG.Clear(Color.White);
182                    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);
183                    templateImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
184                }
185                //原图与模版比例不等，裁剪后缩放
186                else
187                {
188                    //裁剪对象
189                    System.Drawing.Image pickedImage = null;
190                    System.Drawing.Graphics pickedG = null;
191
192                    //定位
193                    Rectangle fromR = new Rectangle(0, 0, 0, 0);//原图裁剪定位
194                    Rectangle toR = new Rectangle(0, 0, 0, 0);//目标定位
195
196                    //宽为标准进行裁剪
197                    if (templateRate > initRate)
198                    {
199                        //裁剪对象实例化
200                        pickedImage = new System.Drawing.Bitmap(initImage.Width, (int)System.Math.Floor(initImage.Width / templateRate));
201                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
202
203                        //裁剪源定位
204                        fromR.X = 0;
205                        fromR.Y = (int)System.Math.Floor((initImage.Height - initImage.Width / templateRate) / 2);
206                        fromR.Width = initImage.Width;
207                        fromR.Height = (int)System.Math.Floor(initImage.Width / templateRate);
208
209                        //裁剪目标定位
210                        toR.X = 0;
211                        toR.Y = 0;
212                        toR.Width = initImage.Width;
213                        toR.Height = (int)System.Math.Floor(initImage.Width / templateRate);
214                    }
215                    //高为标准进行裁剪
216                    else
217                    {
218                        pickedImage = new System.Drawing.Bitmap((int)System.Math.Floor(initImage.Height * templateRate), initImage.Height);
219                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
220
221                        fromR.X = (int)System.Math.Floor((initImage.Width - initImage.Height * templateRate) / 2);
222                        fromR.Y = 0;
223                        fromR.Width = (int)System.Math.Floor(initImage.Height * templateRate);
224                        fromR.Height = initImage.Height;
225
226                        toR.X = 0;
227                        toR.Y = 0;
228                        toR.Width = (int)System.Math.Floor(initImage.Height * templateRate);
229                        toR.Height = initImage.Height;
230                    }
231
232                    //设置质量
233                    pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
234                    pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
235
236                    //裁剪
237                    pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
238
239                    //按模版大小生成最终图片
240                    System.Drawing.Image templateImage = new System.Drawing.Bitmap(maxWidth, maxHeight);
241                    System.Drawing.Graphics templateG = System.Drawing.Graphics.FromImage(templateImage);
242                    templateG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
243                    templateG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
244                    templateG.Clear(Color.White);
245                    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);
246
247                    //关键质量控制
248                    //获取系统编码类型数组,包含了jpeg,bmp,png,gif,tiff
249                    ImageCodecInfo[] icis = ImageCodecInfo.GetImageEncoders();
250                    ImageCodecInfo ici = null;
251                    foreach (ImageCodecInfo i in icis)
252                    {
253                        if (i.MimeType == "image/jpeg" || i.MimeType == "image/bmp" || i.MimeType == "image/png" || i.MimeType == "image/gif")
254                        {
255                            ici = i;
256                        }
257                    }
258                    EncoderParameters ep = new EncoderParameters(1);
259                    ep.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);
260
261                    //保存缩略图
262                    templateImage.Save(fileSaveUrl, ici, ep);
263                    //templateImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
264
265                    //释放资源
266                    templateG.Dispose();
267                    templateImage.Dispose();
268
269                    pickedG.Dispose();
270                    pickedImage.Dispose();
271                }
272            }
273
274            //释放资源
275            initImage.Dispose();
276        }
277        #endregion
278
279        #region 等比缩放
280
281        /// <summary>
282        /// 图片等比缩放
283        /// </summary>
284        /// <remarks>吴剑 2012-08-08</remarks>
285        /// <param name="fromFile">原图Stream对象</param>
286        /// <param name="savePath">缩略图存放地址</param>
287        /// <param name="targetWidth">指定的最大宽度</param>
288        /// <param name="targetHeight">指定的最大高度</param>
289        /// <param name="watermarkText">水印文字(为""表示不使用水印)</param>
290        /// <param name="watermarkImage">水印图片路径(为""表示不使用水印)</param>
291        public static void ZoomAuto(System.IO.Stream fromFile, string savePath, System.Double targetWidth, System.Double targetHeight, string watermarkText, string watermarkImage)
292        {
293            //创建目录
294            string dir = Path.GetDirectoryName(savePath);
295            if (!Directory.Exists(dir))
296                Directory.CreateDirectory(dir);
297
298            //原始图片（获取原始图片创建对象，并使用流中嵌入的颜色管理信息）
299            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);
300
301            //原图宽高均小于模版，不作处理，直接保存
302            if (initImage.Width <= targetWidth && initImage.Height <= targetHeight)
303            {
304                //文字水印
305                if (watermarkText != "")
306                {
307                    using (System.Drawing.Graphics gWater = System.Drawing.Graphics.FromImage(initImage))
308                    {
309                        System.Drawing.Font fontWater = new Font("黑体", 10);
310                        System.Drawing.Brush brushWater = new SolidBrush(Color.White);
311                        gWater.DrawString(watermarkText, fontWater, brushWater, 10, 10);
312                        gWater.Dispose();
313                    }
314                }
315
316                //透明图片水印
317                if (watermarkImage != "")
318                {
319                    if (File.Exists(watermarkImage))
320                    {
321                        //获取水印图片
322                        using (System.Drawing.Image wrImage = System.Drawing.Image.FromFile(watermarkImage))
323                        {
324                            //水印绘制条件：原始图片宽高均大于或等于水印图片
325                            if (initImage.Width >= wrImage.Width && initImage.Height >= wrImage.Height)
326                            {
327                                Graphics gWater = Graphics.FromImage(initImage);
328
329                                //透明属性
330                                ImageAttributes imgAttributes = new ImageAttributes();
331                                ColorMap colorMap = new ColorMap();
332                                colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
333                                colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
334                                ColorMap[] remapTable = { colorMap };
335                                imgAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);
336
337                                float[][] colorMatrixElements = { 
338                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
339                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
340                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
341                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
342                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
343                                };
344
345                                ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);
346                                imgAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
347                                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);
348
349                                gWater.Dispose();
350                            }
351                            wrImage.Dispose();
352                        }
353                    }
354                }
355
356                //保存
357                initImage.Save(savePath, System.Drawing.Imaging.ImageFormat.Jpeg);
358            }
359            else
360            {
361                //缩略图宽、高计算
362                double newWidth = initImage.Width;
363                double newHeight = initImage.Height;
364
365                //宽大于高或宽等于高（横图或正方）
366                if (initImage.Width > initImage.Height || initImage.Width == initImage.Height)
367                {
368                    //如果宽大于模版
369                    if (initImage.Width > targetWidth)
370                    {
371                        //宽按模版，高按比例缩放
372                        newWidth = targetWidth;
373                        newHeight = initImage.Height * (targetWidth / initImage.Width);
374                    }
375                }
376                //高大于宽（竖图）
377                else
378                {
379                    //如果高大于模版
380                    if (initImage.Height > targetHeight)
381                    {
382                        //高按模版，宽按比例缩放
383                        newHeight = targetHeight;
384                        newWidth = initImage.Width * (targetHeight / initImage.Height);
385                    }
386                }
387
388                //生成新图
389                //新建一个bmp图片
390                System.Drawing.Image newImage = new System.Drawing.Bitmap((int)newWidth, (int)newHeight);
391                //新建一个画板
392                System.Drawing.Graphics newG = System.Drawing.Graphics.FromImage(newImage);
393
394                //设置质量
395                newG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
396                newG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
397
398                //置背景色
399                newG.Clear(Color.White);
400                //画图
401                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);
402
403                //文字水印
404                if (watermarkText != "")
405                {
406                    using (System.Drawing.Graphics gWater = System.Drawing.Graphics.FromImage(newImage))
407                    {
408                        System.Drawing.Font fontWater = new Font("宋体", 10);
409                        System.Drawing.Brush brushWater = new SolidBrush(Color.White);
410                        gWater.DrawString(watermarkText, fontWater, brushWater, 10, 10);
411                        gWater.Dispose();
412                    }
413                }
414
415                //透明图片水印
416                if (watermarkImage != "")
417                {
418                    if (File.Exists(watermarkImage))
419                    {
420                        //获取水印图片
421                        using (System.Drawing.Image wrImage = System.Drawing.Image.FromFile(watermarkImage))
422                        {
423                            //水印绘制条件：原始图片宽高均大于或等于水印图片
424                            if (newImage.Width >= wrImage.Width && newImage.Height >= wrImage.Height)
425                            {
426                                Graphics gWater = Graphics.FromImage(newImage);
427
428                                //透明属性
429                                ImageAttributes imgAttributes = new ImageAttributes();
430                                ColorMap colorMap = new ColorMap();
431                                colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
432                                colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
433                                ColorMap[] remapTable = { colorMap };
434                                imgAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);
435
436                                float[][] colorMatrixElements = { 
437                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
438                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
439                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
440                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
441                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
442                                };
443
444                                ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);
445                                imgAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
446                                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);
447                                gWater.Dispose();
448                            }
449                            wrImage.Dispose();
450                        }
451                    }
452                }
453
454                //保存缩略图
455                newImage.Save(savePath, System.Drawing.Imaging.ImageFormat.Jpeg);
456
457                //释放资源
458                newG.Dispose();
459                newImage.Dispose();
460                initImage.Dispose();
461            }
462        }
463
464        #endregion
465
466        #region 其它
467
468        /// <summary>
469        /// 判断文件类型是否为WEB格式图片
470        /// (注：JPG,GIF,BMP,PNG)
471        /// </summary>
472        /// <param name="contentType">HttpPostedFile.ContentType</param>
473        /// <returns></returns>
474        public static bool IsWebImage(string contentType)
475        {
476            if (contentType == "image/pjpeg" || contentType == "image/jpeg" || contentType == "image/gif" || contentType == "image/bmp" || contentType == "image/png")
477            {
478                return true;
479            }
480            else
481            {
482                return false;
483            }
484        }
485
486        #endregion
487
488    }//end class
489}