C# 图片生成缩略图方法：
1 /// <summary> 2 /// 生成缩略图 3 /// </summary> 4 /// <param name="fileName">原图路径</param> 5 /// <param name="newFile">缩略图路径</param> 6 /// <param name="maxHeight">最大高度</param> 7 /// <param name="maxWidth">最大宽度</param> 8 public string ThumbnailImage(string fileName, string newFile, int maxHeight, int maxWidth) 9 { 10 System.Drawing.Image img = System.Drawing.Image.FromFile(fileName); 11 System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat; 12 //缩略图尺寸 13 double w = 0.0; //图片的宽 14 double h = 0.0; //图片的高 15 double sw = Convert.ToDouble(img.Width); 16 double sh = Convert.ToDouble(img.Height); 17 double mw = Convert.ToDouble(maxWidth); 18 double mh = Convert.ToDouble(maxHeight); 19 if (sw < mw && sh < mh) 20 { 21 w = sw; 22 h = sh; 23 } 24 else if ((sw / sh) > (mw / mh)) 25 { 26 w = maxWidth; 27 h = (w * sh) / sw; 28 } 29 else 30 { 31 h = maxHeight; 32 w = (h * sw) / sh; 33 } 34 Size newSize = new Size(Convert.ToInt32(w), Convert.ToInt32(h)); 35 Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height); 36 Graphics g = Graphics.FromImage(outBmp); 37 //设置画布的描绘质量 38 g.CompositingQuality = CompositingQuality.HighQuality; 39 g.SmoothingMode = SmoothingMode.HighQuality; 40 g.InterpolationMode = InterpolationMode.HighQualityBicubic; 41 g.DrawImage(img, new Rectangle(0, 0, newSize.Width, newSize.Height), 0, 0, img.Width, img.Height, GraphicsUnit.Pixel); 42 g.Dispose(); 43 //以下代码为保存图片时,设置压缩质量 44 EncoderParameters encoderParams = new EncoderParameters(); 45 long[] quality = new long[1]; 46 quality[0] = 100; 47 EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality); 48 encoderParams.Param[0] = encoderParam; 49 //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象. 50 ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders(); 51 ImageCodecInfo jpegICI = null; 52 for (int x = 0; x < arrayICI.Length;x++) 53 { 54 if (arrayICI[x].FormatDescription.Equals("JPEG")) 55 { 56 jpegICI = arrayICI[x]; 57 //设置JPEG编码 58 break; 59 } 60 } 61 if (jpegICI != null) 62 { 63 Bitmap newbit = new Bitmap(outBmp); 64 newbit.Save(newFile, jpegICI, encoderParams); 65 } 66 else 67 { 68 outBmp.Save(newFile, 69 thisFormat); 70 } 71 img.Dispose(); 72 outBmp.Dispose(); 73 return newFile; 74 }