图片处理是C#程序开发中时常会涉及到的一个业务，除了图像的上传、保存以及下载等功能外，根据上传的图片生成一个缩略图也是常见业务，在C#语言中，可以通过Image类提供的相关方法对图片进行操作，如指定宽高对图片进行缩放， 指定高宽裁减裁剪图片、生成图片水印等。
定义一个图片处理工具类PicDeal，该类实现了生成缩略图、在图片上生成图片水印等相应功能。具体的业务代码如下：
////// 枚举,生成缩略图模式 /// public enum ThumbnailMod : byte { ////// HW /// HW, ////// W /// W, ////// H /// H, ////// Cut /// Cut }; ////// 操作图片类, 生成缩略图,添加水印 /// public static class PicDeal { private static Hashtable htmimes = new Hashtable(); internal static readonly string AllowExt = ".jpe|.jpeg|.jpg|.png|.tif|.tiff|.bmp"; #region 生成缩略图 ////// 生成缩略图 /// /// /// /// /// ///public static bool MakeThumbnail(string originalImagePath, int width, int height, ThumbnailMod mode) { string thumbnailPath = originalImagePath.Substring(0, originalImagePath.LastIndexOf('.')) + "s.jpg"; Image originalImage = Image.FromFile(originalImagePath); int towidth = width; int toheight = height; int x = 0; int y = 0; int ow = originalImage.Width; int oh = originalImage.Height; switch (mode) { case ThumbnailMod.HW://指定高宽缩放（可能变形） break; case ThumbnailMod.W://指定宽，高按比例 toheight = originalImage.Height * width / originalImage.Width; break; case ThumbnailMod.H://指定高，宽按比例 towidth = originalImage.Width * height / originalImage.Height; break; case ThumbnailMod.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; default: break; } //新建一个bmp图片 Image bitmap = new Bitmap(towidth, toheight); //新建一个画板 Graphics g = 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 Rectangle(0, 0, towidth, toheight), new Rectangle(x, y, ow, oh), GraphicsUnit.Pixel); bool isok = false; try { //以jpg格式保存缩略图 bitmap.Save(thumbnailPath, ImageFormat.Jpeg); isok = true; } catch (Exception) { thumbnailPath = originalImagePath; } finally { originalImage.Dispose(); bitmap.Dispose(); g.Dispose(); } return isok; } #endregion #region 在图片上生成图片水印 ///// ///// 在图片上生成图片水印 ///// ///// 原服务器图片路径 ///// 生成的带图片水印的图片路径 ///// 水印图片路径 ////// 在图片上生成图片水印 /// /// 原服务器图片路径 /// 水印图片路径 public static void AddWaterPic(string Path, string Path_sypf) { try { Image image = Image.FromFile(Path); Image copyImage = Image.FromFile(Path_sypf); Graphics g = Graphics.FromImage(image); g.DrawImage(copyImage, new System.Drawing.Rectangle(image.Width - copyImage.Width, image.Height - copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, System.Drawing.GraphicsUnit.Pixel); g.Dispose(); image.Save(Path + ".temp"); image.Dispose(); System.IO.File.Delete(Path); File.Move(Path + ".temp", Path); } catch { } } #endregion ////// 公共方法 /// private static void GetImgType() { htmimes[".jpe"] = "image/jpeg"; htmimes[".jpeg"] = "image/jpeg"; htmimes[".jpg"] = "image/jpeg"; htmimes[".png"] = "image/png"; htmimes[".tif"] = "image/tiff"; htmimes[".tiff"] = "image/tiff"; htmimes[".bmp"] = "image/bmp"; } #region 返回新图片尺寸 ////// 返回新图片尺寸 /// /// 原始宽 /// 原始高 /// 新图片最大宽 /// 新图片最大高 ///public static Size ResizeImage(int width, int height, int maxWidth, int maxHeight) { decimal MAX_WIDTH = (decimal)maxWidth; decimal MAX_HEIGHT = (decimal)maxHeight; decimal ASPECT_RATIO = MAX_WIDTH / MAX_HEIGHT; int newWidth, newHeight; decimal originalWidth = (decimal)width; decimal originalHeight = (decimal)height; if (originalWidth > MAX_WIDTH || originalHeight > MAX_HEIGHT) { decimal factor; // determine the largest factor if (originalWidth / originalHeight > ASPECT_RATIO) { factor = originalWidth / MAX_WIDTH; newWidth = Convert.ToInt32(originalWidth / factor); newHeight = Convert.ToInt32(originalHeight / factor); } else { factor = originalHeight / MAX_HEIGHT; newWidth = Convert.ToInt32(originalWidth / factor); newHeight = Convert.ToInt32(originalHeight / factor); } } else { newWidth = width; newHeight = height; } return new Size(newWidth, newHeight); } #endregion }
备注：原文转载自。