asp.net 为什么生成的缩略图比源文件还要大
明明源文件只有50多K 320*280
生成的缩略图竟然是源文件的2倍多 196*196
public class ImageThumbnailMake { /// <summary> /// 生成缩略图 /// </summary> /// <param name="originalImagePath">源图路径（相对路径）</param> /// <param name="thumbnailPath">缩略图路径（相对路径）</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 void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode) { System.Drawing.Image originalImage = System.Drawing.Image.FromFile(Utils.GetMapPath(originalImagePath)); 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; 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 bitmap.Save(Utils.GetMapPath(thumbnailPath)); } catch (System.Exception e) { throw e; } finally { originalImage.Dispose(); bitmap.Dispose(); g.Dispose(); } } } /// <summary> /// 获得当前绝对路径 /// </summary> /// <param name="strPath">指定的路径</param> /// <returns>绝对路径</returns> public static string GetMapPath(string strPath) { string path = ""; if (HttpContext.Current != null) { return HttpContext.Current.Server.MapPath(strPath); } else //非web程序引用 { strPath = strPath.Replace("/", "\\"); if (strPath.StartsWith("\\")) { strPath = strPath.Substring(strPath.IndexOf('\\', 1)).TrimStart('\\'); } path = System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, strPath); return path; } }
// 指定高质量的双三次插值法。执行预筛选以确保高质量的收缩。此模式可产生质量最高的转换图像。g.InterpolationMode = InterpolationMode.HighQualityBicubic;// 指定高质量、低速度呈现。g.SmoothingMode = SmoothingMode.HighQuality;