生成縮略圖是一個十分常用功能，找到了一個方法，重寫部分代碼，實用又好用，.net又一個生成縮略圖的方法，不變形
/// <summary> /// 為圖片生成縮略圖 /// </summary> /// <param name="phyPath">原圖片的路徑</param> /// <param name="width">縮略圖寬</param> /// <param name="height">縮略圖高</param> /// <returns></returns> public System.Drawing.Image GetHvtThumbnail(System.Drawing.Image image, int width, int height) { Bitmap m_hovertreeBmp = new Bitmap(width, height); //從Bitmap創建一個System.Drawing.Graphics Graphics m_HvtGr = Graphics.FromImage(m_hovertreeBmp); //設置 m_HvtGr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; //下面這個也設成高質量 m_HvtGr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality; //下面這個設成High m_HvtGr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; //把原始圖像繪制成上面所設置寬高的縮小圖 Rectangle rectDestination = new Rectangle(0, 0, width, height); int m_width, m_height; if (image.Width * height > image.Height * width) { m_height = image.Height; m_width = (image.Height * width) / height; } else { m_width = image.Width; m_height = (image.Width * height) / width; } m_HvtGr.DrawImage(image, rectDestination, 0, 0, m_width, m_height, GraphicsUnit.Pixel); return m_hovertreeBmp; } C#縮略圖生成類，采用高質量插值法實現縮略圖生成，高質量,低速度呈現平滑程度，可以保持縮略圖縱橫比，在獲取縮略圖的時候一開始就根據百分比獲取圖片的尺寸、根據設定的大小返回圖片的大小，并高質量保存縮略圖圖片，為原圖片設置EncoderParameters 對象。
以下為類文件，建議保存文件名為：ImageHelper.cs
using System;using System.Collections.Generic;using System.Drawing;using System.Drawing.Imaging;namespace HtmlSnap{ public static class ImageHelper { /// 獲取縮略圖 public static Image GetThumbnailImage(Image image, int width, int height) { if (image == null || width < 1 || height < 1) return null; // 新建一個bmp圖片 Image bitmap = new System.Drawing.Bitmap(width, height); // 新建一個畫板 using (Graphics g = System.Drawing.Graphics.FromImage(bitmap)) { // 設置高質量插值法 g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; // 設置高質量,低速度呈現平滑程度 g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; // 高質量、低速度復合 g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality; // 清空畫布并以透明背景色填充 g.Clear(Color.Transparent); // 在指定位置并且按指定大小繪制原圖片的指定部分 g.DrawImage(image, new Rectangle(0, 0, width, height), new Rectangle(0, 0, image.Width, image.Height), GraphicsUnit.Pixel); return bitmap; } } /// <summary> /// 生成縮略圖，并保持縱橫比 /// </summary> /// <returns>生成縮略圖后對象</returns> public static Image GetThumbnailImageKeepRatio(Image image, int width, int height) { Size imageSize = GetImageSize(image, width, height); return GetThumbnailImage(image, imageSize.Width, imageSize.Height); } /// <summary> /// 根據百分比獲取圖片的尺寸 /// </summary> public static Size GetImageSize(Image picture, int percent) { if (picture == null || percent < 1) return Size.Empty; int width = picture.Width * percent / 100; int height = picture.Height * percent / 100; return GetImageSize(picture, width, height); } /// <summary> /// 根據設定的大小返回圖片的大小，考慮圖片長寬的比例問題 /// </summary> public static Size GetImageSize(Image picture, int width, int height) { if (picture == null || width < 1 || height < 1) return Size.Empty; Size imageSize; imageSize = new Size(width, height); double heightRatio = (double)picture.Height / picture.Width; double widthRatio = (double)picture.Width / picture.Height; int desiredHeight = imageSize.Height; int desiredWidth = imageSize.Width; imageSize.Height = desiredHeight; if (widthRatio > 0) imageSize.Width = Convert.ToInt32(imageSize.Height * widthRatio); if (imageSize.Width > desiredWidth) { imageSize.Width = desiredWidth; imageSize.Height = Convert.ToInt32(imageSize.Width * heightRatio); } return imageSize; } /// <summary> /// 獲取圖像編碼解碼器的所有相關信息 /// </summary> /// <param name="mimeType">包含編碼解碼器的多用途網際郵件擴充協議 (MIME) 類型的字符串</param> /// <returns>返回圖像編碼解碼器的所有相關信息</returns> public static ImageCodecInfo GetCodecInfo(string mimeType) { ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders(); foreach (ImageCodecInfo ici in CodecInfo) { if (ici.MimeType == mimeType) return ici; } return null; } public static ImageCodecInfo GetImageCodecInfo(ImageFormat format) { ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders(); foreach (ImageCodecInfo icf in encoders) { if (icf.FormatID == format.Guid) { return icf; } } return null; } public static void SaveImage(Image image, string savePath, ImageFormat format) { SaveImage(image, savePath, GetImageCodecInfo(format)); } /// <summary> /// 高質量保存圖片 /// </summary> private static void SaveImage(Image image, string savePath, ImageCodecInfo ici) { // 設置 原圖片 對象的 EncoderParameters 對象 EncoderParameters parms = new EncoderParameters(1); EncoderParameter parm = new EncoderParameter(Encoder.Quality, ((long)95)); parms.Param[0] = parm; image.Save(savePath, ici, parms); parms.Dispose(); } }} 
