.net等比缩放生成缩略图的方法

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 /// 为图片生成缩略图 /// 
 /// 原图片的路径 /// 缩略图宽 /// 缩略图高 ///  public System.Drawing.Image GetHvtThumbnail(System.Drawing.Image image, int width, int height) { Bitmap m_hovertreeBmp = new Bitmap(width, height); //从Bitmap创建一个System.Drawing.Graphics Graphics m_HvtGr = Graphics.FromImage(m_hovertreeBmp); //设置 m_HvtGr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; //下面这个也设成高质量 m_HvtGr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality; //下面这个设成High m_HvtGr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; //把原始图像绘制成上面所设置宽高的缩小图 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; } 

 using System; using System.Collections.Generic; using System.Drawing; using System.Drawing.Imaging; namespace HtmlSnap { public static class ImageHelper { /// 获取缩略图 public static Image GetThumbnailImage(Image image, int width, int height) { if (image == null || width <1 || height < 1) return null;> /// 生成缩略图，并保持纵横比 ///  /// 生成缩略图后对象 public static Image GetThumbnailImageKeepRatio(Image image, int width, int height) { Size imageSize = GetImageSize(image, width, height); return GetThumbnailImage(image, imageSize.Width, imageSize.Height); } /// 
 /// 根据百分比获取图片的尺寸 /// 
 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); } /// 
 /// 根据设定的大小返回图片的大小，考虑图片长宽的比例问题 /// 
 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> 0) imageSize.Width = Convert.ToInt32(imageSize.Height * widthRatio); if (imageSize.Width > desiredWidth) { imageSize.Width = desiredWidth; imageSize.Height = Convert.ToInt32(imageSize.Width * heightRatio); } return imageSize; } /// 
 /// 获取图像编码解码器的所有相关信息 /// 
 /// 包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串 /// 返回图像编码解码器的所有相关信息 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)); } /// 
 /// 高质量保存图片 /// 
 private static void SaveImage(Image image, string savePath, ImageCodecInfo ici) { // 设置 原图片 对象的 EncoderParameters 对象 EncoderParameters parms = new EncoderParameters(1); EncoderParameter parm = new EncoderParameter(Encoder.Quality, ((long)95)); parms.Param[0] = parm; image.Save(savePath, ici, parms); parms.Dispose(); } } }