标签：style blog http io color ar os sp strong
一、问题场景
针对一张正方形图片生成 48px × 48px 的缩略图并保存为图片文件，但发现生成的缩略图很模糊。
生成的模糊的缩略图如下：
原始图片（300px × 300px, png格式）：
代码中调用的是 System.Drawing.Image. GetThumbnailImage() 方法，主要实现代码如下：
1 private void SaveThumbnail(Bitmap bitmap, int width, int height, string directory, string filename, string extension) 2 { 3 var physicalPath = directory + filename + extension; 4 using (var thumbnail = bitmap.GetThumbnailImage(width, height, () => { return true; }, IntPtr.Zero)) 5 { 6 using (var encoderParameters = new EncoderParameters(1)) 7 { 8 encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 100L); 9 thumbnail.Save(physicalPath, 10 ImageCodecInfo.GetImageEncoders() 11 .Where(x => x.FilenameExtension.Contains(extension.ToUpperInvariant())) 12 .FirstOrDefault(), 13 encoderParameters); 14 } 15 } 16 }
二、解决方法
改为调用 System.Drawing.Graphics.DrawImage() 方法， 主要实现代码如下：
1 private void SaveThumbnail(Bitmap originBitmap, int width, int height, string directory, string filename, string extension) 2 { 3 var physicalPath = directory + filename + extension; 4 5 using (var newImage = new Bitmap(width, height)) 6 { 7 using (var graphic = GetGraphic(originBitmap, newImage)) 8 { 9 graphic.DrawImage(originBitmap, 0, 0, width, height); 10 using (var encoderParameters = new EncoderParameters(1)) 11 { 12 encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 100L); 13 newImage.Save(physicalPath, 14 ImageCodecInfo.GetImageEncoders() 15 .Where(x => x.FilenameExtension.Contains(extension.ToUpperInvariant())) 16 .FirstOrDefault(), 17 encoderParameters); 18 } 19 } 20 } 21 } 22 23 private Graphics GetGraphic(Image originImage, Bitmap newImage) 24 { 25 newImage.SetResolution(originImage.HorizontalResolution, originImage.VerticalResolution); 26 var graphic = Graphics.FromImage(newImage); 27 graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; 28 graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; 29 graphic.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality; 30 graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality; 31 return graphic; 32 }
生成的缩略图效果如下：
三、参考资料
Cropping image using jQuery, Jcrop and ASP.NET
Resizing an Image without losing any quality
标签：style blog http io color ar os sp strong
原文地址：http://www.cnblogs.com/XingchenStudio/p/4095141.html
