[轉] [C#] 解決產生的縮圖模糊的問題

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一、問題情境

針對一張正方形圖片產生 48px × 48px 的縮圖並儲存為圖片檔案，但發現產生的縮圖很模糊。

產生的模糊的縮圖如下：

原始圖片（300px × 300px, png格式）：

代碼中調用的是 System.Drawing.Image. GetThumbnailImage() 方法，主要實現代碼如下：

 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、解決方案

改為調用 System.Drawing.Graphics.DrawImage() 方法， 主要實現代碼如下：

 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 }

產生的縮圖效果如下：

三、參考資料

Cropping image using jQuery, Jcrop and ASP.NET

Resizing an Image without losing any quality

[轉] [C#] 解決產生的縮圖模糊的問題