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：

private void SaveThumbnail(Bitmap bitmap, int width, int height, string directory, string filename, string extension){    var physicalPath = directory + filename + extension;    using (var thumbnail = bitmap.GetThumbnailImage(width, height, () => { return true; }, IntPtr.Zero))    {        using (var encoderParameters = new EncoderParameters(1))        {            encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 100L);            thumbnail.Save(physicalPath,                        ImageCodecInfo.GetImageEncoders()                            .Where(x => x.FilenameExtension.Contains(extension.ToUpperInvariant()))                            .FirstOrDefault(),                        encoderParameters);        }    }           }

二、解决方法

改为调用 System.Drawing.Graphics.DrawImage() 方法， 主要实现代码如下：

private void SaveThumbnail(Bitmap originBitmap, int width, int height, string directory, string filename, string extension){    var physicalPath = directory + filename + extension;                using (var newImage = new Bitmap(width, height))    {        using (var graphic = GetGraphic(originBitmap, newImage))        {            graphic.DrawImage(originBitmap, 0, 0, width, height);            using (var encoderParameters = new EncoderParameters(1))            {                encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, 100L);                newImage.Save(physicalPath,                            ImageCodecInfo.GetImageEncoders()                                .Where(x => x.FilenameExtension.Contains(extension.ToUpperInvariant()))                                .FirstOrDefault(),                            encoderParameters);            }        }    }            }private Graphics GetGraphic(Image originImage, Bitmap newImage){    newImage.SetResolution(originImage.HorizontalResolution, originImage.VerticalResolution);    var graphic = Graphics.FromImage(newImage);    graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;    graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;    graphic.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;    graphic.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;    return graphic;}

 生成的缩略图效果如下：

三、参考资料