[转载]C#解决生成的缩略图模糊的问题 - dudu - 博客园

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[转载][C#]解决生成的缩略图模糊的问题 – dudu – 博客园.

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:

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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); } } }
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二、解决方法

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

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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; }
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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

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