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  • [C#]解决生成的缩略图模糊的问题

    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

    Cropping image using jQuery, Jcrop and ASP.NET

    Resizing an Image without losing any quality

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  • 原文地址:https://www.cnblogs.com/dongh/p/15070024.html
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