[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
