C# 调整大小后的低质量图像

您好，我正在使用此功能调整图像大小/上载图像。我可以进行任何快速调整，以便在不改变全部功能的情况下提高调整后的图像质量吗

   FileUpload FileUpload1 =(FileUpload)ListView1.InsertItem.FindControl("FileUpload1");
                string virtualFolder = "~/albume/";
                string physicalFolder = Server.MapPath(virtualFolder);
                string fileName = Guid.NewGuid().ToString();
                string extension = System.IO.Path.GetExtension(FileUpload1.FileName);
                FileUpload1.SaveAs(System.IO.Path.Combine(physicalFolder, fileName + extension));
                //test resize
                System.Drawing.Image img = System.Drawing.Image.FromFile(Server.MapPath("~/albume/") + fileName + extension);
                int srcWidth = img.Width;
                int srcHeight = img.Height;
                int thumbHeight = (int)((800.0 / srcWidth) * srcHeight);
                System.Drawing.Image thumb = img.GetThumbnailImage(800, thumbHeight, null, IntPtr.Zero);
                img.Dispose();
                FileUpload1.Dispose();
                thumb.Save(Server.MapPath("~/albume/") + fileName + extension, System.Drawing.Imaging.ImageFormat.Jpeg);

                //end resize
                myAlbum.poza = fileName + extension;

使用以下代码段：

Bitmap newImage = new Bitmap(newWidth, newHeight);
using (Graphics gr = Graphics.FromImage(newImage))
{
    gr.SmoothingMode = SmoothingMode.AntiAlias;
    gr.InterpolationMode = InterpolationMode.HighQualityBicubic;
    gr.PixelOffsetMode = PixelOffsetMode.HighQuality;
    gr.DrawImage(srcImage, new Rectangle(0, 0, newWidth, newHeight));
}

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从这个问题/答案中盗取：查看Kris的超级投票答案并进行投票：）

在我的网站上，我使用以下代码在用户图像发送到页面之前调整其大小

您可以使用类似的方法—尝试研究各种插值模式

using (Graphics graphics = Graphics.FromImage(target))
{
    graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

    graphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighSpeed;
    graphics.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
    graphics.Clear(ColorTranslator.FromHtml("#F4F6F5"));
    graphics.DrawImage(bmp, 0, 0, 145, 145);
    using (System.IO.MemoryStream memoryStream = new System.IO.MemoryStream())
    {
        target.Save(memoryStream, System.Drawing.Imaging.ImageFormat.Jpeg);                    
        memoryStream.WriteTo(context.Response.OutputStream);
    }
}

最好不要使用“GetThumbnailImage”，这会降低质量。据

通过如下方式重新绘制图像，调整图像大小：

private static Image resizeImage(Image imgToResize, Size size)
{
   int sourceWidth = imgToResize.Width;
   int sourceHeight = imgToResize.Height;

   float nPercent = 0;
   float nPercentW = 0;
   float nPercentH = 0;

   nPercentW = ((float)size.Width / (float)sourceWidth);
   nPercentH = ((float)size.Height / (float)sourceHeight);

   if (nPercentH < nPercentW)
      nPercent = nPercentH;
   else
      nPercent = nPercentW;

   int destWidth = (int)(sourceWidth * nPercent);
   int destHeight = (int)(sourceHeight * nPercent);

   Bitmap b = new Bitmap(destWidth, destHeight);
   Graphics g = Graphics.FromImage((Image)b);
   g.InterpolationMode = InterpolationMode.HighQualityBicubic;

   g.DrawImage(imgToResize, 0, 0, destWidth, destHeight);
   g.Dispose();

   return (Image)b;
}

private static Image resizeImage（图像imgToResize，大小）
{
int sourceWidth=imgToResize.Width；
int sourceHeight=imgToResize.Height；
浮动百分比=0；
浮动nPercentW=0；
浮点数nPercentH=0；
nPercentW=（（float）size.Width/（float）sourceWidth）；
nPercentH=（（浮点）size.Height/（浮点）sourceHeight）；
如果（nPercentH

代替此代码：

thumb.Save(Server.MapPath("~/albume/") + fileName + extension, System.Drawing.Imaging.ImageFormat.Jpeg);

使用这个：

System.Drawing.Imaging.ImageCodecInfo[] info = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
System.Drawing.Imaging.EncoderParameters param = new System.Drawing.Imaging.EncoderParameters(1);
param.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
thumb.Save(Server.MapPath("~/albume/") + fileName + extension, info[1], param);

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您的图像是否包含缩略图？如果是这样，这可能适用：“如果您从具有嵌入缩略图的图像请求一个大的缩略图图像（例如，300 x 300），缩略图图像的质量可能会明显下降。通过调用DrawImage方法缩放主图像（而不是缩放嵌入的缩略图）可能会更好。”从。可能重复的正确图像大小可能重复。支持jpeg的正确实现需要5页代码。使用GIF支持的正确实现需要80页代码。我建议。谢谢。我正在尝试实现您推荐的功能，但我得到System.Runtime.InteropServices.ExternalException:GDI+中发生一般错误。。在这方面我是C的新手#