//调用方法
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using CLJIMG;

System.Drawing.Image image = System.Drawing.Image.FromStream(FileUp.PostedFile.InputStream);
                    int width = image.Width;
                    int height = image.Height;

if (width > 760)
                    {
                        width = 760;
                        height = image.Height * 760 / image.Width;

newwidth = 760;
                        newheight = image.Height * newwidth / image.Width;

// SendSmallImage(image, filename, newwidth, newheight);
                        CLJIMG.ImgClass simg = new ImgClass();
                        simg.SendSmallImage(image, Server.MapPath(filename), newwidth, newheight);

}

//生成高质量缩略图
#region
private Size NewSize(int maxWidth, int maxHeight, int width, int height)
    {
        double w = 0.0;
        double h = 0.0;
        double sw = Convert.ToDouble(width);
        double sh = Convert.ToDouble(height);
        double mw = Convert.ToDouble(maxWidth);
        double mh = Convert.ToDouble(maxHeight);

if (sw < mw && sh < mh)
        {
            w = sw;
            h = sh;
        }
        else if ((sw / sh) > (mw / mh))
        {
            w = maxWidth;
            h = (w * sh) / sw;
        }
        else
        {
            h = maxHeight;
            w = (h * sw) / sh;
        }

return new Size(Convert.ToInt32(w), Convert.ToInt32(h));
    }
    //生成高质量缩略图
    private void SendSmallImage(System.Drawing.Image img, string fileName, int maxWidth, int maxHeight)
    {
        //  System.Drawing.Image img = System.Drawing.Image.FromFile(Server.MapPath(fileName));
        System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;

Size newSize = NewSize(maxWidth, maxHeight, img.Width, img.Height);
        Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
        Graphics g = Graphics.FromImage(outBmp);

// 设置画布的描绘质量

g.CompositingQuality = CompositingQuality.HighQuality;
        g.SmoothingMode = SmoothingMode.HighQuality;
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;

g.DrawImage(img, new Rectangle(0, 0, newSize.Width, newSize.Height),
            0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
        g.Dispose();

if (thisFormat.Equals(ImageFormat.Gif))
        {
            Response.ContentType = "image/gif";
        }
        else
        {
            Response.ContentType = "image/jpeg";
        }

// 以下代码为保存图片时，设置压缩质量
        EncoderParameters encoderParams = new EncoderParameters();
        long[] quality = new long[1];
        quality[0] = 100;

EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        encoderParams.Param[0] = encoderParam;

//获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
        ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
        ImageCodecInfo jpegICI = null;
        for (int x = 0; x < arrayICI.Length; x++)
        {
            if (arrayICI[x].FormatDescription.Equals("JPEG"))
            {
                jpegICI = arrayICI[x];//设置JPEG编码
                break;
            }
        }

if (jpegICI != null)
        {
            // outBmp.Save(Response.OutputStream, jpegICI, encoderParams);
            outBmp.Save(Server.MapPath(fileName), jpegICI, encoderParams);
        }
        else
        {
            outBmp.Save(Response.OutputStream, thisFormat);
            outBmp.Save(Server.MapPath(fileName), thisFormat);
        }

img.Dispose();
        outBmp.Dispose();
    }
#endregion