using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;

/// <summary>
/// ImageHelper 的摘要说明
/// </summary>
public class ImageHelper
{
    /// <summary>
    /// 生成缩略图
    /// </summary>
    /// <param name="fileName">原图路径</param>
    /// <param name="newFile">缩略图路径</param>
    /// <param name="maxHeight">最大高度</param>
    /// <param name="maxWidth">最大宽度</param>
    public static void ThumbnailImage(string fileName, string newFile, int maxHeight, int maxWidth)
    {
        System.Drawing.Image img = System.Drawing.Image.FromFile(fileName);
        System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;
        //缩略图尺寸
        double w = 0.0;
        double h = 0.0;
        double sw = Convert.ToDouble(img.Width);
        double sh = Convert.ToDouble(img.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;
        }
        Size newSize = new Size(Convert.ToInt32(w),Convert.ToInt32(h));
        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();
        //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(newFile, jpegICI, encoderParams);
        }
        else
        {
            outBmp.Save(newFile,
            thisFormat);
        }
        img.Dispose();
        outBmp.Dispose();
    }
}