C#高质量缩略图

private static 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 ) );
}

public static void SendSmallImage( string fileName,
string newFile,
int maxHeight,
int maxWidth )  
{
    System.Drawing.Image img = System.Drawing.Image.FromFile( 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( );
    // 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( );
}