.NET 图片处理剪裁

/// <summary>   
/// 图片转换（裁剪并缩放）   
/// </summary>   
/// <param name="ASrcFileName">源文件名称</param>   
/// <param name="ADestFileName">目标文件名称</param>   
/// <param name="AWidth">转换后的宽度（像素）</param>   
/// <param name="AHeight">转换后的高度（像素）</param>   
/// <param name="AQuality">保存质量（取值在1-100之间）</param>   
public static void DoConvert(string ASrcFileName, string ADestFileName, int AWidth, int AHeight, int AQuality)   
{   
    Image ASrcImg = Image.FromFile(ASrcFileName);   
    if (ASrcImg.Width <= AWidth && ASrcImg.Height <= AHeight)   
    {//图片的高宽均小于目标高宽，直接保存   
        ASrcImg.Save(ADestFileName);   
        return;   
    }   
    double ADestRate = AWidth * 1.0 / AHeight;   
    double ASrcRate = ASrcImg.Width * 1.0 / ASrcImg.Height;   
    //裁剪后的宽度   
    double ACutWidth = ASrcRate > ADestRate ? (ASrcImg.Height * ADestRate) : ASrcImg.Width;   
    //裁剪后的高度   
    double ACutHeight = ASrcRate > ADestRate ? ASrcImg.Height : (ASrcImg.Width / ADestRate);   
    //待裁剪的矩形区域，根据原图片的中心进行裁剪   
    Rectangle AFromRect = new Rectangle(Convert.ToInt32((ASrcImg.Width - ACutWidth) / 2), Convert.ToInt32((ASrcImg.Height - ACutHeight) / 2), (int)ACutWidth, (int)ACutHeight);   
    //目标矩形区域   
    Rectangle AToRect = new Rectangle(0, 0, AWidth, AHeight);   
  
    Image ADestImg = new Bitmap(AWidth, AHeight);   
    Graphics ADestGraph = Graphics.FromImage(ADestImg);   
    ADestGraph.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;   
    ADestGraph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;   
    ADestGraph.DrawImage(ASrcImg, AToRect, AFromRect, GraphicsUnit.Pixel);   
  
    //获取系统image/jpeg编码信息   
    ImageCodecInfo[] AInfos = ImageCodecInfo.GetImageEncoders();   
    ImageCodecInfo AInfo = null;   
    foreach (ImageCodecInfo i in AInfos)   
    {   
        if (i.MimeType == "image/jpeg")   
        {   
            AInfo = i;   
            break;   
        }   
    }   
    //设置转换后图片质量参数   
    EncoderParameters AParams = new EncoderParameters(1);   
    AParams.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)AQuality);   
    //保存   
    ADestImg.Save(ADestFileName, AInfo, AParams);   
}