图片处理工具类

    /// <summary>
    /// 图片处理工具类
    /// </summary>
    public class ImageUtils
    {
        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static System.IO.Stream GenerateThumbnail(System.IO.Stream imageStream, int width, int height)
        {
            System.IO.Stream ms;

            using (var originalImage = System.Drawing.Image.FromStream(imageStream))
            {
                int towidth = width;
                int toheight = height;

                int x = 0;
                int y = 0;
                int ow = originalImage.Width;
                int oh = originalImage.Height;

                if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                {
                    oh = originalImage.Height;
                    ow = originalImage.Height * towidth / toheight;
                    y = 0;
                    x = (originalImage.Width - ow) / 2;
                }
                else
                {
                    ow = originalImage.Width;
                    oh = originalImage.Width * height / towidth;
                    x = 0;
                    y = (originalImage.Height - oh) / 2;
                }

                using (System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight))
                using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap))
                {
                    //设置高质量插值法
                    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

                    //设置高质量,低速度呈现平滑程度
                    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

                    //清空画布并以透明背景色填充
                    g.Clear(System.Drawing.Color.Transparent);

                    //在指定位置并且按指定大小绘制原图片的指定部分
                    g.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
                    new System.Drawing.Rectangle(x, y, ow, oh),
                    System.Drawing.GraphicsUnit.Pixel);

                    ms = new System.IO.MemoryStream();
                    bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
            }

            return ms;
        }

        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static void GenerateThumbnail(System.IO.Stream imageStream, int width, int height, string outputFilePath)
        {
            using (var stream = GenerateThumbnail(imageStream, width, height))
            using (var fileStream = System.IO.File.Open(outputFilePath, System.IO.FileMode.OpenOrCreate))
            {
                ((System.IO.MemoryStream)stream).WriteTo(fileStream);
            }
        }

        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static System.IO.Stream GenerateThumbnail(byte[] imageBytes, int width, int height)
        {
            System.IO.Stream ms;

            using (var stream = new System.IO.MemoryStream(imageBytes))
            {
                ms = GenerateThumbnail(stream, width, height);
            }

            return ms;
        }

        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static void GenerateThumbnail(byte[] imageBytes, int width, int height, string outputFilePath)
        {
            using (var stream = GenerateThumbnail(imageBytes, width, height))
            using (var fileStream = System.IO.File.Open(outputFilePath, System.IO.FileMode.OpenOrCreate))
            {
                ((System.IO.MemoryStream)stream).WriteTo(fileStream);
            }
        }

        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static System.IO.Stream GenerateThumbnail(string imageFilePath, int width, int height)
        {
            System.IO.Stream ms;

            using (var stream = new System.IO.FileStream(imageFilePath, System.IO.FileMode.Open))
            {
                ms = GenerateThumbnail(stream, width, height);
            }

            return ms;
        }

        /// <summary>
        /// 产生缩略图
        /// </summary>
        public static void GenerateThumbnail(string imageFilePath, int width, int height, string outputFilePath)
        {
            using (var stream = GenerateThumbnail(imageFilePath, width, height))
            using (var fileStream = System.IO.File.Open(outputFilePath, System.IO.FileMode.OpenOrCreate))
            {
                ((System.IO.MemoryStream)stream).WriteTo(fileStream);
            }
        }