我的更改图片的大小

注意先建立目录 

 #region    自己写的不改变形状
        /// <summary>创建规定大小的图像
        /// 源图像只能是JPG格式
        /// </summary>
        /// <param name="oPath">源图像绝对路径</param>
        /// <param name="tPath">生成图像绝对路径</param>
        /// <param name="width">生成图像的宽度</param>
        /// <param name="height">生成图像的高度</param>
        public void CreateImage(string oPath, string tPath, int width, int height)
        {
            Bitmap originalBmp = new Bitmap(oPath);
            // 源图像在新图像中的位置
            int left, top;

            if (originalBmp.Width <= width && originalBmp.Height <= height)
            {
                // 原图像的宽度和高度都小于生成的图片大小
                left = (int)Math.Round((decimal)(width - originalBmp.Width) / 2);
                top = (int)Math.Round((decimal)(height - originalBmp.Height) / 2);

                // 最终生成的图像
                Bitmap bmpOut = new Bitmap(width, height);
                using (Graphics graphics = Graphics.FromImage(bmpOut))
                {
                    // 设置高质量插值法
                    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    // 清空画布并以白色背景色填充
                    graphics.Clear(Color.White);
                    // 把源图画到新的画布上
                    graphics.DrawImage(originalBmp, left, top);
                }
                bmpOut.Save(tPath);
                bmpOut.Dispose();

                return;
            }

            // 新图片的宽度和高度，如400*200的图像，想要生成160*120的图且不变形，
            // 那么生成的图像应该是160*80，然后再把160*80的图像画到160*120的画布上
            int newWidth, newHeight;
            if (width * originalBmp.Height < height * originalBmp.Width)
            {
                newWidth = width;
                newHeight = (int)Math.Round((decimal)originalBmp.Height * width / originalBmp.Width);
                // 缩放成宽度跟预定义的宽度相同的，即left=0，计算top
                left = 0;
                top = (int)Math.Round((decimal)(height - newHeight) / 2);
            }
            else
            {
                newWidth = (int)Math.Round((decimal)originalBmp.Width * height / originalBmp.Height);
                newHeight = height;
                // 缩放成高度跟预定义的高度相同的，即top=0，计算left
                left = (int)Math.Round((decimal)(width - newWidth) / 2);
                top = 0;
            }

            // 生成按比例缩放的图，如：160*80的图
            Bitmap bmpOut2 = new Bitmap(newWidth, newHeight);
            using (Graphics graphics = Graphics.FromImage(bmpOut2))
            {
                graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                graphics.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);
                graphics.DrawImage(originalBmp, 0, 0, newWidth, newHeight);
            }
            // 再把该图画到预先定义的宽高的画布上，如160*120
            Bitmap lastbmp = new Bitmap(width, height);
            using (Graphics graphics = Graphics.FromImage(lastbmp))
            {
                // 设置高质量插值法
                graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                // 清空画布并以白色背景色填充
                graphics.Clear(Color.White);
                // 把源图画到新的画布上
                graphics.DrawImage(bmpOut2, left, top);
            }
            lastbmp.Save(tPath);
            lastbmp.Dispose();
        }
        #endregion

 

 public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

            int towidth = width;
            int toheight = height;

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

            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形）               
                    break;
                case "W"://指定宽，高按比例                   
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减（不变形）               
                    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;
                    }
                    break;
                default:
                    break;
            }

            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板
            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);

            //以jpg格式保存缩略图
            bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();

        }