C#生成圆角缩略图

private void MakeRoundedThumbnails(Stream fileStream, string filePath, string newFileName, int newWidth, int newHeight, ref string newSaveFilePath)
        {
            System.Drawing.Image myImage = System.Drawing.Image.FromStream(fileStream);
            //先将图片处理为圆角
            myImage = DrawTransparentRoundCornerImage(myImage);
            //取得图片大小
            System.Drawing.Size mySize = new Size(newWidth, newHeight);
            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width, mySize.Height);
            //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;
            //清空一下画布
            g.Clear(Color.Transparent);
            //在指定位置画图
            g.DrawImage(myImage, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height),
            new System.Drawing.Rectangle(0, 0, myImage.Width, myImage.Height),
            System.Drawing.GraphicsUnit.Pixel);

            //保存缩略图,强制保存为png格式，否则圆角部分无法呈现透明
            Stream newFileStream = new MemoryStream();
            bitmap.Save(newFileStream, ImageFormat.Png);
     //此处为上传操作，可根据自己需要TODO不同
            newSaveFilePath = filePath + "/" + newFileName;
            FtpUpload ftpUpload = new FtpUpload("UploadFtpServer", newSaveFilePath);
            newFileStream.Position = 0;
            bool flag = ftpUpload.UploadFile(newFileStream);

            newFileStream.Dispose();
            g.Dispose();
            myImage.Dispose();
            bitmap.Dispose();
        }

 //图片处理为圆角
        public static System.Drawing.Image DrawTransparentRoundCornerImage(System.Drawing.Image image)
        {
            Bitmap bm = new Bitmap(image.Width, image.Height);
            Graphics g = Graphics.FromImage(bm);
            g.FillRectangle(Brushes.Transparent, new Rectangle(0, 0, image.Width, image.Height));

            using (System.Drawing.Drawing2D.GraphicsPath path = CreateRoundedRectanglePath(new Rectangle(0, 0, image.Width, image.Height), image.Width / 10))
            {
                g.SetClip(path);
            }

            g.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height), new Rectangle(0, 0, image.Width, image.Height), GraphicsUnit.Pixel);
            g.Dispose();

            return bm;
        }
 //设置图片四个边角弧度
        private static System.Drawing.Drawing2D.GraphicsPath CreateRoundedRectanglePath(Rectangle rect, int cornerRadius)
        {
            System.Drawing.Drawing2D.GraphicsPath roundedRect = new System.Drawing.Drawing2D.GraphicsPath();
            roundedRect.AddArc(rect.X, rect.Y, cornerRadius * 2, cornerRadius * 2, 180, 90);
            roundedRect.AddLine(rect.X + cornerRadius, rect.Y, rect.Right - cornerRadius * 2, rect.Y);
            roundedRect.AddArc(rect.X + rect.Width - cornerRadius * 2, rect.Y, cornerRadius * 2, cornerRadius * 2, 270, 90);
            roundedRect.AddLine(rect.Right, rect.Y + cornerRadius * 2, rect.Right, rect.Y + rect.Height - cornerRadius * 2);
            roundedRect.AddArc(rect.X + rect.Width - cornerRadius * 2, rect.Y + rect.Height - cornerRadius * 2, cornerRadius * 2, cornerRadius * 2, 0, 90);
            roundedRect.AddLine(rect.Right - cornerRadius * 2, rect.Bottom, rect.X + cornerRadius * 2, rect.Bottom);
            roundedRect.AddArc(rect.X, rect.Bottom - cornerRadius * 2, cornerRadius * 2, cornerRadius * 2, 90, 90);
            roundedRect.AddLine(rect.X, rect.Bottom - cornerRadius * 2, rect.X, rect.Y + cornerRadius * 2);
            roundedRect.CloseFigure();
            return roundedRect;
        }