画图

一.捕获原图部分视图

        /// 

        /// 捕获原图部分视图（以中心为起点向四周捕获）
        /// 
        /// 原图地址
        /// 目标地址
        /// 要捕获的宽度
        /// 要捕获的高度
        public static void CaptureImage(string fromImagePath, string toImagePath, int width, int height)
        {
            //原图片文件
            Image fromImage = Image.FromFile(fromImagePath);
            int originalHeight = fromImage.Height;
            int originalWidth = fromImage.Width;
            int offsetY = (originalHeight - height) / 2;
            int offsetX = (originalWidth - width) / 2;
            //创建新图位图
            Bitmap bitmap = new Bitmap(width, height);
            //创建作图区域
            Graphics graphic = Graphics.FromImage(bitmap);
            //设置高质量插值法
            graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //设置高质量,低速度呈现平滑程度
            graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清除整个绘图表面,并在其中填充指定背景颜色
            graphic.Clear(Color.White);
            //截取原图相应区域写入作图区
            graphic.DrawImage(fromImage, 0, 0, new Rectangle(offsetX, offsetY, width, height), GraphicsUnit.Pixel);
            //从作图区生成新图
            Image saveImage = Image.FromHbitmap(bitmap.GetHbitmap());
            //保存图片
            saveImage.Save(toImagePath, ImageFormat.Png);
            //释放资源   
            saveImage.Dispose();
            graphic.Dispose();
            bitmap.Dispose();
        }

二.生成缩略图

        /// 

        /// 生成缩略图
        /// 
        /// 图片地址
        /// 缩略图地址
        /// 图片宽度
        /// 图片高度
        /// 
        public static void GetThumbnail(string serverImagePath, string thumbnailImagePath, int width, int height)
        {
            Image serverImage = Image.FromFile(serverImagePath);
            //画板大小
            int towidth = width;
            int toheight = height;
            //原图矩形框的像素点
            int ow = serverImage.Width;
            int oh = serverImage.Height;
            if (ow > oh)
                toheight = serverImage.Height * width / serverImage.Width;
            else
                towidth = serverImage.Width * height / serverImage.Height;
            //新建一个bmp图片
            Image bm = new Bitmap(width, height);
            //新建一个画板
            Graphics g = Graphics.FromImage(bm);
            //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(Color.White);
            //在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(serverImage, new Rectangle((width - towidth) / 2, (height - toheight) / 2, towidth, toheight), 0, 0, ow, oh, GraphicsUnit.Pixel);
            try
            {
                //以jpg格式保存缩略图
                bm.Save(thumbnailImagePath, ImageFormat.Jpeg);
            }
            catch (Exception e)
            {
                throw e;
            }
            finally
            {
                serverImage.Dispose();
                bm.Dispose();
                g.Dispose();
            }
        }