C# 生成缩略图、转换图片大小

转载自:http://www.wxzzz.com/1413.html

该方法可以将现有路径中的一个图片文件转换为指定大小的图片。

如果你是Image对象需要转换呢，可以自己更改下这个方法是很简单的，删掉部分代码即可。

/// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="localImagePath">图片地址</param>
        /// <param name="thumbnailImagePath">缩略图地址</param>
        /// <param name="width">图片宽度</param>
        /// <param name="height">图片高度</param>
        /// <param name="p"></param>
        public static void GetThumbnail(string localImagePath, string thumbnailImagePath, int width, int height)
        {
            System.Drawing.Image serverImage = System.Drawing.Image.FromFile(localImagePath);
            //画板大小
            int towidth = width;
            int toheight = height;
            //缩略图矩形框的像素点
            int x = 0;
            int y = 0;
            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
            System.Drawing.Image bm = new System.Drawing.Bitmap(width, height);
            //新建一个画板
            System.Drawing.Graphics g = System.Drawing.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(System.Drawing.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 System.Drawing.Rectangle((width - towidth) / 2, (height - toheight) / 2, towidth, toheight),
                0, 0, ow, oh,
                System.Drawing.GraphicsUnit.Pixel);
            try
            {
                //以jpg格式保存缩略图
                bm.Save(thumbnailImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                serverImage.Dispose();
                bm.Dispose();
                g.Dispose();
            }
        }