基于winForm生成缩略图

编程目的：利用OpenFileDialog打开指定目录的图片文件，点击button按钮将图片以缩略图形式显示在piturebox控件中，同时在打开的文件目录创建原文件名_new的缩略图文件。

预备操作：在Form窗体添加一个picturebox和一个button控件，OpenFileDialog控件 

1、生成缩略图的关键类

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">源图路径（物理路径）</param>
        /// <param name="thumbnailPath">缩略图路径（物理路径）</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">生成缩略图的方式</param>    
        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);

            try
            {
                //以jpg格式保存缩略图
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        }

2、button的click事件中调用代码：

 private void button1_Click(object sender, EventArgs e)
        {
            byte[] imagebytes = null; 
            openFileDialog1.Filter = "图片文件(*.jpg,*.gif,*.bmp)|*.jpg|*.gif|*.bmp";
     
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                string filename = openFileDialog1.FileName;
                string filenameWithNoExtension=filename.Substring(0, filename.Length - 4);
                string fileExtension = filename.Substring(filename.Length - 4, 4);
                string filepath = filenameWithNoExtension + "_new" + fileExtension;

                ImageClass.MakeThumbnail(filename, filepath, 100, 100, "Cat");
                pictureBox1.Image = Image.FromFile(filepath);
            }           
        }

3、运行结果

本文参考：http://www.sufeinet.com/