• 等比例缩放生成缩略图


        ///
        /// 等比例缩放生成缩略图
        ///
        /// 源图路径(物理路径)
        /// 缩略图宽度
        /// 缩略图高度(依缩略图宽度等比例计算所得)
        public void MakeThumbnail(String originalImagePath, Int32 width, Int32 height)
        {
            //获取原始图片
            using (System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath))
            {
                double orwidth = (double)originalImage.Width;
                if (orwidth < 320)
                {
                    width = Convert.ToInt32(orwidth);
                }
                height = Convert.ToInt32(((double)originalImage.Height) / (orwidth / (double)width));
                //缩略图画布宽高
                Int32 towidth = width;
                Int32 toheight = height;
                //原始图片写入画布坐标和宽高(用来设置裁减溢出部分)
                Int32 x = 0;
                Int32 y = 0;
                Int32 ow = originalImage.Width;
                Int32 oh = originalImage.Height;
                //原始图片画布,设置写入缩略图画布坐标和宽高(用来原始图片整体宽高缩放)
                Int32 bg_x = 0;
                Int32 bg_y = 0;
                Int32 bg_w = towidth;
                Int32 bg_h = toheight;
                //倍数变量
                double multiple = 0;
                //获取宽长的或是高长与缩略图的倍数
                if (originalImage.Width >= originalImage.Height)
                {
                    multiple = (double)originalImage.Width / (double)width;
                }
                else
                {
                    multiple = (double)originalImage.Height / (double)height;
                }
                //上传的图片的宽和高小等于缩略图
                if (ow <= width && oh <= height)
                {
                    //缩略图按原始宽高
                    bg_w = originalImage.Width;
                    bg_h = originalImage.Height;
                    //空白部分用背景色填充
                    bg_x = Convert.ToInt32(((double)towidth - (double)ow) / 2);
                    bg_y = Convert.ToInt32(((double)toheight - (double)oh) / 2);
                }
                //上传的图片的宽和高大于缩略图
                else
                {
                    //宽高按比例缩放
                    bg_w = Convert.ToInt32((double)originalImage.Width / multiple);
                    bg_h = Convert.ToInt32((double)originalImage.Height / multiple);
                    //空白部分用背景色填充
                    bg_y = Convert.ToInt32(((double)height - (double)bg_h) / 2);
                    bg_x = Convert.ToInt32(((double)width - (double)bg_w) / 2);
                }
                //新建一个bmp图片,并设置缩略图大小.
                using (System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(towidth, toheight))
                {
                    //新建一个画板
                    using (System.Drawing.Graphics gr = System.Drawing.Graphics.FromImage(bitmap))
                    {
                        gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;//设置高质量插值法
                        gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;//设置高质量,低速度呈现平滑程度
                        gr.Clear(System.Drawing.ColorTranslator.FromHtml("#F2F2F2")); //清空画布并设置背景色
                        //在指定位置并且按指定大小绘制原图片的指定部分
                        //第一个System.Drawing.Rectangle是原图片的画布坐标和宽高,第二个是原图片写在画布上的坐标和宽高,最后一个参数是指定数值单位为像素
                        gr.DrawImage(originalImage, new System.Drawing.Rectangle(bg_x, bg_y, bg_w, bg_h), new System.Drawing.Rectangle(x, y, ow, oh), System.Drawing.GraphicsUnit.Pixel);
                        Int32 index = originalImagePath.LastIndexOf('\') + 1;
                        String path = String.Concat(originalImagePath.Substring(0, index), "App_", originalImagePath.Substring(index));
                        try
                        {
                            //获取图片类型
                            string fileExtension = System.IO.Path.GetExtension(originalImagePath).ToLower();
                            //按原图片类型保存缩略图片,不按原格式图片会出现模糊,锯齿等问题.
                            switch (fileExtension)
                            {
                                case ".gif": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Gif); break;
                                case ".jpg": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg); break;
                                case ".bmp": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Bmp); break;
                                case ".png": bitmap.Save(path, System.Drawing.Imaging.ImageFormat.Png); break;
                            }
                        }
                        catch (System.Exception e)
                        {
                            throw e;
                        }
                        finally
                        {
                            originalImage.Dispose();
                            bitmap.Dispose();
                            gr.Dispose();
                        }
                    }

                }
               
            }
        }

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  • 原文地址:https://www.cnblogs.com/lvjy-net/p/8297501.html
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