Common下ImageHelper.cs

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本文介绍了一种生成图片缩略图的方法及图片上传的具体实现。包括如何根据不同的需求调整缩略图尺寸，确保图片质量的同时减少加载时间。此外，还详细说明了文件上传过程中的路径处理、格式验证等关键步骤。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.UI.WebControls;
using System.Web.UI;
using System.IO;

namespace Common
{
    public class ImageHelper:Page
    {
        /// <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();
            }
        }

        /// <summary>
        /// 上传图片
        /// </summary>
        /// <returns></returns>
        private string upimg(FileUpload up,string oldimgurl)
        {
            string result = "";
            if (up.HasFile)
            {
                string fileContentType = up.PostedFile.ContentType;
                if (fileContentType == "image/bmp" || fileContentType == "image/gif" || fileContentType == "image/pjpeg" || fileContentType == "image/jpeg" || fileContentType == "image/x-png")
                {
                    string ImgFileName = DateTime.Now.ToString("yyyyMMddHHmmss");//该商品图片存放文件夹名称
                    string fileName = ImgFileName + ".jpg"; // 文件名称
                    string JueDuiUrl = Server.MapPath("~/proimages");
                    string xiangduiurl = "~/proimages" + "/" + fileName;

                    if (!Directory.Exists(JueDuiUrl))
                    {
                        Directory.CreateDirectory(JueDuiUrl);//如果不存在，则创建
                    }
                    string webFilePath = JueDuiUrl + "//" + fileName;        // 服务器端文件路径
                    if (!File.Exists(webFilePath))
                    {
                        if (!string.IsNullOrEmpty(oldimgurl))
                        {
                            new Common.FileHelper().DeleteImg(oldimgurl);
                        }
                        up.SaveAs(webFilePath);
                        result = xiangduiurl;
                    }
                }
                else
                {
                    Common.MessageBox.Show(Page, "请选择正确图片格式");
                    return "";
                }
            }
            return result;
        }
    }
}