C#固定宽度生成缩略图

Question

固定宽度200，高度按图片不变形的尺寸，这里高度不能固定，如果原图800*800，那么生成的缩略图应为200*200，如果原图片800*700此时缩略图的高度就会发生变化，应该怎么来计算高度，请高手指点。c#

Answer 1

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Web.UI;        /// <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)
        {
            Image originalImage = 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
            Image bitmap = new System.Drawing.Bitmap(towidth, toheight);            //新建一个画板
            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(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 Rectangle(0, 0, towidth, toheight),
                new Rectangle(x, y, ow, oh),
                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();
            }
        }

Answer 2

<%@ WebHandler Language="C#" Class="createThumbnail" %>using System;
using System.Web;using System.Drawing;
public class createThumbnail : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "image/jpeg";
        //获取url上的路径
        string path = context.Request.QueryString["url"];
        path = context.Request.MapPath("images/" + path);
        //原始图片
        using (Image img = Image.FromFile(path))
        {
             //保证原始图片的高宽比例
            int smallWidth = 150;
            int smallHeight = 100;
            if (img.Width > img.Height)
            {
                smallHeight = smallWidth * img.Height / img.Width;
            }
            else
            {
                smallWidth = smallHeight * img.Width / img.Height;
            }
            //缩略图
            using (Bitmap bitmap = new Bitmap(smallWidth, smallHeight))
            {
                //
                using (Graphics g = Graphics.FromImage(bitmap))
                {
                    g.DrawImage(img, 0, 0, bitmap.Width, bitmap.Height);
                    //输出
                    bitmap.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
            }
        }
    }    public bool IsReusable
    {
        get
        {
            return false;
        }
    }}