模拟QQ心情图片上传预览示例

public class Thumbnial
{
///

/// 生成缩略图
///

/// 原图片
/// 缩略图宽度
/// 缩略图高度
/// 是否裁剪（以中心点）
///
public static Image GetThumbnail(System.Drawing.Image imgSource, int newWidth, int newHeight, bool isCut)
{
int rWidth = 0; // 等比例缩放后的宽度
int rHeight = 0; // 等比例缩放后的高度
int sWidth = imgSource.Width; // 原图片宽度
int sHeight = imgSource.Height; // 原图片高度
double wScale = (double)sWidth / newWidth; // 宽比例
double hScale = (double)sHeight / newHeight; // 高比例
double scale = wScale < hScale ? wScale : hScale;
rWidth = (int)Math.Floor(sWidth / scale);
rHeight = (int)Math.Floor(sHeight / scale);
Bitmap thumbnail = new Bitmap(rWidth, rHeight);
try
{
// 如果是截取原图，并且原图比例小于所要截取的矩形框，那么保留原图
if (!isCut && scale <= 1)
{
return imgSource;
}

using (Graphics tGraphic = Graphics.FromImage(thumbnail))
{
tGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; /* new way */
Rectangle rect = new Rectangle(0, 0, rWidth, rHeight);
Rectangle rectSrc = new Rectangle(0, 0, sWidth, sHeight);
tGraphic.DrawImage(imgSource, rect, rectSrc, GraphicsUnit.Pixel);
}

if (!isCut)
{
return thumbnail;
}
else
{
int xMove = 0; // 向右偏移（裁剪）
int yMove = 0; // 向下偏移（裁剪）
xMove = (rWidth - newWidth) / 2;
yMove = (rHeight - newHeight) / 2;
Bitmap final_image = new Bitmap(newWidth, newHeight);
using (Graphics fGraphic = Graphics.FromImage(final_image))
{
fGraphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic; /* new way */
Rectangle rect1 = new Rectangle(0, 0, newWidth, newHeight);
Rectangle rectSrc1 = new Rectangle(xMove, yMove, newWidth, newHeight);
fGraphic.DrawImage(thumbnail, rect1, rectSrc1, GraphicsUnit.Pixel);
}

thumbnail.Dispose();

return final_image;
}
}
catch (Exception e)
{
return new Bitmap(newWidth, newHeight);
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;

namespace Mood
{
///

/// Upload 的摘要说明
///

public class Upload : IHttpHandler
{
Image thumbnail;

public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
try
{
string id = System.Guid.NewGuid().ToString();
HttpPostedFile jpeg_image_upload = context.Request.Files["Filedata"];
Image original_image = System.Drawing.Image.FromStream(jpeg_image_upload.InputStream);
original_image.Save(System.Web.HttpContext.Current.Server.MapPath("~/Files/" + id + ".jpg"));
int target_width = 200;
int target_height = 150;
string path = "Files/Files200/" + id + ".jpg";
string saveThumbnailPath = System.Web.HttpContext.Current.Server.MapPath("~/" + path);
thumbnail = Thumbnial.GetThumbnail(original_image, target_width, target_height, true);
thumbnail.Save(saveThumbnailPath);
context.Response.Write(path);
}
catch (Exception e)
{
// If any kind of error occurs return a 500 Internal Server error
context.Response.StatusCode = 500;
context.Response.Write("上传过程中出现错误!");
}
finally
{
if (thumbnail != null)
{
thumbnail.Dispose();
}
}
}

public bool IsReusable
{
get
{
return false;
}
}
}
}

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Mood.aspx.cs" Inherits="Mood.Mood" %>

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上传图片