1.添加一个html
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> <title></title> </head> <body> <form action="Getmin.ashx" method="post" enctype="multipart/form-data"> 图片:<input type="file" name="file" id="file" onchange="javascript:fileInfo();" /> <p style="font-size:12px;">原图宽:<label id="ow">0</label> 原图高:<label id="oh">0</label> 原图大小:<label id="os">0</label>KB</p> <p>设置宽度:<input type="text" name="width" style="50px;"/> <span style="color:#09a02c;font-size:12px">高度按原图比例折算</span></p> <p><input type="submit" style="color:#ff6a00" value="下载缩略图" /> </p> </form> </body> </html> <script type="text/javascript"> //上传前获取图片信息(用html5的File) function fileInfo() { var f = document.getElementById("file").files[0]; var reader = new FileReader(); reader.readAsDataURL(f); reader.onload = function (e) { var data = e.target.result; //加载一个图片获取宽度高度 var image = new Image(); image.src = data; image.onload = function () { var width = image.width; var height = image.height; var size = parseInt(f.size / 1024); document.getElementById("ow").innerHTML = width; document.getElementById("oh").innerHTML = height; document.getElementById("os").innerHTML = size; }; } } </script>
2.添加一个处理程序:ashx
public void ProcessRequest(HttpContext context) { //1.获取用户上传的文件流 HttpPostedFile file = context.Request.Files[0]; //获取文件名 string fileName = file.FileName; //获取扩展名 string Extension = Path.GetExtension(fileName).ToUpper(); //2.根据用户上传的文件流创建一个图片 using (Image originalImage = Image.FromStream(file.InputStream)) { //获取原始图片的宽和高 int owidth = originalImage.Width; int oheight = originalImage.Height; //缩略图的宽 int mwidth = Convert.ToInt32(context.Request.Form["width"]); //等比例的高,取整数 int mheight = mwidth * oheight / owidth; //3.根据原始图片，等比例创建一个缩小后的图片 using (Image minImage = new Bitmap(mwidth, mheight)) { //4.把大图片内容画到小图片上 //基于小图创建一个画布对象 Graphics gmin = Graphics.FromImage(minImage); //把大图画到小图上 gmin.DrawImage(originalImage, 0, 0, mwidth, mheight); //5.下载缩略图 MemoryStream ms = new MemoryStream(); //判断图片类型 ImageFormat imageFormat = null; string ContentType = ""; switch (Extension) { case ".JPG": imageFormat = ImageFormat.Jpeg; ContentType = "image/jpeg"; break; case ".PNG": imageFormat = ImageFormat.Png; ContentType = "image/png"; break; case ".GIF": imageFormat = ImageFormat.Gif; ContentType = "image/gif"; break; //................如需要其他图片格式继续添加 } minImage.Save(ms,imageFormat); context.Response.ClearContent(); context.Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8)); context.Response.ContentType=ContentType; context.Response.BinaryWrite(ms.ToArray()); context.Response.End(); } } } public bool IsReusable { get { return false; } }
