前台JS限制上传图片质量大小和尺寸！（转）<html>?
<head>?
<meta http-equiv="Content-Type" content="text/html; charset=??????">?
<script language="javascript">?
<!--?
function imgSel()?
{?
var img = new Image();?
img.src = document.imageForm.file.value;?
document.imageForm.width.value = img.width;?
document.imageForm.height.value = img.height;?
document.imageForm.size.value = img.fileSize;?
document.images['image'].src = img.src;?
}?
-->?
</script>?
</head>?
<body>?
<form name="imageForm">?
宽: <input name="width" type="text" size="6"> 高: <input name="height" type="text" size="6"> 大小: <input name="size" type="text" size="6"><br>?
<input name="file" type="file" onChange="imgSel()"><br>?
<img src="" name="image">?
</form>?
</body>?
</html>?
用CSS实现的方法：?
??? 把一副大图片按比例缩小或者放大到某个尺寸，对于标准浏览器（如Firefox），或者最新都IE7浏览器，直接使用max-width,max-height；或者min-width,min-height的CSS属性即可。如：?
img{max-width:100px;max-height:100px;}?
img{min-width:100px;min-height:100px;}?
对于IE6及其以下版本的浏览器，则可以利用其支持的expression属性，在css code中嵌入javascript code来实现图片的缩放?
.thumbImage {max-width: 100px;max-height: 100px;} /* for Firefox & IE7 */?
* html .thumbImage { /* for IE6 */?
width: expression(this.width > 100 && this.width > this.height ? 100 : auto);?
height: expression(this.height > 100 ? 100 : auto);?
}?
由于把图片放大，可能存在图片锯齿化的问题，一般用在图片缩小的情况是较多的。?
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有时候图片太大，会破环网页整齐的布局。这时可以用css来强制按比例压缩图片的高度或宽度?
css代码如下：?
img,a img{?
border:0;??
margin:0;??
padding:0;?
max-width:590px;?
width:expression(this.width>590?"590px":this.width);?
max-height:590px;?
height:expression(this.height>590?"590px":this.height);?
}?
这样当图片的高度或宽度若超过590px，将会按比例压缩成590px，如果不超过则按原大小显示。?
用JavaScript实现的方法：?
用JavaScript实现网页图片等比例缩放?
如何让网页中的图片等比例缩放呢，我参考了一些代码并自己写了个图片缩放的脚本，可以点击放大，同时用鼠标滑轮自由缩放，希望提出不同意见。?
首先看看resizeimg函数的源代码：?
function resizeimg(ImgD,iwidth,iheight) {?
???? var image=new Image();?
???? image.src=ImgD.src;?
???? if(image.width>0 && image.height>0){?
??????? if(image.width/image.height>= iwidth/iheight){?
?????????? if(image.width>iwidth){?
?????????????? ImgD.width=iwidth;?
?????????????? ImgD.height=(image.height*iwidth)/image.width;?
?????????? }else{?
????????????????? ImgD.width=image.width;?
????????????????? ImgD.height=image.height;?
??????????????? }?
?????????????? ImgD.alt=image.width+"×"+image.height;?
??????? }?
??????? else{?
??????????????? if(image.height>iheight){?
?????????????????????? ImgD.height=iheight;?
?????????????????????? ImgD.width=(image.width*iheight)/image.height;?
??????????????? }else{?
??????????????????????? ImgD.width=image.width;?
??????????????????????? ImgD.height=image.height;?
???????????????????? }?
??????????????? ImgD.alt=image.width+"×"+image.height;?
??????????? }?
ImgD.style.cursor= "pointer"; //改变鼠标指针?
ImgD.onclick = function() { window.open(this.src);} //点击打开大图片?
if (navigator.userAgent.toLowerCase().indexOf("ie") > -1) { //判断浏览器，如果是IE?
ImgD.title = "请使用鼠标滚轮缩放图片，点击图片可在新窗口打开";?
ImgD.onmousewheel = function img_zoom() //滚轮缩放?
{?
var zoom = parseInt(this.style.zoom, 10) || 100;?
zoom += event.wheelDelta / 12;?
if (zoom> 0) this.style.zoom = zoom + "%";?
return false;?
}?
? } else { //如果不是IE?
???? ImgD.title = "点击图片可在新窗口打开";?
?? }?
??? }?
}?
在需要实现等比缩放的图片上加上onload语句，图片装载时初始化大小。?
具体实现代码如下:?
<img name="" src="" onload="javascript:resizeimg(this,100,200)">?
赶快行动，把这个特效加入到你的网页图片中去。?
----------------------------------------------------------------------------?
<script?? language="JavaScript">???
? {???
? var?? flag=false;???
? function?? DrawImage(ImgD){???
??????? var?? image=new?? Image();???
??????? image.src=ImgD.src;???
??????? if(image.width>0?? &&?? image.height>0){???
????????? flag=true;???
????????? if(image.width/image.height>=0){???
??????????? if(image.width>520){???????
??????????? ImgD.width=520;???
??????????? ImgD.height=(image.height*520)/image.width;???
??????????? }else{???
??????????? ImgD.width=image.width;???????
??????????? ImgD.height=image.height;???
??????????? }???
??????????? //ImgD.alt=image.width+"×"+image.height;?
?? ImgD.alt="点击此处在新窗口中打开!"?
??????????? }???
????????? else{???
??????????? if(image.height>235){???????
??????????? ImgD.height=235;???
??????????? ImgD.width=(image.width*235)/image.height;?????????????
??????????? }else{???
??????????? ImgD.width=image.width;???????
??????????? ImgD.height=image.height;???
??????????? }???
??????????? //ImgD.alt=image.width+"×"+image.height;???
?? ImgD.alt="点击此处在新窗口中打开!"?
??????????? }???
????????? }???
? }?????
? }???
? </script>?
例:<img src="2.gif" border="0" class="borderpic" onload="javascript:DrawImage(this);"></a>?
?原文地址：http://www.cnblogs.com/nuke/archive/2010/12/09/1901276.html