JS HTML图片显示Canvas 压缩功能
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2023-09-06 18:47:07
简单到延伸
最新需要js 文件压缩图片上传 以前没搞过，新手把学习过程分享
一.选择图片并显示
简单到延伸
最新需要js 文件压缩图片上传 以前没搞过，新手把学习过程分享
一.选择图片并显示
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>title</title>
</head>
<body>
<input id="imginput" type="file" accept="image/*" onchange="showimg(this)">
<div id="img1">
<canvas class="convas01"></canvas>
</div>
</body>
<script>
window.url=window.url||window.webkiturl;
var divimg1 = document.getelementbyid("img1");
function showimg(obj){
var files = obj.files;
var img = new image();
img.width = 100;
if(window.url){
img.src = window.url.createobjecturl(files[0]);
}else{
//opera不支持createobjecturl/revokeobjecturl方法。需要用filereader对象来处理
var reader = new filereader();
reader.readasdataurl(files[0]);
reader.onload = function(e){
img.src = this.result;
img.width = 200;
img.id="img01";
divimg1.appendchild(img);
}
}
img.id="img01";
divimg1.appendchild(img);
}
</script>
</html>
二.使用canvas代码
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>title</title>
</head>
<body>
<input id="imginput" type="file" accept="image/*" onchange="showimg(this)">
<div id="img1">
<canvas id="convas01"></canvas>
</div>
</body>
<script>
window.url=window.url||window.webkiturl;
var divimg1 = document.getelementbyid("img1");
var convas = document.getelementbyid("convas01");
var ht = convas01.getcontext("2d");
convas.width = 200;
convas.height = 200;
function showimg(obj){
var files = obj.files;
var img = new image();
img.width = 200;
if(window.url){
img.src = window.url.createobjecturl(files[0]);
img.onload = function(e){
window.url.revokeobjecturl(this.src);//方便引用无效回收
ht.clearrect(0, 0, convas.width, convas.width);//clearrect() 方法清空给定矩形内的指定像素。
ht.drawimage(img,0,0,convas.width,convas.height);
convas.todataurl("image/png");
}
}else{
//opera不支持createobjecturl/revokeobjecturl方法。需要用filereader对象来处理
var reader = new filereader();
reader.readasdataurl(files[0]);
reader.onload = function(){
img.src = this.result;
img.width = 200;
img.id="img01";
divimg1.appendchild(img);
}
}
}
</script>
</html>
三.压缩处理
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>title</title>
</head>
<body>
<input id="imginput" type="file" accept="image/*" onchange="showimg(this)">
<div id="img1">
canvas图片
<canvas id="convas01"></canvas>
</div>
<div id="img2">
压缩图片
</div>
</body>
<script>
window.url=window.url||window.webkiturl;
var divimg1 = document.getelementbyid("img1");
var divimg2 = document.getelementbyid("img2");
var convas = document.getelementbyid("convas01");
var ht = convas01.getcontext("2d");
convas.width = 200;
convas.height = 200;
function showimg(obj){
var files = obj.files;
var img = new image();
img.width = 200;
if(window.url){
img.src = window.url.createobjecturl(files[0]);
img.onload = function(e){
window.url.revokeobjecturl(this.src);//方便引用无效回收
ht.drawimage(img,0,0,convas01.width,convas01.height);
var imgdata = convas.todataurl("image/png");
//将canvas转化成blob对象
var imgobj = new image();
var blob =dataurltoblob(imgdata);
var url = window.url.createobjecturl(blob);
imgobj.onload = function(e){
window.url.revokeobjecturl(this.src);
}
imgobj.src= url;
divimg2.appendchild(imgobj);
}
}else{
//opera不支持createobjecturl/revokeobjecturl方法。需要用filereader对象来处理
var reader = new filereader();
reader.readasdataurl(files[0]);
reader.onload = function(){
img.src = this.result;
img.width = 200;
img.id="img01";
divimg1.appendchild(img);
}
}
}
function dataurltoblob(dataurl) {
var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
bstr = atob(arr[1]), n = bstr.length, u8arr = new uint8array(n);
while(n--){
u8arr[n] = bstr.charcodeat(n);
}
return new blob([u8arr], {type:mime});
}
</script>
</html>
四.分辨率调节尝试
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>document</title>
<style>
*{
margin:0;padding:0;
}
body{
width:100%;height:100%;background:black;
}
canvas{
width:800px;height:480px;outline:1px solid pink;position:absolute;
left:0;top:0;right:0;bottom:0;margin:auto;
}
</style>
</head>
<body>
<button>240x120</button>
<button>320x240</button>
<button>480x320</button>
<button>640x420</button>
<button>800x480</button>
<canvas id="canvasid" width="480" height="320">
your browser does not support the canvas element.
</canvas>
<script>
var canvas = document.getelementbyid('canvasid');
var context = canvas.getcontext('2d');
var btns = document.getelementsbytagname('button');
var resolution = [
[240, 120],
[320, 240],
[480, 320],
[640, 420],
[800, 480]
];
//canvas分辨率
var resolutionw = canvas.getattribute('width');
var resolutionh = canvas.getattribute('height');
//canvas大小
var sizew = canvas.offsetwidth;
var sizeh = canvas.offsetheight;
console.log(resolutionw);
console.log(resolutionh);
console.log(sizew);
console.log(sizeh);
var img = new image();
img.src = "http://img5.niutuku.com/phone/1301/0920/0920-niutuku.com-483082.jpg"; //这张图片像素为800x480
img.onload = function() {
draw(3);
for (var i = 0; i < btns.length; i++) {
(function(i) {
btns[i].onclick = function() {
draw(i);
}
})(i);
}
}
function draw(i) {
canvas.setattribute('width', resolution[i][0]);
canvas.setattribute('height', resolution[i][1]);
context.clearrect(0, 0, sizew, sizeh);
context.drawimage(img, 0, 0, sizew, sizeh, 0, 0, resolution[i][0], resolution[i][1]);
}
</script>
</body>
</html>
总结
以上所述是小编给大家介绍的js html图片显示canvas 压缩功能，希望对大家有所帮助
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