这篇文章主要介绍了JS+HTML图片显示Canvas压缩功能的方法，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。
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 = "https://cache.yisu.com/upload/information/20200622/114/71251.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>感谢你能够认真阅读完这篇文章，希望小编分享的“JS+HTML图片显示Canvas压缩功能的方法”这篇文章对大家有帮助，同时也希望大家多多支持亿速云，关注亿速云行业资讯频道，更多相关知识等着你来学习!
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