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this is a working code to convert jpg or png to webp
google's new image format that is in average 30-40% smaller than jpg's or png's
1.Open with Chrome
2.Set The quality
3.Drop an image inside the page
4.Wait (depends on the size .. try small images first)
5.Hover the image to see the size difference
6.To properly save it as webp just click on it
Basycally chrome adde the possibility to add image/webp and the quality to the toDataURL function
canvas.toDataURL('image/webp',quality(0-1))
The pression is fantastic.But i have a small problem... png's are not transparent..
what could it be? maybe set the canvas to transparent? how?
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
html,body{
width:100%;
height:100%;
margin:0;
padding:0;
display:-webkit-flex;
display: flex;
}
a{margin: auto;}
.imG{
max-width:800px;
max-height:400px;
}
form{
position:fixed;
bottom:0px;left:0px;
}
</style>
<script>
(function(W){
W.URL=W.URL||W.webkitURL;
var D;
function init(){
D=W.document;
D.body.addEventListener('dragstart',pdrop,false);
D.body.addEventListener('dragenter',pdrop,false)
D.body.addEventListener('dragover',pdrop,false);
D.body.addEventListener('dragleave',pdrop,false);
D.body.addEventListener('dragend',pdrop,false);
D.body.addEventListener('drop',drop,false);
}
function readablizeBytes(bytes) {
var s=['bytes','kB','MB','GB','TB','PB'],m=Math,e=m.floor(m.log(bytes)/m.log(1024));
return (bytes/Math.pow(1024,e)).toFixed(2)+" "+s[e];
}
function pdrop(e){
e.stopPropagation();
e.preventDefault();
}
function drop(e){
e.stopPropagation();
e.preventDefault();
console.log(e.dataTransfer.files[0]);
var f=e.dataTransfer.files[0];
var i=document.createElement('img');
i.onload=function(e){
window.URL.revokeObjectURL(this.src);
var b=document.createElement('canvas');
b.width=this.width;b.height=this.height;
var c=b.getContext("2d");
c.drawImage(this,0,0);
this.onload=function(){
this.className='imG';
var d=document.createElement('a');
g=f.name.split('.');g.pop();
d.download=g.join('')+'.webp';
d.href=this.src;
d.title=readablizeBytes(atob(this.src.split(',')[1]).length)+' vs '+readablizeBytes(f.size);
d.appendChild(this);
D.body.appendChild(d);
}
this.src=b.toDataURL('image/webp',D.getElementsByName('o')[0].innerText*0.01);
};
i.src=window.URL.createObjectURL(f);
}
W.addEventListener('load',init,false);
})(window)
</script>
<title>Image To Google's webp format</title>
</head>
<body>
<form onsubmit="return false" oninput="o.value=v.valueAsNumber">
<label for="q">Choose the quality and then drop a image</label>
<input name="v" id="q" type="range" min="0" max="100" value="0">
<output for="q" name="o">0</output>/100
</form>
</body>
</html>
ps.:for best results use jpg's and reload the page every time as it just appends every new image
this is a working code to convert jpg or png to webp
google's new image format that is in average 30-40% smaller than jpg's or png's
1.Open with Chrome
2.Set The quality
3.Drop an image inside the page
4.Wait (depends on the size .. try small images first)
5.Hover the image to see the size difference
6.To properly save it as webp just click on it
Basycally chrome adde the possibility to add image/webp and the quality to the toDataURL function
canvas.toDataURL('image/webp',quality(0-1))
The pression is fantastic.But i have a small problem... png's are not transparent..
what could it be? maybe set the canvas to transparent? how?
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<style>
html,body{
width:100%;
height:100%;
margin:0;
padding:0;
display:-webkit-flex;
display: flex;
}
a{margin: auto;}
.imG{
max-width:800px;
max-height:400px;
}
form{
position:fixed;
bottom:0px;left:0px;
}
</style>
<script>
(function(W){
W.URL=W.URL||W.webkitURL;
var D;
function init(){
D=W.document;
D.body.addEventListener('dragstart',pdrop,false);
D.body.addEventListener('dragenter',pdrop,false)
D.body.addEventListener('dragover',pdrop,false);
D.body.addEventListener('dragleave',pdrop,false);
D.body.addEventListener('dragend',pdrop,false);
D.body.addEventListener('drop',drop,false);
}
function readablizeBytes(bytes) {
var s=['bytes','kB','MB','GB','TB','PB'],m=Math,e=m.floor(m.log(bytes)/m.log(1024));
return (bytes/Math.pow(1024,e)).toFixed(2)+" "+s[e];
}
function pdrop(e){
e.stopPropagation();
e.preventDefault();
}
function drop(e){
e.stopPropagation();
e.preventDefault();
console.log(e.dataTransfer.files[0]);
var f=e.dataTransfer.files[0];
var i=document.createElement('img');
i.onload=function(e){
window.URL.revokeObjectURL(this.src);
var b=document.createElement('canvas');
b.width=this.width;b.height=this.height;
var c=b.getContext("2d");
c.drawImage(this,0,0);
this.onload=function(){
this.className='imG';
var d=document.createElement('a');
g=f.name.split('.');g.pop();
d.download=g.join('')+'.webp';
d.href=this.src;
d.title=readablizeBytes(atob(this.src.split(',')[1]).length)+' vs '+readablizeBytes(f.size);
d.appendChild(this);
D.body.appendChild(d);
}
this.src=b.toDataURL('image/webp',D.getElementsByName('o')[0].innerText*0.01);
};
i.src=window.URL.createObjectURL(f);
}
W.addEventListener('load',init,false);
})(window)
</script>
<title>Image To Google's webp format</title>
</head>
<body>
<form onsubmit="return false" oninput="o.value=v.valueAsNumber">
<label for="q">Choose the quality and then drop a image</label>
<input name="v" id="q" type="range" min="0" max="100" value="0">
<output for="q" name="o">0</output>/100
</form>
</body>
</html>
ps.:for best results use jpg's and reload the page every time as it just appends every new image
Share Improve this question edited Jun 23, 2015 at 14:00 Unihedron 11.1k13 gold badges63 silver badges72 bronze badges asked Aug 18, 2013 at 14:40 coccococco 16.7k7 gold badges64 silver badges77 bronze badges 2- maybe ... .globalAlpha need to test that some day. – cocco Commented Dec 27, 2013 at 2:07
- downvote... explain? does alpha now work in native js? – cocco Commented Jun 23, 2015 at 14:53
2 Answers
Reset to default 5 +50Canvas status
This is an known issue with Chrome.
From the ments from the link above it's stated:
WebCore discards the alpha channel in toDataURL("image/webp") and encodes the image from the RGB pixels because WEBP never supported alpha channel. toDataURL("image/webp") has been that way since http://trac.webkit/changeset/99319 (shipped over a year ago).
WEBP only recently added support for alpha channel and there is no way to select that in a toDataURL. We could force it one way or the other, I suppose, but should the default encoding be 1) no-alpha as now, or 2) alpha as requesting in this bug?
The issue has currently not been solved but will likely be addressed in near future.
Possible work-around
For a possible work-around you can use a custom implementation of the WEBP format which states it supports the alpha channel. It can convert PNG (and JPEG) to WEBP format.
The solution is called WEBPJS and can be found here (and examples can be found here).
(but there is also the possibility that Chrome won't be able to decode webp images even if they contain alpha channel..).
Conclusion
webp images with alpha channel has poor support at the moment even with Google's (the inventor) own Chrome, and lack support in other browsers. My advice is that you put this on ice until support is improved and instead use PNG as this has wide support.
Use tools such as tinypng. to reduce the sizes of the files.
Compresspic is render a better support to press any type of image like that PNG, BMP, JPEG, GIF, etc. Today many websites can't accept high MB's images. So you can use presspic tool to press images as your need.
本文标签： javascriptOn the fly clientside image to webp converterbut png39s are not transparentStack Overflow
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