Get image width and height from the Base64 code in JavaScript

Question

I have a Base64 image encoded that you can find here. How can I get the height and the width of it?

Soemba

Link rot has set in for this question – Macintosh

Yep. "Hmm. We’re having trouble finding that site. We can’t connect to the server at soo.gd." – Disruptive

Answer 1

var i = new Image();

i.onload = function(){
  alert(i.width + ", " + i.height);
};

i.src = imageData;

Aponeurosis

too bad that this is an asynchronous process. – Leucopoiesis

@CoenDamen yep. I need synchronous process as well. – Pend

I would also add that the order here is very important. If you do this the other way around (src before onload) you may miss the event. See: https://mcmap.net/q/75729/-waiting-for-image-to-load-in-javascript – Isopropanol

@CoenDamen why should the whole script block just to get information on the image size? – Phenanthrene

can't we do it without loading the image from the string ? – Conde

string or url, the image has to be loaded for client to get the dimension. do you have something else in mind? – Aponeurosis

imageData should be in the format data:image/png;base64, then the base 64 image data. – Macintosh

To get width and height synchronously inside an asyc function you can use decode() as described in one of the other answers: stackoverflow.com/a/71804221 – Famed

Answer 2

For synchronous use just wrap it into a promise like this:

function getImageDimensions(file) {
  return new Promise (function (resolved, rejected) {
    var i = new Image()
    i.onload = function(){
      resolved({w: i.width, h: i.height})
    };
    i.src = file
  })
}

then you can use await to get the data in synchronous coding style:

var dimensions = await getImageDimensions(file)

Chink

It's still asynchronous though. Just using syntactic sugar. – Oestrin

'naturalWidth' and 'naturalHeight` are the better choices no? #28167637 – Wiggs

Answer 3

I found that using .naturalWidth and .naturalHeight had the best results.

const img = new Image();

img.src = 'https://via.placeholder.com/350x150';

img.onload = function() {
  const imgWidth = img.naturalWidth;
  const imgHeight = img.naturalHeight;

  console.log('imgWidth: ', imgWidth);
  console.log('imgHeight: ', imgHeight);
};

Documentation:

• HTMLImageElement.naturalWidth
• HTMLImageElement.naturalHeight

This is only supported in modern browsers. NaturalWidth and NaturalHeight in IE

Eugenioeugenius

Exactly, it is the original size of image before being resized by object-fit – Arliearliene

Answer 4

A more modern solution is to use HTMLImageElement.decode() instead of the onload event. decode() returns a promise and thus can be used synchronously with await.

Asynchronous use:

let img = new Image();
img.src = "myImage.png";
img.decode().then(() => {
    let width = img.width;
    let height = img.height;
    // Do something with dimensions
});

Synchronous use (inside an async function):

let img = new Image();
img.src = "myImage.png";
await img.decode();
let width = img.width;
let height = img.height;
// Do something with dimensions

Famed

Awesome answer, learned something new today. – Dowsabel

Answer 5

Create a hidden <img> with that image and then use jQuery's .width() and . height()

$("body").append("<img id='hiddenImage' src='" + imageData + "' />");
var width = $('#hiddenImage').width();
var height = $('#hiddenImage').height();
$('#hiddenImage').remove();
alert("width:" + width + " height:" + height);

Test here: JSFiddle

The image is not initially created hidden. It gets created, and then you get width and height and then remove it. This may cause a very short visibility in large images. In this case, you have to wrap the image in another container and make that container hidden, not the image itself.

---

Another Fiddle that does not add to the DOM as per gp.'s answer: here

Jae

var i = new Image(); i.src = imageData; setTimeout(function(){ alert ( "width:"+ i.width+" height:" + i.height ); },100); – Aponeurosis

this is only a fix needed because of the nature of the jsfiddle, you can change onLoad to onDomReady instead to fix that initial 0 width and height problem. Code assumes you call this function somewhere in your work where document is already loaded. – Jae

Guess your point being was, that you do not need to add anything to dom to get width and height. Will modify answer to reflect your suggestions. – Jae

Answer 6

const img = new Image();
img.src = dataUrl;
await img.decode();
const width, height =  img.width, img.height;

Lashanda