W3cubDocs

/DOM

HTMLCanvasElement.toDataURL

The HTMLCanvasElement.toDataURL() method returns a data URI containing a representation of the image in the format specified by the type parameter (defaults to PNG). The returned image is in a resolution of 96 dpi.

  • If the height or width of the canvas is 0, the string "data:," is returned.
  • If the requested type is not image/png, but the returned value starts with data:image/png, then the requested type is not supported.
  • Chrome also supports the image/webp type.

Syntax

canvas.toDataURL(type, encoderOptions);

Parameters

type Optional
A DOMString indicating the image format. The default format type is image/png.
encoderOptions Optional
A Number between 0 and 1 indicating image quality if the requested type is image/jpeg or image/webp.
If this argument is anything else, the default value for image quality is used. The default value is 0.92. Other arguments are ignored.

Return value

A DOMString containing the requested data URI.

Examples

Given this <canvas> element:

<canvas id="canvas" width="5" height="5"></canvas>

You can get a data-URL of the canvas with the following lines:

var canvas = document.getElementById('canvas');
var dataURL = canvas.toDataURL();
console.log(dataURL);
// "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNby
// blAAAADElEQVQImWNgoBMAAABpAAFEI8ARAAAAAElFTkSuQmCC"

Setting image quality with jpegs

var fullQuality = canvas.toDataURL('image/jpeg', 1.0);
// data:image/jpeg;base64,/9j/4AAQSkZJRgABAQ...9oADAMBAAIRAxEAPwD/AD/6AP/Z"
var mediumQuality = canvas.toDataURL('image/jpeg', 0.5);
var lowQuality = canvas.toDataURL('image/jpeg', 0.1);

Example: Dynamically change images

You can use this technique in association with mouse events in order to dynamically change images (gray-scale versus color in this example):

HTML

<img class="grayscale" src="myPicture.png" alt="Description of my picture" />

JavaScript

window.addEventListener('load', removeColors);

function showColorImg() {
  this.style.display = 'none';
  this.nextSibling.style.display = 'inline';
}

function showGrayImg() {
  this.previousSibling.style.display = 'inline';
  this.style.display = 'none';
}

function removeColors() {
  var aImages = document.getElementsByClassName('grayscale'),
      nImgsLen = aImages.length,
      oCanvas = document.createElement('canvas'),
      oCtx = oCanvas.getContext('2d');
  for (var nWidth, nHeight, oImgData, oGrayImg, nPixel, aPix, nPixLen, nImgId = 0; nImgId < nImgsLen; nImgId++) {
    oColorImg = aImages[nImgId];
    nWidth = oColorImg.offsetWidth;
    nHeight = oColorImg.offsetHeight;
    oCanvas.width = nWidth;
    oCanvas.height = nHeight;
    oCtx.drawImage(oColorImg, 0, 0);
    oImgData = oCtx.getImageData(0, 0, nWidth, nHeight);
    aPix = oImgData.data;
    nPixLen = aPix.length;
    for (nPixel = 0; nPixel < nPixLen; nPixel += 4) {
      aPix[nPixel + 2] = aPix[nPixel + 1] = aPix[nPixel] = (aPix[nPixel] + aPix[nPixel + 1] + aPix[nPixel + 2]) / 3;
    }
    oCtx.putImageData(oImgData, 0, 0);
    oGrayImg = new Image();
    oGrayImg.src = oCanvas.toDataURL();
    oGrayImg.onmouseover = showColorImg;
    oColorImg.onmouseout = showGrayImg;
    oCtx.clearRect(0, 0, nWidth, nHeight);
    oColorImg.style.display = "none";
    oColorImg.parentNode.insertBefore(oGrayImg, oColorImg);
  }
}

Specifications

Specification Status Comment
WHATWG HTML Living Standard
The definition of 'HTMLCanvasElement.toDataURL' in that specification.
Living Standard No change since the latest snapshot, HTML5
HTML5.1
The definition of 'HTMLCanvasElement.toDataURL' in that specification.
Recommendation
HTML5
The definition of 'HTMLCanvasElement.toDataURL' in that specification.
Recommendation Snapshot of the WHATWG HTML Living Standard containing the initial definition.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 4 (Yes) 3.6 (1.9.2) 9 9 4.0
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 3.2 18 (Yes) 1.0 (1.9.2) (Yes) 19 3.0

See also

© 2005–2017 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL