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

See also

• The interface defining it, HTMLCanvasElement.
• Data URIs in the HTTP reference.