HTMLCanvasElement.toDataURL()

The HTMLCanvasElement.toDataURL() method returns a data URI containing a representation of the image in the format specified by the type parameter.

The desired file format and image quality may be specified. If the file format is not specified, or if the given format is not supported, then the data will be exported as image/png. In other words, if the returned value starts with data:image/png for any other requested type, then that format is not supported.

Browsers are required to support image/png; many will support additional formats including image/jpg and image/webp.

The created image data will have a resolution of 96dpi for file formats that support encoding resolution metadata.

Syntax

canvas.toDataURL(type, encoderOptions);

Parameters

type Optional

A DOMString indicating the image format. The default type is image/png; this image format will be also used if the specified type is not supported.

encoderOptions Optional

A Number between 0 and 1 indicating the image quality to be used when creating images using file formats that support lossy compression (such as image/jpeg or image/webp). A user agent will use its default quality value if this option is not specified, or if the number is outside the allowed range.

Return value

A DOMString containing the requested data URI.

If the height or width of the canvas is 0 or larger than the maximum canvas size, the string "data:," is returned.

Exceptions

SecurityError

The canvas's bitmap is not origin clean; at least some of its contents have or may have been loaded from a site other than the one from which the document itself was loaded.

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 coordination with mouse events in order to dynamically change images (gray-scale vs. 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
HTML Standard (HTML)
# dom-canvas-todataurl-dev

Browser compatibility

BCD tables only load in the browser

See also