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 withdata:image/png
, then the requested type is not supported. - Chrome also supports the
image/webp
type.
Syntax
JavaScript
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<var>canvas.toDataURL(type, encoderOptions);</var>
Parameters
type
Optional- A
DOMString
indicating the image format. The default type isimage/png
. encoderOptions
Optional- A
Number
between0
and1
indicating image quality if the requested type isimage/jpeg
orimage/webp
.
If this argument is anything else, the default value for image quality is used. The default value is0.92
. Other arguments are ignored.
Return value
A DOMString
containing the requested data URI.
Examples
Given this <canvas>
element:
HTML
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<canvas id="canvas" width="5" height="5"></canvas>
You can get a data-URL of the canvas with the following lines:
JavaScript
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var canvas = document.getElementById("canvas"); var dataURL = canvas.toDataURL(); console.log(dataURL); // "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNby // blAAAADElEQVQImWNgoBMAAABpAAFEI8ARAAAAAElFTkSuQmCC"
Setting image quality with jpegs
JavaScript
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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
HTML
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<img class="grayscale" src="myPicture.png" alt="Description of my picture" />
JavaScript
js;highlight:[33]
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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. |
Working Draft | |
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 | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 4 | 3.6 (1.9.2) | 9 | 9 | 4.0 |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | 3.2 | 18 | 1.0 (1.9.2) | (Yes) | 19 | 3.0 |
See also
- The interface defining it,
HTMLCanvasElement
. - Data URIs in the HTTP reference.
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/htmlcanvaselement/todataurl