--- title: HTMLCanvasElement.toDataURL() slug: Web/API/HTMLCanvasElement/toDataURL translation_of: Web/API/HTMLCanvasElement/toDataURL ---
{{APIRef("Canvas API")}}

HTMLCanvasElement.toDataURL() 方法返回一个包含图片展示的 data URI 。可以使用 type 参数其类型，默认为 PNG 格式。图片的分辨率为96dpi。

语法

canvas.toDataURL(type, encoderOptions);

参数

type {{optional_inline}}
图片格式，默认为 image/png
encoderOptions {{optional_inline}}
在指定图片格式为 image/jpeg 或 image/webp的情况下，可以从 0 到 1 的区间内选择图片的质量。如果超出取值范围，将会使用默认值 0.92。其他参数会被忽略。

返回值

包含 data URI 的{{domxref("DOMString")}}。

示例

有如下{{HTMLElement("canvas")}}元素

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

可以用这样的方式获取一个 data-URL

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

设置jpegs图片的质量

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);

示例：动态更改图片

可以使用鼠标事件来动态改变图片（这个例子中改变图片灰度）。

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);
  }
}

规范

规范 状态 备注
{{SpecName('HTML WHATWG', "scripting.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}} {{Spec2('HTML WHATWG')}} No change since the latest snapshot, {{SpecName('HTML5 W3C')}}
{{SpecName('HTML5.1', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}} {{Spec2('HTML5.1')}}
{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}} {{Spec2('HTML5 W3C')}} Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.

浏览器兼容性

{{Compat("api.HTMLCanvasElement.toDataURL")}}

参考