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。
- 如果画布的高度或宽度是0,那么会返回字符串“
data:,”。
- 如果传入的类型非“
image/png
”,但是返回的值以“data:image/png
”开头,那么该传入的类型是不支持的。 - Chrome支持“
image/webp
”类型。
语法
canvas.toDataURL(type, encoderOptions);
参数
type
可选- 图片格式,默认为
image/png
encoderOptions
可选- 图片质量。取值范围为
0
到1
。如果指定图片格式为image/jpeg 或
image/webp
。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
示例
有如下<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 |
---|---|---|
WHATWG HTML Living Standard HTMLCanvasElement.toDataURL |
Living Standard | No change since the latest snapshot, HTML5 |
HTML5.1 HTMLCanvasElement.toDataURL |
Working Draft | |
HTML5 HTMLCanvasElement.toDataURL |
Recommendation | Snapshot of the WHATWG HTML Living Standard containing the initial definition. |
浏览器兼容性
特性 | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
基础支持 | 4 | 3.6 (1.9.2) | 9 | 9 | 4.0 |
特性 | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
基础支持t | 3.2 | 18 | 1.0 (1.9.2) | (Yes) | 19 | 3.0 |
参考
- 定义接口,
HTMLCanvasElement
- HTTP引用中的Data URIs