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EDIT
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" />
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);
}
}
