HTMLCanvasElement.toDataURL()
HTMLCanvasElement.toDataURL()
方法回傳含有圖像和參數設置特定格式的 data URIs (預設 PNG). 回傳的圖像解析度為 96 dpi.
- 如果 canvas 的高度或是寬度為
0
, 將會回傳字串"data:,"
. - 如果要求的圖像類型並非
image/png
, 但是回傳的類型卻是data:image/png
, 表示要求的圖像類型並不支援. - Chrome 也支援
image/webp
類型.
表達式
canvas.toDataURL(type, encoderOptions);
參數
回傳值
範例
創建 <canvas>
元素:
<canvas id="canvas" width="5" height="5"></canvas>
可以使用下面的方式獲取 data-URL:
var canvas = document.getElementById("canvas");
var dataURL = canvas.toDataURL();
console.log(dataURL);
// "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNby
// blAAAADElEQVQImWNgoBMAAABpAAFEI8ARAAAAAElFTkSuQmCC"
設置圖像的品質
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);
範例: 動態改變圖像
為了動態改變圖像, 可以與滑鼠事件一起使用 (gray-scale versus 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);
}
}
規範
Specification |
---|
HTML Standard # dom-canvas-todataurl-dev |
瀏覽器相容性
BCD tables only load in the browser
參見
- The interface defining it,
HTMLCanvasElement
. - Data URIs in the HTTP reference.