path: root/files/zh-tw/web/api/htmlcanvaselement/todataurl/index.html

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

<p><strong><code>HTMLCanvasElement.toDataURL()</code></strong> 方法回傳含有圖像和參數設置特定格式的 <a href="/en-US/docs/Web/HTTP/data_URIs">data URIs</a> (預設 <a href="https://en.wikipedia.org/wiki/Portable_Network_Graphics">PNG</a>). 回傳的圖像解析度為 96 dpi.</p>

<ul>
 <li>如果 canvas 的高度或是寬度為 <code>0</code>, 將會回傳字串 <code>"data:,"</code>.</li>
 <li>如果要求的圖像類型並非 <code>image/png</code>, 但是回傳的類型卻是 <code>data:image/png</code>, 表示要求的圖像類型並不支援.</li>
 <li>Chrome 也支援 <code>image/webp</code> 類型.</li>
</ul>

<h2 id="Syntax" name="Syntax">表達式</h2>

<pre class="syntaxbox"><var><em>canvas</em>.toDataURL(<em>type</em>, <em>encoderOptions</em>);</var>
</pre>

<h3 id="參數">參數</h3>

<dl>
 <dt><code>type</code> {{optional_inline}}</dt>
 <dd>圖像格式的 {{domxref("DOMString")}}. 預設為 <code>image/png</code>.</dd>
 <dt><code>encoderOptions</code> {{optional_inline}}</dt>
 <dd><code>表示 image/jpeg 或是 image/webp 的圖像品質, 為0</code> 到 <code>1</code> 之間的 {{jsxref("Number")}}.<br>
 如果值不在上述範圍中, 將會使用預設值. 其他的會忽略.</dd>
</dl>

<h3 id="回傳值">回傳值</h3>

<p>包含 <a href="/en-US/docs/Web/HTTP/data_URIs">data URI</a> 的 {{domxref("DOMString")}}.</p>

<h2 id="範例">範例</h2>

<p>創建 {{HTMLElement("canvas")}} 元素:</p>

<pre class="brush: html">&lt;canvas id="canvas" width="5" height="5"&gt;&lt;/canvas&gt;
</pre>

<p>可以使用下面的方式獲取 data-URL:</p>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var dataURL = canvas.toDataURL();
console.log(dataURL);
// "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNby
// blAAAADElEQVQImWNgoBMAAABpAAFEI8ARAAAAAElFTkSuQmCC"
</pre>

<h3 id="設置圖像的品質">設置圖像的品質</h3>

<pre class="brush: js">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);
</pre>

<h3 id="Example:_Dynamically_change_images" name="Example:_Dynamically_change_images">範例: 動態改變圖像</h3>

<p>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):</p>

<h4 id="HTML">HTML</h4>

<pre class="brush: html">&lt;img class="grayscale" src="myPicture.png" alt="Description of my picture" /&gt;</pre>

<h4 id="JavaScript">JavaScript</h4>

<pre class="brush: js;highlight:[33]">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 &lt; 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 &lt; 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);
  }
}</pre>

<h2 id="規範">規範</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">規範</th>
   <th scope="col">狀態</th>
   <th scope="col">註</th>
  </tr>
  <tr>
   <td>{{SpecName('HTML WHATWG', "scripting.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}</td>
   <td>{{Spec2('HTML WHATWG')}}</td>
   <td>No change since the latest snapshot, {{SpecName('HTML5 W3C')}}</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5.1', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}</td>
   <td>{{Spec2('HTML5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-todataurl", "HTMLCanvasElement.toDataURL")}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="瀏覽器相容性">瀏覽器相容性</h2>

<p>{{ CompatibilityTable() }}</p>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{ CompatChrome(4) }}</td>
   <td>{{ CompatGeckoDesktop("1.9.2") }}</td>
   <td>{{ CompatIE(9) }}</td>
   <td>{{ CompatOpera(9) }}</td>
   <td>{{ CompatSafari(4.0) }}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{ CompatAndroid(3.2) }}</td>
   <td>{{ CompatAndroid(18) }}</td>
   <td>{{ CompatGeckoMobile("1.9.2") }}</td>
   <td>{{ CompatVersionUnknown() }}</td>
   <td>{{ CompatOpera(19) }}</td>
   <td><span style="font-size: 12px; line-height: 18px;">{{ CompatSafari(3.0) }}</span></td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_Also" name="See_Also">參見</h2>

<ul>
 <li>The interface defining it, {{domxref("HTMLCanvasElement")}}.</li>
 <li><a href="/en-US/docs/Web/HTTP/data_URIs">Data URIs</a> in the <a href="/en-US/docs/Web/HTTP">HTTP</a> reference.</li>
</ul>