path: root/files/es/web/api/htmlcanvaselement/toblob/index.html

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

<p>EL metodo <strong><code>HTMLCanvasElement.toBlob()</code></strong> crea un objeto {{domxref("Blob")}} que representa la imagen contenida en el canvas; este archivo puede ser cacheado en el disco oo guardado en la memoria a desicion del  user agent. Si la propiedad <code>type</code> no se especifica el tipo de la imagen será <code>image/png</code>. La imagen creada tiene una resolución de 96dpi.<br>
 El tercer argumento es usado con las imagenes  <code>image/jpeg</code> para especificar la calidad de salida.</p>

<h2 id="Syntax">Syntax</h2>

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

<h3 id="Parameters">Parameters</h3>

<dl>
 <dt>callback</dt>
 <dd>A callback function with the resulting {{domxref("Blob")}} object as a single argument.</dd>
 <dt><code>type</code> {{optional_inline}}</dt>
 <dd>A {{domxref("DOMString")}} indicating the image format. The default type is <code>image/png</code>.</dd>
 <dt><code>encoderOptions</code> {{optional_inline}}</dt>
 <dd>A {{jsxref("Number")}} between <code>0</code> and <code>1</code> indicating image quality if the requested type is <code>image/jpeg </code>or <code>image/webp</code>. If this argument is anything else, the default value for image quality is used. Other arguments are ignored.</dd>
</dl>

<h3 id="Return_value">Return value</h3>

<p>None.</p>

<h2 id="Examples">Examples</h2>

<h3 id="Getting_a_file_representing_the_canvas">Getting a file representing the canvas</h3>

<p>Once you have drawn content into a canvas, you can convert it into a file of any supported image format. The code snippet below, for example, takes the image in the {{HTMLElement("canvas")}} element whose ID is "canvas", obtains a copy of it as a PNG image, then appends a new {{HTMLElement("img")}} element to the document, whose source image is the one created using the canvas.</p>

<pre class="brush: js">var canvas = document.getElementById("canvas");

canvas.toBlob(function(blob) {
  var newImg = document.createElement("img"),
      url = URL.createObjectURL(blob);

  newImg.onload = function() {
    // no longer need to read the blob so it's revoked
    URL.revokeObjectURL(url);
  };

  newImg.src = url;
  document.body.appendChild(newImg);
});
</pre>

<p>Note that here we're creating a PNG image; if you add a second parameter to the <code>toBlob()</code> call, you can specify the image type. For example, to get the image in JPEG format:</p>

<pre class="brush: js"> canvas.toBlob(function(blob){...}, "image/jpeg", 0.95); // JPEG at 95% quality</pre>

<div>
<h3 id="A_way_to_convert_a_canvas_to_an_ico_(Mozilla_only)">A way to convert a canvas to an ico (Mozilla only)</h3>

<p>This uses <code>-moz-parse</code> to convert the canvas to ico. Windows XP doesn't support converting from PNG to ico, so it uses bmp instead. A download link is created by setting the download attribute. The value of the download attribute is the name it will use as the file name.</p>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var d = canvas.width;
ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.moveTo(d / 2, 0);
ctx.lineTo(d, d);
ctx.lineTo(0, d);
ctx.closePath();
ctx.fillStyle = "yellow";
ctx.fill();

function blobCallback(iconName) {
  return function(b) {
    var a = document.createElement("a");
    a.textContent = "Download";
    document.body.appendChild(a);
    a.style.display = "block";
    a.download = iconName + ".ico";
    a.href = window.URL.createObjectURL(b);
  }
}
canvas.toBlob(blobCallback('passThisString'), 'image/vnd.microsoft.icon',
              '-moz-parse-options:format=bmp;bpp=32');</pre>
</div>

<h3 id="Save_toBlob_to_disk_with_OS.File_(chromeadd-on_context_only)">Save toBlob to disk with OS.File (chrome/add-on context only)</h3>

<div class="note">
<p>This technique saves it to the desktop and is only useful in Firefox chrome context or add-on code as OS APIs are not present on web sites.</p>
</div>

<pre class="brush: js">var canvas = document.getElementById("canvas");
var d = canvas.width;
ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.moveTo(d / 2, 0);
ctx.lineTo(d, d);
ctx.lineTo(0, d);
ctx.closePath();
ctx.fillStyle = "yellow";
ctx.fill();

function blobCallback(iconName) {
  return function(b) {
    var r = new FileReader();
    r.onloadend = function () {
    // r.result contains the ArrayBuffer.
    Cu.import('resource://gre/modules/osfile.jsm');
    var writePath = OS.Path.join(OS.Constants.Path.desktopDir,
                                 iconName + '.ico');
    var promise = OS.File.writeAtomic(writePath, new Uint8Array(r.result),
                                      {tmpPath:writePath + '.tmp'});
    promise.then(
      function() {
        console.log('successfully wrote file');
      },
      function() {
        console.log('failure writing file')
      }
    );
  };
  r.readAsArrayBuffer(b);
  }
}

canvas.toBlob(blobCallback('passThisString'), 'image/vnd.microsoft.icon',
              '-moz-parse-options:format=bmp;bpp=32');</pre>

<h2 id="Polyfill">Polyfill</h2>

<p>A low performance polyfill based on toDataURL.</p>

<pre class="brush: js">if (!HTMLCanvasElement.prototype.toBlob) {
 Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
  value: function (callback, type, quality) {

    var binStr = atob( this.toDataURL(type, quality).split(',')[1] ),
        len = binStr.length,
        arr = new Uint8Array(len);

    for (var i=0; i&lt;len; i++ ) {
     arr[i] = binStr.charCodeAt(i);
    }

    callback( new Blob( [arr], {type: type || 'image/png'} ) );
  }
 });
}
</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('HTML WHATWG', "scripting.html#dom-canvas-toblob", "HTMLCanvasElement.toBlob")}}</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-toblob", "HTMLCanvasElement.toBlob")}}</td>
   <td>{{Spec2('HTML5.1')}}</td>
   <td>No change</td>
  </tr>
  <tr>
   <td>{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-toblob", "HTMLCanvasElement.toBlob")}}</td>
   <td>{{Spec2('HTML5 W3C')}}</td>
   <td>Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</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>{{CompatNo}}<sup>[1]</sup></td>
   <td>{{CompatGeckoDesktop('19')}}</td>
   <td>{{CompatIE(10)}}{{property_prefix("ms")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}<sup>[2]</sup></td>
  </tr>
  <tr>
   <td>Image quality parameter (jpeg)</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoDesktop('25')}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</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>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoMobile("19")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
  <tr>
   <td>Image quality parameter (jpeg)</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatGeckoMobile("25")}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<p>[1] Chrome does not implement this feature yet. See <a href="http://crbug.com/67587">bug 67587</a>.</p>

<p>[2] WebKit does not implement this feature yet. See {{WebKitBug("71270")}}.</p>

<h2 id="See_also">See also</h2>

<ul>
 <li>The interface defining it, {{domxref("HTMLCanvasElement")}}.</li>
 <li>{{domxref("Blob")}}</li>
</ul>