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  <section id="previews-configuration">
<h1>Previews configuration<a class="headerlink" href="#previews-configuration" title="Link to this heading"></a></h1>
<p>The Nextcloud thumbnail system generates previews of files for all
Nextcloud apps that display files, such as Files and Gallery.</p>
<p>The following image shows some examples of previews of various file types.</p>
<figure class="align-default">
<img alt="Thumbnails of various image and audio/video files." src="../_images/preview_images.png" />
</figure>
<p>By default, Nextcloud can generate previews for the following filetypes:</p>
<ul class="simple">
<li><p>Images files</p></li>
<li><p>Text documents</p></li>
</ul>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Nextcloud can also generate previews of other file types (such as PDF, SVG,
various Office document formats, and various video formats). Due to security and
performance concerns those providers are disabled by default. While those providers
are still available, we discourage enabling them and they are considered unsupported.
The full list of the preview providers that are enabled by default (as well as those
disabled by default) can be found under the <code class="docutils literal notranslate"><span class="pre">enabledPreviewProviders</span></code>
<a class="reference internal" href="../configuration_server/config_sample_php_parameters.html"><span class="doc">configuration parameter</span></a>.</p>
</div>
<section id="parameters">
<h2>Parameters<a class="headerlink" href="#parameters" title="Link to this heading"></a></h2>
<p>Please notice that the Nextcloud preview system comes already with sensible
defaults, and therefore it is usually unnecessary to adjust those configuration
values.</p>
<p>But deemed necessary, following changes have to be made in <code class="docutils literal notranslate"><span class="pre">config/config.php</span></code> file. As a best practice, take a backup of this config file before making a lot of changes.</p>
<p>After changing one or more of the following parameters, you might want to run the <code class="docutils literal notranslate"><span class="pre">preview:cleanup</span></code> occ command to get rid of the previews with obsolete settings.
See <a class="reference internal" href="../occ_command.html#occ-cleanup-previews"><span class="std std-ref">Cleanup previews</span></a> to learn more.</p>
<section id="disabling-previews">
<h3>Disabling previews:<a class="headerlink" href="#disabling-previews" title="Link to this heading"></a></h3>
<p>Under certain circumstances, for example if the server has limited
resources, you might want to consider disabling the generation of previews.
Note that if you do this all previews in all apps are disabled, including
the Gallery app, and will display generic icons instead of
thumbnails.</p>
<p>Set the configuration option <code class="docutils literal notranslate"><span class="pre">enable_previews</span></code> to <code class="docutils literal notranslate"><span class="pre">false</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;enable_previews&#39; =&gt; false,
</pre></div>
</div>
</section>
<section id="maximum-preview-size">
<h3>Maximum preview size:<a class="headerlink" href="#maximum-preview-size" title="Link to this heading"></a></h3>
<p>There are two configuration options to set the maximum size of a preview.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_x&#39; =&gt; null,
  &#39;preview_max_y&#39; =&gt; null,
</pre></div>
</div>
<p>By default, both options are set to null. ‘Null’ is equal to no limit.
Numeric values represent the size in pixels. The following code limits previews
to a maximum size of 100×100px:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_x&#39; =&gt; 100,
  &#39;preview_max_y&#39; =&gt; 100,
</pre></div>
</div>
<p>‘preview_max_x’ represents the x-axis and ‘preview_max_y’ represents the y-axis.</p>
</section>
<section id="maximum-scale-factor">
<h3>Maximum scale factor:<a class="headerlink" href="#maximum-scale-factor" title="Link to this heading"></a></h3>
<p>If a lot of small pictures are stored on the Nextcloud instance and the preview
system generates blurry previews, you might want to consider setting a maximum
scale factor. By default, pictures are upscaled to 10 times the original size:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_scale_factor&#39; =&gt; 10,
</pre></div>
</div>
<p>If you want to disable scaling at all, you can set the config value to ‘1’:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_scale_factor&#39; =&gt; 1,
</pre></div>
</div>
<p>If you want to disable the maximum scaling factor, you can set the config value
to ‘null’:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_scale_factor&#39; =&gt; null,
</pre></div>
</div>
</section>
<section id="jpeg-quality-setting">
<h3>JPEG quality setting:<a class="headerlink" href="#jpeg-quality-setting" title="Link to this heading"></a></h3>
<p>Default JPEG quality setting for preview images is ‘80’. Change this with:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">occ</span> <span class="n">config</span><span class="p">:</span><span class="n">app</span><span class="p">:</span><span class="nb">set</span> <span class="n">preview</span> <span class="n">jpeg_quality</span> <span class="o">--</span><span class="n">value</span><span class="o">=</span><span class="s2">&quot;60&quot;</span>
</pre></div>
</div>
</section>
<section id="maximum-memory-for-image-generation">
<h3>Maximum memory for image generation:<a class="headerlink" href="#maximum-memory-for-image-generation" title="Link to this heading"></a></h3>
<p>By default, Nextcloud generates image previews using the GD Graphics Library.
This configuration option limits the amount of memory that is allowed for preview generation.
If creating the preview image would allocate more memory than the limit,
preview generation will be disabled and the default mimetype icon is shown.</p>
<p>Default limit is 256 MB. Set to <code class="docutils literal notranslate"><span class="pre">-1</span></code> for no limit.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>&lt;?php
  &#39;preview_max_memory&#39; =&gt; 256,
</pre></div>
</div>
</section>
</section>
</section>

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