# ownCloud Administrators Manual

# Preview Configuration

The ownCloud thumbnail system is used to generate thumbnails from various file types, which are then shown as thumbnails in the Files application of the web interface, or as a larger preview for public shared links.

The following image shows a file (A) where the ownCloud server generates a preview image, and another file (B) that it could not generate a preview for. In this case a generic icon (depending on the filetype) is displayed.

By default, ownCloud can generate previews for the following filetypes:

- Images files
- Cover of MP3 files
- Text documents

Note

Older versions of ownCloud also supported the preview generation of other file types such as PDF, SVG or various office documents. Due to security concerns those providers have been disabled by default and are considered unsupported. While those providers are still available, we discourage enabling them, and they are not documented.

## Parameters

Please notice that the ownCloud preview system comes already with sensible defaults, and therefore it is usually unecessary to adjust those configuration values.

### Disabling previews:

Under certain circumstances, for example if the server has only very limited resources, you might want to consider disabling the generation of previews. Set the configuration option `enable_previews` in config.php to `false`:

    <?php
      'enable_previews' => false,

### Maximum preview size:

There are two configuration options to set the maximum size of a preview.

    <?php
      'preview_max_x' => null,
      'preview_max_y' => null,

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:

    <?php
      'preview_max_x' => 100,
      'preview_max_y' => 100,

‘preview_max_x’ represents the x-axis and ‘preview_max_y’ represents the y-axis.

### Maximum scale factor:

If a lot of small pictures are stored on the ownCloud 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:

    <?php
      'preview_max_scale_factor' => 10,

If you want to disable scaling at all, you can set the config value to ‘1’:

    <?php
      'preview_max_scale_factor' => 1,

If you want to disable the maximum scaling factor, you can set the config value to ‘null’:

    <?php
      'preview_max_scale_factor' => null,