Previews Configuration

If you handle the security risk and decide to allow creating previews for PDF files, change the following imagick security policy. Use an editor of your choice like nano and change the following file, adapt the path if using ImageMagick 7:

Search for the following content:

and change:

After changing the policy file for ImageMagick, restart your Apache web server or your php-fpm service. ImageMagick uses ghostscript for converting PDF. Please also make sure, that ghostscript is installed and the PDF format is listed when invoking the following command:

To be able to create previews for video files when using the OC\Preview\Movie provider, you must install ffmpeg. There can be significant load on the server during conversion when video thumbnail generation is enabled.

To get a list of file extensions linked to the image or video provider, change into the owncloud directory and run the following example command. Use a different filter for other provider types.

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 and will display generic icons instead of thumbnails.

Set the configuration option enable_previews to false:

The example below adds the preview provider for SGI and HEIC images:

Images up to a certain size feature preview generation (thumbnails and media viewer renderings). Images above that size show a default icon. The default value is defined in config/config.sample.php as 6016x4000 which is sufficient for 24MP landscape images.

The following example would change the limit so that 24MP portrait images also feature preview generation:

There are two configuration options for setting the maximum size (in pixels) of a preview. These are preview_max_x which represents the x-axis and preview_max_y which represents the y-axis. The default value you can reference in config/config.sample.php is set to 2048.

The following example would limit previews to a maximum size of 100 px × 100 px:

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:

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

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

The JP(E)G image quality can be defined in [%] for displaying thumbnails and image previews for apps like Files or Files Mediaviewer. Note that this setting is for displaying only and has no impact on the stored thumbnail / preview quality or size.

The scale ranges from 1 to 100, where 1 is the lowest and 100 the highest. It defaults to -1 which is equivalent to approximately 75% of the original image quality. Consider that any value over 80 may result in an unnecessary increase of the displayed image and has larger response sizes when requesting images, without much increase of the image quality. Usually it is not necessary to have a quality setting over 75, but it can be increased if there is the need to display previews in high quality with the cost that every image requested generates a higher response load. Note that this setting does not affect downloading images. Setting a value takes immediate effect and nothing needs to be regenerated as it is for display requests only.

For more information see: PHP imagejpeg — Output image to browser or file