Incorrect docs on switching thumbnailer

[zerocrates]

On the Configuration Settings page: the thumbnailer is changed in the "aliases" section. The item on thumbnailer_options should also be mentioning the imagemagick_path setting.

[sharonmleon]

@zerocrates I'm not sure that I'm competent to update this one.

[allanaaa]

It looks like this is done - current text of this page is

The thumbnails configuration key holds most thumbnail settings:

'thumbnails' => [
    'types' => [
        'large' => ['constraint' => 800],
        'medium' => ['constraint' => 200],
        'square' => ['constraint' => 200],
    ],
    'thumbnailer_options' => [
        'imagemagick_dir' => null,
    ],
],

Under types, set the maximum dimensions for derivative images for media files. There are separate options for large, medium, and square. Defaults for these are 800, 200, and 200 respectively (all sizes are pixels)

thumbnailer_options is an array of options passed to the specific thumbnailer in use. For example, the imagemagick_dir thumbnail option sets the path to the folder where ImageMagick's convert command can be found on the server. This can be useful if Omeka S can't auto-detect the correct path for ImageMagick.

The thumbnailer to use is set under the service_manager key, by setting the alias for Omeka\File\Thumbnailer:

'service_manager' => [
    'aliases' => [
        'Omeka\File\Thumbnailer' => 'Omeka\File\Thumbnailer\ImageMagick',
    ],
],

The default thubnailer is Omeka\File\Thumbnailer\ImageMagick. Also available are Omeka\File\Thumbnailer\Imagick (which uses the imagick PHP extension) and Omeka\File\Thumbnailer\Gd (which uses the commonly available gd PHP extension).

You can also set the thumbnailer to Omeka\File\Thumbnailer\NoThumbnail, which will prevent your Omeka S installation from generating thumbnails.