Manual:$wgGalleryOptions

<translate> Images</translate>: $wgGalleryOptions
Default settings for the ‎<gallery> tag.
<translate> Introduced in version:</translate>	1.17.0 (r63707)
<translate> Removed in version:</translate>	<translate> still in use</translate>
<translate> Allowed values:</translate>	(associative array)
<translate> Default value:</translate>	see below
<translate> Other settings:</translate> <translate> Alphabetical</translate> | <translate> By function</translate>

Details

The default settings for the ‎<gallery> tag, and galleries in categories.

See the "default value" below for the possible keys, and a description of each setting.

Some of these settings correspond, in a confusing way, to attributes that can be specified for the ‎<gallery> tag itself. See Help:Images#Optional gallery attributes for information on each of the attributes.

This key in $wgGalleryOptions...	...sets the default value for this ‎<gallery> tag attribute
imagesPerRow	perrow=
imageWidth	widths=
imageHeight	heights=
mode	mode= (New in MediaWiki 1.22 – see Help:Images#Mode parameter for more information)

Default value

$wgGalleryOptions = [
	'imagesPerRow' => 0, // Default number of images per-row in the gallery. 0: Adapt to screensize
	'imageWidth' => 120, // Width of the cells containing images in galleries (in "px")
	'imageHeight' => 120, // Height of the cells containing images in galleries (in "px")
	'captionLength' => true, // Length of caption to truncate (in characters) in special pages or when the showfilename parameter is used
	                         // A value of 'true' will truncate the filename to one line using CSS.
	                         // Deprecated since 1.28. Default value of 25 before 1.28.
	'showBytes' => true, // Show the filesize in bytes in categories
    'mode' => 'traditional', // One of "traditional", "nolines", "packed", "packed-hover", "packed-overlay", "slideshow" (1.28+)
];