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filter is not described

admin_post_thumbnail_size filter-hook . WP 4.4.0

Filters the size used to display the post thumbnail image in the 'Featured Image' meta box.

Note: When a theme adds 'post-thumbnail' support, a special 'post-thumbnail' image size is registered, which differs from the 'thumbnail' image size managed via the Settings > Media screen. See the $size parameter description for more information on default values.

Usage

add_filter( 'admin_post_thumbnail_size', 'filter_function_name_3459', 10, 3 );
function filter_function_name_3459( $size, $thumbnail_id, $post ){
	// filter...

	return $size;
}
$size(string/array)
Post thumbnail image size to display in the meta box. Accepts any valid image size, or an array of width and height values in pixels (in that order). If the 'post-thumbnail' size is set. Otherwise, default is an array with 266 as both the height and width values.
Default: 'post-thumbnail'
$thumbnail_id(int)
Post thumbnail attachment ID.
$post(WP_Post)
The post object associated with the thumbnail.

Where the hook is called

_wp_post_thumbnail_html()
admin_post_thumbnail_size
wp-admin/includes/post.php 1441
$size = apply_filters( 'admin_post_thumbnail_size', $size, $thumbnail_id, $post );

Where the hook is used (in WP core)

Does not used.