Add size in Gallery Settings in Media Library

I would like to add the size in the Gallery Settings in the Add Media.

I know to add the in the front-end by editing the media.php.

However, when I added the the lines in gallery.dev.js, they don’t seem to work.

Here are the lines I had added in gallery.dev.js

Added size

 setup : function()
      var t = this, a, ed = t.editor, g, columns,size, link, order, orderby;

Added galsize in the same setup : function (approx line 128)

 if ( getUserSetting('galsize') ) t.I('size').value = getUserSetting('galsize');

Added in setup : function (approx line 141)

 size = a.match(/order='"['"]/i);

Added in setup : function (approx line 150 )

 if ( size && size[1] ) t.I('size').value = size[1];

Added size in update : function (approx line 170)

   all = all.replace(/\s*(order|link|columns|size|orderby)=['"]([^'"]+)['"]/gi, '');

Added in getsettings : function

    if ( I('size').value != 'medium' ) {
            s += ' size="'+I('size').value+'"';
            setUserSetting('galsize', I('size').value);
        }

Solutions Collecting From Web of "Add size in Gallery Settings in Media Library"

first +1 for the first commenter .
NEVER CHANGE CORE FILES.

this function will do the trick for your media upload :

function dl_custom_image_sizes_add_settings($sizes) {
       unset( $sizes['thumbnail']); //comment to remove size if needed
       //unset( $sizes['medium']);// uncomment to remove size if needed
       //unset( $sizes['large']);// uncomment to restore size if needed
       unset( $sizes['full'] ); // comment to remove size if needed
       $mynewimgsizes = array(
              "your-custom-size_name-1" => __( "Name_to_display1" ),
              "your-custom-size_name-2" => __( "Name_to_display2" ),
              "your-custom-size_name-3" => __( "Name_to_display3" )
       );
       $newimgsizes = array_merge($sizes, $mynewimgsizes);
       return $newimgsizes;
}
add_filter('image_size_names_choose', 'dl_custom_image_sizes_add_settings');

of course , this will work only if you define them first like so :

/*
Post Thumbnails Support
*/
add_theme_support( 'post-thumbnails', array( 'post' ) ); // Add it for posts
add_image_size( 'your-custom-size_name-1', 220, 100, true ); // Permalink thumbnail size
add_image_size( 'your-custom-size_name-2', 50, 50, true ); // example home  thumbnail size
add_image_size( 'your-custom-size_name-3', 470, 350, false ); //  slider size

otherwise it will show greyed out buttons..