\wp-admin\includes\image.php
$threshold = (int) apply_filters( ‘big_image_size_threshold’, 1920, $imagesize, $file, $attachment_id );

\wp-includes\media.php
function _wp_add_additional_image_sizes() {

\wp-admin\includes\image.php
$threshold = (int) apply_filters( 'big_image_size_threshold', 1920, $imagesize, $file, $attachment_id );

\wp-includes\media.php
function _wp_add_additional_image_sizes() {