gistfile1.php

<?php
/**
 * Filters the image quality for thumbnails to be at the highest ratio possible.
 *
 * Supports the new 'wp_editor_set_quality' filter added in WP 3.5.
 *
 * @since 1.0.0
 *
 * @param int $quality The default quality (90)
 * @return int $quality Amended quality (100)
 */
function image_full_quality( $quality ) {
    return 100;
}
add_filter( 'jpeg_quality', 'image_full_quality' );
add_filter( 'wp_editor_set_quality', 'image_full_quality' );