 The affiliate program closed for new signups in February 2012, with Google announcing that it would scale down the initiative, making it private and invitation-only.The mobile Android app has seen several significant updates since its introduction, including different reading modes with color contrasts, support for text highlighting and note-taking, a zoomed-out view with easy page sliding in an effort to improve reading experiences for books not read cover-to-cover, a vertical scrolling mode for comic books, a "Night Light" feature that gradually filters blue light to reduce eye strain after sunset, using machine learning imaging technologies to expand speech bubbles in comics, and listening to audiobooks.As the Play Books store had been noted to hold much pirated content, Google discontinued new sign-ups to its publisher program in 2015.