stream: reduce scope of readable bitmap details

PR-URL: #49963
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Raz Luvaton <rluvaton@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: ronag