The clear-external-image-conversions function clears the external image conversions for a port. If gp-or-null is nil all conversions are cleared using the image-color-users. If all is non- nil all conversions for all ports are cleared using gp-or-null . Conversions are also freed if free-image is non- nil . By default, free-image is t , all is (null gp-or-null ) , and errorp is t .