def start_preview(self, **options):
    '\n        Displays the preview overlay.\n\n        This method starts a camera preview as an overlay on the Pi\'s primary\n        display (HDMI or composite). A :class:`PiRenderer` instance (more\n        specifically, a :class:`PiPreviewRenderer`) is constructed with the\n        keyword arguments captured in *options*, and is returned from the\n        method (this instance is also accessible from the :attr:`preview`\n        attribute for as long as the renderer remains active).  By default, the\n        renderer will be opaque and fullscreen.\n\n        This means the default preview overrides whatever is currently visible\n        on the display. More specifically, the preview does not rely on a\n        graphical environment like X-Windows (it can run quite happily from a\n        TTY console); it is simply an overlay on the Pi\'s video output. To stop\n        the preview and reveal the display again, call :meth:`stop_preview`.\n        The preview can be started and stopped multiple times during the\n        lifetime of the :class:`PiCamera` object.\n\n        All other camera properties can be modified "live" while the preview is\n        running (e.g. :attr:`brightness`).\n\n        .. note::\n\n            Because the default preview typically obscures the screen, ensure\n            you have a means of stopping a preview before starting one. If the\n            preview obscures your interactive console you won\'t be able to\n            Alt+Tab back to it as the preview isn\'t in a window. If you are in\n            an interactive Python session, simply pressing Ctrl+D usually\n            suffices to terminate the environment, including the camera and its\n            associated preview.\n        '
    self._check_camera_open()
    self._preview.close()
    options.setdefault('layer', self._preview_layer)
    options.setdefault('alpha', self._preview_alpha)
    options.setdefault('fullscreen', self._preview_fullscreen)
    options.setdefault('window', self._preview_window)
    renderer = PiPreviewRenderer(self, self._camera.outputs[self.CAMERA_PREVIEW_PORT], **options)
    self._preview = renderer
    return renderer
Displays the preview overlay.

This method starts a camera preview as an overlay on the Pi's primary
display (HDMI or composite). A :class:`PiRenderer` instance (more
specifically, a :class:`PiPreviewRenderer`) is constructed with the
keyword arguments captured in *options*, and is returned from the
method (this instance is also accessible from the :attr:`preview`
attribute for as long as the renderer remains active).  By default, the
renderer will be opaque and fullscreen.

This means the default preview overrides whatever is currently visible
on the display. More specifically, the preview does not rely on a
graphical environment like X-Windows (it can run quite happily from a
TTY console); it is simply an overlay on the Pi's video output. To stop
the preview and reveal the display again, call :meth:`stop_preview`.
The preview can be started and stopped multiple times during the
lifetime of the :class:`PiCamera` object.

All other camera properties can be modified "live" while the preview is
running (e.g. :attr:`brightness`).

.. note::

    Because the default preview typically obscures the screen, ensure
    you have a means of stopping a preview before starting one. If the
    preview obscures your interactive console you won't be able to
    Alt+Tab back to it as the preview isn't in a window. If you are in
    an interactive Python session, simply pressing Ctrl+D usually
    suffices to terminate the environment, including the camera and its
    associated preview.
def start_preview(self, **options):
    '\n        Displays the preview overlay.\n\n        This method starts a camera preview as an overlay on the Pi\'s primary\n        display (HDMI or composite). A :class:`PiRenderer` instance (more\n        specifically, a :class:`PiPreviewRenderer`) is constructed with the\n        keyword arguments captured in *options*, and is returned from the\n        method (this instance is also accessible from the :attr:`preview`\n        attribute for as long as the renderer remains active).  By default, the\n        renderer will be opaque and fullscreen.\n\n        This means the default preview overrides whatever is currently visible\n        on the display. More specifically, the preview does not rely on a\n        graphical environment like X-Windows (it can run quite happily from a\n        TTY console); it is simply an overlay on the Pi\'s video output. To stop\n        the preview and reveal the display again, call :meth:`stop_preview`.\n        The preview can be started and stopped multiple times during the\n        lifetime of the :class:`PiCamera` object.\n\n        All other camera properties can be modified "live" while the preview is\n        running (e.g. :attr:`brightness`).\n\n        .. note::\n\n            Because the default preview typically obscures the screen, ensure\n            you have a means of stopping a preview before starting one. If the\n            preview obscures your interactive console you won\'t be able to\n            Alt+Tab back to it as the preview isn\'t in a window. If you are in\n            an interactive Python session, simply pressing Ctrl+D usually\n            suffices to terminate the environment, including the camera and its\n            associated preview.\n        '
    self._check_camera_open()
    self._preview.close()
    options.setdefault('layer', self._preview_layer)
    options.setdefault('alpha', self._preview_alpha)
    options.setdefault('fullscreen', self._preview_fullscreen)
    options.setdefault('window', self._preview_window)
    renderer = PiPreviewRenderer(self, self._camera.outputs[self.CAMERA_PREVIEW_PORT], **options)
    self._preview = renderer
    return renderer