visual_angle_from_length_ppd
============================



.. py:function:: stimupy.utils.visual_angle_from_length_ppd(length, ppd)


   Calculate visual angle (degrees) from length (pixels) and pixels-per-degree

   :param length: length in pixels
   :type length: int or None
   :param ppd: pixels per degree
   :type ppd: int or None

   :rtype: Length (pixels) translated to visual angle (degrees)