def __init__(self,<EOL>pixel_width,<EOL>pixel_height=None,<EOL>mm_per_pixel=None,<EOL>):
self.pixel_width = pixel_width<EOL>self.pixel_height = pixel_height<EOL>self.mm_per_pixel = mm_per_pixel<EOL>
constructor:

:param pixel_width: Double
:param pixel_height: Double
:param mm_per_pixel: Double