contrasts.py

import numpy as np
import cv2 as cv


class LightDark(object):
    """docstring for LightDark"""
    def __init__(self, img, method='luminance'):
        self._img = img

        meth = getattr(LightDark, method)
        self.ctrst = meth(self)
        
    def luminance(self):
        """Creates light/dark values using luminance quantifiers for RGB

           The array has the same dimensions as the image. However the third
           does only have the size 1 which contains the luminance value
        """
        # Luminance Faktoren nach http://introcs.cs.princeton.edu/python/31datatype/luminance.py.html
        luminance_factors = np.array([.114, .587, .299])

        # Erzeugung eines eindimensionalen Arrays für die effizientere Berechnung
        self._img = np.multiply(self._img, luminance_factors)

        # addiert alle Werte auf einer bestimmten Achse
        luminances = np.sum(self._img, axis=2)

        return luminances

    def value(self):
        """Creates light/dark values using the value channel in HSV"""
        img = cv.cvtColor(self._img, cv.COLOR_BGR2HSV)
        values = img[:, :, 2].copy()

        return values

    def lightness(self):
        """Creates light/dark values using the value channel in HSV"""
        img = cv.cvtColor(self._img, cv.COLOR_BGR2HLS)
        lightness = img[:, :, 1].copy()

        return lightness