Preprocess image using LARCOTM algorithm

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LARCOTM algorithm

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import cv2
from cv2.ximgproc import guidedFilter
import numpy as np

def larcotm(filepath, strength=0):
    """Preprocess image using LARCOTM algorithm

    Locally Adaptive Rank-Constrained Optimal Tone Mapping
    https://dl.acm.org/citation.cfm?id=3243123.3225219

    Args:
        filepath: path to input image
        strength: strength of applied LARCOTM algorithm
    
    Returns:
        OpenCV image processed by LARCOTM algorithm
    """
    img_bgr = cv2.imread(filepath, flags=cv2.IMREAD_COLOR)  # BGR
    
    img = np.float32(img_bgr) / 255.
    src = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

    if strength == 0:
        gmean = np.mean(src) * 255
        gstre = np.minimum(
            np.maximum((25 - gmean) * 5, 50),
            100
        )
        strength = gstre
    
    log_min