#this script is for image preprocess. ICM is time confused to do
#hsv and rgb stretching, so just replace with rgb stretching,
import cv2
import numpy as np

clahe = cv2.createCLAHE(clipLimit=2.0, tileGridSize=(8,8))

def gray_stretching(image):
    #stretching gray image with single channel.
    Imax=np.max(image)
    Imin=np.min(image)
    MAX=255
    MIN=0
    image=(image - Imin)  / (Imax - Imin)* (MAX - MIN) + MIN
    #return image.astype('uint8')
    return image

def BGR_stretching(image):
    #accept a BGR image read from cv2, split channel and do stretch seperately.
    B,G,R=cv2.split(image)
    '''
    B=gray_stretching(B)
    G=gray_stretching(G)
    R=gray_stretching(R)
    '''
    B=clahe.apply(B)
    G=clahe.apply(G)
    R=clahe.apply(R)
    image=cv2.merge([B,G,R]).astype('uint8')
    return image