What are some methods to analyze image brightness using Python?

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I'd like some advice on performing a simple image analysis in python. I need to calculate a value for the "brightness" of an image. I know PIL is the goto library for doing something like this. There is a built-in histogram function.

What I need is a "perceived brightness" values I can decide if further adjustments to the image are necessary. So what are something of the basic techniques that will work in this situation? Should I just work with the RGB values, or will histogram give me something close enough?

One possible solution might be to combine the two, and generate average R,G,and B values using the histogram, then apply the "perceived brightness" formula.

image-processing python
6 Answers

the code below will give you the brightness level of an image from 0-10

1- calculate the average brightness of the image after converting the image to HSV format using opencv.

2- find where this value lies in the list of brightness range.

 import numpy as np
 import cv2
 import sys
 from collections import namedtuple

#brange brightness range
#bval brightness value
BLevel = namedtuple("BLevel", ['brange', 'bval'])

#all possible levels
_blevels = [
    BLevel(brange=range(0, 24), bval=0),
    BLevel(brange=range(23, 47), bval=1),
    BLevel(brange=range(46, 70), bval=2),
    BLevel(brange=range(69, 93), bval=3),
    BLevel(brange=range(92, 116), bval=4),
    BLevel(brange=range(115, 140), bval=5),
    BLevel(brange=range(139, 163), bval=6),
    BLevel(brange=range(162, 186), bval=7),
    BLevel(brange=range(185, 209), bval=8),
    BLevel(brange=range(208, 232), bval=9),
    BLevel(brange=range(231, 256), bval=10),
]


def detect_level(h_val):
     h_val = int(h_val)
     for blevel in _blevels:
        if h_val in blevel.brange:
            return blevel.bval
    raise ValueError("Brightness Level Out of Range")


 def get_img_avg_brightness():
     if len(sys.argv) < 2:
        print("USAGE: python3.7 brightness.py <image_path>")
        sys.exit(1)
     img = cv2.imread(sys.argv[1])
     hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
     _, _, v = cv2.split(hsv)

     return int(np.average(v.flatten()))

 if __name__ == '__main__':

     print("the image brightness level is: 
            {0}".format(detect_level(get_img_avg_brightness())))
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user_103205110 
def calculate_brightness(image):

    greyscale_image = image.convert('L')
    histogram = greyscale_image.histogram()
    pixels = sum(histogram)
    brightness = scale = len(histogram)

    for index in range(0, scale):

        ratio = histogram[index] / pixels
        brightness += ratio * (-scale + index)
    return 1 if brightness == 255 else brightness / scale
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