Calculate Image brightness with Python Pillow

brightness.py

import sys
from PIL import Image


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


if __name__ == '__main__':
    for file in sys.argv[1:]:
        image = Image.open(file)
        print("%s\t%s" % (file, calculate_brightness(image)))

@kmohrf #kmohrf I know this is super old but I'm trying to understand what the 'L' means in your script?

@TylerG398 see the reference in the PIL Image.convert documentation or more specifically the list of available modes. It basically converts the image to black and white.

Hey i have the exact problem.. i hope this link
https://github.com/imneonizer/How-to-find-if-an-image-is-bright-or-dark/
would help you out achieving the same.
In this blog i have explained how i divided the image into smaller segments and find brightness in those segments and finally took the average of all those calculated brightness to get the brightness level of image
It can easily tell which images are brighter and which are dark.
Hope it could help you with something.

@kmohrf so in this would 1 be white and 0 be black? when I run it on a dark image I get +/- .3 where a light image I get roughly +/- .8

In my case imaged below 45 threshold were considered dark..
Try to play with image sizes and Percentage of circles
In this code is 3% distance between circles try to have 1% for a better precision

In my case imaged below 45 threshold were considered dark..
Try to play with image sizes and Percentage of circles
In this code is 3% distance between circles try to have 1% for a better precision

so what is the number representative of... I understand brightness but what is it specifically? whats it comparing it to? and circles? what do you mean by circles? and if I use PIL and manually set the brightness of an image to .5 that's saying set it to 50% of original brightness, however, I want to match the brightness of another image, will I be able to literally set the second image to the result of this code? or is that the wrong number?

This code gives average brightness level of an image, those circles are indicating that we are picking 3x3 matrix segment of image from that part and finding the brightness and we are doing it for each segment i.e each circles and at the end we are finding average out of them.
There is no absolute value for brightness or darkness higher the value more brighter the image

Does anyone know the motivation for the implementation? why does it subtract from the length/range of the histogram?