Finding the brightness of an image using pygame

[Zman350x]

As part of my science fair, I need to order images by brightness, so I created this bit of code below:

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#imports   import pygame from pygame.locals import * pygame.init()   #images to test for brightness   TESTS = [ pygame.image.load("T1-0.png"), pygame.image.load("T1-1.png"), pygame.image.load("T1-2.png"), pygame.image.load("T1-3.png"), pygame.image.load("T2-0.png"), pygame.image.load("T2-1.png"), pygame.image.load("T2-2.png"), pygame.image.load("T2-3.png"), pygame.image.load("T3-0.png"), pygame.image.load("T3-1.png"), pygame.image.load("T3-2.png"), pygame.image.load("T3-3.png")]   #testing loop   for image in TESTS:       #set up display       screen = pygame.display.set_mode((image.get_width(),image.get_height()))     screen.blit(image,(0,0))     pygame.display.update()       #reset value       value = []       #loop to test each pixel       for x in range(image.get_width()):         for y in range(image.get_height()):               #find brightness               color = screen.get_at((x, y))             color = (color[0]+color[1]+color[2])/3               #add brightness to the value of the image               value.append(color)       #average the value of the image and display it to user       print(sum(value)/len(value))   #end program   pygame.quit() quit()

The premise behind it is that it blits an image to the screen and then goes pixel by pixel and finds the "brightness". It does this by averaging the RGB values (A white pixel would return 255, while a black would return 0). It then puts all those values in a list and averages that out. For whatever reason, one image, which is visibly brighter than another, outputs a lower score. Why? Is there a bug in my code? Or do I need to scrap it and re-write the whole thing?

Please reply ASAP, the Science Fair is due Friday (I may or may not have procrastinated).

[metulburr]

It can actually be shorter using PIL/Pillow

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from PIL import Image, ImageStat   def brightness_level(ifile):    im = Image.open(ifile).convert('L')    stat = ImageStat.Stat(im)    return stat.mean[0]   images = [ 'img1.jpg', 'img2.jpg', 'img3.jpg', 'img4.jpg', 'img5.jpg', 'img6.jpg' ]     for i in images:     print('{} is {}'.format(i, brightness_level(i)))

Output:
img1.jpg is 37.026747637272514
img2.jpg is 40.700101538701865
img3.jpg is 33.871631648832306
img4.jpg is 10.251659915123456
img5.jpg is 102.22194878472222
img6.jpg is 213.753125

   
Although you would have to upload the images you were using to test if it came up with the same results as pygame.

Variations...


Convert image to greyscale, return average pixel brightness.

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def brightness( im_file ):    im = Image.open(im_file).convert('L')    stat = ImageStat.Stat(im)    return stat.mean[0]

Convert image to greyscale, return RMS pixel brightness.

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def brightness( im_file ):    im = Image.open(im_file).convert('L')    stat = ImageStat.Stat(im)    return stat.rms[0]

Average pixels, then transform to "perceived brightness".

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def brightness( im_file ):    im = Image.open(im_file)    stat = ImageStat.Stat(im)    r,g,b = stat.mean    return math.sqrt(0.241*(r**2) + 0.691*(g**2) + 0.068*(b**2))

RMS of pixels, then transform to "perceived brightness".

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def brightness( im_file ):    im = Image.open(im_file)    stat = ImageStat.Stat(im)    r,g,b = stat.rms    return math.sqrt(0.241*(r**2) + 0.691*(g**2) + 0.068*(b**2))

Calculate "perceived brightness" of pixels, then return average.

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def brightness( im_file ):    im = Image.open(im_file)    stat = ImageStat.Stat(im)    gs = (math.sqrt(0.241*(r**2) + 0.691*(g**2) + 0.068*(b**2))          for r,g,b in im.getdata())    return sum(gs)/stat.count[0]

[Zman350x]

K, thanks