How it is possible that Gimp while exporting histogram counts more pixels than there

[niitard]

Hello,

I'm currently learning programming in python, one of subject that i'm trying to cover now is working with image.  So i wanted to created o program that's counting how many pixel of each colour is in my image (which is 10x10 pixel gray scale). So i created the image all black with 24 white pixel and my program, all works well. It counts 24 pixel of "255" and 76 of "0.

But here comes the problem:

when i have used the Gimp [color] -> [information] -> [export histogram] to file i got the results like this

Range start,Value

0 , 76.0

1 , 0.0

2 , 0.0
[...]

253 , 0.0

254 , 24.0

255 , 24.0


it looks like, the Gimp software counted white pixel two times, so when they are summed up that makes 24 + 24 + 76 = 124 , and yet the picture size is still 10x10  = 100

i've searched the internet but cant find the clue:
How it is possible that Gimp while exporting histogram counts more pixels than there are really in the picture?

Thank you for help

[Ofnuts]

Yes, likely a bug, nice finding.

Didn't see you code, but if you access each pixel in turn using get_pixel(), you code will not scale to real-life images. In Python your can use "pixel regions", which is a nbig array-like structure that you can access in Python (it even supports slices).

[niitard]

(06-12-2020, 03:40 PM)Ofnuts Wrote: Yes, likely a bug, nice finding.

Didn't see you code, but if you access each pixel in turn using get_pixel(), you code will not scale to real-life images. In Python your can use "pixel regions", which is a nbig array-like structure that you can access in Python (it even supports slices).

from PIL import Image
import numpy as np

img = Image.open('start.bmp')

arr=np.array(img)
print (arr)

#im still learning arrays so i changed it to list that im more familiar with

b=arr.tolist()

print ()

flat_list=[]

for sublist in b:
    for item in sublist:
        flat_list.append(item)




white_dots=0
black_dots=0

for i in flat_list:
    if i == 255:
        white_dots+=1
    if i == 0:
        black_dots+=1

print ('number 255: ', white_dots)
print ('number 0: ', black_dots)


thats my code 
thank you very much

[Ofnuts]

Oh, I thought you where doing a Python Gimp script...

You may be more familiar with lists, but the numpy array is much faster. Not as bad as a Gimp get_pixel() but for real-size images numpy will make a very significant difference.

[niitard]

(06-12-2020, 04:16 PM)Ofnuts Wrote: Oh, I thought you where doing a Python Gimp script...

You may be more familiar with lists, but the numpy array is much faster. Not as bad as a Gimp get_pixel() but for real-size images numpy will make a very significant difference.

Thank you