CODEWITHSUNDEEP
pythonpython-imaging-library
Richard Knop
Richard Knop

Reputation: 83695

How to loop all image pixels and tell whether they are black or white

I have a simple black and white only gif image (400x400px let's say).

I need to get all pixels from that image and find whether they are black or white. I need to create a dictionary with the information about the pixels and their colors then.

I'm pretty new to python so I am kinda struggling with this. But here goes my script so far:

#!/usr/bin/env python

import os
import Image

os.chdir("D:/python-projects")
aImage = Image.open("input.gif")

aPixelsBlackOrWhiteDictionary = {}
# now I need to fill the dictionary with values such as
# "X,Y": 0
# "X,Y": 1
# where X,Y are coordinates and 0/1 i the pixel color (b/w)

Basically I want the final dictionary to be something like this:

"0,0" : 0 # pixel with X=0,Y=0 coordinates is black
"1,0" : 1 # pixel with X=1,Y=0 coordinates is White

EDIT:

When I try:

print aImage[0, 0]

I get an error:

Traceback (most recent call last):
  File "D:\python-projects\backprop.py", line 15, in <module>
    print aImage[0, 0]
  File "C:\Python26\lib\site-packages\pil-1.1.7-py2.6-win32.egg\Image.py", line
512, in __getattr__
    raise AttributeError(name)
AttributeError: __getitem__

Upvotes: 7

Views: 28184

Answers (5)

Thiago Druciaki
Thiago Druciaki

Reputation: 1

If you can ensure that your image is in black&white mode, you may do:

aPixelsBlackOrWhiteDictionary = {}
for y in range(0,aImage.size[1]):
    for x in range(0,aImage.size[0]):
        aPixelsBlackOrWhiteDictionary[ (x,y) ] = aImage.getpixel( (x,y) )

This uses the getpixel mentioned in other answers and the key of your dictionary will be the tuple (x,y)

print aPixelsBlackOrWhiteDictionary
{(0, 1): 1, (1, 2): 1, (3, 2): 0, (0, 0): 0, (3, 3): 1, (3, 0): 0, (3, 1): 1, (2, 1): 0, (0, 2): 0, (2, 0): 1, (1, 3): 0, (2, 3): 0, (2, 2): 1, (1, 0): 1, (0, 3): 1, (1, 1): 0}

verify that getpixel is returning ones and zeros

Upvotes: 0

Brian
Brian

Reputation: 25834

You should be using getpixel rather than using indexing operators. Note that this may be very slow. You would be better off using getdata, which returns all of pixels as a sequence.

See http://effbot.org/imagingbook/image.htm .

Upvotes: 9

Dantalion
Dantalion

Reputation: 343

If you wanted to see if a thumb was mono you could try this:-

def is_mono(image, variance=5):
    img_dta = list(im.getdata())   
    colour_test = lambda r,g,b : abs(r-g) > variance or abs(g-b) > variance
    if any([colour_test(r,g,b) for (r,g,b) in img_dta]):  return False
    return True

url1 = 'http://farm5.static.flickr.com/4145/5090947066_0d9d45edf4_s.jpg' # Mono
url2 = 'http://farm5.static.flickr.com/4087/5090362043_03c2da75d4_s.jpg' # Colour
for url in (url1, url2):
    dta = urllib.urlopen(url).read()
    im = Image.open(StringIO(dta))
    print is_mono(im)

>

True
False

Upvotes: 1

Paulo Scardine
Paulo Scardine

Reputation: 77271

Try:

pix = aImage.load()
print pix[x, y]

Also note that you can use tuples as dictionary keys, you can use mydict[(x, y)] instead of mydict["x,y"].

This pixel information is already stored in the image, why store it in a dict?

Upvotes: 8

SamB
SamB

Reputation: 9224

Are you sure you want to do that? It would be horrendously inefficient to use a dictionary to store this data.

I would think a numpy array would be much more appropriate...

Upvotes: -1

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