Convert black and white array into an image in python?

Question

I have an array of 50x50 elements of which each is either True or False - this represents a 50x50 black and white image.

I can't convert this into image? I've tried countless different functions and none of them work.

import numpy as np
from PIL import Image

my_array = np.array([[True,False,False,False THE DATA IS IN THIS ARRAY OF 2500 elements]])

im = Image.fromarray(my_array)

im.save("results.jpg")

^ This one gives me: "Cannot handle this data type".

I've seen that PIL has some functions but they only convert a list of RGB pixels and I have a simple black and white array without the other channels.

To clarify: If you have an array [True, False] then you want that to represent two pixels, one being black and the other white? — matt
– matt, Commented Apr 7, 2014 at 1:10
If the value is True - it means white pixel if it's False it's a black pixel. So each element corresponds to just one pixel. That's why I have just 2500 elements for each 50x50 image. — user3010273
– user3010273, Commented Apr 7, 2014 at 1:11
And you just have one numpy array of length 2500? In other words, it's a 2500x1 array and not a 50x50 array? — matt
– matt, Commented Apr 7, 2014 at 1:14
I have 50x50 array. 50 elements of 50 pixels - of which one element is one row. I can't seem to convert this into a simple 50x50 image. — user3010273
– user3010273, Commented Apr 7, 2014 at 1:16

askewchan · Accepted Answer · 2014-04-07 02:06:54Z

15

First you should make your array 50x50 instead of a 1d array:

my_array = my_array.reshape((50, 50))

Then, to get a standard 8bit image, you should use an unsigned 8-bit integer dtype:

my_array = my_array.reshape((50, 50)).astype('uint8')

But you don't want the Trues to be 1, you want them to be 255:

my_array = my_array.reshape((50, 50)).astype('uint8')*255

Finally, you can convert to a PIL image:

im = Image.fromarray(my_array)

I'd do it all at once like this:

im = Image.fromarray(my_array.reshape((50,50)).astype('uint8')*255)

edited Apr 7, 2014 at 2:06

answered Apr 7, 2014 at 1:17

askewchan

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13 Comments

askewchan Over a year ago

This assumes that your array has 50 * 50 = 2500 elements. What is my_array.shape?

askewchan Over a year ago

Oh I see, somehow your array is not a uniform array, but is a like an array of arrays. How do you create your array? What is my_array[0].dtype?

user3010273 Over a year ago

my_array[0].dtype shows Attribute Error: 'list' has no attribute dtype, I deleted one pair of outer parenthesis and I think it might have been causing some of the problems. But when I run your solution on this modified array I get: Value Error: only 2 non-keyword arguments accepted.

askewchan Over a year ago

Is my_array.dtype now bool?

askewchan Over a year ago

Oh, they are 0 and 1 and jpeg runs 0 to 255. Try multiplying the array by 255 :P

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