Argthtjtr

I'm doing some prototype code for a project. I'm using Pillow to open the image and other minor things, but I want to invert the image manually using its pixel values. I used two's complement in hopes of inverting it. However, when I display the final image, it's a solid grey square instead of inverted colors. I just used a picture of a possum, 275 pixels by 183 pixels. Any idea why it displays grey block and not an inverted image?

#importing Image module



from PIL import Image

import numpy

#sets numpy to print out full array

numpy.set_printoptions(threshold=numpy.inf)





def twos_comp(val, bits):

    """compute the 2's complement of int value val"""

    if (val & (1 << (bits - 1))) != 0: # if sign bit is set e.g., 8bit: 128-255

    val = val - (1 << bits)        # compute negative value

return val





im = Image.open('possum.jpg')

#im.show()



data = numpy.asarray(im)

#print(data)

#print("FINISHED PRINTING")



#print('NOW PRINTING BINARY')

data_binary = numpy.unpackbits(data)

data_binary.ravel()



#print(data_binary)



#print('FINISHED PRINTING')



#getting string of binary array

binaryString = numpy.array2string(data_binary)

binaryString = ''.join(binaryString.split())

binaryString = binaryString[:-1]

binaryString = binaryString[1:]



#print("Binary String: " + binaryString)



out = twos_comp(int(binaryString,2), len(binaryString))



#print('Now printing twos:')

#print(out)





#formatting non-binary two's comp as binary

outBinary = "{0:b}".format(out)

#print('Now printing binary twos: ' + outBinary)





outBinary = outBinary.encode('utf-8')



a_pil_image = Image.frombytes('RGB', (275, 183), outBinary)



a_pil_image.show()

You can invert quite simply with PIL/Pillow:

from PIL import Image, ImageChops



# Load image from disk and ensure RGB

im = Image.open('lena.png').convert('RGB')



# Invert image and save to disk

res = ImageChops.invert(im)

res.save('result.png')

Turns Lena into negated Lena:

Or, if you want to be more mathematical about it:

from PIL import Image                                                                       

import numpy as np                                                                          



im = Image.open('lena.png').convert('RGB')                                                    



# Make Numpy array

imnp = np.array(im)                                                                         

# Invert

imnp = 255 - imnp                                                                           

# Save

Image.fromarray(imnp).save('result.png') 

If you imagine a black image is represented by (0,0,0) and a white image by (255,255,255), it is hopefully not hard to see that inversion of colours is achieved by subtracting from 255 rather than using two's complement.