How can I save an image with PIL?

Question

I have just done some image processing using the Python image library (PIL) using a post I found earlier to perform fourier transforms of images and I can’t get the save function to work. The whole code works fine but it just wont save the resulting image:

from PIL import Image
import numpy as np

i = Image.open("C:/Users/User/Desktop/mesh.bmp")
i = i.convert("L")
a = np.asarray(i)
b = np.abs(np.fft.rfft2(a))
j = Image.fromarray(b)
j.save("C:/Users/User/Desktop/mesh_trans",".bmp")

The error I get is the following:

save_handler = SAVE[string.upper(format)] # unknown format
    KeyError: '.BMP'

How can I save an image with Pythons PIL?

Asked By: user1999274

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Source

Answer 1

Try removing the . before the .bmp (it isn’t matching BMP as expected). As you can see from the error, the save_handler is upper-casing the format you provided and then looking for a match in SAVE. However the corresponding key in that object is BMP (instead of .BMP).

I don’t know a great deal about PIL, but from some quick searching around it seems that it is a problem with the mode of the image. Changing the definition of j to:

j = Image.fromarray(b, mode='RGB')

Seemed to work for me (however note that I have very little knowledge of PIL, so I would suggest using @mmgp’s solution as s/he clearly knows what they are doing 🙂 ). For the types of mode, I used this page – hopefully one of the choices there will work for you.

Answered By: RocketDonkey

Answer 2

You should be able to simply let PIL get the filetype from extension, i.e. use:

j.save("C:/Users/User/Desktop/mesh_trans.bmp")

Answered By: wim

Answer 3

The error regarding the file extension has been handled, you either use BMP (without the dot) or pass the output name with the extension already. Now to handle the error you need to properly modify your data in the frequency domain to be saved as an integer image, PIL is telling you that it doesn’t accept float data to save as BMP.

Here is a suggestion (with other minor modifications, like using fftshift and numpy.array instead of numpy.asarray) for doing the conversion for proper visualization:

import sys
import numpy
from PIL import Image

img = Image.open(sys.argv[1]).convert('L')

im = numpy.array(img)
fft_mag = numpy.abs(numpy.fft.fftshift(numpy.fft.fft2(im)))

visual = numpy.log(fft_mag)
visual = (visual - visual.min()) / (visual.max() - visual.min())

result = Image.fromarray((visual * 255).astype(numpy.uint8))
result.save('out.bmp')

Answered By: mmgp

Answer 4

I know that this is old, but I’ve found that (while using Pillow) opening the file by using open(fp, 'w') and then saving the file will work. E.g:

with open(fp, 'w') as f:
    result.save(f)

fp being the file path, of course.

Answered By: Code Enjoyer

Answer 5

Here is what I did to import and then export an bmp image with PIL.

def read_img(path):
   """
   Read image and store it as an array, given the image path. 
   Returns the 3 dimensional image array.
   """
   img = Image.open(path)
   img_arr = np.array(img, dtype='int32')
   img.close()
   return img_arr


def write_image(arr, filename):
   """
   write the image
   input : 3 dimensional array
   """
   path = "output/" + filename + ".bmp"
   arr = arr.astype(dtype='uint8')
   img = Image.fromarray(arr, 'RGB')
   img.save(path)

Answered By: Aaron C

How can I save an image with PIL?

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