PIL cannot write mode F to jpeg

Question

I am taking a jpg image and using numpy's fft2 to create/save a new image. However it throws this error

"IOError: cannot write mode F as JPEG"

Is there an issue with CMYK and JPEG files in PIL???

p = Image.open('kibera.jpg')
bw_p = p.convert('L')
array_p = numpy.asarray(bw_p)
fft_p = abs(numpy.fft.rfft2(array_p))
new_p = Image.fromarray(fft_p)
new_p.save('kibera0.jpg')
new_p.histogram()

score 80 · Answer 1 · answered Sep 18 '13 at 18:13

80

Try convert the image to RGB:

...
new_p = Image.fromarray(fft_p)
if new_p.mode != 'RGB':
    new_p = new_p.convert('RGB')
...

answered Sep 18 '13 at 18:13

semente

7,265
3
34
35

17

What if an image is in grayscale? – cerebrou Dec 14 '16 at 07:05
10

Bump, what if I want to save as grayscale? – Hakaishin Jul 02 '17 at 04:29
4

Just use this. It works just fine with grayscale as well. – Zeroth Sep 07 '17 at 02:42

score 50 · Answer 2 · answered Aug 18 '18 at 14:28

50

Semente's answer is right for color images For grayscale images you can use below:-

new_p = Image.fromarray(fft_p)
new_p = new_p.convert("L")

If you use new_p = new_p.convert('RGB') for a grayscale image then the image will still have 24 bit depth instead of 8 bit and would occupy thrice the size on hard disk and it wont be a true grayscale image.

answered Aug 18 '18 at 14:28

Himanshu Punetha

699
7
7

2

More info on convert here: https://pillow.readthedocs.io/en/stable/reference/Image.html#PIL.Image.Image.convert – Aaron Swan Apr 06 '19 at 00:34

score 19 · Answer 3 · answered Feb 01 '20 at 04:54

19

I think it may be that your fft_p array is in float type and the image should have every pixel in the format 0-255 (which is uint8), so maybe you can try doing this before creating the image from array:

fft_p = fft_p.astype(np.uint8)
new_p = Image.fromarray(fft_p)

But be aware that every element in the fft_p array should be in the 0-255 range, so maybe you would need to do some processing to that before to get the desired results, for example if you every element is a float between 0 and 1 you can multiply them by 255.

answered Feb 01 '20 at 04:54

xhenryx14

704
6
10

This is the true answer because it does not changing the actual value of the numpy array (just the type format). – Muhammad Yasirroni Jun 30 '21 at 00:49
Very useful hint that it should be `uint8`. I was trying to preview the mnist grayscale data on jupyter and encountered this issue. The correct code should be like `Image.fromarray((mnist_images[0]*255).astype(np.uint8)) – Kassian Sun Jul 16 '21 at 06:52

score 0 · Answer 4 · edited Oct 11 '22 at 17:09

0

def save_img(img, path):

    img = Image.fromarray(img)

    img.save(path)

raise OSError(f"cannot write mode {mode} as PNG") from e

OSError: cannot write mode F as PNG

Here the meaning of mode F is the floating point value in the image. So please convert the floating point image to the uint8 image before saving.

image.astype(np.uint8)

edited Oct 11 '22 at 17:09

Tyler2P

2,324
26
22
31

answered Oct 06 '22 at 07:13

ravindra soni

1
2

Aneesh R P · Answer 5 · 2022-10-20T10:56:37.050

0

If you are working with PyTorch

import torchvision.transforms as T
    
        
transform=T.ToPILImage()
imt=transform(img)

edited Oct 20 '22 at 10:56

answered Oct 20 '22 at 10:47

Aneesh R P

69
3

1

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Oct 27 '22 at 07:27

PIL cannot write mode F to jpeg

5 Answers5