How to convert a PIL Image into a numpy array?

问题:

Alright, I\'m toying around with converting a PIL image object back and forth to a numpy array so I can do some faster pixel by pixel transformations than PIL\'s PixelAccess object would allow. I\'ve figured out how to place the pixel information in a useful 3D numpy array by way of:

pic = Image.open(\"foo.jpg\")
pix = numpy.array(pic.getdata()).reshape(pic.size[0], pic.size[1], 3)

But I can\'t seem to figure out how to load it back into the PIL object after I\'ve done all my awesome transforms. I\'m aware of the putdata() method, but can\'t quite seem to get it to behave.

回答1:

You\'re not saying how exactly putdata() is not behaving. I\'m assuming you\'re doing

>>> pic.putdata(a)
Traceback (most recent call last):
  File \"...blablabla.../PIL/Image.py\", line 1185, in putdata
    self.im.putdata(data, scale, offset)
SystemError: new style getargs format but argument is not a tuple

This is because putdata expects a sequence of tuples and you\'re giving it a numpy array. This

>>> data = list(tuple(pixel) for pixel in pix)
>>> pic.putdata(data)

will work but it is very slow.

As of PIL 1.1.6, the \"proper\" way to convert between images and numpy arrays is simply

>>> pix = numpy.array(pic)

although the resulting array is in a different format than yours (3-d array or rows/columns/rgb in this case).

Then, after you make your changes to the array, you should be able to do either pic.putdata(pix) or create a new image with Image.fromarray(pix).

回答2:

Open I as an array:

>>> I = numpy.asarray(PIL.Image.open(\'test.jpg\'))

Do some stuff to I, then, convert it back to an image:

>>> im = PIL.Image.fromarray(numpy.uint8(I))

Filter numpy images with FFT, Python

If you want to do it explicitly for some reason, there are pil2array() and array2pil() functions using getdata() on this page in correlation.zip.

回答3:

I am using Pillow 4.1.1 (the successor of PIL) in Python 3.5. The conversion between Pillow and numpy is straightforward.

from PIL import Image
import numpy as np
im = Image.open(\'1.jpg\')
im2arr = np.array(im) # im2arr.shape: height x width x channel
arr2im = Image.fromarray(im2arr)

One thing that needs noticing is that Pillow-style im is column-major while numpy-style im2arr is row-major. However, the function Image.fromarray already takes this into consideration. That is, arr2im.size == im.size and arr2im.mode == im.mode in the above example.

We should take care of the HxWxC data format when processing the transformed numpy arrays, e.g. do the transform im2arr = np.rollaxis(im2arr, 2, 0) or im2arr = np.transpose(im2arr, (2, 0, 1)) into CxHxW format.

回答4:

You need to convert your image to a numpy array this way:

import numpy
import PIL

img = PIL.Image.open(\"foo.jpg\").convert(\"L\")
imgarr = numpy.array(img) 

回答5:

The example, I have used today:

import PIL
import numpy
from PIL import Image

def resize_image(numpy_array_image, new_height):
    # convert nympy array image to PIL.Image
    image = Image.fromarray(numpy.uint8(numpy_array_image))
    old_width = float(image.size[0])
    old_height = float(image.size[1])
    ratio = float( new_height / old_height)
    new_width = int(old_width * ratio)
    image = image.resize((new_width, new_height), PIL.Image.ANTIALIAS)
    # convert PIL.Image into nympy array back again
    return array(image)