How to Convert a PIL Image to a NumPy Array and Back?

Converting PIL Image to NumPy Array

Problem:

How can you convert a PIL Image to a NumPy array to perform faster pixel-wise transformations, and then load it back into the PIL Image after modifying the array?

Answer:

Conversion to NumPy Array:

To convert a PIL Image into a NumPy array, use the following code:

import numpy as np
from PIL import Image

pic = Image.open("foo.jpg")
pix = np.array(pic)

This will create a 3D array of shape (height, width, channels) containing pixel values.

Conversion Back to PIL Image:

To load the modified array back into the PIL Image, there are multiple ways:

1. Using Image.putdata():

Convert the array back to a sequence of tuples:

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

2. Using Image.fromarray() (PIL 1.1.6 or higher):

Simply assign the modified array to the image:

pic = Image.fromarray(pix)

Additional Notes:

• The PIL Image's getdata() method returns a flattened array, so you need to reshape it to obtain a 3D array.
• The NumPy array from np.array(pic) has the channels axis as the last dimension, while the getdata() method assumes the channels axis as the first dimension.
• The Image.fromarray() method provides a faster conversion, especially for large images.

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