Image processing with Python image library Pillow

We'll work on a virtual environment with Python 3.

$ virtualenv -p python3 venv3
$ source venv3/bin/activate
(venv3)$

Install the pillow library:

(venv3)$ pip install pillow

That's it.

Now, we can play with our images.

Let's open a file and display it:

>>> from PIL import Image
>>> img = Image.open('Glacier-National-Park-US.jpg')
>>> img.show()

The variable img is a Pillow object, and we can retrieve some information about the opened image:

>>> img
<PIL.JpegImagePlugin.JpegImageFile image mode=RGB size=1000x666 at 0x7F805659F7F0>
>>> img.size
(1000, 666)
>>> img.format
'JPEG'

We can convert the image from jpg to png and save it:

>>> img.save('Glacier-National-Park-US.png')

We can resize the image using thumbnail() method of Pillow:

>>> img.thumbnail((300,300))
>>> img.show()

We may want to save it:

>>> img.save('Glacier-National-Park-US-thumb.jpg')

Let's make a grayscale picture:

>>> gray_img = Image.open('Glacier-National-Park-US.jpg').convert('L')
>>> gray_img.show()

The 'L' stands for 'luminous', and we're taking luminosity values from RGB.

We may want to save it:

>>> gray_img.save('Glacier-National-Park-US-gray','png')

As a coding exercise as well as for future use, we want to create thumbnail images from the images in working directory, and place them into a subfolder.

Current directory looks like this.

Here is the code:

from PIL import Image
import os

# make subfolder
newdir = './thumb300'
if not os.path.exists(newdir):
   os.makedirs(newdir)

# thumbnail size as tuple
thumb_size = (300, 300)

files = [f for f in os.listdir('.') if os.path.isfile(f)]
for f in files:
   name, ext = f.split('.')
   # jpg only
   if ext == 'jpg':
      newname = name + '_300' + '.' + ext
      image = Image.open(f)
      image.thumbnail(thumb_size)
      image.save(os.path.join(newdir,newname))