Manipulating images

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Python image library

• Image

Introduction to Image Manipulation

• Image manipulation involves altering or transforming images using various techniques and tools.
• This can include resizing, cropping, rotating, adjusting colours, and applying filters.

Loading Images

• To manipulate images, we first need to load them into our environment.
• In Python, we can use the PIL (also called Pillow) module from Image.
• Note we are using imshow() now and not just show().

images.py

from PIL import Image

import matplotlib.pyplot as plt

img_1 = Image.open('hand-x-ray.jpg')

plt.imshow(img_1)

plt.show()

Loading Images

• You will also need to use the pyplot module.

images.py

from PIL import Image

import matplotlib.pyplot as plt

img_1 = Image.open('hand-x-ray.jpg')

plt.imshow(img_1)

plt.show()

Loading Images

• And then open the image file.

images.py

from PIL import Image

import matplotlib.pyplot as plt

img_1 = Image.open('hand-x-ray.jpg')

plt.imshow(img_1)

plt.show()

Loading Images

• And then prepare to show the image and then actually show it.

images.py

from PIL import Image

import matplotlib.pyplot as plt

img_1 = Image.open('hand-x-ray.jpg')

plt.imshow(img_1)

plt.show()

Resizing Images

• To resize an image, you can use the resize method from the PIL library.
• img_1.resize((width, height)) needs a tuple with the new width and height.
• This stretches or compresses the image.

resize.py

resized_img_1 = img_1.resize((50, 300))

plt.imshow(resized_img_1)
plt.show()

Cropping Images

• Define the top-left and bottom-right coordinates of the area you want to crop.
• Then use the crop method from the PIL library.
• This uses pixel coordinates.
• The top-left corner is (0, 0).
• Coordinates are (new_top_left_x, new_top_left_y, new_bottom_right_x, new_bottom_right_y).

crop.py

box = (3900, 2900, 6000, 5500)

cropped_img_1 = img_1.crop(box)

Rotate Images

• Use the rotate method from the PIL library to rotate an image.
• Just provide an angle in degrees.

rotate.py

rotated_img_2 = img_2.rotate(10)

Inverting Images

• Here we can invert the colours of an image.
• Use the invert method.

rotate.py

from PIL import ImageOps

inverted_img_3 = ImageOps.invert(img_3)

Change file type

• Specify the new file type in the name and then,
• Use the save method from the PIL library to save the image in a different format.

rotate.py

bmp_filename = 'converted_image_3.bmp'

img_4.save(bmp_filename)

Now try it yourself!

• Go to the Lesson 4 folder.
• Open lesson_4.ipynb.
• Don’t forget to ask your tutor if you need help.
• See you in 20 minutes.

If you finish lesson 4 (but no need to rush), you can try your hand at lesson 5.

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