18. Rescale, resize, and downscale

Rescale operation resizes an image by a given scaling factor. The scaling factor can either be a single floating point value, or multiple values - one along each axis.

Resize serves the same purpose, but allows to specify an output image shape instead of a scaling factor.

Note that when down-sampling an image, resize and rescale should perform Gaussian smoothing to avoid aliasing artifacts. See the anti_aliasing and anti_aliasing_sigma arguments to these functions.

Downscale serves the purpose of down-sampling an n-dimensional image by integer factors using the local mean on the elements of each block of the size factors given as a parameter to the function.

import matplotlib.pyplot as plt

from skimage import data, color
from skimage.transform import rescale, resize, downscale_local_mean

18.1. Transformations

image = color.rgb2gray(data.astronaut())

image_rescaled = rescale(image, 1.0 / 4.0, anti_aliasing=False)
image_resized = resize(image, (image.shape[0] / 4, image.shape[1] / 4),
image_downscaled = downscale_local_mean(image, (4, 3))

18.2. Show

fig, axes = plt.subplots(nrows=2, ncols=2,figsize=(8,8))

ax = axes.ravel()

ax[0].imshow(image, cmap='gray')
ax[0].set_title("Original image")

ax[1].imshow(image_rescaled, cmap='gray')
ax[1].set_title("Rescaled image (aliasing)")

ax[2].imshow(image_resized, cmap='gray')
ax[2].set_title("Resized image (no aliasing)")

ax[3].imshow(image_downscaled, cmap='gray')
ax[3].set_title("Downscaled image (no aliasing)")

ax[0].set_xlim(0, 512)
ax[0].set_ylim(512, 0)