Resizing and cropping¶

Creating thumbnails (by resizing images) and cropping are most frequent works about images. This guide explains ways to deal with sizes of images.

Above all, to get the current size of the image check width and height properties:

>>> from urllib2 import urlopen
>>> from wand.image import Image
>>> f = urlopen('http://api.twitter.com/1/users/profile_image/hongminhee')
>>> with Image(file=f) as img:
...     width = img.width
...     height = img.height
...
>>> f.close()
>>> width
48
>>> height
48

If you want the pair of (width, height), check size property also.

Note

These three properties are all readonly.

Resize images¶

It scales an image into a desired size even if the desired size is larger than the original size. ImageMagick provides so many algorithms for resizing. The constant FILTER_TYPES contains names of filtering algorithms.

Sample images¶

Although Image.resize() provides many filter options, it’s relatively slow. If speed is important for the job, you’d better use Image.sample() instead. It works in similar way to Image.resize() except it doesn’t provide filter and blur options:

>>> img.size
(500, 600)
>>> img.sample(50, 60)
>>> img.size
(50, 60)

Crop images¶

To extract a sub-rectangle from an image, use the crop() method. It crops the image in-place. Its parameters are left, top, right, bottom in order.

>>> img.size
(200, 300)
>>> img.crop(10, 20, 50, 100)
>>> img.size
(40, 80)

It can also take keyword arguments width and height. These parameters replace right and bottom.

>>> img.size
(200, 300)
>>> img.crop(10, 20, width=40, height=80)
>>> img.size
(40, 80)

There is an another way to crop images: slicing operator. You can crop an image by [left:right, top:bottom] with maintaining the original:

>>> img.size
(300, 300)
>>> with img[10:50, 20:100] as cropped:
...     print(cropped.size)
...
(40, 80)
>>> img.size
(300, 300)

Transform images¶

Use this function to crop and resize and image at the same time, using ImageMagick geometry strings. Cropping is performed first, followed by resizing.

For example, if you want to crop your image to 300x300 pixels and then scale it by 2x for a final size of 600x600 pixels, you can call:

img.transform('300x300', '200%')

Other example calls:

# crop top left corner
img.transform('50%')

# scale height to 100px and preserve aspect ratio
img.transform(resize='x100')

# if larger than 640x480, fit within box, preserving aspect ratio
img.transform(resize='640x480>')

# crop a 320x320 square starting at 160x160 from the top left
img.transform(crop='320+160+160')

Seam carving (also known as content-aware resizing)¶

New in version 0.3.0.

Seam carving is an algorithm for image resizing that functions by establishing a number of seams (paths of least importance) in an image and automatically removes seams to reduce image size or inserts seams to extend it.

In short: you can magickally resize images without distortion! See the following examples:

Original	Resized

Cropped	Seam carving

You can easily rescale images with seam carving using Wand: use Image.liquid_rescale() method:

>>> image = Image(filename='seam.jpg')
>>> image.size
(320, 234)
>>> with image.clone() as resize:
...     resize.resize(234, 234)
...     resize.save(filename='seam-resize.jpg')
...     resize.size
...
(234, 234)
>>> with image[:234, :] as crop:
...     crop.save(filename='seam-crop.jpg')
...     crop.size
...
(234, 234)
>>> with image.clone() as liquid:
...     liquid.liquid_rescale(234, 234)
...     liquid.save(filename='seam-liquid.jpg')
...     liquid.size
...
(234, 234)

Note

It may raise MissingDelegateError if your ImageMagick is configured --without-lqr option. In this case you should recompile ImageMagick.

Navigation

Resizing and cropping¶

Resize images¶

Sample images¶

Crop images¶

Transform images¶

Seam carving (also known as content-aware resizing)¶