# 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 urllib.request import urlopen
    >>> from wand.image import Image
    >>> f = urlopen('http://pbs.twimg.com/profile_images/712673855341367296/WY6aLbBV_normal.jpg')
    >>> 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.

See also

ImageMagick Resize Filters

  Demonstrates the results of resampling three images using the various resize filters and blur settings available in ImageMagick, and the file size of the resulting thumbnail images.

`Image.resize()` method takes `width` and `height` of a desired size, optional `filter` (`'undefined'` by default which means IM will try to guess best one to use) and optional `blur` (default is 1). It returns nothing but resizes itself in-place.

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

## 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)

Specifying `gravity` along with `width` and `height` keyword arguments allows a simplified cropping alternative.

    >>> img.size
    (300, 300)
    >>> img.crop(width=40, height=80, gravity='center')
    >>> img.size
    (40, 80)

## Transform images

Use this function to crop and resize an 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')

See also

ImageMagick Geometry Specifications

  Cropping and resizing geometry for the `transform` method are specified according to ImageMagick’s geometry string format. The ImageMagick documentation provides more information about geometry strings.

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

Added 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.

See also

Seam carving — Wikipedia

  The article which explains what seam carving is on Wikipedia.

Note

The image `seam.jpg` used in the above example is taken by D. Sharon Pruitt and licensed under CC-BY-2.0. It can be found the original photography from Flickr.