[docs]def center_crop(img, size, return_param=False, copy=False):
"""Center crop an image by `size`.
An image is cropped to :obj:`size`. The center of the output image
and the center of the input image are same.
Args:
img (~numpy.ndarray): An image array to be cropped. This is in
CHW format.
size (tuple): The size of output image after cropping.
This value is :math:`(height, width)`.
return_param (bool): If :obj:`True`, this function returns information
of slices.
copy (bool): If :obj:`False`, a view of :obj:`img` is returned.
Returns:
~numpy.ndarray or (~numpy.ndarray, dict):
If :obj:`return_param = False`,
returns an array :obj:`out_img` that is cropped from the input
array.
If :obj:`return_param = True`,
returns a tuple whose elements are :obj:`out_img, param`.
:obj:`param` is a dictionary of intermediate parameters whose
contents are listed below with key, value-type and the description
of the value.
* **y_slice** (*slice*): A slice used to crop the input image.\
The relation below holds together with :obj:`x_slice`.
* **x_slice** (*slice*): Similar to :obj:`y_slice`.
.. code::
out_img = img[:, y_slice, x_slice]
"""
_, H, W = img.shape
oH, oW = size
if oH > H or oW > W:
raise ValueError('shape of image needs to be larger than size')
y_offset = int(round((H - oH) / 2.))
x_offset = int(round((W - oW) / 2.))
y_slice = slice(y_offset, y_offset + oH)
x_slice = slice(x_offset, x_offset + oW)
img = img[:, y_slice, x_slice]
if copy:
img = img.copy()
if return_param:
return img, {'y_slice': y_slice, 'x_slice': x_slice}
else:
return img