safe_padded_read¶

safe_padded_read(image, bounds, stride=1, padding=0, pad_mode='constant', pad_constant_values=0, pad_kwargs=None)[source]¶

Read a region of a numpy array with padding applied to edges.

Safely ‘read’ regions, even outside the image bounds. Accepts integer bounds only.

Regions outside the source image are padded using any of the pad modes available in numpy.pad().

Note that padding of the output is not guaranteed to be integer/pixel aligned if using a stride != 1.

Illustration for reading a region with negative coordinates using zero padding and reflection padding.
Parameters:

  • image (numpy.ndarray or glymur.Jp2k) – Input image to read from.

  • bounds (tuple(int)) – Bounds of the region in (left, top, right, bottom) format.

  • stride (int or tuple(int)) – Stride when reading from img. Defaults to 1. A tuple is interpreted as stride in x and y (axis 1 and 0 respectively). Also applies to padding.

  • padding (int or tuple(int)) – Padding to apply to each bound. Default to 0.

  • pad_mode (str) – Method for padding when reading areas outside the input image. Default is constant (0 padding). Possible values are: constant, reflect, wrap, symmetric. See numpy.pad() for more.

  • pad_constant_values (int, tuple(int)) – Constant values to use when padding with constant pad mode. Passed to the numpy.pad() constant_values argument. Default is 0.

  • pad_kwargs (dict) – Arbitrary keyword arguments passed through to the padding function numpy.pad().

Returns:

Padded image region.

Return type:

numpy.ndarray

Raises:

  • ValueError – Bounds must be integers.

  • ValueError – Padding can’t be negative.

Examples

>>> bounds = (-5, -5, 5, 5)
>>> safe_padded_read(img, bounds)

>>> bounds = (-5, -5, 5, 5)
>>> safe_padded_read(img, bounds, pad_mode="reflect")

>>> bounds = (1, 1, 6, 6)
>>> safe_padded_read(img, bounds, padding=2, pad_mode="reflect")