stouputils.image.auto_crop module#

Automatically crop an image to remove zero or uniform regions.

This function crops the image to keep only the region where pixels are non-zero (or above a threshold). It can work with a mask or directly analyze the image.

Parameters:

image (Image.Image | NDArray) – The image to crop.
mask (NDArray[bool] | None) – Optional binary mask indicating regions to keep.
threshold (int | float | Callable) – Threshold value or function (default: np.min).
return_type (type | str) – Type of the return value (Image.Image, NDArray[np.number], or “same” to match input type).
contiguous (bool) – If True (default), crop to bounding box. If False, remove entire rows/columns with no content.

Returns:

The cropped image.

Return type:

Image.Image | NDArray[np.number]

Examples

>>> # Test with numpy array with zeros on edges
>>> import numpy as np
>>> array = np.zeros((100, 100, 3), dtype=np.uint8)
>>> array[20:80, 30:70] = 255  # White rectangle in center
>>> cropped = auto_crop(array, return_type=np.ndarray)
>>> cropped.shape
(60, 40, 3)

>>> # Test with custom mask
>>> mask = np.zeros((100, 100), dtype=bool)
>>> mask[10:90, 10:90] = True
>>> cropped_with_mask = auto_crop(array, mask=mask, return_type=np.ndarray)
>>> cropped_with_mask.shape
(80, 80, 3)

>>> # Test with PIL Image
>>> from PIL import Image
>>> pil_image = Image.new('RGB', (100, 100), (0, 0, 0))
>>> from PIL import ImageDraw
>>> draw = ImageDraw.Draw(pil_image)
>>> draw.rectangle([25, 25, 75, 75], fill=(255, 255, 255))
>>> cropped_pil = auto_crop(pil_image)
>>> cropped_pil.size
(51, 51)

>>> # Test with threshold
>>> array_gray = np.ones((100, 100), dtype=np.uint8) * 10
>>> array_gray[20:80, 30:70] = 255
>>> cropped_threshold = auto_crop(array_gray, threshold=50, return_type=np.ndarray)
>>> cropped_threshold.shape
(60, 40)

>>> # Test with callable threshold (using lambda to avoid min value)
>>> array_gray2 = np.ones((100, 100), dtype=np.uint8) * 10
>>> array_gray2[20:80, 30:70] = 255
>>> cropped_max = auto_crop(array_gray2, threshold=lambda x: 50, return_type=np.ndarray)
>>> cropped_max.shape
(60, 40)

>>> # Test with non-contiguous crop
>>> array_sparse = np.zeros((100, 100, 3), dtype=np.uint8)
>>> array_sparse[10, 10] = 255
>>> array_sparse[50, 50] = 255
>>> array_sparse[90, 90] = 255
>>> cropped_contiguous = auto_crop(array_sparse, contiguous=True, return_type=np.ndarray)
>>> cropped_contiguous.shape  # Bounding box from (10,10) to (90,90)
(81, 81, 3)
>>> cropped_non_contiguous = auto_crop(array_sparse, contiguous=False, return_type=np.ndarray)
>>> cropped_non_contiguous.shape  # Only rows/cols 10, 50, 90
(3, 3, 3)

>>> # Test with 3D crop on depth dimension
>>> array_3d = np.zeros((50, 50, 10), dtype=np.uint8)
>>> array_3d[10:40, 10:40, 2:8] = 255  # Content only in depth slices 2-7
>>> cropped_3d = auto_crop(array_3d, contiguous=True, return_type=np.ndarray)
>>> cropped_3d.shape  # Should crop all 3 dimensions
(30, 30, 6)