Fixed CenterCropPad incorrectly using fill value for the mask

[iRyoka]

Summary by Sourcery

Fix the issue with CenterCropPad incorrectly using the fill value for the mask and add a corresponding test to ensure correct behavior.

Bug Fixes:

• Fix CenterCropPad to correctly use the fill value for the mask during padding operations.

Tests:

• Add a test to verify that BaseCropAndPad uses the correct fill values for constant borders in images and masks.

[sourcery-ai]

Reviewer's Guide by Sourcery

This PR fixes a bug in the CenterCropPad transformation where the fill value for masks was not being properly applied. The implementation adds a new apply_to_mask method to handle mask padding with the correct fill value and includes tests to verify the behavior.

Class diagram for CenterCropPad changes

classDiagram
    class CenterCropPad {
        +apply(img, crop_coords, **params)
        +apply_to_mask(mask, crop_coords, **params)
        +apply_to_bboxes(bboxes, **params)
    }
    class BaseCrop {
        +apply(self, mask, crop_coords, **params)
    }
    CenterCropPad --|> BaseCrop
    note for CenterCropPad "apply_to_mask method added to handle mask padding with correct fill value"

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File-Level Changes

Change	Details	Files
Added dedicated mask handling in BaseCropAndPad	Implemented apply_to_mask method to handle mask padding separately from image padding Used fill_mask value for mask padding instead of the image fill value Prevented double padding by calling BaseCrop.apply directly	albumentations/augmentations/crops/transforms.py
Added test cases for fill value behavior	Created test to verify correct fill values for both image and mask padding Added test case for default fill_mask value Verified padding behavior with different fill values for image and mask	tests/test_crop.py

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[sourcery-ai]

Hey @iRyoka - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[iRyoka]

A minimal example to reprodice the addressed problem it:

import albumentations as A
import numpy as np

c = A.CenterCrop(
    4, 
    3,
    pad_if_needed = True,
    fill = 1,
    fill_mask = 2
)

out = c(image = np.zeros((1,1,3)), mask = np.zeros((1,1)))

assert 2 in out['mask'], f"Wrong padding: {np.unique(out['mask'])}"

[ternaus]

@iRyoka

Thanks, good catch!