albucore-conventions

name	albucore-conventions
description	Albucore image processing conventions - shapes (H,W,C), dtypes (uint8/float32), benchmark-driven backend routing (OpenCV, NumPy, LUT, NumKong), tests, and lockfile discipline. Use when implementing or modifying albucore modules, writing tests, or reviewing image-processing code. Use when this capability is needed.
metadata	{"author":"albumentations-team"}

Albucore Conventions

When to Apply

• Implementing or changing code under albucore/.
• Adding or modifying tests.
• Reviewing image-processing code.
• Answering questions about shapes, dtypes, backend choice, or dependency lock consistency.

Critical Rules

1. Image Shapes - Always Explicit Channel Dimension

# Correct
grayscale = (H, W, 1)
rgb = (H, W, 3)
batch = (N, H, W, C)
volume = (D, H, W, C)
batch_volumes = (N, D, H, W, C)

# Wrong - never use implicit channels
gray = (H, W)
gray_vol = (D, H, W)

Dimension indexing is always:

num_channels = image.shape[-1]
width = image.shape[-2]
height = image.shape[-3]

2. Supported Dtypes - uint8 and float32 Only

No float64 in public paths. Raise ValueError for unsupported dtypes.

3. Backend Routing - Benchmark-Driven Only

• Do not assume LUT is fastest for uint8; benchmark.
• NumKong is used where benchmarks win (blend, moments, scale, cdist, etc.); see docs/numkong-performance.md.
• OpenCV has a 4-channel limit for many ops. Use MAX_OPENCV_WORKING_CHANNELS, then fall back to NumPy or chunking for more channels.
• Route from benchmark evidence in benchmarks/ and docs/numkong-performance.md, not convention.

4. OpenCV LUT - Source vs Table Dtype

• cv2.LUT source image: for uint8 LUT paths, pass a uint8 (H, W, C) image.
• cv2.LUT lookup table: for float outputs, the table must be float32, not float64. OpenCV stats often promote to float64; cast the small LUT to float32 so the output does not widen.

5. Normalize / Float Work - float32 Only

Keep intermediate buffers float32 unless a benchmark proves otherwise. Public API supports uint8 and float32 only.

6. Utilities and Decorators

• Utilities: get_num_channels, convert_value, clip, etc. in albucore.utils.
• Decorators: @preserve_channel_dim, @contiguous, @clipped, @batch_transform, etc. in albucore.decorators.

7. Tests

• Test uint8 and float32 only.
• Test single images, batches, volumes, and batch-of-volumes where the router supports them.
• Cover 1-channel and >4-channel edge cases.

8. Dependency Lock Consistency

• When changing dependencies in pyproject.toml, update uv.lock in the same PR.
• Validate with uv lock --check.
• Release flow uses uv export --frozen; stale uv.lock can break release artifact generation.

Quick Reference

Convention	Rule
Grayscale shape	(H, W, 1) never (H, W)
Dtypes	uint8, float32 only
Backend	Choose by benchmark
LUT	uint8 image in; float32 LUT table when output is float32
Normalize / math	float32 buffers; no float64 in public paths
OpenCV limit	4 channels unless chunked or using NumPy
Benchmarks	benchmarks/ and docs/numkong-performance.md
Lockfile	Keep uv.lock in sync with pyproject.toml

---

Source: albumentations-team/albucore — distributed by TomeVault.