utils/transforms.py

from __future__ import annotations

import random
import cv2
import numpy as np

def random_color_distort(
    img: np.ndarray,
    brightness_delta: int = 32,
    contrast_low: float = 0.5,
    contrast_high: float = 1.5,
    saturation_low: float = 0.5,
    saturation_high: float = 1.5,
    hue_delta: int = 18,
) -> np.ndarray:
    """SSD-style random colour jittering.

    Operates on an HWC **RGB uint8** image and returns the same format.
    """
    cv_img = cv2.cvtColor(img, cv2.COLOR_RGB2BGR)

    def _convert(arr, alpha=1.0, beta=0.0):
        arr = arr.astype(np.float32) * alpha + beta
        return np.clip(arr, 0, 255).astype(np.uint8)

    # Brightness
    if random.random() < 0.5:
        cv_img = _convert(cv_img, beta=random.uniform(-brightness_delta, brightness_delta))

    # Decide order: contrast first or saturation/hue first
    if random.random() < 0.5:
        order = ["contrast", "saturation", "hue"]
    else:
        order = ["saturation", "hue", "contrast"]

    for aug in order:
        if aug == "contrast" and random.random() < 0.5:
            cv_img = _convert(cv_img, alpha=random.uniform(contrast_low, contrast_high))
        elif aug == "saturation" and random.random() < 0.5:
            hsv = cv2.cvtColor(cv_img, cv2.COLOR_BGR2HSV)
            hsv[:, :, 1] = _convert(hsv[:, :, 1], alpha=random.uniform(saturation_low, saturation_high))
            cv_img = cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR)
        elif aug == "hue" and random.random() < 0.5:
            hsv = cv2.cvtColor(cv_img, cv2.COLOR_BGR2HSV)
            hsv[:, :, 0] = ((hsv[:, :, 0].astype(int) + random.randint(-hue_delta, hue_delta)) % 180).astype(np.uint8)
            cv_img = cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR)

    return cv2.cvtColor(cv_img, cv2.COLOR_BGR2RGB)

def random_flip(image: np.ndarray, label: np.ndarray):
    """Random horizontal and/or vertical flip."""
    if random.random() < 0.5:
        image = np.ascontiguousarray(image[:, ::-1])
        label = np.ascontiguousarray(label[:, ::-1])
    if random.random() < 0.5:
        image = np.ascontiguousarray(image[::-1])
        label = np.ascontiguousarray(label[::-1])
    return image, label

def random_rotate90(image: np.ndarray, label: np.ndarray):
    """Random 0/90/180/270° rotation."""
    k = random.randint(0, 3)
    if k > 0:
        image = np.rot90(image, k, axes=(0, 1)).copy()
        label = np.rot90(label, k, axes=(0, 1)).copy()
    return image, label

def random_crop(image: np.ndarray, label: np.ndarray, crop_size: int):
    """Extract a random crop of ``crop_size × crop_size`` from image/label."""
    h, w = image.shape[:2]
    top = random.randint(0, h - crop_size)
    left = random.randint(0, w - crop_size)
    image = image[top : top + crop_size, left : left + crop_size]
    label = label[top : top + crop_size, left : left + crop_size]
    return image, label

def center_crop(image: np.ndarray, label: np.ndarray, crop_size: int):
    """Center crop for validation."""
    h, w = image.shape[:2]
    top = (h - crop_size) // 2
    left = (w - crop_size) // 2
    image = image[top : top + crop_size, left : left + crop_size]
    label = label[top : top + crop_size, left : left + crop_size]
    return image, label

def pad_to_size(
    image: np.ndarray,
    label: np.ndarray,
    min_size: int,
    pad_label_value: int = 0,
) -> tuple[np.ndarray, np.ndarray]:
    """Symmetric-pad image and label so both sides are ≥ min_size."""
    h, w = image.shape[:2]
    if h >= min_size and w >= min_size:
        return image, label

    H = max(h, min_size)
    W = max(w, min_size)
    py1, px1 = (H - h) // 2, (W - w) // 2
    py2, px2 = H - h - py1, W - w - px1

    image = np.pad(image, ((py1, py2), (px1, px2), (0, 0)), mode="symmetric")
    label = np.pad(label, ((py1, py2), (px1, px2)), mode="constant", constant_values=pad_label_value)
    return image, label

def get_training_augmentation(
    image: np.ndarray,
    label: np.ndarray,
    crop_size: int = 400,
    color_distort: bool = True,
) -> tuple[np.ndarray, np.ndarray]:
    """Full training augmentation pipeline.

    Steps:
      1. Optional colour distortion
      2. Pad if smaller than crop_size
      3. Random flip
      4. Random 90° rotation
      5. Random crop
    """
    if color_distort:
        image = random_color_distort(image)

    image, label = pad_to_size(image, label, crop_size, pad_label_value=0)
    image, label = random_flip(image, label)
    image, label = random_rotate90(image, label)
    image, label = random_crop(image, label, crop_size)
    return image, label

def get_validation_transform(
    image: np.ndarray,
    label: np.ndarray,
    crop_size: int = 480,
) -> tuple[np.ndarray, np.ndarray]:
    """Validation transform:  pad → center crop (deterministic)."""
    image, label = pad_to_size(image, label, crop_size, pad_label_value=255)
    image, label = center_crop(image, label, crop_size)
    return image, label