src/data/preprocessing.py

"""
Per-modality preprocessing for satellite imagery.

Handles different channel counts:
- Optical RGB: 3 channels (R, G, B)
- SAR: 2 channels (VV, VH)
- Multispectral: 12 channels (Sentinel-2 bands)
"""

import torch
import torch.nn.functional as F
from torchvision import transforms
from PIL import Image
import numpy as np


# ImageNet normalization for RGB
IMAGENET_MEAN = [0.485, 0.456, 0.406]
IMAGENET_STD = [0.229, 0.224, 0.225]

# Sentinel-2 band statistics (approximate)
SENTINEL2_MEAN = [1353.0, 1117.0, 1042.0, 947.0, 1199.0, 1645.0, 1849.0, 1793.0, 1859.0, 1008.0, 1593.0, 1064.0]
SENTINEL2_STD = [235.0, 309.0, 392.0, 597.0, 490.0, 625.0, 736.0, 755.0, 846.0, 487.0, 561.0, 459.0]

# SAR statistics (approximate, in dB)
SAR_MEAN = [-12.0, -18.0]
SAR_STD = [5.0, 5.0]


def get_optical_transform(size: int = 224) -> transforms.Compose:
    """Get transforms for optical RGB images."""
    return transforms.Compose([
        transforms.Resize(size),
        transforms.CenterCrop(size),
        transforms.ToTensor(),
        transforms.Normalize(mean=IMAGENET_MEAN, std=IMAGENET_STD)
    ])


def get_sar_transform(size: int = 224) -> transforms.Compose:
    """Get transforms for SAR images (VV/VH channels)."""
    return transforms.Compose([
        transforms.Resize(size),
        transforms.CenterCrop(size),
        transforms.ToTensor(),
        transforms.Normalize(mean=SAR_MEAN, std=SAR_STD)
    ])


def get_multispectral_transform(size: int = 224) -> transforms.Compose:
    """Get transforms for multispectral images (12 channels)."""
    return transforms.Compose([
        transforms.Resize(size),
        transforms.CenterCrop(size),
        transforms.ToTensor(),
        transforms.Normalize(mean=SENTINEL2_MEAN, std=SENTINEL2_STD)
    ])


def preprocess_image(
    image: Image.Image,
    modality: str,
    size: int = 224
) -> torch.Tensor:
    """
    Preprocess image based on modality.
    
    Args:
        image: Input PIL image
        modality: "optical", "sar", or "multispectral"
        size: Output image size
        
    Returns:
        Preprocessed tensor
    """
    # Handle channel mismatch before applying transform
    if modality == "sar":
        # SAR expects 2 channels, but PIL images are typically 3 channels
        # Convert to numpy, take first 2 channels, convert back
        img_array = np.array(image)
        if img_array.shape[-1] == 3:
            img_array = img_array[..., :2]
        image = Image.fromarray(img_array)
        transform = get_sar_transform(size)
    elif modality == "optical":
        transform = get_optical_transform(size)
    elif modality == "multispectral":
        transform = get_multispectral_transform(size)
    else:
        raise ValueError(f"Unknown modality: {modality}")
    
    return transform(image)


def handle_channels(
    image: np.ndarray,
    target_channels: int,
    modality: str
) -> np.ndarray:
    """
    Handle channel mismatch for different modalities.
    
    Args:
        image: Input image array (H, W, C)
        target_channels: Expected number of channels
        modality: Modality type
        
    Returns:
        Image with correct number of channels
    """
    current_channels = image.shape[-1] if len(image.shape) == 3 else 1
    
    if current_channels == target_channels:
        return image
    
    # ponytail: simple channel handling, not perfect but works for v1
    if modality == "optical" and current_channels >= 3:
        # Take first 3 channels (RGB)
        return image[..., :3]
    elif modality == "sar" and current_channels >= 2:
        # Take first 2 channels (VV, VH)
        return image[..., :2]
    elif modality == "multispectral":
        if current_channels < target_channels:
            # Pad with zeros
            padding = np.zeros((*image.shape[:-1], target_channels - current_channels))
            return np.concatenate([image, padding], axis=-1)
        else:
            # Take first 12 channels
            return image[..., :target_channels]
    
    return image


# Self-check
if __name__ == "__main__":
    # Create dummy images for testing
    dummy_rgb = Image.fromarray(np.random.randint(0, 255, (256, 256, 3), dtype=np.uint8))
    dummy_sar = Image.fromarray(np.random.randint(0, 255, (256, 256, 2), dtype=np.uint8))
    
    # Test preprocessing
    optical_tensor = preprocess_image(dummy_rgb, "optical")
    sar_tensor = preprocess_image(dummy_sar, "sar")
    
    print(f"Optical shape: {optical_tensor.shape}")  # Should be [3, 224, 224]
    print(f"SAR shape: {sar_tensor.shape}")  # Should be [2, 224, 224]
    
    print("Preprocessing test passed!")