src/data/joint_augmentor.py

"""Joint augmentation for fingerprint images and minutiae.

Applies the same geometric transform to both the image and minutiae
coordinates simultaneously, ensuring spatial consistency.

Augmentations:
    - Random rotation: rotates image + rotation matrix on (x,y) + adds angle to θ
    - Random translation: shifts image + adds offset to (x,y)
    - Minutia dropout: randomly drops points (keeps ≥ min_keep)
    - Coordinate jitter: Gaussian noise on (x,y) — minutiae only
"""

import math
import random

import torch
import torch.nn.functional as F

from ..configs.default import AugmentConfig


class JointAugmentor:
    """Applies the same geometric transform to image and minutiae simultaneously.

    Parameters
    ----------
    cfg : AugmentConfig
        Augmentation configuration.
    """

    def __init__(self, cfg: AugmentConfig):
        self.cfg = cfg

    def __call__(
        self,
        image: torch.Tensor,
        minutiae: torch.Tensor,
    ) -> tuple[torch.Tensor, torch.Tensor]:
        """
        Args:
            image:    ``(1, H, W)`` normalized [0, 1] fingerprint image.
            minutiae: ``(N, 3)`` raw ``[x, y, θ]`` in pixel coordinates.

        Returns:
            image:    ``(1, H, W)`` augmented image.
            minutiae: ``(N', 3)`` augmented minutiae (N' ≤ N after dropout).
        """
        _, H, W = image.shape
        m = minutiae.clone()

        # Center of image for rotation
        cx, cy = (W - 1) / 2.0, (H - 1) / 2.0

        # 1. Random rotation
        if self.cfg.rotate:
            angle_deg = random.uniform(-self.cfg.rotate_range, self.cfg.rotate_range)
            angle_rad = math.radians(angle_deg)
            cos_a, sin_a = math.cos(angle_rad), math.sin(angle_rad)

            # Rotate image using affine grid
            # Rotation matrix (clockwise in pixel coords)
            theta = torch.tensor(
                [
                    [cos_a, -sin_a, 0.0],
                    [sin_a, cos_a, 0.0],
                ],
                dtype=image.dtype,
            ).unsqueeze(0)  # (1, 2, 3)

            grid = F.affine_grid(theta, [1, 1, H, W], align_corners=True)
            image = F.grid_sample(
                image.unsqueeze(0),
                grid,
                mode="bilinear",
                padding_mode="zeros",
                align_corners=True,
            ).squeeze(0)

            # Rotate minutiae coordinates around image center
            x_centered = m[:, 0] - cx
            y_centered = m[:, 1] - cy
            m[:, 0] = cos_a * x_centered - sin_a * y_centered + cx
            m[:, 1] = sin_a * x_centered + cos_a * y_centered + cy

            # Rotate orientation
            m[:, 2] = m[:, 2] + angle_rad
            m[:, 2] = torch.atan2(torch.sin(m[:, 2]), torch.cos(m[:, 2]))

        # 2. Random translation
        if self.cfg.translate and self.cfg.translate_range > 0:
            tx = random.uniform(-self.cfg.translate_range, self.cfg.translate_range)
            ty = random.uniform(-self.cfg.translate_range, self.cfg.translate_range)

            # Translate image using affine grid
            theta = torch.tensor(
                [
                    [1.0, 0.0, -2.0 * tx / (W - 1)],
                    [0.0, 1.0, -2.0 * ty / (H - 1)],
                ],
                dtype=image.dtype,
            ).unsqueeze(0)

            grid = F.affine_grid(theta, [1, 1, H, W], align_corners=True)
            image = F.grid_sample(
                image.unsqueeze(0),
                grid,
                mode="bilinear",
                padding_mode="zeros",
                align_corners=True,
            ).squeeze(0)

            # Translate minutiae
            m[:, 0] += tx
            m[:, 1] += ty

        # 3. Minutia dropout
        if self.cfg.minutia_dropout > 0 and m.shape[0] > self.cfg.min_keep:
            keep = torch.rand(m.shape[0]) > self.cfg.minutia_dropout
            if keep.sum() < self.cfg.min_keep:
                keep[: self.cfg.min_keep] = True
            m = m[keep]

        # 4. Coordinate jitter (minutiae only, image unchanged)
        if self.cfg.jitter_std > 0:
            noise = torch.randn(m.shape[0], 2) * self.cfg.jitter_std
            m[:, :2] += noise

        # 5. Spurious minutiae insertion
        spurious_rate = getattr(self.cfg, "spurious_rate", 0.0)
        if spurious_rate > 0 and m.shape[0] > 0:
            n_spurious = max(1, int(m.shape[0] * spurious_rate))
            xy_min = m[:, :2].min(dim=0).values
            xy_max = m[:, :2].max(dim=0).values
            xy_range = (xy_max - xy_min).clamp(min=1.0)
            fake_xy = xy_min + torch.rand(n_spurious, 2) * xy_range
            fake_theta = torch.rand(n_spurious, 1) * 2 * math.pi - math.pi
            fake = torch.cat([fake_xy, fake_theta], dim=-1)
            m = torch.cat([m, fake], dim=0)

        return image, m