utils.py

"""
Utility functions for YOLOv3 (simplifié pour Gradio)
"""

import torch


def intersection_over_union(boxes_preds, boxes_labels, box_format="midpoint"):
    """
    Calcule l'intersection over union (IoU) entre deux bounding boxes
    
    Args:
        boxes_preds: Prédictions [x, y, w, h] ou [x1, y1, x2, y2]
        boxes_labels: Labels [x, y, w, h] ou [x1, y1, x2, y2]
        box_format: "midpoint" ou "corners"
    
    Returns:
        IoU score
    """
    if box_format == "midpoint":
        box1_x1 = boxes_preds[..., 0:1] - boxes_preds[..., 2:3] / 2
        box1_y1 = boxes_preds[..., 1:2] - boxes_preds[..., 3:4] / 2
        box1_x2 = boxes_preds[..., 0:1] + boxes_preds[..., 2:3] / 2
        box1_y2 = boxes_preds[..., 1:2] + boxes_preds[..., 3:4] / 2
        box2_x1 = boxes_labels[..., 0:1] - boxes_labels[..., 2:3] / 2
        box2_y1 = boxes_labels[..., 1:2] - boxes_labels[..., 3:4] / 2
        box2_x2 = boxes_labels[..., 0:1] + boxes_labels[..., 2:3] / 2
        box2_y2 = boxes_labels[..., 1:2] + boxes_labels[..., 3:4] / 2
    else:  # corners
        box1_x1 = boxes_preds[..., 0:1]
        box1_y1 = boxes_preds[..., 1:2]
        box1_x2 = boxes_preds[..., 2:3]
        box1_y2 = boxes_preds[..., 3:4]
        box2_x1 = boxes_labels[..., 0:1]
        box2_y1 = boxes_labels[..., 1:2]
        box2_x2 = boxes_labels[..., 2:3]
        box2_y2 = boxes_labels[..., 3:4]

    x1 = torch.max(box1_x1, box2_x1)
    y1 = torch.max(box1_y1, box2_y1)
    x2 = torch.min(box1_x2, box2_x2)
    y2 = torch.min(box1_y2, box2_y2)

    intersection = (x2 - x1).clamp(0) * (y2 - y1).clamp(0)
    box1_area = abs((box1_x2 - box1_x1) * (box1_y2 - box1_y1))
    box2_area = abs((box2_x2 - box2_x1) * (box2_y2 - box2_y1))

    return intersection / (box1_area + box2_area - intersection + 1e-6)


def non_max_suppression(bboxes, iou_threshold, threshold, box_format="corners"):
    """
    Applique le Non-Maximum Suppression (NMS)
    
    Args:
        bboxes: Liste de bboxes [class_pred, prob_score, x, y, w, h]
        iou_threshold: Seuil IoU pour supprimer les boxes
        threshold: Seuil de confiance minimum
        box_format: "midpoint" ou "corners"
    
    Returns:
        Liste de bboxes après NMS
    """
    assert type(bboxes) == list

    # Filtrer par confiance
    bboxes = [box for box in bboxes if box[1] > threshold]
    bboxes = sorted(bboxes, key=lambda x: x[1], reverse=True)
    bboxes_after_nms = []

    while bboxes:
        chosen_box = bboxes.pop(0)

        bboxes = [
            box
            for box in bboxes
            if box[0] != chosen_box[0]  # Différente classe
            or intersection_over_union(
                torch.tensor(chosen_box[2:]),
                torch.tensor(box[2:]),
                box_format=box_format,
            )
            < iou_threshold  # IoU faible
        ]

        bboxes_after_nms.append(chosen_box)

    return bboxes_after_nms


def cells_to_bboxes(predictions, anchors, S, is_preds=True):
    """
    Convertit les prédictions YOLOv3 en bounding boxes
    
    Args:
        predictions: Tensor [N, 3, S, S, num_classes+5]
        anchors: Anchors pour cette échelle
        S: Taille de la grille (13, 26, ou 52)
        is_preds: Si True, applique sigmoid/exp
    
    Returns:
        Liste de bboxes converties
    """
    BATCH_SIZE = predictions.shape[0]
    num_anchors = len(anchors)
    box_predictions = predictions[..., 1:5]
    
    if is_preds:
        anchors = anchors.reshape(1, len(anchors), 1, 1, 2)
        box_predictions[..., 0:2] = torch.sigmoid(box_predictions[..., 0:2])
        box_predictions[..., 2:] = torch.exp(box_predictions[..., 2:]) * anchors
        scores = torch.sigmoid(predictions[..., 0:1])
        best_class = torch.argmax(predictions[..., 5:], dim=-1).unsqueeze(-1)
    else:
        scores = predictions[..., 0:1]
        best_class = predictions[..., 5:6]

    # Indices de cellules
    cell_indices = (
        torch.arange(S)
        .repeat(predictions.shape[0], 3, S, 1)
        .unsqueeze(-1)
        .to(predictions.device)
    )
    
    # Convertir en coordonnées absolues [0, 1]
    x = 1 / S * (box_predictions[..., 0:1] + cell_indices)
    y = 1 / S * (box_predictions[..., 1:2] + cell_indices.permute(0, 1, 3, 2, 4))
    w_h = 1 / S * box_predictions[..., 2:4]
    
    converted_bboxes = torch.cat((best_class, scores, x, y, w_h), dim=-1).reshape(
        BATCH_SIZE, num_anchors * S * S, 6
    )
    
    return converted_bboxes.tolist()