pytorch生成锚框

锚框是以图像的每个像素为中心生成不同形状的边界框

from PIL import Image
import numpy as np
import math
import matplotlib.pyplot as plt
import torch


def MultiBoxPrior(feature_map, sizes=[0.75, 0.5, 0.25], ratios=[1, 2, 0.5]):
    """
    (xmin,ymin,xmax,ymax)
    Args:
        feature_map: torch tensor, Shape: [N, C, H, W].
        sizes: List of sizes (0~1) of generated MultiBoxPriores.
        ratios: List of aspect ratios (non-negative) of generated MultiBoxPriores.
    Returns:
        anchors of shape (1, num_anchors, 4). 由于batch里每个都一样, 所以第一维为1
    """
    pairs = []  # pair of (size, sqrt(ration))
    for r in ratios:
        pairs.append([sizes[0], math.sqrt(r)])
    for s in sizes[1:]:
        pairs.append([s, math.sqrt(ratios[0])])

    pairs = np.array(pairs)

    ss1 = pairs[:, 0] * pairs[:, 1]  # size * sqrt(ration)
    ss2 = pairs[:, 0] / pairs[:, 1]  # size / sqrt(ration)

    base_anchors = np.stack([