基础---目标检测小记

用来表达bbox的格式通常有两种，(x1, y1, x2, y2) 和 (c_x, c_y, w, h) ，如图3-3所示：

之所以使用两种不同的目标框信息表达格式，是因为两种格式会分别在后续不同场景下更加便于计算。

两种格式互相转换的实现：

def xy_to_cxcy(xy):
    """
    Convert bounding boxes from boundary coordinates (x_min, y_min, x_max, y_max) to center-size coordinates (c_x, c_y, w, h).

    :param xy: bounding boxes in boundary coordinates, a tensor of size (n_boxes, 4)
    :return: bounding boxes in center-size coordinates, a tensor of size (n_boxes, 4)
    """
    return torch.cat([(xy[:, 2:] + xy[:, :2]) / 2,  # c_x, c_y
                      xy[:, 2:] - xy[:, :2]], 1)  # w, h


def cxcy_to_xy(cxcy):
    """
    Convert bounding boxes from center-size coordinates (c_x, c_y, w, h) to boundary coordinates (x_min, y_min, x_max, y_max