    def __init__(self, in_channels=3, out_channels=64, norm="BN"):
        """
        Args:
            norm (str or callable): norm after the first conv layer.
                See :func:`layers.get_norm` for supported format.
        """
        super(BasicStem, self).__init__(in_channels, out_channels, 4)
        self.in_channels = in_channels
        self.conv1 = Conv2d(
            in_channels,
            out_channels,
            kernel_size=7,
            stride=2,
            padding=3,
            bias=False,
            norm=get_norm(norm, out_channels), )
Args:
norm (str or callable): norm after the first conv layer.
See :func:`layers.get_norm` for supported format.
ptstructure/vqa/pytorchnlp/transformers/layoutxlm/visual_backbone.py