def basic_bn_stem(model, data, **kwargs):
    """Add a basic ResNet stem. For a pre-trained network that used BN.
    An AffineChannel op replaces BN during fine-tuning.
    """

    dim = 64
    p = model.Conv(data, 'conv1', 3, dim, 7, pad=3, stride=2, no_bias=1)
    p = model.AffineChannel(p, 'res_conv1_bn', dim=dim, inplace=True)
    p = model.Relu(p, p)
    p = model.MaxPool(p, 'pool1', kernel=3, pad=1, stride=2)
    return p, dim
Add a basic ResNet stem. For a pre-trained network that used BN.
    An AffineChannel op replaces BN during fine-tuning.
    
detectron/modeling/ResNet.py