heads.py

import torch.nn as nn
from .modules import Flatten, Activation


class SegmentationHead(nn.Sequential):

    def __init__(self, in_channels, out_channels, kernel_size=3, activation=None, upsampling=1):
        conv2d = nn.Conv2d(in_channels, out_channels, kernel_size=kernel_size, padding=kernel_size // 2)
        upsampling = nn.UpsamplingBilinear2d(scale_factor=upsampling) if upsampling > 1 else nn.Identity()
        activation = Activation(activation)
        super().__init__(conv2d, upsampling, activation)


class ClassificationHead(nn.Sequential):

    def __init__(self, in_channels, classes, pooling="avg", dropout=0.2, activation=None):
        if pooling not in ("max", "avg"):
            raise ValueError("Pooling should be one of ('max', 'avg'), got {}.".format(pooling))
        pool = nn.AdaptiveAvgPool2d(1) if pooling == 'avg' else nn.AdaptiveMaxPool2d(1)
        flatten = Flatten()
        dropout = nn.Dropout(p=dropout, inplace=True) if dropout else nn.Identity()
        linear = nn.Linear(in_channels, classes, bias=True)
        activation = Activation(activation)
        super().__init__(pool, flatten, dropout, linear, activation)