libs/ssn/loss.py

import torch

def reconstruction(assignment, labels, hard_assignment=None):
    """
    reconstruction

    Args:
        assignment: torch.Tensor
            A Tensor of shape (B, n_spixels, n_pixels)
        labels: torch.Tensor
            A Tensor of shape (B, C, n_pixels)
        hard_assignment: torch.Tensor
            A Tensor of shape (B, n_pixels)
    """
    labels = labels.permute(0, 2, 1).contiguous()

    # matrix product between (n_spixels, n_pixels) and (n_pixels, channels)
    spixel_mean = torch.bmm(assignment, labels) / (assignment.sum(2, keepdim=True) + 1e-16)
    if hard_assignment is None:
        # (B, n_spixels, n_pixels) -> (B, n_pixels, n_spixels)
        permuted_assignment = assignment.permute(0, 2, 1).contiguous()
        # matrix product between (n_pixels, n_spixels) and (n_spixels, channels)
        reconstructed_labels = torch.bmm(permuted_assignment, spixel_mean)
    else:
        # index sampling
        reconstructed_labels = torch.stack([sm[ha, :] for sm, ha in zip(spixel_mean, hard_assignment)], 0)
    return reconstructed_labels.permute(0, 2, 1).contiguous()


def reconstruct_loss_with_cross_etnropy(assignment, labels, hard_assignment=None):
    """
    reconstruction loss with cross entropy

    Args:
        assignment: torch.Tensor
            A Tensor of shape (B, n_spixels, n_pixels)
        labels: torch.Tensor
            A Tensor of shape (B, C, n_pixels)
        hard_assignment: torch.Tensor
            A Tensor of shape (B, n_pixels)
    """
    reconstracted_labels = reconstruction(assignment, labels, hard_assignment)
    reconstracted_labels = reconstracted_labels / (1e-16 + reconstracted_labels.sum(1, keepdim=True))
    mask = labels > 0
    return -(reconstracted_labels[mask] + 1e-16).log().mean()


def reconstruct_loss_with_mse(assignment, labels, hard_assignment=None):
    """
    reconstruction loss with mse

    Args:
        assignment: torch.Tensor
            A Tensor of shape (B, n_spixels, n_pixels)
        labels: torch.Tensor
            A Tensor of shape (B, C, n_pixels)
        hard_assignment: torch.Tensor
            A Tensor of shape (B, n_pixels)
    """
    reconstracted_labels = reconstruction(assignment, labels, hard_assignment)
    return torch.nn.functional.mse_loss(reconstracted_labels, labels)