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import torch
from torch.nn import functional as F
from typing import List, Optional
import utils.misc as misc
def point_sample(input, point_coords, **kwargs):
"""
A wrapper around :function:`torch.nn.functional.grid_sample` to support 3D point_coords tensors.
Unlike :function:`torch.nn.functional.grid_sample` it assumes `point_coords` to lie inside
[0, 1] x [0, 1] square.
Args:
input (Tensor): A tensor of shape (N, C, H, W) that contains features map on a H x W grid.
point_coords (Tensor): A tensor of shape (N, P, 2) or (N, Hgrid, Wgrid, 2) that contains
[0, 1] x [0, 1] normalized point coordinates.
Returns:
output (Tensor): A tensor of shape (N, C, P) or (N, C, Hgrid, Wgrid) that contains
features for points in `point_coords`. The features are obtained via bilinear
interplation from `input` the same way as :function:`torch.nn.functional.grid_sample`.
"""
add_dim = False
if point_coords.dim() == 3:
add_dim = True
point_coords = point_coords.unsqueeze(2)
output = F.grid_sample(input, 2.0 * point_coords - 1.0, **kwargs)
if add_dim:
output = output.squeeze(3)
return output
def cat(tensors: List[torch.Tensor], dim: int = 0):
"""
Efficient version of torch.cat that avoids a copy if there is only a single element in a list
"""
assert isinstance(tensors, (list, tuple))
if len(tensors) == 1:
return tensors[0]
return torch.cat(tensors, dim)
def get_uncertain_point_coords_with_randomness(
coarse_logits, uncertainty_func, num_points, oversample_ratio, importance_sample_ratio
):
"""
Sample points in [0, 1] x [0, 1] coordinate space based on their uncertainty. The unceratinties
are calculated for each point using 'uncertainty_func' function that takes point's logit
prediction as input.
See PointRend paper for details.
Args:
coarse_logits (Tensor): A tensor of shape (N, C, Hmask, Wmask) or (N, 1, Hmask, Wmask) for
class-specific or class-agnostic prediction.
uncertainty_func: A function that takes a Tensor of shape (N, C, P) or (N, 1, P) that
contains logit predictions for P points and returns their uncertainties as a Tensor of
shape (N, 1, P).
num_points (int): The number of points P to sample.
oversample_ratio (int): Oversampling parameter.
importance_sample_ratio (float): Ratio of points that are sampled via importnace sampling.
Returns:
point_coords (Tensor): A tensor of shape (N, P, 2) that contains the coordinates of P
sampled points.
"""
assert oversample_ratio >= 1
assert importance_sample_ratio <= 1 and importance_sample_ratio >= 0
num_boxes = coarse_logits.shape[0]
num_sampled = int(num_points * oversample_ratio)
point_coords = torch.rand(num_boxes, num_sampled, 2, device=coarse_logits.device)
point_logits = point_sample(coarse_logits, point_coords, align_corners=False)
# It is crucial to calculate uncertainty based on the sampled prediction value for the points.
# Calculating uncertainties of the coarse predictions first and sampling them for points leads
# to incorrect results.
# To illustrate this: assume uncertainty_func(logits)=-abs(logits), a sampled point between
# two coarse predictions with -1 and 1 logits has 0 logits, and therefore 0 uncertainty value.
# However, if we calculate uncertainties for the coarse predictions first,
# both will have -1 uncertainty, and the sampled point will get -1 uncertainty.
point_uncertainties = uncertainty_func(point_logits)
num_uncertain_points = int(importance_sample_ratio * num_points)
num_random_points = num_points - num_uncertain_points
idx = torch.topk(point_uncertainties[:, 0, :], k=num_uncertain_points, dim=1)[1]
shift = num_sampled * torch.arange(num_boxes, dtype=torch.long, device=coarse_logits.device)
idx += shift[:, None]
point_coords = point_coords.view(-1, 2)[idx.view(-1), :].view(
num_boxes, num_uncertain_points, 2
)
if num_random_points > 0:
point_coords = cat(
[
point_coords,
torch.rand(num_boxes, num_random_points, 2, device=coarse_logits.device),
],
dim=1,
)
return point_coords
def dice_loss(
inputs: torch.Tensor,
targets: torch.Tensor,
num_masks: float,
):
"""
Compute the DICE loss, similar to generalized IOU for masks
Args:
inputs: A float tensor of arbitrary shape.
The predictions for each example.
targets: A float tensor with the same shape as inputs. Stores the binary
classification label for each element in inputs
(0 for the negative class and 1 for the positive class).
"""
inputs = inputs.sigmoid()
inputs = inputs.flatten(1)
numerator = 2 * (inputs * targets).sum(-1)
denominator = inputs.sum(-1) + targets.sum(-1)
loss = 1 - (numerator + 1) / (denominator + 1)
return loss.sum() / num_masks
dice_loss_jit = torch.jit.script(
dice_loss
) # type: torch.jit.ScriptModule
def sigmoid_ce_loss(
inputs: torch.Tensor,
targets: torch.Tensor,
num_masks: float,
):
"""
Args:
inputs: A float tensor of arbitrary shape.
The predictions for each example.
targets: A float tensor with the same shape as inputs. Stores the binary
classification label for each element in inputs
(0 for the negative class and 1 for the positive class).
Returns:
Loss tensor
"""
loss = F.binary_cross_entropy_with_logits(inputs, targets, reduction="none")
return loss.mean(1).sum() / num_masks
sigmoid_ce_loss_jit = torch.jit.script(
sigmoid_ce_loss
) # type: torch.jit.ScriptModule
def calculate_uncertainty(logits):
"""
We estimate uncerainty as L1 distance between 0.0 and the logit prediction in 'logits' for the
foreground class in `classes`.
Args:
logits (Tensor): A tensor of shape (R, 1, ...) for class-specific or
class-agnostic, where R is the total number of predicted masks in all images and C is
the number of foreground classes. The values are logits.
Returns:
scores (Tensor): A tensor of shape (R, 1, ...) that contains uncertainty scores with
the most uncertain locations having the highest uncertainty score.
"""
assert logits.shape[1] == 1
gt_class_logits = logits.clone()
return -(torch.abs(gt_class_logits))
def loss_masks(src_masks, target_masks, num_masks, oversample_ratio=3.0):
"""Compute the losses related to the masks: the focal loss and the dice loss.
targets dicts must contain the key "masks" containing a tensor of dim [nb_target_boxes, h, w]
"""
# No need to upsample predictions as we are using normalized coordinates :)
with torch.no_grad():
# sample point_coords
point_coords = get_uncertain_point_coords_with_randomness(
src_masks,
lambda logits: calculate_uncertainty(logits),
112 * 112,
oversample_ratio,
0.75,
)
# get gt labels
point_labels = point_sample(
target_masks,
point_coords,
align_corners=False,
).squeeze(1)
point_logits = point_sample(
src_masks,
point_coords,
align_corners=False,
).squeeze(1)
loss_mask = sigmoid_ce_loss_jit(point_logits, point_labels, num_masks)
loss_dice = dice_loss_jit(point_logits, point_labels, num_masks)
del src_masks
del target_masks
return loss_mask, loss_dice
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