import numpy as np
import torch
import torch.nn as nn
def calc_iou(a, b):
area = (b[:, 2] - b[:, 0]) * (b[:, 3] - b[:, 1])
iw = torch.min(torch.unsqueeze(
a[:, 2], dim=1), b[:, 2]) - torch.max(torch.unsqueeze(a[:, 0], 1), b[:, 0])
ih = torch.min(torch.unsqueeze(
a[:, 3], dim=1), b[:, 3]) - torch.max(torch.unsqueeze(a[:, 1], 1), b[:, 1])
iw = torch.clamp(iw, min=0)
ih = torch.clamp(ih, min=0)
ua = torch.unsqueeze((a[:, 2] - a[:, 0]) *
(a[:, 3] - a[:, 1]), dim=1) + area - iw * ih
ua = torch.clamp(ua, min=1e-8)
intersection = iw * ih
IoU = intersection / ua
return IoU
class FocalLoss(nn.Module):
# def __init__(self):
def forward(self, classifications, regressions, anchors, annotations):
alpha = 0.25
gamma = 2.0
batch_size = classifications.shape[0]
classification_losses = []
regression_losses = []
anchor = anchors[0, :, :]
anchor_widths = anchor[:, 2] - anchor[:, 0]
anchor_heights = anchor[:, 3] - anchor[:, 1]
anchor_ctr_x = anchor[:, 0] + 0.5 * anchor_widths
anchor_ctr_y = anchor[:, 1] + 0.5 * anchor_heights
for j in range(batch_size):
classification = classifications[j, :, :]
regression = regressions[j, :, :]
bbox_annotation = annotations[j, :, :]
bbox_annotation = bbox_annotation[bbox_annotation[:, 4] != -1]
if bbox_annotation.shape[0] == 0:
regression_losses.append(torch.tensor(0).float().cuda())
classification_losses.append(torch.tensor(0).float().cuda())
continue
classification = torch.clamp(classification, 1e-4, 1.0 - 1e-4)
# num_anchors x num_annotations
IoU = calc_iou(anchors[0, :, :], bbox_annotation[:, :4])
IoU_max, IoU_argmax = torch.max(IoU, dim=1) # num_anchors x 1
#import pdb
# pdb.set_trace()
# compute the loss for classification
targets = torch.ones(classification.shape) * -1
targets = targets.cuda()
targets[torch.lt(IoU_max, 0.4), :] = 0
positive_indices = torch.ge(IoU_max, 0.5)
num_positive_anchors = positive_indices.sum()
assigned_annotations = bbox_annotation[IoU_argmax, :]
targets[positive_indices, :] = 0
targets[positive_indices,
assigned_annotations[positive_indices, 4].long()] = 1
alpha_factor = torch.ones(targets.shape).cuda() * alpha
alpha_factor = torch.where(
torch.eq(targets, 1.), alpha_factor, 1. - alpha_factor)
focal_weight = torch.where(
torch.eq(targets, 1.), 1. - classification, classification)
focal_weight = alpha_factor * torch.pow(focal_weight, gamma)
bce = -(targets * torch.log(classification) +
(1.0 - targets) * torch.log(1.0 - classification))
# cls_loss = focal_weight * torch.pow(bce, gamma)
cls_loss = focal_weight * bce
cls_loss = torch.where(
torch.ne(targets, -1.0), cls_loss, torch.zeros(cls_loss.shape).cuda())
classification_losses.append(
cls_loss.sum()/torch.clamp(num_positive_anchors.float(), min=1.0))
# compute the loss for regression
if positive_indices.sum() > 0:
assigned_annotations = assigned_annotations[positive_indices, :]
anchor_widths_pi = anchor_widths[positive_indices]
anchor_heights_pi = anchor_heights[positive_indices]
anchor_ctr_x_pi = anchor_ctr_x[positive_indices]
anchor_ctr_y_pi = anchor_ctr_y[positive_indices]
gt_widths = assigned_annotations[:,
2] - assigned_annotations[:, 0]
gt_heights = assigned_annotations[:,
3] - assigned_annotations[:, 1]
gt_ctr_x = assigned_annotations[:, 0] + 0.5 * gt_widths
gt_ctr_y = assigned_annotations[:, 1] + 0.5 * gt_heights
# clip widths to 1
gt_widths = torch.clamp(gt_widths, min=1)
gt_heights = torch.clamp(gt_heights, min=1)
targets_dx = (gt_ctr_x - anchor_ctr_x_pi) / anchor_widths_pi
targets_dy = (gt_ctr_y - anchor_ctr_y_pi) / anchor_heights_pi
targets_dw = torch.log(gt_widths / anchor_widths_pi)
targets_dh = torch.log(gt_heights / anchor_heights_pi)
targets = torch.stack(
(targets_dx, targets_dy, targets_dw, targets_dh))
targets = targets.t()
targets = targets/torch.Tensor([[0.1, 0.1, 0.2, 0.2]]).cuda()
negative_indices = 1 + (~positive_indices)
regression_diff = torch.abs(
targets - regression[positive_indices, :])
regression_loss = torch.where(
torch.le(regression_diff, 1.0 / 9.0),
0.5 * 9.0 * torch.pow(regression_diff, 2),
regression_diff - 0.5 / 9.0
)
regression_losses.append(regression_loss.mean())
else:
regression_losses.append(torch.tensor(0).float().cuda())
return torch.stack(classification_losses).mean(dim=0, keepdim=True), torch.stack(regression_losses).mean(dim=0, keepdim=True)
