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"""
Implementation of Yolo Loss Function similar to the one in Yolov3 paper,
the difference from what I can tell is I use CrossEntropy for the classes
instead of BinaryCrossEntropy.
"""
import random
import torch
import torch.nn as nn
from utils import intersection_over_union
class YoloLoss(nn.Module):
def __init__(self):
super().__init__()
self.mse = nn.MSELoss()
self.bce = nn.BCEWithLogitsLoss()
self.entropy = nn.CrossEntropyLoss()
self.sigmoid = nn.Sigmoid()
# Constants signifying how much to pay for each respective part of the loss
self.lambda_class = 1
self.lambda_noobj = 10
self.lambda_obj = 1
self.lambda_box = 10
def forward(self, predictions, target, anchors):
# Check where obj and noobj (we ignore if target == -1)
obj = target[..., 0] == 1 # in paper this is Iobj_i
noobj = target[..., 0] == 0 # in paper this is Inoobj_i
# ======================= #
# FOR NO OBJECT LOSS #
# ======================= #
no_object_loss = self.bce(
(predictions[..., 0:1][noobj]), (target[..., 0:1][noobj]),
)
# ==================== #
# FOR OBJECT LOSS #
# ==================== #
anchors = anchors.reshape(1, 3, 1, 1, 2)
box_preds = torch.cat([self.sigmoid(predictions[..., 1:3]), torch.exp(predictions[..., 3:5]) * anchors], dim=-1)
ious = intersection_over_union(box_preds[obj], target[..., 1:5][obj]).detach()
object_loss = self.mse(self.sigmoid(predictions[..., 0:1][obj]), ious * target[..., 0:1][obj])
# ======================== #
# FOR BOX COORDINATES #
# ======================== #
predictions[..., 1:3] = self.sigmoid(predictions[..., 1:3]) # x,y coordinates
target[..., 3:5] = torch.log(
(1e-16 + target[..., 3:5] / anchors)
) # width, height coordinates
box_loss = self.mse(predictions[..., 1:5][obj], target[..., 1:5][obj])
# ================== #
# FOR CLASS LOSS #
# ================== #
class_loss = self.entropy(
(predictions[..., 5:][obj]), (target[..., 5][obj].long()),
)
#print("__________________________________")
#print(self.lambda_box * box_loss)
#print(self.lambda_obj * object_loss)
#print(self.lambda_noobj * no_object_loss)
#print(self.lambda_class * class_loss)
#print("\n")
return (
self.lambda_box * box_loss
+ self.lambda_obj * object_loss
+ self.lambda_noobj * no_object_loss
+ self.lambda_class * class_loss
) |