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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 | |
| ) |