Tôi đang cố gắng để hiểu chức năng mất Yolo v2:
Nếu bất kỳ người nào có thể chi tiết các chức năng.
Tôi đang cố gắng để hiểu chức năng mất Yolo v2:
Nếu bất kỳ người nào có thể chi tiết các chức năng.
Câu trả lời:
Giải thích về các điều khoản khác nhau:
Lưu ý rằng tôi đã sử dụng hai chỉ số và j cho mỗi dự đoán bbox, đây không phải là trường hợp trong bài viết vì luôn có yếu tố 1 o b j i j hoặc 1 n o o b j i j nên không có cách giải thích mơ hồ: những j được chọn là một trong những tương ứng với số điểm cao nhất sự tự tin trong ô đó.
Giải thích chung hơn về mỗi kỳ hạn của tổng:
B*(5+C)
? Atleast đó là trường hợp của YOLO v3.
Doesn't the YOLOv2 Loss function looks scary? It's not actually! It is one of the boldest, smartest loss function around.
Let's first look at what the network actually predicts.
If we recap, YOLOv2 predicts detections on a 13x13 feature map, so in total, we have 169 maps/cells.
We have 5 anchor boxes. For each anchor box we need Objectness-Confidence Score (whether any object was found?), 4 Coordinates ( and ) for the anchor box, and 20 top classes. This can crudely be seen as 20 coordinates, 5 confidence scores, and 100 class probabilities for all 5 anchor box predictions put together.
We have few things to worry about:
All losses are mean-squared errors, except classification loss, which uses cross-entropy function.
Now, let's break the code in the image.
We need to compute losses for each Anchor Box (5 in total)
We need to do this for each of the 13x13 cells where S = 12 (since we start index from 0)
is 1 when there is an object in the cell , else 0.
var1 | var2 | (var1 - var2)^2 | (sqrtvar1 - sqrtvar2)^2
0.0300 | 0.020 | 9.99e-05 | 0.001
0.0330 | 0.022 | 0.00012 | 0.0011
0.0693 | 0.046 | 0.000533 | 0.00233
0.2148 | 0.143 | 0.00512 | 0.00723
0.3030 | 0.202 | 0.01 | 0.01
0.8808 | 0.587 | 0.0862 | 0.0296
4.4920 | 2.994 | 2.2421 | 0.1512
Not that scary, right!
Read HERE for further details.
Your loss function is for YOLO v1 and not YOLO v2. I was also confused with the difference in the two loss functions and seems like many people are: https://groups.google.com/forum/#!topic/darknet/TJ4dN9R4iJk
YOLOv2 paper explains the difference in architecture from YOLOv1 as follows:
We remove the fully connected layers from YOLO(v1) and use anchor boxes to predict bounding boxes... When we move to anchor boxes we also decouple the class prediction mechanism from the spatial location and instead predict class and objectness for every anchorbox.
This means that the confidence probability above should depend not only on and but also an anchor box index, say . Therefore, the loss needs to be different from above. Unfortunately, YOLOv2 paper does not explicitly state its loss function.
I try to make a guess on the loss function of YOLOv2 and discuss it here: https://fairyonice.github.io/Part_4_Object_Detection_with_Yolo_using_VOC_2012_data_loss.html
Here is my Study Note
Loss function: sum-squared error
a. Reason: Easy to optimize
b. Problem: (1) Does not perfectly align with our goal of maximize average precision. (2) In every image, many grid cells do not contain any object. This pushes the confidence scores of those cells towards 0, often overpowering the gradient from cells that do contain an object.
c. Solution: increase loss from bounding box coordinate predictions and decrease the loss from confidence predictions from boxes that don't contain objects. We use two parameters
Only one bounding box should be responsible for each obejct. We assign one predictor to be responsible for predicting an object based on which prediction has the highest current IOU with the ground truth.
a. Loss from bound box coordinate (x, y) Note that the loss comes from one bounding box from one grid cell. Even if obj not in grid cell as ground truth.
b. Loss from width w and height h. Note that the loss comes from one bounding box from one grid cell, even if the object is not in the grid cell as ground truth.
c. Loss from the confidence in each bound box. Not that the loss comes from one bounding box from one grid cel, even if the object is not in the grid cell as ground truth.
Loss function only penalizes classification if obj is present in the grid cell. It also penalize bounding box coordinate if that box is responsible for the ground box (highest IOU)
The loss formula you wrote is of the original YOLO paper loss, not the v2, or v3 loss.
There are some major differences between versions. I suggest reading the papers, or checking the code implementations. Papers: v2, v3.
Some major differences I noticed:
Class probability is calculated per bounding box (hence output is now S∗S∗B*(5+C) instead of SS(B*5 + C))
Bounding box coordinates now have a different representation
In v3 they use 3 boxes across 3 different "scales"
You can try getting into the nitty-gritty details of the loss, either by looking at the python/keras implementation v2, v3 (look for the function yolo_loss) or directly at the c implementation v3 (look for delta_yolo_box, and delta_yolo_class).