简介

我正在使用Mmdetection来使用自定义COCO数据集训练可变形DETR模型。表示使用COCO注解格式的自定义数据集。该数据集使用与COCO相同的图像，具有不同的“玩具”注解用于“Playground”实验，并且注解文件仅使用pycocotools和json包创建。
我对这个Playground数据集做了五个变化：2个数据集有3个类（类1、2和3），1个数据集有6个类（类1到6），2个数据集有7个类（类1到7）。

问题

现在，在使用mmdet.datasets.build_dataset在mmdetection中创建数据集之后，我使用以下代码来检查是否一切正常：

from pycocotools.coco import COCO
from os import path as osp
from mmdet.datasets import build_dataset

cfg = start_config() # this is simply a function to startup the config file
ann_file = osp.join(cfg.data.train.data_root, cfg.data.train.ann_file)
coco = COCO(ann_file)
img_ids = coco.getImgIds()
ann_ids = coco.getAnnIds(imgIds=img_ids)
anns = coco.loadAnns(ids=ann_ids)

cats_counter = {}
for ann in anns:
  if ann['category_id'] in cats_counter:
    cats_counter[ann['category_id']]+=1
  else:
    cats_counter[ann['category_id']] = 1
print(cats_counter)

cats = {cat['id']:cat for cat in coco.loadCats(coco.getCatIds())}
for i in range(len(cats_counter)):
  print("{} ({}) \t|\t{}".format(i, cats[i]['name'], cats_counter[i]))

ds = build_dataset(cfg.data.train)
print(ds)

对于其中三个数据集，来自json文件和来自构造的mmdet数据集的量几乎完全相等。然而，对于3类数据集之一和6类数据集，结果是非常不同的，其中此代码返回以下内容：

{3: 1843, 1: 659, 4: 1594, 2: 582, 0: 1421, 5: 498}
0 (1)   |   1421
1 (2)   |   659
2 (3)   |   582
3 (4)   |   1843
4 (5)   |   1594
5 (6)   |   498
loading annotations into memory...
Done (t=0.06s)
creating index...
index created!

CocoDataset Train dataset with number of images 1001, and instance counts: 
+---------------+-------+---------------+-------+---------------+-------+---------------+-------+---------------+-------+
| category      | count | category      | count | category      | count | category      | count | category      | count |
+---------------+-------+---------------+-------+---------------+-------+---------------+-------+---------------+-------+
| 0 [1]         | 1421  | 1 [2]         | 659   | 2 [3]         | 581   | 3 [4]         | 1843  | 4 [5]         | 1594  |
|               |       |               |       |               |       |               |       |               |       |
| 5 [6]         | 0     | -1 background | 45    |               |       |               |       |               |       |
+---------------+-------+---------------+-------+---------------+-------+---------------+-------+---------------+-------+

和

{1: 1420, 0: 4131, 2: 1046}
0 (1)   |   4131
1 (2)   |   1420
2 (3)   |   1046
loading annotations into memory...
Done (t=0.06s)
creating index...
index created!

CocoDataset Train dataset with number of images 1001, and instance counts: 
+----------+-------+------------+-------+----------+-------+---------------+-------+----------+-------+
| category | count | category   | count | category | count | category      | count | category | count |
+----------+-------+------------+-------+----------+-------+---------------+-------+----------+-------+
|          |       |            |       |          |       |               |       |          |       |
| 0 [1]    | 1419  | 1 [2]      | 0     | 2 [3]    | 0     | -1 background | 443   |          |       |
+----------+-------+------------+-------+----------+-------+---------------+-------+----------+-------+

你可以看到在注解json中没有“-1”id，而且来自3-classes数据集的一些类有0个注解，而json清楚地显示了更多。有人在使用MmmDetection时遇到过类似的情况吗？是什么导致了这个问题？