There is something wrong with the COCO folder structure in the readme.md

[zeng-yifei]

The "images" folder actually shouldn't appear. Otherwise, custom_dataset will not able to access data and will raise error like this:

cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) cv2.error: OpenCV(3.4.4) C:\projects\opencv python\opencv\modules\imgproc\src\color.cpp:181: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'

the structure below would be the right structure. Anyway, thank you for your really really great work. Hope this tip will help :-)

data{coco{annotations/train2017/val2017}}

instead of

data{coco{annotations/images{train2017/val2017}}}

for example, the train2017 folder should be like
<repo_root>/data/coco/train2017/xxx.jpg
instead of
<repo_root>/data/coco/images/train2017/xxx.jpg