Aug 09, 20212 min read ☕ (Last updated: Jan 19, 2023)

(Kaggle) COVID-19 Detection - 47th (top 4%) place solution


I only got Kaggle GPU/TPU, couldn't experiment with many models with various training recipes. So, I try to implement the training codes which work on TPU as possible as I can! Usually, I trained the object-detection model on GPU, image classifier for study-level on TPU.

Anyway, I hope this solution helps you in some ways :)


I used effnet-b7 and effnet-b6 models w/o the auxiliary branches (for segmentation head). The models were trained on grouped 5 folds and on different resolutions, 640, 800 respectively.

And simply averaging for ensembling the models. LB score for mAP is 0.453.

Additionally, I utilized multi-paths dropout (total 5 paths) to regularize the model & found proper augmentations on my training recipes. Compared to the public notebooks, which introduce effnet-b7 as a baseline, I guess those helps to boost CV/LB score.

Lastly, I didn't apply TTA for the study-level because of the limitation of inference time.

None Classifier

I just used study-level models' negative confidence scores, and it boosts LB +0.003. Also, I tried to ensemble study-level models and opacity 2class classifier, but it dropped CV/LB scores.


Overall, I experimented with 3 types of models, Yolov5, CascadeRCNN, VFNet. In my recipes, VFNet achieves bbox mAP 0.55~, but the LB/PB score is lower than I guess.

And CascadeRCNN didn't go well with Yolov5 models. Yolov5 and Yolov5 + CascadeRCNN have comparable CV/LB scores, but only the Yolov5 series have better LB/PB scores than the combined. (maybe the correlation of both models is high, I didn't check yet).

Finally, I ensembles 3 series of Yolov5, yolov5x6, yolov5l6, yolov5m6 respectively, and applied WBF with the same weights.

Works for me

  • label smoothing (0.05 is best on my experiments)
  • 640 ~ 800 resolutions for study-level (It's better than 512 on my experiments)
  • 512 resolution for image-level
  • WBF (iou_threshold : 0.6, skip_box_threshold : 0.01)
  • TTA for image-level
  • inference higher resolution.
    • train 512 and inference 640 resolution for image-level (LB +0.003)
  • light augmentations
    • HorizontalFlip
    • CutOut (huge patch, small number of patches)
    • Brightness
    • Scale/Shift/Rotate

Not-works for me

  • train on high-resolution for study-level & image-level
    • got higher CV score, but comparable LB, PB scores for image-level
  • effnetv2 series
  • the auxiliary losses
  • external data (w/ pseudo labeling)
  • heavy augmentations for study-level models
  • post-processing
    • calibrating the confidence score to filter none class
    • modified WBF which introduced in here


  • One thing I regretted is the diversity of the models. Both study/image-level models of mine have a high prediction correlation because they are the same series (e.g. effnet, yolov5).
  • trust CV

Source Code

You can check out my inference pipeline. inference code

Thank you very much!