YOLOv4: Training Tips

Model zoo

YOLOv4 model zoo

  • Pretrained models

  • Proper configuration based on GPU

    We do NOT suggest you train the model with subdivisions equal or larger than 32, it will takes very long training time.

FAQ

Low accuracy 1

The most common problem - you do NOT follow strictly the manual.

  • You must use
    • default anchors
    • learning_rate=0.001
    • batch=64
    • max_batches = max(6000, number_of_training_images, 2000*classes)
  • You can only change subdivisions
  • Do not do anything that is not written in the manual. 🙅‍♂️

Your datasets are wrong.

  • check the AP50 (average precision) for validation and training dataset by using ./darknet detector map obj.data yolo.cfg yolo.weights

    • If you get high mAP for both Training and Validation datasets, but the network detects objects poorly in real life, then your training dataset is not representative –> add more images from real life to it

    • If you get high mAP for Training dataset, but low for Validation dataset, then your Training dataset isn’t suitable for Validation dataset.

      For example

      • Training dataset contains: cars (rear view) from distance 100m
      • Test dataset contains: cars (side view) from distance 5m

    • if you get low mAP for both Training and Validation datasets, then labels in your Training dataset are wrong

      • Run training with flag -show_imgs, i.e. ./darknet detector train ... -show_imgs , do you see correct bounded boxes?
      • Or check your dataset by using Yolo_mark tool

Darknet training/detection crashes with an error 2

  • If CUDA Out of memory error occurs, then increase subdivisions= 2 times in cfg-file, but not higher than batch= (don’t change batch)!
    • If it doesn’t help - set random=0 and width=416 height=416 in cfg-file.
  • Check content of files bad.list and bad_label.list if they exist near with ./darknet executable file.
  • Do not move some files from Darknet folder - you may forget the necessary files.
  • Download libraries CUDA, cuDNN, OpenCV, … only from official sources. Don’t download libs from other sites.
  • Make sure that you do everything in accordance with the manual, and do not do anything that is not written in the manual.

Train with multiple GPUs 3

  1. Train it first on 1 GPU for like 1000 iterations:

    ./darknet detector train cfg/coco.data cfg/yolov4.cfg yolov4.conv.137

  2. Then stop and by using partially-trained model /backup/yolov4_1000.weights. Run training with multigpu (up to 4 GPUs): ./darknet detector train cfg/coco.data cfg/yolov4.cfg /backup/yolov4_1000.weights -gpus 0,1,2,3

    If you get a Nan, then for some datasets better to decrease learning rate, for 4 GPUs set learning_rate = 0,00065 (i.e. learning_rate = 0.00261 / GPUs). In this case also increase 4x times burn_in = in your cfg-file. I.e. use burn_in = 4000 instead of 1000.

Train custom datasets

Configuration setup see: Train YOLO v4 on Custom Dataset

Start training:

./darknet detector train data/obj.data <custom-cfg> yolov4.conv.137

  • File <custom-cfg>_last.weights will be saved to backup/ for each 100 iterations

  • File <custom-cfg>_xxxx.weights will be saved to backup/ for each 1000 iterations

  • if you train on server without monitor, disable Loss-window by using argument --dont_show. I.e.

    ./darknet detector train data/obj.data <custom-cfg> yolov4.conv.137 -dont_show

  • To see the mAP & Loss-chart during training on remote server without GUI, use

    ./darknet detector train data/obj.data <custom-cfg> yolov4.conv.137 -dont_show -mjpeg_port 8090 -map

    Then open URL http://ip-address:8090 in browser

  • For training with mAP calculation for each 4 Epochs, you need to

    • set valid=valid.txt or train.txt in obj.data file

    • run training with -map argument

      ./darknet detector train data/obj.data <custom-cfg> yolov4.conv.137 -map

  • After training is complete - get result yolo-obj_final.weights from backup/

  • After each 100 iterations you can stop and later start training from this point. For example, after 2000 iterations you can stop training, and later just start training using:

    ./darknet detector train data/obj.data <custom-cfg> backup/yolo-obj_2000.weights

  • You can get result earlier than all 45000 iterations.

Notes 📝

  • If during training you see nan values for avg (loss) field, then training goes wrong. 😭

    But if nan is in some other lines, then training goes well. 🙏

  • If you changed width= or height= in your cfg-file, then new width and height must be divisible by 32.

  • If error Out of memory occurs then in .cfg-file you should increase subdivisions=16, 32 or 64

When should I stop training 4

  • Usually sufficient 2000 iterations for each class(object),

    • but NOT less than number of training images and
    • NOT less than 6000 iterations in total.

  • During training, you will see varying indicators of error, and you should stop when no longer decreases 0.XXXXXXX avg

    For example

    9002: 0.211667, 0.60730 avg, 0.001000 rate, 3.868000 seconds, 576128 images Loaded: 0.000000 seconds

    • 9002 - iteration number (number of batch)
    • 0.60730 avg - average loss (error) - the lower, the better

    he final avgerage loss can be from 0.05 (for a small model and easy dataset) to 3.0 (for a big model and a difficult dataset).

  • if you train with flag -map then you will see mAP indicator like Last accuracy mAP@0.5 = 18.50% in the console. This indicator is better than Loss, so keep training while mAP increases.

Choose the best weights

Once training is stopped, you should take some of last .weights-files from backup/ and choose the best of them.

For example, you stopped training after 9000 iterations, but the best result can give one of previous weights (7000, 8000, 9000). It can happen due to overfitting.

In order to choose best weight, just train with -map flag

./darknet detector train data/obj.data <custom-cfg> yolov4.conv.137 -dont_show -map

So you will see mAP-chart (red-line) in the Loss-chart Window looks like the following figure. mAP will be calculated for each 4 Epochs using valid=valid.txt file that is specified in obj.data file (1 Epoch = images_in_train_txt / batch iterations)

loss_chart_map_chart

How to improve object detection5

Before training

  • Set flag random=1 in your .cfg-file - it will increase precision by training Yolo for different resolutions

  • increase network resolution in your .cfg-file (height=608, width=608 or any value multiple of 32) - it will increase precision

  • Check that each object that you want to detect is mandatory labeled in your dataset - no one object in your data set should not be without label.

  • My Loss is very high and mAP is very low, is training wrong?

    –> Run training with -show_imgs flag at the end of training command, do you see correct bounded boxes of objects? If no, your training dataset is wrong.

  • For each object which you want to detect - there must be at least 1 similar object in the Training dataset with about the same: shape, side of object, relative size, angle of rotation, tilt, illumination.

    • So desirable that your training dataset include images with objects at diffrent: scales, rotations, lightings, from different sides, on different backgrounds
    • You should preferably have 2000 different images for each class or more, and you should train 2000*classes iterations or more

  • Desirable that your training dataset include images with non-labeled objects that you do not want to detect, i.e. negative samples without bounded box (empty .txt files). Use as many images of negative samples as there are images with objects.

  • More see: https://github.com/AlexeyAB/darknet#how-to-improve-object-detection

After training, for detection:

  • Increase network-resolution by set in your .cfg-file (height=608 and width=608) or (height=832 and width=832) or (any value multiple of 32). This increases the precision and makes it possible to detect small objects.

  • It is not necessary to train the network again, just use .weights-file already trained for 416x416 resolution

  • To get even greater accuracy you should train with higher resolution 608x608 or 832x832.

    • Note: if error Out of memory occurs then in .cfg-file you should increase subdivisions=16, 32 or 64

Other questions

Will darknet automaticly resize the image size?

Yes (see: https://github.com/AlexeyAB/darknet/issues/5842)

Does the network have to be perfectly square?

No.

The default network sizes in the common template configuration files is defined as 416x416 or 608x608, but those are only examples!

Choose a size that works for you and your images. The only restrictions are:

  • the width has to be evenly divisible by 32
  • the height has to be evenly divisible by 32
  • you must have enough video memory to train a network of that size

Whatever size you choose, Darknet will stretch (without preserving the aspect ratio!) your images to be exactly that size prior to processing the image. This includes both training and inference. So use a size that makes sense for you and the images you need to process, but remember that there are important speed and memory limitations. The larger the size, the slower it will be to train and run, and the more GPU memory will be required.

See:

https://www.ccoderun.ca/programming/2020-09-25_Darknet_FAQ/#square_network

Detection with aspect ratio change

  1. First of all, the high network resolution is important (the higher - the better). I.e. 800 x 800 will be better than 736 x 416, even if your input image 1600 x 900.
  2. And only In second place in importance is the aspect ratio.

See: https://github.com/AlexeyAB/darknet/issues/131

Useful resources

  1. FAQ: I get low accuracy ↩︎

  2. FAQ: Darknet training/detection crashes with an error ↩︎

  3. How to train with multi-GPU ↩︎

  4. When should I stop training ↩︎

  5. How to improve object detection ↩︎

Computer Vision Object Detection YOLOv4
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Last updated on Apr 3, 2022

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