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YOLOv2 in PyTorch

NOTE: This project is no longer maintained and may not compatible with the newest pytorch (after 0.4.0).

This is a PyTorch implementation of YOLOv2. This project is mainly based on darkflow and darknet.

I used a Cython extension for postprocessing and multiprocessing.Pool for image preprocessing. Testing an image in VOC2007 costs about 13~20ms.

For details about YOLO and YOLOv2 please refer to their project page and the paper: YOLO9000: Better, Faster, Stronger by Joseph Redmon and Ali Farhadi.

NOTE 1: This is still an experimental project. VOC07 test mAP is about 0.71 (trained on VOC07+12 trainval, reported by @cory8249). See issue1 and issue23 for more details about training.

NOTE 2: I recommend to write your own dataloader using since multiprocessing.Pool.imap won't stop even there is no enough memory space. An example of dataloader for VOCDataset: issue71.

NOTE 3: Upgrade to PyTorch 0.4:

Installation and demo

  1. Clone this repository

    git clone
  2. Build the reorg layer (tf.extract_image_patches)

    cd yolo2-pytorch
  3. Download the trained model yolo-voc.weights.h5 and set the model path in

  4. Run demo python

Training YOLOv2

You can train YOLO2 on any dataset. Here we train it on VOC2007/2012.

  1. Download the training, validation, test data and VOCdevkit

  2. Extract all of these tars into one directory named VOCdevkit

    tar xvf VOCtrainval_06-Nov-2007.tar
    tar xvf VOCtest_06-Nov-2007.tar
    tar xvf VOCdevkit_08-Jun-2007.tar
  3. It should have this basic structure

    $VOCdevkit/                           # development kit
    $VOCdevkit/VOCcode/                   # VOC utility code
    $VOCdevkit/VOC2007                    # image sets, annotations, etc.
    # ... and several other directories ...
  4. Since the program loading the data in yolo2-pytorch/data by default, you can set the data path as following.

    cd yolo2-pytorch
    mkdir data
    cd data
    ln -s $VOCdevkit VOCdevkit2007
  5. Download the pretrained darknet19 model and set the path in yolo2-pytorch/cfgs/exps/

  6. (optional) Training with TensorBoard.

    To use the TensorBoard, set use_tensorboard = True in yolo2-pytorch/cfgs/ and install TensorboardX ( Tensorboard log will be saved in training/runs.

  7. Run the training program: python


Set the path of the trained_model in yolo2-pytorch/cfgs/

cd faster_rcnn_pytorch
mkdir output

Training on your own data

The forward pass requires that you supply 4 arguments to the network:

  • im_data - image data.
    • This should be in the format C x H x W, where C corresponds to the color channels of the image and H and W are the height and width respectively.
    • Color channels should be in RGB format.
    • Use the imcv2_recolor function provided in utils/ to preprocess your image. Also, make sure that images have been resized to 416 x 416 pixels
  • gt_boxes - A list of numpy arrays, where each one is of size N x 4, where N is the number of features in the image. The four values in each row should correspond to x_bottom_left, y_bottom_left, x_top_right, and y_top_right.
  • gt_classes - A list of numpy arrays, where each array contains an integer value corresponding to the class of each bounding box provided in gt_boxes
  • dontcare - a list of lists

License: MIT license (MIT)

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