Overfitting in Tensorflow Object detection API
Asked Answered
L

1

4

I am training tensorflow object detection API model on the custom dataset i.e. License plate dataset. My goal is to deploy this model to the edge device using tensorflow lite so I can't use any RCNN family model. Because, I can't convert any RCNN family object detection model to tensorflow lite model (this is the limitation from tensorflow object detection API). I am using ssd_mobilenet_v2_coco model to train the custom dataset. Following is the code snippet of my config file:

model {
  ssd {
    num_classes: 1
    box_coder {
      faster_rcnn_box_coder {
        y_scale: 10.0
        x_scale: 10.0
        height_scale: 5.0
        width_scale: 5.0
      }
    }
    matcher {
      argmax_matcher {
        matched_threshold: 0.5
        unmatched_threshold: 0.5
        ignore_thresholds: false
        negatives_lower_than_unmatched: true
        force_match_for_each_row: true
      }
    }
    similarity_calculator {
      iou_similarity {
      }
    }
    anchor_generator {
      ssd_anchor_generator {
        num_layers: 6
        min_scale: 0.2
        max_scale: 0.95
        aspect_ratios: 1.0
        aspect_ratios: 2.0
        aspect_ratios: 0.5
        aspect_ratios: 3.0
        aspect_ratios: 0.3333
      }
    }
    image_resizer {
      fixed_shape_resizer {
        height: 300
        width: 300
      }
    }
    box_predictor {
      convolutional_box_predictor {
        min_depth: 0
        max_depth: 0
        num_layers_before_predictor: 0
        use_dropout: false
        dropout_keep_probability: 0.8
        kernel_size: 1
        box_code_size: 4
        apply_sigmoid_to_scores: false
        conv_hyperparams {
          activation: RELU_6,
          regularizer {
            l2_regularizer {
              weight: 0.00004
            }
          }
          initializer {
            truncated_normal_initializer {
              stddev: 0.03
              mean: 0.0
            }
          }
          batch_norm {
            train: true,
            scale: true,
            center: true,
            decay: 0.9997,
            epsilon: 0.001,
          }
        }
      }
    }
    feature_extractor {
      type: 'ssd_mobilenet_v2'
      min_depth: 16
      depth_multiplier: 1.0
      conv_hyperparams {
        activation: RELU_6,
        regularizer {
          l2_regularizer {
            weight: 0.00004
          }
        }
        initializer {
          truncated_normal_initializer {
            stddev: 0.03
            mean: 0.0
          }
        }
        batch_norm {
          train: true,
          scale: true,
          center: true,
          decay: 0.9997,
          epsilon: 0.001,
        }
      }
    }
    loss {
      classification_loss {
        weighted_sigmoid {
        }
      }
      localization_loss {
        weighted_smooth_l1 {
        }
      }
      hard_example_miner {
        num_hard_examples: 3000
        iou_threshold: 0.99
        loss_type: CLASSIFICATION
        max_negatives_per_positive: 3
        min_negatives_per_image: 3
      }
      classification_weight: 1.0
      localization_weight: 1.0
    }
    normalize_loss_by_num_matches: true
    post_processing {
      batch_non_max_suppression {
        score_threshold: 1e-8
        iou_threshold: 0.6
        max_detections_per_class: 100
        max_total_detections: 100
      }
      score_converter: SIGMOID
    }
  }
}

train_config: {
  batch_size: 24
  optimizer {
    rms_prop_optimizer: {
      learning_rate: {
        exponential_decay_learning_rate {
          initial_learning_rate: 0.004
          decay_steps: 800720
          decay_factor: 0.95
        }
      }
      momentum_optimizer_value: 0.9
      decay: 0.9
      epsilon: 1.0
    }
  }
  fine_tune_checkpoint: "/home/sach/DL/Pycharm_Workspace/TF1.14/License_Plate_F-RCNN/dataset/experiments/training_SSD/ssd_mobilenet_v2_coco_2018_03_29/model.ckpt"
  fine_tune_checkpoint_type:  "detection"
  num_steps: 150000
  data_augmentation_options {
    random_horizontal_flip {
    }
  }
  data_augmentation_options {
    ssd_random_crop {
    }
  }
}

train_input_reader: {
  tf_record_input_reader {
    input_path: "/home/sach/DL/Pycharm_Workspace/TF1.14/License_Plate_F-RCNN/dataset/records/training.record"
  }
  label_map_path: "/home/sach/DL/Pycharm_Workspace/TF1.14/License_Plate_F-RCNN/dataset/records/classes.pbtxt"
}

eval_config: {
  num_examples: 488
  num_visualizations : 488
}

eval_input_reader: {
  tf_record_input_reader {
    input_path: "/home/sach/DL/Pycharm_Workspace/TF1.14/License_Plate_F-RCNN/dataset/records/testing.record"
  }
  label_map_path: "/home/sach/DL/Pycharm_Workspace/TF1.14/License_Plate_F-RCNN/dataset/records/classes.pbtxt"
  shuffle: false
  num_readers: 1
}

I have total 1932 images (train images: 1444 and val images: 448). I have trained the model for 150000 steps. Following is the output from tensorboard:

DetectionBoxes Precision [email protected] IOU: After 150K steps, the object detection model accuracy ([email protected] IOU) is ~0.97 i.e. 97%. Which seems to be fine at the moment.

DetectionBoxes_Precision_mAP

Training Loss: After 150K steps, the training loss is ~1.3. This seems to be okay.

Training Loss

Evaluation/Validation Loss: After 150K steps, the evaluation/validation loss is ~3.90 which is pretty high. However, there is huge difference between training and evaluation loss. Is there any overfitting exist? How can I overcome this problem? In my point of view, training and evaluation loss should be close to each other.

Eval Loss Loss

  • How can I reduce validation/evaluation loss?
  • I am using the default config file so by default use_dropout: false. Should I change it to use_dropout: true in case overfitting exist?
  • What should be the acceptable range of training and validation loss for object detection model?

Please share your views. Thanking you!

Lamson answered 4/3, 2020 at 12:44 Comment(8)
why is the num_classes is 1 ? is it the way it is supposed to be ? or am i missing somthing ?Amphitropous
Hi, it should be 1 because of I am looking for only one class i.e "License Plate".Lamson
oh right.. as you mentioned, you can go ahead with using dropouts. Then as a first step, I would recommend you to add some augmentations. choose augmentations specifically considering the license plates. Step 2 would be adjusting your anchors. Have a look at this url to check how to optmize detection by generating anchors. github.com/joydeepmedhi/Anchor-Boxes-with-KMeansAmphitropous
Should I also enable learning rate decay of about 10% every 5000 steps? Because in the default config file learning rate decay is n't enabled. Bcoz of decay_steps: 800720 it will work after only 800720 steps.Lamson
yes. cant keep it a crude way at 5000 steps. will be too often. try setting it around 20000 or even 30000. typically i would say atleast 2 epochs.Amphitropous
I looked at github.com/joydeepmedhi/Anchor-Boxes-with-KMeans but I can't find any "How can I specify anchor for SSD?" That's not clear. Could you please guide me? Thank you!Lamson
Just one question: What you mean by atleast 2 epochs? Can you please map this epochs field to config file? Setting decay_steps : 20000 or decay_steps: 30000 (this is clear).Lamson
Let us continue this discussion in chat.Lamson
E
5

There are several reasons for overfitting problem In Neural networks, by looking at your config file, I would like to suggest a few things to try to avoid overfitting.

use_dropout: true so that it makes the Neurons less sensitive to minor changes in the weights.

Try increasing iou_threshold in batch_non_max_suppression.

Use l1 regularizer or combination of l1 and l2 regularizer.

Change the optimizer to Nadam or Adam Optimizers.

Include more Augmentation techniques.

You can also use Early Stopping to track your accuracy.

Alternatively, you can observe the Tensorboard visualization, take the weights before the step where the validation loss starts increasing.

I hope trying these steps will resolve the overfitting issue of your model.

Eliott answered 9/5, 2020 at 16:0 Comment(0)

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