Faster RCNN Model

Source

Faster RCNN is one of the most popular object detection model. It was introduced in the following paper: Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks

Usage

To train a Faster RCNN model, you need to call the following highlighted functions shown here below.

Common part to both Fastai and Pytorch-Lightning Training Loop

DataLoaders: Manstisshrimp creates common train DataLoader and valid DataLoader to both fastai Learner and Pytorch-Lightning Trainer

# DataLoaders
train_dl = faster_rcnn.train_dl(train_ds, batch_size=16, num_workers=4, shuffle=True)
valid_dl = faster_rcnn.valid_dl(valid_ds, batch_size=16, num_workers=4, shuffle=False)

Model: IceVision creates a Faster RCNN model implemented in torchvision FasterRCNN. The model accepts a variety of backbones. In following example, we use the default fasterrcnn_resnet50_fpn model. We can also choose one of the following backbones: resnet18, resnet34, resnet50, resnet101, resnet152, resnext50_32x4d, resnext101_32x8d, wide_resnet50_2, wide_resnet101_2

# Model
model = faster_rcnn.model(num_classes=len(class_map))

How to use a different backbone: "resnet18" example

# Backbone
backbone = faster_rcnn.backbones.resnet_fpn.resnet18(pretrained=True)
# Model
model = faster_rcnn.model(backbone=backbone, num_classes=len(class_map))

Fastai Example

Once the DataLoaders and the Faster RCNN model are created, we create the fastai Learner. The latter uses the DataLoaders and the Faster RCNN model shared with the Pytorch-Lightning Trainer (as shown in the Pytorch-Lightning example here below):

Fastai Learner: It glues the Faster RCNN model with the DataLoaders as well as the metrics and any other fastai Learner arguments. In the code snippet shown here below, we highlight the parts related to the Faster RCNN model.

# Fastai Learner
metrics = [COCOMetric()]
learn = faster_rcnn.fastai.learner(
    dls=[train_dl, valid_dl], model=model, metrics=metrics
)
learn.fine_tune(10, 1e-2, freeze_epochs=1)

Pytorch-Lightning Example

The Pytorch-Lightning example is quiet similar to the fastai one in a sense it uses the same DataLoaders objects, and the same Faster RCNN model. Those are subsenquently passed on to the Pytorch-Lightning Trainer:

Pytorch-Lightning Trainer: It glues the Faster RCNN model with the DataLoaders. In Pytorch-Lightning, the metrics are passed to the model object as opposed to fastai where it is passed to the Learner object. In the code snippet shown here below, we highlight the parts related to the Faster RCNN model.

# Train using pytorch-lightning
class LightModel(faster_rcnn.lightning.ModelAdapter):
    def configure_optimizers(self):
        return SGD(self.parameters(), lr=1e-4)

light_model = LightModel(model, metrics=metrics)

trainer = pl.Trainer(max_epochs=10, gpus=1)
trainer.fit(light_model, train_dl, valid_dl)

How to train the PETS Dataset using Faster RCNN

Source Code

Paper Introduction

Faster R-CNN is built upon the knowledge of Fast RCNN which indeed built upon the ideas of RCNN and SPP-Net. In their paper, the authors introduced a Region Proposal Network (RPN) that shares full-image convolutional features with the detection network, thus enabling nearly cost-free region proposals. An RPN is a fully convolutional network that simultaneously predicts object bounds and objectness scores at each position.

References