pages/OWLv2/OWLv2.md

Explaining the 👑 of zero-shot open-vocabulary object detection: OWLv2 🦉🧶 

![image_1](image_1.jpg)

OWLv2 is scaled version of a model called OWL-ViT, so let's take a look at that first. 
📝 OWLViT is an open vocabulary object detector, meaning, it can detect objects it didn't explicitly see during the training. 
👀 What's cool is that it can take both image and text queries! This is thanks to how the image and text features aren't fused together.

![image_2](image_2.jpg)

Taking a look at the architecture, the authors firstly do contrastive pre-training of a vision and a text encoder (just like CLIP). 
They take that model, remove the final pooling layer and attach a lightweight classification and box detection head and fine-tune. 

![image_3](image_3.jpg)

During fine-tuning for object detection, they calculate the loss over bipartite matches. 
Simply put, loss is calculated over the predicted objects against ground truth objects and the goal is to find a perfect match of these two sets where each object is matched to one object in ground truth.

OWL-ViT is very scalable. 
One can easily scale most language models or vision-language models because they require no supervision, but this isn't the case for object detection: you still need supervision. 
Moreover, only scaling the encoders creates a bottleneck after a while. 

![image_1](image_1.jpg)

The authors wanted to scale OWL-ViT with more data, so they used OWL-ViT for labelling to train a better detector, "self-train" a new detector on the labels, and fine-tune the model on human-annotated data. (see below) 

![image_4](image_4.jpg)

Thanks to this, OWLv2 scaled very well and is tops leaderboards on open vocabulary object detection 👑 

![image_5](image_5.jpg)

Want to try OWL models? I've created a [notebook](https://t.co/ick5tA6nyx ) for you to see how to use it with 🤗 Transformers.  
If you want to play with it directly, you can use this [Space](https://t.co/oghdLOtoa5).  
All the models and the applications of OWL-series is in this [collection](https://huggingface.co/collections/merve/owl-series-65aaac3114e6582c300544df).  

> [!TIP]
Ressources:  
[Scaling Open-Vocabulary Object Detection](https://arxiv.org/abs/2306.09683) 
by Matthias Minderer, Alexey Gritsenko, Neil Houlsby (2023) 
[GitHub](https://github.com/google-research/scenic/tree/main/scenic/projects/owl_vit)  
[Hugging Face documentation](https://huggingface.co/docs/transformers/model_doc/owlv2)  


> [!NOTE]
[Original tweet](https://twitter.com/mervenoyann/status/1748411972675150040) (January 19, 2024)