CLIP: Learning Transferable Visual Models From Natural Language Supervision


Labelled image data is scare and expensive. But the internet is full of images with captions. These researchers used a language transformer architecture and a vision transformer architecture to predict captions for a given image. The resulting model is very good at 'understanding' and describing a wide variety of images. They named this approach CLIP {Contrastive Language-Image Pretraining}.


The authors propose a novel method for training vision models using natural language supervision. They exploit the vast amount of text data available on the internet to train visual models that can understand and generate meaningful descriptions of images.

Model Architecture

The model architecture consists of two parts:

  1. A transformer-based vision model, which processes images into a fixed-length vector representation.
  2. A transformer-based language model, which processes text inputs into a fixed-length vector representation.

The key idea is to create an alignment in the embedding space such that image and text representations of the same concept are closer to each other compared to representations of different concepts.

The architecture of the model can be represented as:

[ f_{\theta}(x) = W_x h_x^L ]

[ g_{\phi}(y) = W_y h_y^L ]

where (x) is the image, (y) is the text, (f_{\theta}(x)) and (g_{\phi}(y)) are the final image and text embeddings respectively, (W_x) and (W_y) are the final layer weights, and (h_x^L) and (h_y^L) are the final layer activations of the vision and language models respectively.


The training process is based on the contrastive learning framework. The objective is to maximize the similarity between the image and text representations of the same concept while minimizing the similarity between the image and text representations of different concepts. This is achieved by using a temperature-scaled cross-entropy loss.


The paper reports that CLIP models trained using this method achieved state-of-the-art performance on a variety of challenging vision benchmarks. They further demonstrate that the model is capable of zero-shot transfer learning, which means it can generalize well to new tasks without any fine-tuning.


The implications of this research are profound. By harnessing the vast amount of text data available on the internet, it is possible to train powerful vision models without the need for large labeled image datasets. This approach could advance the field of computer vision by making it easier to train highly capable models, and it could also lead to new ways of integrating vision and language understanding in AI systems.

For a more visual representation of the architecture, here is a simplified diagram:

Text Input ---> [Language Transformer] ---> Text Embedding ---> [Contrastive Loss]

Image Input ---> [Vision Transformer] ---> Image Embedding ---> [Contrastive Loss]

The key is

The arrows in the illustration above denote the flow of data. The text and image inputs go through their respective transformers to generate embeddings. These embeddings are then passed to the contrastive loss function, which compares them and provides feedback to the transformers during training.

The novelty of this work lies in the joint learning of the image and text transformers under the contrastive learning framework. By aligning image and text representations, the model is able to leverage the information in text data to understand images, and vice versa.

Overall, this approach shows promise for developing more powerful and versatile AI models that can understand and generate both text and visual content. The potential applications are vast, ranging from automated image captioning and content generation to visual question answering and beyond.

Please let me know if you need more details or if there's a specific aspect of the paper you're interested in.

Tags: CLIP, Visual Models, 2021, Optimization
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