CLIP (Contrastive Language–Image Pretraining) is a neural network model developed by OpenAI that learns to associate images with corresponding text descriptions. Unlike traditional computer vision models trained on labeled datasets with fixed categories, CLIP is trained on a vast collection of image-text pairs scraped from the internet. This approach allows it to understand a wide range of visual concepts by leveraging natural language as a flexible source of supervision. The core idea is to align images and text in a shared embedding space, where similar concepts from both modalities are positioned close together.
CLIP uses a dual-encoder architecture: one encoder processes images (e.g., a Vision Transformer or ResNet), and another processes text (e.g., a transformer-based model). During training, the model is shown millions of image-text pairs and learns to maximize the similarity between embeddings of matching pairs while minimizing similarity for mismatched pairs. This contrastive learning objective ensures that, for example, an image of a dog is closer in the embedding space to the text “a dog” than to unrelated phrases like “a car.” The model doesn’t predict labels directly; instead, it compares an input image’s embedding to embeddings of potential text labels to find the best match.
Developers can use CLIP for zero-shot image classification, where the model categorizes images without task-specific training. For instance, given an image of a cat and a set of text options like “cat,” “dog,” or “car,” CLIP computes similarity scores to select the correct label. It’s also used in multimodal applications like image retrieval (searching images via text queries) or enhancing generative models like DALL·E by grounding generated images in text prompts. OpenAI provides pretrained CLIP models accessible via libraries like PyTorch or Hugging Face Transformers, allowing developers to integrate it into workflows with minimal setup. For example, a developer could use CLIP to filter user-uploaded images by comparing them against prohibited text descriptions, enabling content moderation without custom training.