What are cross-modal embeddings?

Cross-modal embeddings are vector representations that allow different types of data—like text, images, audio, or video—to be mapped into a shared numerical space. This enables direct comparison or interaction between modalities, even though they originate in distinct formats. For example, an image of a dog and the text “a brown dog running” can both be converted into embeddings (arrays of numbers) that are close to each other in this shared space. This alignment makes it possible to perform tasks like searching for images using text queries or generating captions for videos, as the embeddings capture semantic similarities across modalities.

To create cross-modal embeddings, models are trained on paired datasets where examples from different modalities are linked (e.g., images with their captions). A common approach involves using neural networks to process each modality separately and then optimizing them to produce embeddings that minimize the distance between related pairs. For instance, OpenAI’s CLIP model uses contrastive learning: it trains a text encoder and an image encoder to align their outputs by rewarding the model when embeddings for matching text-image pairs are closer in the vector space than non-matching pairs. Techniques like triplet loss or cosine similarity are often used to enforce this alignment. The result is a system where, say, a photo of a sunset and the word “sunset” have embeddings that are mathematically similar, even though their raw data forms (pixels vs. characters) are unrelated.

Developers use cross-modal embeddings in applications that require bridging modalities. A search engine might use them to let users find products by describing them in text, even if the database contains only images. In accessibility, embeddings can link spoken words to text transcripts or sign language videos. Another example is recommendation systems: a music streaming service could link song audio embeddings to user reviews or playlist descriptions to improve suggestions. The key advantage is that embeddings simplify complex, multimodal data into a unified framework, enabling flexible comparisons without needing handcrafted rules. This approach reduces the need for siloed models for each data type, streamlining development and improving scalability.