Retrieval-Enhanced Contrastive Vision-Text Models
Authors: name: Ahmet Iscen, name: Mathilde Caron, name: Alireza Fathi, name: Cordelia Schmid

Contrastive image-text models such as CLIP form the building blocks of many
state-of-the-art systems. While they excel at recognizing common generic
concepts, they still struggle on fine-grained entities which are rare, or even
absent from the pre-training dataset. Hence, a key ingredient to their success
has been the use of large-scale curated pre-training data aiming at expanding
the set of concepts that they can memorize during the pre-training stage. In
this work, we explore an alternative to encoding fine-grained knowledge
directly into the model's parameters: we instead train the model to retrieve
this knowledge from an external memory. Specifically, we propose to equip
existing vision-text models with the ability to refine their embedding with
cross-modal retrieved information from a memory at inference time, which
greatly improves their zero-shot predictions. Remarkably, we show that this can
be done with a light-weight, single-layer, fusion transformer on top of a
frozen CLIP. Our experiments validate that our retrieval-enhanced contrastive
(RECO) training improves CLIP performance substantially on several challenging
fine-grained tasks: for example +10.9 on Stanford Cars, +10.2 on CUB-2011 and
+7.3 on the recent OVEN benchmark.