We present a simple and effective architecture for fine-grained visual recognition called Bilinear Convolutional Neural Networks (B-CNNs). These networks represent an image as a pooled outer product of features derived from two CNNs and capture localized feature interactions in a translationally invariant manner. B-CNNs belong to the class of orderless texture representations but unlike prior work they can be trained in an end-to-end manner. Our most accurate model obtains 84.1%, 79.4%, 86.9% and 91.3% per-image accuracy on the Caltech-UCSD birds, NABirds, FGVC aircraft, and Stanford cars datasets respectively and runs at 30 frames-per-second on an NVIDIA Titan X GPU. We then present a systematic analysis of these networks and show that (1) the bilinear features are highly redundant and can be reduced by an order of magnitude in size without significant loss in accuracy, (2) are also effective for other image classification tasks such as texture and scene recognition, and (3) can be trained from scratch on the ImageNet dataset offering consistent improvements over the baseline architecture. Finally, we present visualizations of these models on various datasets using top activations of neural units and gradient-based inversion techniques.



Accuracy on various fine-grained recognition datasets are below. See Table 2 in the PAMI paper for a detailed comparison.
Model Caltech-UCSD birds   FGVC aircrafts   Stanford cars   NA birds
Improved B-CNN (vgg-m) 81.3 84.0 88.5 -
Improved B-CNN (vgg-d) 85.8 88.5 92.1 -
B-CNN (vgg-m) 78.1 79.5 86.5 -
B-CNN (vgg-d) 84.0 86.9† 90.6 -
B-CNN (vgg-m+vgg-d) 84.1 86.6† 91.3 79.4
† improvements over the ICCV'15 numbers are due to improved cropping (central 448x448 crop from a 512x512 image)

Talk slides


This research was supported in part by the NSF IIS-1617917, a faculty gift from Facebook, and IARPA IAR2014-14071600010. The experiments were performed using high performance computing equipment obtained under a grant from the Collaborative R&D Fund managed by the Massachusetts Tech Collaborative and GPUs donated by NVIDIA.